May 31, 2023 • 44 mins
This textbook is designed specifically for Kansas State's Biology 198 Class. The course is taught using the studio approach and based on active learning. The studio manual contains all of the learning objectives for each class period and is the record of all student activities. Hence, this textbook is more of a reference tool while the studio manual is the learning tool.
Authors: Robert Bear, David Rintoul, Bruce Snyder, Martha Smith-Caldas, Christopher Herren, and Eva Horne
Kansas State University Libraries
New Prairie Press
Bear, Robert; Rintoul, David; Snyder, Bruce; Smith-Caldas, Martha; Herren, Christopher; and Horne, Eva, "Principles of Biology" (2016). Open Access Textbooks. 1. https://newprairiepress.org/textbooks/1
The textbook was originally published and is also available to download at http://cnx.org/contents/db89c8f8-a27c-4685-ad2a-19d11a2a7e2e@24.1.It is licensed under a Creative Commons Attribution License 4.0 license.
Authors: Robert Bear, David Rintoul, Bruce Snyder, Martha Smith-Caldas, Christopher Herren, and Eva Horne
Kansas State University Libraries
New Prairie Press
Bear, Robert; Rintoul, David; Snyder, Bruce; Smith-Caldas, Martha; Herren, Christopher; and Horne, Eva, "Principles of Biology" (2016). Open Access Textbooks. 1. https://newprairiepress.org/textbooks/1
The textbook was originally published and is also available to download at http://cnx.org/contents/db89c8f8-a27c-4685-ad2a-19d11a2a7e2e@24.1.It is licensed under a Creative Commons Attribution License 4.0 license.
Mark as Played
Transcript
Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
(00:00):
Welcome to Principles of Biology. Thisbook was written by the Open Alternative Textbook
Initiative at Kansas State University and isbeing released as a podcast and distributed under
the terms of the Creative Commons AttributionLicense. Today's episode is chapter twenty eight
the integumentary System. All hyperlinks,images and sources can be found at the
(00:23):
link to the book. In thedescription, I am not this hair,
I am not this skin. Iam the soul that lives within jalal ad
Din Rumy. Rumy's line plays onthe unusual focus on hair color and skin
color that humans have had for manycenturies and asks us to look more deeply
than those superficial layers. That isgood advice, but at the same time,
(00:45):
those superficial layers of hair, skin, nails, et cetera, known
collectively as the integument, have manyinteresting structures and many important biological functions.
They protect organisms from many environmental hazardsand injuries, including disease as well as
heat or cold. To do this, the integument relies on interactions with many
(01:06):
other organ systems, including the circulatory, nervous, and immune systems. Its
beauty is indeed more than skin deep. The structure of skin. Although you
may not typically think of the skinas an organ, it is in fact
made of tissues that work together asa single structure to perform unique and critical
functions. The skin and its accessorystructures make up the integumentary system, which
(01:30):
provides the body with overall protection.The skin is made of multiple layers of
cells and tissues, which are heldto underlying structures by connective tissue. Figure
one. The deeper layer of skinis well vascularized has numerous blood vessels.
It also has numerous sensory and autonomicand sympathetic nerve fibers, ensuring communication to
(01:52):
and from the brain. There aretwo main layers, epidermis and dermis,
with a third connective layer, thehypodermis layer of skin. This illustration shows
a cross section of skin tissue.The outermost layer is called the epidermis and
occupies one fifth of the cross section. Several hairs are emerging from the surface.
(02:13):
The epidermis dives around one of thehairs, forming a follicle. The
middle layer is called the dermis,which occupies four fifths of the cross section.
The dermis contains an erector pilli muscleconnected to one of the follicles.
The dermis also contains an acrone sweatgland composed of a bunch of tubules.
One tubule travels up from the bunchthrough the epidermis, opening onto the surface
(02:38):
of poor There are two string likenerves traveling vertically through the dermis. The
right nerve is attached to a Pissiniancorpusal, which is a yellow structure consisting
of concentric ovals similar to an onion. The lowest level of the skin,
the hypodermis, contains fatty tissue,arteries and veins. Blood vessels travel from
(02:59):
the hypodermis and connect to hair folliclesand erector pilli muscle in the dermis.
The skin is composed of two mainlayers, the epidermis, made of closely
packed upithelial cells, and the dermis, made of dense, irregular connective tissue
that houses blood vessels, hair follicles, sweat glands, and other structures.
Beneath the dermis lies the hypodermis,which is composed mainly of loose, connective
(03:23):
and fatty tissues the epidermis. Theepidermis is composed of keratinized, stratified squamous
epithelium. It is made of fouror five layers of epithelial cells, depending
on its location in the body.It does not have any blood vessels within
it. Ie. It is avascular skin that has four layers of cells
(03:44):
is referred to as thin skin fromdeep to superficial. These layers are the
stratum bile, stratum spinosum, stratumgranulosum, and stratum cornium. Most of
the skin can be classified as thinskin. Thick skin is found only on
the palms of the hands and thesaals of the feet. It has a
fifth layer called the stratum lucidum,located between the stratum cornium and the stratum
(04:08):
granulosum. Figure thin skin versus thickskin part A is a micrograph showing a
cross section of thin skin. Thetopmost layer is a thin, translucent layer
with irregular texture in areas where cellsare slowing off. The deepest layer is
dark purple and extends into the thirdlayer with finger like projections. The third
(04:30):
light purple layer contains thin bands offibers and small dark cells. The fourth
and deepest layer is darker than thethird layer, but is still light purple.
It contains thick fiber bands that areloosely packed. Part B is a
magnified view of the epidermis of thickskin. It shows the topmost layers five
times thicker than the topmost layer ofthin skin. The topmost layer of thick
(04:55):
skin is also denser and less translucentthan the topmost layer of thin skin.
These slides show cross sections of theepidermis and dermis of a thin end B
thick skin. Note the significant differencein the thickness of the epithelial layer of
the thick skin from top ALM timesforty ALAM times forty micrographs provided by the
(05:17):
Regions of University of Michigan Medical School, copyright twenty twelve. The cells in
all of the layers except the stratumbile are called keratinocytes. A keratinosite is
a salt that manufactures and stores theprotein keratin. Keratin is an intracellular fibrous
protein that gives hair, nails,and skin their hardness and water resistant properties.
(05:40):
The keratinosites and the stratum cornium aredead and regularly slew away, being
replaced by cells from the deeper layersfigure epidermis. The outer layer of cells
in this micrograph is the thinnest layerand stained deep purple due to full keratinization
of dead cells. The next layer, occupies one quarter of the micrograph,
is lightly stained and is a densecollection of cells. The third layer from
(06:03):
the top is mostly white, withlightly stained, loosely packed strands radiating in
random directions. The bottommost layer isdensely packed with thick bands of highly organized
muscle tissue that are darkly stained.The epidermis is epithelium composed of multiple layers
of cells. The basal layer consistsof cuboidal cells, whereas the outer layers
(06:26):
are squamous keratenized cells, so thewhole epithelium is often described as being keratenized
stratified squamous epithelium ALAM times forty micrographprovided by the Regions of University of Michigan
Medical School, copyright two twelve.Layer of the epidermis stratum bile. The
stratum bio, also called the stratumgerminativum, is the deepest epidermal layer and
(06:48):
attaches the epidermis to the basal laminabelow, which lie the layers of the
dermis. The cells in the stratumbile bond to the dermis via intertwining collagen
fibers referred to as the basement membrane. A fingerlike projection or fold known as
the dermal popilla plural equals dermal popilli, is found in the superficial portion of
(07:09):
the dermis. Dermal popilli increase thestrength of the connection between the epidermis and
dermis. The greater the folding,the stronger the connections made Figure point two.
Other cell types are found dispersed amongthe basal cells and the straightum bile.
The first is a mercal cell,which functions as a receptor and is
responsible for stimulating sensory nerves that thebrain perceives as touch. These cells are
(07:31):
especially abundant on the surfaces of thehands and feet. The second is a
melanocyte, a cell that produces thepigment melanin. Melanin gives hair and skin
its color and also helps protect theliving cells of the epidermis from ultraviolet UV
radiation damage layers of the epidermis.This illustration shows a cross section of the
(07:54):
epidermis. The cells of the innermostlayer, the straightum bile, are large
and have a pal nucleus. Thestratum bile curls around the dermis, which
projects into the epidermis. The stratumbile contains four layers of large, triangle
shaped keratinocytes. Fibers are visible withinthe spaces between caratinocytes and the stratum biole.
(08:16):
A melanocyte is also present in thislayer. The melanocyte possesses fingerlike projections
extending from its main cell body.The projections branch through the extracellular spaces between
nearby caratinocytes. Above the stratum bileis the stratum spinosum, which consists of
eight layers of oval shaped keratinocytes.The nucleus is present in these keratinocytes,
(08:41):
but has faded to a lighter purple. The stratum granulosum contains five layers of
keratinocytes, each containing spots in itscytoplasm labeled the lamellar granules. The stratum
lucidium contains four layers of diamond shapedcells with no nucleus. The stratum cornium
contains nine layers of keratinosites with nonucleus nor cytoplasm. A few of the
(09:03):
cells in the topmost layer of thestratum cornium are flaking off from the skin.
The epidermis of thick skin has fivelayers straightum bio stratum spinosom, Stratum
granulosum, Stratum lucidum, and stratumcornium stratum spinosome. As the name suggests,
the stratum spinosom is spiny in appearancedue to the protruding cell processes that
(09:26):
join the cells via a structure calledthe desmosome. The desmosome's interlock with each
other and strengthen the bond between thecells. It is interesting to note that
the spiny nature of this layer isan artifact of the staining process. Unstained
epidermis samples do not exhibit this characteristicappearance. The stratum spinosom is composed of
(09:46):
eight to ten layers of keratinosites formedas a result of cell division in the
stratum bio figure. Interspersed among thekeratinosites of this layer is a type of
dendritic cell called the longer Han cell, which functions as a macrophage by engulfing
bacteria, foreign particles, and damagedcells that occur in this layer. The
(10:07):
keratinosites and the stratum spinosome begin thesynthesis of keratin and release a water repelling
glycolipit that helps prevent water loss fromthe body, making the skin relatively waterproof.
As new keratinosites are produced atop thestratum bio, the keratinosites of the
stratum spinosom are pushed into the Stratumgranulosum Stratum granulosum. The stratum granulosum has
(10:30):
a grainy appearance due to further changesto the keratinosites. As they are pushed
from the Stratum spinosum. The cellsthree to five layers deep, become flatter,
their cell membranes thicken, and theygenerate large amounts of the protein's keratin,
which is fibrous, and keratohylin,which accumulates as lamellar granules within the
cells sea figure. These two proteinsmake up the bulk of the keratinosite mass
(10:52):
and the stratum granulosum, and givethe layer its grainy appearance. The nuclei
and other cell organelles dis integrate asthe cells die, leaving behind the keratin,
keratohylin, and cell membranes that willform the Stratum lucidum, the stratum
cornium, and the accessory structures ofhair and nails. Stratum lucidum. The
Stratum lucidum is a smooth, seeminglytranslucent layer of the epidermis, located just
(11:16):
above the stratum granulosum and below thestratum cornium. This thin layer of cells
is found only in the thick skinof the palms. Cells and digits.
The keratinocytes that compose the stratum lucidumare dead and flattened Sea figure. These
cells are densely packed with a lyden, a clear protein rich in lipids derived
(11:37):
from keratohylin, which gives these cellsthey're transparent i e. Lucid appearance and
provides a barrier to water. Stratumcornium. The stratum cornium is the most
superficial layer of the epidermis and isthe layer exposed to the outside environment Sea
figure. The increased keratinization, alsocalled cornification, of the cells in this
(11:58):
layer gives it its name. Thereare usually fifteen to thirty layers of cells
in the stratum cornium. This dry, dead layer helps prevent the penetration of
microbes and the dehydration of underlying tissues, and provides a mechanical protection against abrasion
for the more delicate underlying layers.Cells in this layer are shed periodically and
are replaced by cells pushed up fromthe stratum granulosum or stratum lucidum in the
(12:22):
case of the palms and cells offeet. The entire layer is replaced during
a period of about four weeks.Cosmetic procedures such as microdermabrasion help remove some
of the dry upper layer and aimto keep the skin looking fresh and healthy.
Dermis the dermis might be considered thecore of the integumentary system. Derma
(12:43):
equal skin as distinct from the epidermisapy equals upon are over and hypodermis hypoequals
below. It contains blood and limpvessels, nerves, and other structures such
as hair, follicles and sweat glands. The dermis is made of two layers
of connective tissue that compose an interconnectedmesh of elastin and colagenous fibers produced by
(13:05):
fibroblasts. Figure layers of the dermis. This micrograph shows layers of skin in
a cross section. The papillary layerof the dermis extends between the downward fingers
of the darkly stained upidermis. Thepapillary layer appears finer than the reticular layer,
consisting of smaller, densely packed fibers. The reticular layer is three times
(13:28):
thicker than the papillary layer and containslarger, thicker fibers. The fibers seem
more loosely packed than those of thepapillary layer, with some separated by empty
spaces. Both layers of the dermiscontained cells with darkly stained nuclei. This
stained slide shows the two components ofthe dermis, the papillary layer and the
reticular layer. Both are made ofconnective tissue, with fibers of collagen extending
(13:54):
from one to the other, makingthe border between the two somewhat indistinct.
The dermal papilli stending into the epidermistsbelonged to the papillary layer, whereas the
dense collagen fiber bundles below belonged tothe reticular layer. Alam times ten credit
modification of work by kill bad SlashWikimedia Commons papillary layer. The papillary layer
(14:16):
is made of loose connective tissue,which means the collagen and elastin fibers of
this layer form a loose mesh.This superficial layer of the dermist projects into
the straight and bile of the epidermistto form fingerlike dermal papilli. SA figure.
Within the papillary layer are fibroblasts,a small number of fat cells,
adipocytes, and an abundance of smallblood vessels. In addition, the papillary
(14:41):
layer contains phagocytes, defensive cells thathelp fight bacteria or other infections that have
breached the skin. This layer alsocontains lymphatic capillaries, nerve fibers, and
touch receptors called the Meisner corpusals reticularlayer. Underlying the papillary layer is the
much thicker reticular layer, composed ofdense, irregular connective tissue. This layer
(15:03):
is well vascularized and has a richsensory and sympathetic nerve supply. The reticular
layer appears reticulated net like due toa tight meshwork of fibers. Elastin fibers
provides some elasticity to the skin,enabling movement. Collagen fibers provide structure and
tensile strength, with strands of collagenextending into both the papillary layer and the
(15:26):
hypodermis. In addition, collogen bindswater to keep the skin hydrated. Collogen
injections and retinate creams help restore skinturger by either introducing collogen externally or stimulating
blood flow and repair of the dermis, respectively hypodermis. The hypodermis, also
(15:46):
called the subcutaneous layer or superficial fascia, is a layer directly below the dermis
and serves to connect the skin tothe underlying fascia fibrous tissue of the bones
and muscles. It is not strictlya part of the skin, though the
border between the hypodermis and dermis canbe difficult to distinguish. The hypodermis consists
of well vascularized loose a realer connectivetissue, and adipose tissue, which functions
(16:11):
as a mode of fat storage andprovides insulation and cushioning for the integument.
Pigmentation, the color of skin isinfluenced by a number of pigments, including
melanin, keratine, and hemoglobin.Recall that melanin is produced by cells called
melanocytes, which are found scattered throughoutthe stratum bile of the epidermis. The
(16:32):
melanin is transferred into the keratinocytes viaa cellular vesicle called a melanosome. Figure
skin pigmentation. This figure consists oftwo diagrams side by side The right diagram
shows development of light colored skin.The left shows development of dark colored skin.
In both. A brown melanocyte sitsat the border between the dermis and
(16:53):
epidermis. The melanocyte has a largenucleus and six fingerlike its engines, these
reach between cells of the stratum basalis. Sections of the extensions detach and travel
through the skins. These are melanosomes. In the left diagram, both the
melanocyte and melanosomes contain melanin particles shownas dark dots. Melanosomes travel upwards to
(17:19):
outer skin layers, releasing melanin.As a result. Keratinocytes in the left
diagram contain several melanin particles that darkenskin color. In light colored skin,
the melanocyte contains no melanin, itstill releases melanosomes into upper layers of the
skin. However, these melanosomes containno melanin. Therefore, the skin does
(17:42):
not darken and remains light. Therelative coloration of the skin depends on the
amount of melanin produced by melanocytes inthe stratum bio and taken up by keratinocytes.
Melanine occurs in two primary forms.Eumelanin exists as black and whereas piomelanin
provides a red color. Dark skinnedindividuals produce more melanin than those with pale
(18:07):
skin. Exposure to the UV raysof the sun or a tanning salon causes
melanin to be manufactured and build upin keratinocytes. As sun exposure stimulates keratinocytes
to secrete chemicals that stimulate melanocytes.The accumulation of melanin in keratinocytes results in
the darkening of the skin or atan This increased melanin accumulation protects the DNA
(18:30):
of epidermal cells from UV ray damageand the breakdown of folic acid and nutrient
necessary for our health and well being. In contrast, too much melanin can
interfere with the production of vitamin D, an important nutrient involved in calcium absorption.
Thus, the amount of melanin presentin our skin is dependent on a
balance between available sunlight and folic aciddestruction and protection from UV radiation and vitamin
(18:55):
D production. It requires about tendays after initial sun exposure for melanin synthesis
to peak, which is why paleskinned individuals tend to suffer sunburns of the
epidermis. Initially dark skinned individuals canalso get sunburns, but are more protected
than are pale skinned individuals. Melanosomesare temporary structures that are eventually destroyed by
(19:17):
fusion with lysosomes. This fact,along with melanin filled keratinocytes in the stratum
corneum sloughing off, makes tanning impermanent. Too much sun exposure can eventually lead
to wrinkling due to the destruction ofthe cellular structure of the skin, and
in severe cases, can cause sufficientDNA damage to result in skin cancer.
When there is an irregular accumulation ofmelanocytes in the skin, freckles appear.
(19:41):
Moles are larger masses of melanocytes,and although most are benign, they should
be monitored for changes that might indicatethe presence of cancer. Figure moles.
Five photos of moles. The threeupper photos show moles that are small,
flat, and dark brown. Thebottom left photo shows a dark black mole
(20:02):
that is raised above the skin.The bottom right photo shows a large,
raised, reddish mole with protruding hairs. Moles range from benign accumulations of melanocytes
to melanomas. These structures populate thelandscape of our skin. Credit the National
Cancer institute accessory structures of the skin. Accessory structures of the skin include hair
(20:25):
nails, sweat glands, and sebaceousglands. These structures embryologically originate from the
epidermis and can extend down through thedermis into the hypodermis. Hair hair is
a caratinous filament growing out of theepidermis. It is primarily made of dead
keratinized cells. Strands of hair originatein an epidermal penetration of the dermis called
(20:48):
the hair follicle. The hair shaftis the part of the hair not anchored
to the follicle, and much ofthis is exposed at the skin surface.
The rest of the hair, whichis anchored in the follicle, lies below
the surface of the skin and isreferred to as the hair root. The
hair root ends deep in the dermisat the hair bulb and includes a layer
of mitotically active basal cells called thehair matrix. The hair bulb surrounds the
(21:14):
hair papilla, which is made ofconnective tissue and contains blood capillaries and nerve
endings from the dermis. Figure hair. This diagram shows a cross section of
the skin containing a hair follicle.The follicle is teardrop shaped. Its enlarged
base, labeled the hair bulb,is embedded in the hypodermis. The outermost
(21:34):
layer of the follicle is the epidermis, which invaginates from the skin surface to
envelope the follicle. Within the epidermisis the outer root sheath, which is
only present on the hair bulb.It does not extend up the shaft of
the hair. Within the outer rootsheath is the inner root sheath. The
inner root sheath extends about half ofthe way up the hair shaft, ending
(21:56):
midway through the dermis. The hairmatrix is the innermost layer. The hair
matrix surrounds the bottom of the hairshaft, where it is embedded within the
hair bowl. The hair shaft initself contains three layers, the outermost cuticle,
a middle layer called the cortex,and an innermost layer called the medulla.
(22:17):
Hair follicles originate in the epidermis andhave many different parts. Just as
the basal layer of the epidermis formsthe layers of epidermists that get pushed to
the surface as the dead skin onthe surface sheds, The basal cells of
the hair bulb divide and push cellsoutward in the hair root and shaft.
As the hair grows. The medullaforms the central core of the hair,
which is surrounded by the cortex,a layer of compressed caratenized cells that is
(22:41):
covered by an outer layer of veryhard caratenized cells known as the cuticle.
These layers are depicted in a longitudinalcross section of the hair follicle figure.
Although not all hair has a medallarylayer, hair texture straight, curly is
determined by the shape and structure ofthe cortex and to the extent that it
is present, the medulla. Theshape and structure of these layers are in
(23:06):
turn determined by the shape of thehair follicle. Hair growth begins with the
production of keratinocytes by the basal cellsof the hair bulb. As new cells
are deposited at the hair bulb,the hair shaft is pushed through the follicle
towards the surface. Keratinization is completedas the cells are pushed to the skin
surface to form the shaft of hairthat is externally visible. The external hair
(23:29):
is completely dead and composed entirely ofkeratin. For this reason, our hair
does not have sensation. Furthermore,you can cut your hair or shave without
damaging the hair structure. Because thecut is superficial. Most chemical hair removers
also act superficially. However, electrolysisand yanking both attempt to destroy the hair
bulb, so hair cannot grow hairfollicle. This micrograph is of the base
(23:55):
of a hair follicle. The protrudinghair is largely transparent, with only its
dark outline visible. The inner rootsheath is visible, surrounding the very bottom
of the hair as a circle ofcells with dark staining nuclei. The inner
sheath extends up the hair shaft.The outer root sheath is much thicker than
the inner root sheath, consisting ofa large oval of lighter staining cells.
(24:18):
The oval surrounds the bottom of thehair and extends into the hypodermis. The
slide shows a cross section of ahair follicle. Basal cells of the hair
matrix in the center differentiate into cellsof the inner root sheath. Basal cells
at the base of the hair rootform the outer root sheath. Alam times
four credit modification of work by killbad Slash Wikimedia Commons. The wall of
(24:44):
the hair follicle is made of threeconcentric layers of cells. The cells of
the internal root sheaths surround the rootof the growing hair and extend just up
to the hair shaft. They arederived from the basal cells of the hair
matrix. The external root sheath,which is an extension of the epidermis,
encloses the hair root. It ismade of basal cells at the base of
(25:06):
the hair root and tends to bemore keratinous in the upper regions. The
glassy membrane is a thick, clear, connective tissue sheath covering the hair root,
connecting it to the tissue of thedermis. Hair serves a variety of
functions including protection, sensory input,thermoregulation, and communication. For example,
(25:26):
hair on the head protects the skullfrom the sun. The hair in the
nose and ears, and around theeyes eyelashes defends the body by trapping and
excluding dust particles that may contain allergensand microbes. Hair of the eyebrows prevents
sweat and other particles from dripping intoand bothering the eyes. Hair also has
a sensory function due to sensory innervationby a hair root plexus surrounding the base
(25:49):
of each hair follicle. Hair isextremely sensitive to air movement or other disturbances
in the environment, much more sothan the skin surface. This feature is
also useful for the detection of thepresence of insects or other potentially damaging substances
on the skin surface. Each hairroot is connected to a smooth muscle called
the erector pylie that contracts in responseto nerve signals from the sympathetic nervous system,
(26:14):
making the external hairshaft stand up.The primary purpose for this is to
trap a layer of air to addinsulation. This is visible in humans as
goose bumps, and even more obviousin animals, such as when a frightened
cat raises its fur. Of course, this is much more obvious in organisms
with a heavier coat than most humans, such as dogs and cats. Hair
(26:37):
growth hair grows and is eventually shedand replaced by new hair. This occurs
in three phases. The first isthe anogen phase, during which cells divide
rapidly at the root of the hair, pushing the hair shaft up and out.
The length of this phase is measuredin years, typically from two to
seven years. The cattagen phase lastsonly two to three weeks and marks a
(27:00):
transition from the hair follicles act ofgrowth. Finally, during the telligen phase,
the hair follicle is at rest andno new growth occurs. At the
end of this phase, which lastsabout two to four months, another anogen
phase begins. The basal cells inthe hair matrix then produce a new hair
follicle, which pushes the old hairout as the growth cycle repeats itself.
(27:22):
Hair typically grows at the rate ofzero point three millimeters per day during the
enogen phase. On average, fiftyhairs are lost and replaced per day.
Hair Loss occurs if there is morehair shed than what is replaced, and
can happen due to hormonal or dietarychanges. Hair loss can also result from
the aging process or the influence ofhormones. Hair color, similar to the
(27:47):
skin, hair gets its color fromthe pigment melanin produced by melanocytes in a
hair papilla. Different hair color resultsfrom differences in the type of melanin,
which is genetically determined. As aper In ages, the melanin production decreases
and hair tends to lose its colorand becomes gray and are white. Nails
the nail bed is a specialized structureof the epidermis that is found at the
(28:11):
tips of our fingers and toes.The nail body is formed on the nail
bed and protects the tips of ourfingers and toes as they are the farthest
extremities and the parts of the bodythat experience the maximum mechanical stress figure.
In addition, the nail body formsa back support for picking up small objects
with the fingers. The nail bodyis composed of densely packed dead caradenosites.
(28:36):
The epidermis in this part of thebody has evolved a specialized structure upon which
nails can form. The nail bodyforms at the nail root, which has
a matrix of proliferating cells from thestraight and bile that enables the nail to
grow continuously. The lateral nail foldoverlaps the nail on the sides, helping
to anchor the nail body. Thenail fold that meets the proximal end of
(28:56):
the nail body forms the nail cuticle, also called the epinichium. The nail
bed is rich in blood vessels,making it a pure pink except at the
base, where a thick layer ofepithelium over the nail matrix forms a crescent
shaped region called the lunula the littlemoon. The area beneath the free edge
of the nail furthest from the cuticleis called the hyponichium. It consists of
(29:19):
a thickened layer of stratum cornium nails. These two images show anatomy of the
finger nail region. The top imageshows a dorsal view of a finger.
The proximal nail fold is the partunderneath where the skin of the finger connects
with the edge of the nail.The epinichium is a thin pink layer between
(29:40):
the white proximal edge of the nail, the lunula, and the edge of
the finger skin. The lunula appearsas a crescent shaped white area at the
proximal edge of the pink shaded nail. The lateral nail folds are where the
sides of the nail contact the fingerskin. The distal edge of the nail
is white and is called the freeedge. An erro indicates that the nail
(30:00):
grows distantly out from the proximal nailfold. The lower image shows a lateral
view of the nail bed anatomy.In this view one can see how the
edge of the nail is located justproximal to the nail fold. This end
of the nail from which the nailgrows is called the nail root. The
nail is an accessory structure of theintegumentary system. Sweat glands. When the
(30:25):
body becomes warm, cuderiforous glands producesweat to cool the body. Sweat glands
develop from epidermal projections into the dermisand are classified as maracrine glands. That
is, the secretions are excreted byexocytosis to reduct without affecting the cells of
the gland. There are two typesof sweat glands, each secreting slightly different
products. An acrin sweat gland istype of gland that produces a hypotonic sweat
(30:51):
for thermoregulation. These glands are foundall over the skin surface, but are
especially abundant on the palms of thehand, the saals of the feet,
and the forehead figure. They arecoiled glands lying deep in the dermis,
with the duck rising up to apore on the skin surface where the sweat
is released. This type of sweatreleased by exocytosis is hypotonic and composed mostly
(31:15):
of water, with some salt antibodies, traces of metabolic waste and dermocitin and
antimicrobial peptide. Ekron glands are aprimary component of thermoregulation in humans and thus
helped to maintain homeostasis. Ekrin gland. This diagram shows an acron sweat gland
embedded in a cross section of skintissue. The ekron sweat gland is a
(31:37):
bundle of white tubes embedded in thedermis. A single white tube travels up
from the bundle and opens onto thesurface of the epidermis. The opening is
called the poor There are several poreson the small block of skin portrayed in
this diagram. Ekron glands are coiledglands in the dermis that release sweat that
is mostly water. An apricrins wetgland is usually associated with hair follicles in
(32:01):
densely hairy areas such as armpits andgenital regions. Apricrine sweat glands are larger
than acrine sweat glands and lie deeperin the dermis, sometimes even reaching the
hypodermis, with the duct normally emptyinginto the hair follicle. In addition to
water and salts, apricrine sweat includesorganic compounds that make the sweat thicker and
(32:22):
subject to bacterial decomposition and subsequent smell. The release of this sweat is under
both nervous and hormonal control and playsa role in the poorly understood human pheromone
response. Most commercial antiperspirants use analuminum based compound as their primary active ingredient
to stop sweat. When the antiperspirandenters the sweat gland duct, the aluminium
(32:45):
based compounds precipitate due to a changein pH and form a physical block in
the duct, which prevents sweat fromcoming out of the poor. Sebaceous glands.
A sebaceous gland is a type ofoil gland that is found all over
the body and helps to lubricate andwater proof the skin and hair. Most
sebaceous glands are associated with hair follicles. They generate an excrete sebum, a
(33:07):
mixture of lipids, onto the skinsurface, thereby naturally lubricating the dry and
dead layer of keratinized cells of thestratum corneum, keeping it pliable. The
fatty acids of sebum also have antibacterialproperties and prevent water loss from the skin.
In low humidity environments. The secretionof sebum is stimulated by hormones,
(33:28):
many of which do not become activeuntil puberty. Thus, sebacious glands are
relatively inactive during childhood. Functions ofthe skin. The skin in accessory structures
perform a variety of essential functions,such as protecting the body from invasion by
microorganisms, chemicals, and other environmentalfactors, preventing dehydration, acting as a
(33:50):
sensory organ, modulating body temperature andelectrolyte balance, and synthesizing vitamin D.
The underlying hypodermis has important roles instoring facts, forming a cushion over underlying
structures, and providing insulation from coldtemperatures. Protection the skin protects the rest
of the body from the basic elementsof nature, such as wind, water,
(34:12):
and UV sunlight. It acts asa protective barrier against water loss due
to the presence of layers of keratinand glycolipids in the stratum corneum. It
also is the first line of defenseagainst abrasive activity due to contact with grit
microbes or harmful chemicals. Sweat excretedfrom sweat glands deeters microbes from overcolonizing the
(34:32):
skin surface by generating dermocytin, whichhas antibiotic properties sensory function. The fact
that you can feel an ant crawlingon your skin, allowing you to flick
it off before it bites is becausethe skin, and especially the hair's projecting
from hair follicles in the skin,can sense changes in the environment. The
hair root plexus surrounding the base ofthe hair follicle senses of disturbance and then
(34:55):
transmits the information to the central nervoussystem, brain and spinal cord, which
can then respond by activating the scalvalmuscles of your eyes to see the ant
and the scalaval muscles of the bodyto act against the ant. The skin
acts as a sense organ because theepidermis, dermis, and the hypodermis contains
specialized sensory nerve structures that detect touch, surface temperature, and pain. These
(35:19):
receptors are more concentrated on the tipsof the fingers, which are most sensitive
to touch, especially the Meisener corpusaltactyle corpusoal figure, which responds to light
touch, and the Picinian corpusal lamellatedcorpusol, which responds to vibration. Mercle
cells scenes scattered in the straight andbio are also touch receptors. In addition
to these specialized receptors, there aresensory nerves connected to each hair follicle,
(35:45):
pain and temperature receptors scattered throughout theskin, and motor nerves innervate the erector,
pyli, muscles, and glands.This reach innervation helps us sense our
environment and react accordingly. Light micrographof a Meisener corpusal. This micrograph shows
a skin cross section at low magnification. The Meisner's corpusal is a large oval
(36:06):
shaped structure located in the papillary layerof the dermis, under the lowest deepest
layer of the epidermis. The corpusalcontains a dark staining oval. Within the
outer light staining oval, several horizontalbars are arranged vertically within the inner oval.
Also, several cells with dark purplenuclei can be seen scattered throughout the
(36:27):
corpusal. In this micrograph of askin cross section, you can see a
Meisner corpusal arrow, a type oftech receptor located in a dermal papilla adjacent
to the basement membrane and straight andbile of the overlying epidermis alm times one
hundred credit Ben Smith slash Wikimedia Commons. Thermoregulation, the integumentary system helps regulate
(36:49):
body temperature through its tight association witha sympathetic nervous system, the division of
the nervous system involved in our fightor flight responses. The sympathetic nervous system
is continuously monitoring body temperature and initiatingappropriate motor responses. Recall that sweat glands,
accessory structures to the skin, secretewater, salt, and other substances
(37:12):
to cool the body when it becomeswarm, even when the body does not
appear to be noticeably sweating, Approximatelyfive hundred millimeters of sweat insensible perspiration are
secreted a day. If the bodybecomes excessively warm due to high temperatures,
vigorous activity figure EEK, or acombination of the two, sweat glands will
be stimulated by the sympathetic nervous systemto produce large amounts of sweat, as
(37:35):
much as zero point seven to onepoint five all per hour for an active
person. When the sweat evaporates fromthe skin surface, the body is cooled
as body heat is dissipated. Inaddition to sweating, arterials in the dermist
dilate so that excess heat carried bythe blood can dissipate through the skin and
into the surrounding environment Figure EBB.This accounts for the skin redness that many
(37:59):
people experience one exercising thermoregulation. PartA is a photo of a man skiing
with several snow covered trees in thebackground. Part B is a diagram with
a right and left half. Theleft half is tidled heat is retained by
the body, while the right halfis tidled heat loss through radiation and convection.
(38:19):
Both show blood flowing from an arterythrough three capillary beds within the skin.
The beds are arranged vertically, withthe topmost bed located along the boundary
of the dermis and epidermis. Thebottomost bed is located deep in the hypodermis.
The middle bed is evenly spaced betweenthe topmost and bottomost beds. In
each bed, oxygenated blood red entersthe bed on the left, and deoxygenated
(38:45):
blood blue leaves the bed on theright. The left diagram shows a picture
of snow flicks above the capillary beds, indicating that the weather is cold.
Blood is only flowing through the deepestof the three capillary beds, as the
upper beds are closed off to reduceheat loss from the outer layers of the
skin. The right diagram shows apicture of the sun above the capillary beds,
(39:07):
indicating that the weather is hot.Blood is flowing through all three capillary
beds, allowing heat to radiate outof the blood, increasing heat loss.
Parts is a photo of a manrunning through a forested trail on a summer
day. During strenuous physical activities suchas skiing, a or running see,
the dermal blood vessels dilate and sweatsecretion increases B. These mechanisms prevent the
(39:31):
body from overheating. In contrast,the dermal blood vessels constrict to minimize heat
loss in response to low temperatures Bcredit a tricyle slash flicker credit c Ralph
Daily. When body temperatures drop,the arterials constrict to minimize heat loss,
particularly in the ends of the digitsand tip of the nose. This reduced
(39:53):
circulation can result in the skin takingon a whitish hue. Although the temperature
or of the skin drops as aresult, passive heat loss is prevented and
internal organs and structures remain warm.If the temperature of the skin drops too
much, such as environmental temperatures belowfreezing, the conservation of body core heat
can result in the skin actually freezing, a condition called frostbite. Aging and
(40:19):
the integumentary system. All systems inthe body accumulate subtle and some not so
subtle changes as a person ages.Among these changes are reductions in cell division,
metabolic activity, blood circulation, hormonallevels, and muscle strength. Figure
in the skin, These changes arereflected in decreased mitosis in the straight and
(40:40):
bio leading to a thinner epidermis.The dermis, which is responsible for the
elasticity and resilience of the skin,exhibits a reduced ability to regenerate, which
leads to slower wound healing. Thehypodermis, with its fat stores, loses
structure due to the reduction and redistributionof fat, which in turn contributes to
the thinning and sagging of skin aging. This figure consists of two photos.
(41:07):
One photo shows a young woman onthe phone. Her skin is smooth and
unwrinkled. The other photo shows anelderly woman in the same posture while on
the phone. The skin of herhands and forearms is wrinkled. Generally,
skin, especially on the face andhands, starts to display the first noticeable
(41:27):
signs of aging as it loses itselasticity over time. Credit Janet Ramsden.
The accessory structures also have lowered activity, generating thinner hair and nails and reduced
amounts of sebum and sweat. Areduced sweating ability can cause them elderly to
be intolerant to extreme heat. Othercells in the skin, such as melanocytes
(41:49):
and dendritic cells, also become lessactive, leading to a paler skin tone
and lowered immunity. Wrinkling of theskin occurs due to break down of its
structure, which results from decreased oologenand elastin production in the dermis, weakening
of muscles lying under the skin,and the inability of the skin to retain
adequate moisture. Many antiaging products canbe found in stores today. In general,
(42:13):
these products try to rehydrate the skinand thereby fill out the wrinkles,
and some stimulate skin growth using hormonesand growth factors. Additionally, invasive techniques
include collagen injections to plump the tissueand injections of Botox, registered the name
brand of the bachelinum neurotoxin that paralyzethe muscles that crease the skin and cause
wrinkling. Vitamin D synthesis The epidermallayer of human skin synthesizes vitamin D when
(42:39):
exposed to UV radiation. In thepresence of sunlight, a form of vitamin
D three called colcalciphril is synthesized froma derivative of the steroid cholesterol. In
the skin, The liver converts colicalcipherlto calcidiol, which is then converted to
calcitriol, the active chemical form ofthe vitamin and the kidneys. Vitamin D
(43:00):
is essential for normal absorption of calciumand phosphorus, which are required for healthy
bones. The absence of sun exposurecan lead to a lack of vitamin D
in the body, leading to acondition called rickets, a painful condition in
children where the bones are misshapen dueto a lack of calcium, causing bolagidness.
Elderly individuals who suffer from vitamin Ddeficiency can develop a condition called osteomolasia,
(43:24):
a softening of the bones. Inpresent day society, vitamin D is
added as a supplement to many foods, including milk and orange juice, compensating
for the need for sun exposure.In addition to its essential role in bone
health, vitamin D is essential forgeneral immunity against bacterial, viral, and
fungal infections. Recent studies are alsofinding a link between insufficient vitamin D and
(43:50):
cancer. This podcast will be releasedepisodically and follow the sections of the text
book in the description. For adeeper under standing, We encourage you review
the text version of this work voiceby voicemaker Donayane. This was produced by
Brandon Castiro as a creative Common Senseproduction.
Welcome to Principles of Biology. Thisbook was written by the Open Alternative Textbook
Initiative at Kansas State University and isbeing released as a podcast and distributed under
the terms of the Creative Commons AttributionLicense. Today's episode is chapter twenty eight
the integumentary System. All hyperlinks,images and sources can be found at the
(00:23):
link to the book. In thedescription, I am not this hair,
I am not this skin. Iam the soul that lives within jalal ad
Din Rumy. Rumy's line plays onthe unusual focus on hair color and skin
color that humans have had for manycenturies and asks us to look more deeply
than those superficial layers. That isgood advice, but at the same time,
(00:45):
those superficial layers of hair, skin, nails, et cetera, known
collectively as the integument, have manyinteresting structures and many important biological functions.
They protect organisms from many environmental hazardsand injuries, including disease as well as
heat or cold. To do this, the integument relies on interactions with many
(01:06):
other organ systems, including the circulatory, nervous, and immune systems. Its
beauty is indeed more than skin deep. The structure of skin. Although you
may not typically think of the skinas an organ, it is in fact
made of tissues that work together asa single structure to perform unique and critical
functions. The skin and its accessorystructures make up the integumentary system, which
(01:30):
provides the body with overall protection.The skin is made of multiple layers of
cells and tissues, which are heldto underlying structures by connective tissue. Figure
one. The deeper layer of skinis well vascularized has numerous blood vessels.
It also has numerous sensory and autonomicand sympathetic nerve fibers, ensuring communication to
(01:52):
and from the brain. There aretwo main layers, epidermis and dermis,
with a third connective layer, thehypodermis layer of skin. This illustration shows
a cross section of skin tissue.The outermost layer is called the epidermis and
occupies one fifth of the cross section. Several hairs are emerging from the surface.
(02:13):
The epidermis dives around one of thehairs, forming a follicle. The
middle layer is called the dermis,which occupies four fifths of the cross section.
The dermis contains an erector pilli muscleconnected to one of the follicles.
The dermis also contains an acrone sweatgland composed of a bunch of tubules.
One tubule travels up from the bunchthrough the epidermis, opening onto the surface
(02:38):
of poor There are two string likenerves traveling vertically through the dermis. The
right nerve is attached to a Pissiniancorpusal, which is a yellow structure consisting
of concentric ovals similar to an onion. The lowest level of the skin,
the hypodermis, contains fatty tissue,arteries and veins. Blood vessels travel from
(02:59):
the hypodermis and connect to hair folliclesand erector pilli muscle in the dermis.
The skin is composed of two mainlayers, the epidermis, made of closely
packed upithelial cells, and the dermis, made of dense, irregular connective tissue
that houses blood vessels, hair follicles, sweat glands, and other structures.
Beneath the dermis lies the hypodermis,which is composed mainly of loose, connective
(03:23):
and fatty tissues the epidermis. Theepidermis is composed of keratinized, stratified squamous
epithelium. It is made of fouror five layers of epithelial cells, depending
on its location in the body.It does not have any blood vessels within
it. Ie. It is avascular skin that has four layers of cells
(03:44):
is referred to as thin skin fromdeep to superficial. These layers are the
stratum bile, stratum spinosum, stratumgranulosum, and stratum cornium. Most of
the skin can be classified as thinskin. Thick skin is found only on
the palms of the hands and thesaals of the feet. It has a
fifth layer called the stratum lucidum,located between the stratum cornium and the stratum
(04:08):
granulosum. Figure thin skin versus thickskin part A is a micrograph showing a
cross section of thin skin. Thetopmost layer is a thin, translucent layer
with irregular texture in areas where cellsare slowing off. The deepest layer is
dark purple and extends into the thirdlayer with finger like projections. The third
(04:30):
light purple layer contains thin bands offibers and small dark cells. The fourth
and deepest layer is darker than thethird layer, but is still light purple.
It contains thick fiber bands that areloosely packed. Part B is a
magnified view of the epidermis of thickskin. It shows the topmost layers five
times thicker than the topmost layer ofthin skin. The topmost layer of thick
(04:55):
skin is also denser and less translucentthan the topmost layer of thin skin.
These slides show cross sections of theepidermis and dermis of a thin end B
thick skin. Note the significant differencein the thickness of the epithelial layer of
the thick skin from top ALM timesforty ALAM times forty micrographs provided by the
(05:17):
Regions of University of Michigan Medical School, copyright twenty twelve. The cells in
all of the layers except the stratumbile are called keratinocytes. A keratinosite is
a salt that manufactures and stores theprotein keratin. Keratin is an intracellular fibrous
protein that gives hair, nails,and skin their hardness and water resistant properties.
(05:40):
The keratinosites and the stratum cornium aredead and regularly slew away, being
replaced by cells from the deeper layersfigure epidermis. The outer layer of cells
in this micrograph is the thinnest layerand stained deep purple due to full keratinization
of dead cells. The next layer, occupies one quarter of the micrograph,
is lightly stained and is a densecollection of cells. The third layer from
(06:03):
the top is mostly white, withlightly stained, loosely packed strands radiating in
random directions. The bottommost layer isdensely packed with thick bands of highly organized
muscle tissue that are darkly stained.The epidermis is epithelium composed of multiple layers
of cells. The basal layer consistsof cuboidal cells, whereas the outer layers
(06:26):
are squamous keratenized cells, so thewhole epithelium is often described as being keratenized
stratified squamous epithelium ALAM times forty micrographprovided by the Regions of University of Michigan
Medical School, copyright two twelve.Layer of the epidermis stratum bile. The
stratum bio, also called the stratumgerminativum, is the deepest epidermal layer and
(06:48):
attaches the epidermis to the basal laminabelow, which lie the layers of the
dermis. The cells in the stratumbile bond to the dermis via intertwining collagen
fibers referred to as the basement membrane. A fingerlike projection or fold known as
the dermal popilla plural equals dermal popilli, is found in the superficial portion of
(07:09):
the dermis. Dermal popilli increase thestrength of the connection between the epidermis and
dermis. The greater the folding,the stronger the connections made Figure point two.
Other cell types are found dispersed amongthe basal cells and the straightum bile.
The first is a mercal cell,which functions as a receptor and is
responsible for stimulating sensory nerves that thebrain perceives as touch. These cells are
(07:31):
especially abundant on the surfaces of thehands and feet. The second is a
melanocyte, a cell that produces thepigment melanin. Melanin gives hair and skin
its color and also helps protect theliving cells of the epidermis from ultraviolet UV
radiation damage layers of the epidermis.This illustration shows a cross section of the
(07:54):
epidermis. The cells of the innermostlayer, the straightum bile, are large
and have a pal nucleus. Thestratum bile curls around the dermis, which
projects into the epidermis. The stratumbile contains four layers of large, triangle
shaped keratinocytes. Fibers are visible withinthe spaces between caratinocytes and the stratum biole.
(08:16):
A melanocyte is also present in thislayer. The melanocyte possesses fingerlike projections
extending from its main cell body.The projections branch through the extracellular spaces between
nearby caratinocytes. Above the stratum bileis the stratum spinosum, which consists of
eight layers of oval shaped keratinocytes.The nucleus is present in these keratinocytes,
(08:41):
but has faded to a lighter purple. The stratum granulosum contains five layers of
keratinocytes, each containing spots in itscytoplasm labeled the lamellar granules. The stratum
lucidium contains four layers of diamond shapedcells with no nucleus. The stratum cornium
contains nine layers of keratinosites with nonucleus nor cytoplasm. A few of the
(09:03):
cells in the topmost layer of thestratum cornium are flaking off from the skin.
The epidermis of thick skin has fivelayers straightum bio stratum spinosom, Stratum
granulosum, Stratum lucidum, and stratumcornium stratum spinosome. As the name suggests,
the stratum spinosom is spiny in appearancedue to the protruding cell processes that
(09:26):
join the cells via a structure calledthe desmosome. The desmosome's interlock with each
other and strengthen the bond between thecells. It is interesting to note that
the spiny nature of this layer isan artifact of the staining process. Unstained
epidermis samples do not exhibit this characteristicappearance. The stratum spinosom is composed of
(09:46):
eight to ten layers of keratinosites formedas a result of cell division in the
stratum bio figure. Interspersed among thekeratinosites of this layer is a type of
dendritic cell called the longer Han cell, which functions as a macrophage by engulfing
bacteria, foreign particles, and damagedcells that occur in this layer. The
(10:07):
keratinosites and the stratum spinosome begin thesynthesis of keratin and release a water repelling
glycolipit that helps prevent water loss fromthe body, making the skin relatively waterproof.
As new keratinosites are produced atop thestratum bio, the keratinosites of the
stratum spinosom are pushed into the Stratumgranulosum Stratum granulosum. The stratum granulosum has
(10:30):
a grainy appearance due to further changesto the keratinosites. As they are pushed
from the Stratum spinosum. The cellsthree to five layers deep, become flatter,
their cell membranes thicken, and theygenerate large amounts of the protein's keratin,
which is fibrous, and keratohylin,which accumulates as lamellar granules within the
cells sea figure. These two proteinsmake up the bulk of the keratinosite mass
(10:52):
and the stratum granulosum, and givethe layer its grainy appearance. The nuclei
and other cell organelles dis integrate asthe cells die, leaving behind the keratin,
keratohylin, and cell membranes that willform the Stratum lucidum, the stratum
cornium, and the accessory structures ofhair and nails. Stratum lucidum. The
Stratum lucidum is a smooth, seeminglytranslucent layer of the epidermis, located just
(11:16):
above the stratum granulosum and below thestratum cornium. This thin layer of cells
is found only in the thick skinof the palms. Cells and digits.
The keratinocytes that compose the stratum lucidumare dead and flattened Sea figure. These
cells are densely packed with a lyden, a clear protein rich in lipids derived
(11:37):
from keratohylin, which gives these cellsthey're transparent i e. Lucid appearance and
provides a barrier to water. Stratumcornium. The stratum cornium is the most
superficial layer of the epidermis and isthe layer exposed to the outside environment Sea
figure. The increased keratinization, alsocalled cornification, of the cells in this
(11:58):
layer gives it its name. Thereare usually fifteen to thirty layers of cells
in the stratum cornium. This dry, dead layer helps prevent the penetration of
microbes and the dehydration of underlying tissues, and provides a mechanical protection against abrasion
for the more delicate underlying layers.Cells in this layer are shed periodically and
are replaced by cells pushed up fromthe stratum granulosum or stratum lucidum in the
(12:22):
case of the palms and cells offeet. The entire layer is replaced during
a period of about four weeks.Cosmetic procedures such as microdermabrasion help remove some
of the dry upper layer and aimto keep the skin looking fresh and healthy.
Dermis the dermis might be considered thecore of the integumentary system. Derma
(12:43):
equal skin as distinct from the epidermisapy equals upon are over and hypodermis hypoequals
below. It contains blood and limpvessels, nerves, and other structures such
as hair, follicles and sweat glands. The dermis is made of two layers
of connective tissue that compose an interconnectedmesh of elastin and colagenous fibers produced by
(13:05):
fibroblasts. Figure layers of the dermis. This micrograph shows layers of skin in
a cross section. The papillary layerof the dermis extends between the downward fingers
of the darkly stained upidermis. Thepapillary layer appears finer than the reticular layer,
consisting of smaller, densely packed fibers. The reticular layer is three times
(13:28):
thicker than the papillary layer and containslarger, thicker fibers. The fibers seem
more loosely packed than those of thepapillary layer, with some separated by empty
spaces. Both layers of the dermiscontained cells with darkly stained nuclei. This
stained slide shows the two components ofthe dermis, the papillary layer and the
reticular layer. Both are made ofconnective tissue, with fibers of collagen extending
(13:54):
from one to the other, makingthe border between the two somewhat indistinct.
The dermal papilli stending into the epidermistsbelonged to the papillary layer, whereas the
dense collagen fiber bundles below belonged tothe reticular layer. Alam times ten credit
modification of work by kill bad SlashWikimedia Commons papillary layer. The papillary layer
(14:16):
is made of loose connective tissue,which means the collagen and elastin fibers of
this layer form a loose mesh.This superficial layer of the dermist projects into
the straight and bile of the epidermistto form fingerlike dermal papilli. SA figure.
Within the papillary layer are fibroblasts,a small number of fat cells,
adipocytes, and an abundance of smallblood vessels. In addition, the papillary
(14:41):
layer contains phagocytes, defensive cells thathelp fight bacteria or other infections that have
breached the skin. This layer alsocontains lymphatic capillaries, nerve fibers, and
touch receptors called the Meisner corpusals reticularlayer. Underlying the papillary layer is the
much thicker reticular layer, composed ofdense, irregular connective tissue. This layer
(15:03):
is well vascularized and has a richsensory and sympathetic nerve supply. The reticular
layer appears reticulated net like due toa tight meshwork of fibers. Elastin fibers
provides some elasticity to the skin,enabling movement. Collagen fibers provide structure and
tensile strength, with strands of collagenextending into both the papillary layer and the
(15:26):
hypodermis. In addition, collogen bindswater to keep the skin hydrated. Collogen
injections and retinate creams help restore skinturger by either introducing collogen externally or stimulating
blood flow and repair of the dermis, respectively hypodermis. The hypodermis, also
(15:46):
called the subcutaneous layer or superficial fascia, is a layer directly below the dermis
and serves to connect the skin tothe underlying fascia fibrous tissue of the bones
and muscles. It is not strictlya part of the skin, though the
border between the hypodermis and dermis canbe difficult to distinguish. The hypodermis consists
of well vascularized loose a realer connectivetissue, and adipose tissue, which functions
(16:11):
as a mode of fat storage andprovides insulation and cushioning for the integument.
Pigmentation, the color of skin isinfluenced by a number of pigments, including
melanin, keratine, and hemoglobin.Recall that melanin is produced by cells called
melanocytes, which are found scattered throughoutthe stratum bile of the epidermis. The
(16:32):
melanin is transferred into the keratinocytes viaa cellular vesicle called a melanosome. Figure
skin pigmentation. This figure consists oftwo diagrams side by side The right diagram
shows development of light colored skin.The left shows development of dark colored skin.
In both. A brown melanocyte sitsat the border between the dermis and
(16:53):
epidermis. The melanocyte has a largenucleus and six fingerlike its engines, these
reach between cells of the stratum basalis. Sections of the extensions detach and travel
through the skins. These are melanosomes. In the left diagram, both the
melanocyte and melanosomes contain melanin particles shownas dark dots. Melanosomes travel upwards to
(17:19):
outer skin layers, releasing melanin.As a result. Keratinocytes in the left
diagram contain several melanin particles that darkenskin color. In light colored skin,
the melanocyte contains no melanin, itstill releases melanosomes into upper layers of the
skin. However, these melanosomes containno melanin. Therefore, the skin does
(17:42):
not darken and remains light. Therelative coloration of the skin depends on the
amount of melanin produced by melanocytes inthe stratum bio and taken up by keratinocytes.
Melanine occurs in two primary forms.Eumelanin exists as black and whereas piomelanin
provides a red color. Dark skinnedindividuals produce more melanin than those with pale
(18:07):
skin. Exposure to the UV raysof the sun or a tanning salon causes
melanin to be manufactured and build upin keratinocytes. As sun exposure stimulates keratinocytes
to secrete chemicals that stimulate melanocytes.The accumulation of melanin in keratinocytes results in
the darkening of the skin or atan This increased melanin accumulation protects the DNA
(18:30):
of epidermal cells from UV ray damageand the breakdown of folic acid and nutrient
necessary for our health and well being. In contrast, too much melanin can
interfere with the production of vitamin D, an important nutrient involved in calcium absorption.
Thus, the amount of melanin presentin our skin is dependent on a
balance between available sunlight and folic aciddestruction and protection from UV radiation and vitamin
(18:55):
D production. It requires about tendays after initial sun exposure for melanin synthesis
to peak, which is why paleskinned individuals tend to suffer sunburns of the
epidermis. Initially dark skinned individuals canalso get sunburns, but are more protected
than are pale skinned individuals. Melanosomesare temporary structures that are eventually destroyed by
(19:17):
fusion with lysosomes. This fact,along with melanin filled keratinocytes in the stratum
corneum sloughing off, makes tanning impermanent. Too much sun exposure can eventually lead
to wrinkling due to the destruction ofthe cellular structure of the skin, and
in severe cases, can cause sufficientDNA damage to result in skin cancer.
When there is an irregular accumulation ofmelanocytes in the skin, freckles appear.
(19:41):
Moles are larger masses of melanocytes,and although most are benign, they should
be monitored for changes that might indicatethe presence of cancer. Figure moles.
Five photos of moles. The threeupper photos show moles that are small,
flat, and dark brown. Thebottom left photo shows a dark black mole
(20:02):
that is raised above the skin.The bottom right photo shows a large,
raised, reddish mole with protruding hairs. Moles range from benign accumulations of melanocytes
to melanomas. These structures populate thelandscape of our skin. Credit the National
Cancer institute accessory structures of the skin. Accessory structures of the skin include hair
(20:25):
nails, sweat glands, and sebaceousglands. These structures embryologically originate from the
epidermis and can extend down through thedermis into the hypodermis. Hair hair is
a caratinous filament growing out of theepidermis. It is primarily made of dead
keratinized cells. Strands of hair originatein an epidermal penetration of the dermis called
(20:48):
the hair follicle. The hair shaftis the part of the hair not anchored
to the follicle, and much ofthis is exposed at the skin surface.
The rest of the hair, whichis anchored in the follicle, lies below
the surface of the skin and isreferred to as the hair root. The
hair root ends deep in the dermisat the hair bulb and includes a layer
of mitotically active basal cells called thehair matrix. The hair bulb surrounds the
(21:14):
hair papilla, which is made ofconnective tissue and contains blood capillaries and nerve
endings from the dermis. Figure hair. This diagram shows a cross section of
the skin containing a hair follicle.The follicle is teardrop shaped. Its enlarged
base, labeled the hair bulb,is embedded in the hypodermis. The outermost
(21:34):
layer of the follicle is the epidermis, which invaginates from the skin surface to
envelope the follicle. Within the epidermisis the outer root sheath, which is
only present on the hair bulb.It does not extend up the shaft of
the hair. Within the outer rootsheath is the inner root sheath. The
inner root sheath extends about half ofthe way up the hair shaft, ending
(21:56):
midway through the dermis. The hairmatrix is the innermost layer. The hair
matrix surrounds the bottom of the hairshaft, where it is embedded within the
hair bowl. The hair shaft initself contains three layers, the outermost cuticle,
a middle layer called the cortex,and an innermost layer called the medulla.
(22:17):
Hair follicles originate in the epidermis andhave many different parts. Just as
the basal layer of the epidermis formsthe layers of epidermists that get pushed to
the surface as the dead skin onthe surface sheds, The basal cells of
the hair bulb divide and push cellsoutward in the hair root and shaft.
As the hair grows. The medullaforms the central core of the hair,
which is surrounded by the cortex,a layer of compressed caratenized cells that is
(22:41):
covered by an outer layer of veryhard caratenized cells known as the cuticle.
These layers are depicted in a longitudinalcross section of the hair follicle figure.
Although not all hair has a medallarylayer, hair texture straight, curly is
determined by the shape and structure ofthe cortex and to the extent that it
is present, the medulla. Theshape and structure of these layers are in
(23:06):
turn determined by the shape of thehair follicle. Hair growth begins with the
production of keratinocytes by the basal cellsof the hair bulb. As new cells
are deposited at the hair bulb,the hair shaft is pushed through the follicle
towards the surface. Keratinization is completedas the cells are pushed to the skin
surface to form the shaft of hairthat is externally visible. The external hair
(23:29):
is completely dead and composed entirely ofkeratin. For this reason, our hair
does not have sensation. Furthermore,you can cut your hair or shave without
damaging the hair structure. Because thecut is superficial. Most chemical hair removers
also act superficially. However, electrolysisand yanking both attempt to destroy the hair
bulb, so hair cannot grow hairfollicle. This micrograph is of the base
(23:55):
of a hair follicle. The protrudinghair is largely transparent, with only its
dark outline visible. The inner rootsheath is visible, surrounding the very bottom
of the hair as a circle ofcells with dark staining nuclei. The inner
sheath extends up the hair shaft.The outer root sheath is much thicker than
the inner root sheath, consisting ofa large oval of lighter staining cells.
(24:18):
The oval surrounds the bottom of thehair and extends into the hypodermis. The
slide shows a cross section of ahair follicle. Basal cells of the hair
matrix in the center differentiate into cellsof the inner root sheath. Basal cells
at the base of the hair rootform the outer root sheath. Alam times
four credit modification of work by killbad Slash Wikimedia Commons. The wall of
(24:44):
the hair follicle is made of threeconcentric layers of cells. The cells of
the internal root sheaths surround the rootof the growing hair and extend just up
to the hair shaft. They arederived from the basal cells of the hair
matrix. The external root sheath,which is an extension of the epidermis,
encloses the hair root. It ismade of basal cells at the base of
(25:06):
the hair root and tends to bemore keratinous in the upper regions. The
glassy membrane is a thick, clear, connective tissue sheath covering the hair root,
connecting it to the tissue of thedermis. Hair serves a variety of
functions including protection, sensory input,thermoregulation, and communication. For example,
(25:26):
hair on the head protects the skullfrom the sun. The hair in the
nose and ears, and around theeyes eyelashes defends the body by trapping and
excluding dust particles that may contain allergensand microbes. Hair of the eyebrows prevents
sweat and other particles from dripping intoand bothering the eyes. Hair also has
a sensory function due to sensory innervationby a hair root plexus surrounding the base
(25:49):
of each hair follicle. Hair isextremely sensitive to air movement or other disturbances
in the environment, much more sothan the skin surface. This feature is
also useful for the detection of thepresence of insects or other potentially damaging substances
on the skin surface. Each hairroot is connected to a smooth muscle called
the erector pylie that contracts in responseto nerve signals from the sympathetic nervous system,
(26:14):
making the external hairshaft stand up.The primary purpose for this is to
trap a layer of air to addinsulation. This is visible in humans as
goose bumps, and even more obviousin animals, such as when a frightened
cat raises its fur. Of course, this is much more obvious in organisms
with a heavier coat than most humans, such as dogs and cats. Hair
(26:37):
growth hair grows and is eventually shedand replaced by new hair. This occurs
in three phases. The first isthe anogen phase, during which cells divide
rapidly at the root of the hair, pushing the hair shaft up and out.
The length of this phase is measuredin years, typically from two to
seven years. The cattagen phase lastsonly two to three weeks and marks a
(27:00):
transition from the hair follicles act ofgrowth. Finally, during the telligen phase,
the hair follicle is at rest andno new growth occurs. At the
end of this phase, which lastsabout two to four months, another anogen
phase begins. The basal cells inthe hair matrix then produce a new hair
follicle, which pushes the old hairout as the growth cycle repeats itself.
(27:22):
Hair typically grows at the rate ofzero point three millimeters per day during the
enogen phase. On average, fiftyhairs are lost and replaced per day.
Hair Loss occurs if there is morehair shed than what is replaced, and
can happen due to hormonal or dietarychanges. Hair loss can also result from
the aging process or the influence ofhormones. Hair color, similar to the
(27:47):
skin, hair gets its color fromthe pigment melanin produced by melanocytes in a
hair papilla. Different hair color resultsfrom differences in the type of melanin,
which is genetically determined. As aper In ages, the melanin production decreases
and hair tends to lose its colorand becomes gray and are white. Nails
the nail bed is a specialized structureof the epidermis that is found at the
(28:11):
tips of our fingers and toes.The nail body is formed on the nail
bed and protects the tips of ourfingers and toes as they are the farthest
extremities and the parts of the bodythat experience the maximum mechanical stress figure.
In addition, the nail body formsa back support for picking up small objects
with the fingers. The nail bodyis composed of densely packed dead caradenosites.
(28:36):
The epidermis in this part of thebody has evolved a specialized structure upon which
nails can form. The nail bodyforms at the nail root, which has
a matrix of proliferating cells from thestraight and bile that enables the nail to
grow continuously. The lateral nail foldoverlaps the nail on the sides, helping
to anchor the nail body. Thenail fold that meets the proximal end of
(28:56):
the nail body forms the nail cuticle, also called the epinichium. The nail
bed is rich in blood vessels,making it a pure pink except at the
base, where a thick layer ofepithelium over the nail matrix forms a crescent
shaped region called the lunula the littlemoon. The area beneath the free edge
of the nail furthest from the cuticleis called the hyponichium. It consists of
(29:19):
a thickened layer of stratum cornium nails. These two images show anatomy of the
finger nail region. The top imageshows a dorsal view of a finger.
The proximal nail fold is the partunderneath where the skin of the finger connects
with the edge of the nail.The epinichium is a thin pink layer between
(29:40):
the white proximal edge of the nail, the lunula, and the edge of
the finger skin. The lunula appearsas a crescent shaped white area at the
proximal edge of the pink shaded nail. The lateral nail folds are where the
sides of the nail contact the fingerskin. The distal edge of the nail
is white and is called the freeedge. An erro indicates that the nail
(30:00):
grows distantly out from the proximal nailfold. The lower image shows a lateral
view of the nail bed anatomy.In this view one can see how the
edge of the nail is located justproximal to the nail fold. This end
of the nail from which the nailgrows is called the nail root. The
nail is an accessory structure of theintegumentary system. Sweat glands. When the
(30:25):
body becomes warm, cuderiforous glands producesweat to cool the body. Sweat glands
develop from epidermal projections into the dermisand are classified as maracrine glands. That
is, the secretions are excreted byexocytosis to reduct without affecting the cells of
the gland. There are two typesof sweat glands, each secreting slightly different
products. An acrin sweat gland istype of gland that produces a hypotonic sweat
(30:51):
for thermoregulation. These glands are foundall over the skin surface, but are
especially abundant on the palms of thehand, the saals of the feet,
and the forehead figure. They arecoiled glands lying deep in the dermis,
with the duck rising up to apore on the skin surface where the sweat
is released. This type of sweatreleased by exocytosis is hypotonic and composed mostly
(31:15):
of water, with some salt antibodies, traces of metabolic waste and dermocitin and
antimicrobial peptide. Ekron glands are aprimary component of thermoregulation in humans and thus
helped to maintain homeostasis. Ekrin gland. This diagram shows an acron sweat gland
embedded in a cross section of skintissue. The ekron sweat gland is a
(31:37):
bundle of white tubes embedded in thedermis. A single white tube travels up
from the bundle and opens onto thesurface of the epidermis. The opening is
called the poor There are several poreson the small block of skin portrayed in
this diagram. Ekron glands are coiledglands in the dermis that release sweat that
is mostly water. An apricrins wetgland is usually associated with hair follicles in
(32:01):
densely hairy areas such as armpits andgenital regions. Apricrine sweat glands are larger
than acrine sweat glands and lie deeperin the dermis, sometimes even reaching the
hypodermis, with the duct normally emptyinginto the hair follicle. In addition to
water and salts, apricrine sweat includesorganic compounds that make the sweat thicker and
(32:22):
subject to bacterial decomposition and subsequent smell. The release of this sweat is under
both nervous and hormonal control and playsa role in the poorly understood human pheromone
response. Most commercial antiperspirants use analuminum based compound as their primary active ingredient
to stop sweat. When the antiperspirandenters the sweat gland duct, the aluminium
(32:45):
based compounds precipitate due to a changein pH and form a physical block in
the duct, which prevents sweat fromcoming out of the poor. Sebaceous glands.
A sebaceous gland is a type ofoil gland that is found all over
the body and helps to lubricate andwater proof the skin and hair. Most
sebaceous glands are associated with hair follicles. They generate an excrete sebum, a
(33:07):
mixture of lipids, onto the skinsurface, thereby naturally lubricating the dry and
dead layer of keratinized cells of thestratum corneum, keeping it pliable. The
fatty acids of sebum also have antibacterialproperties and prevent water loss from the skin.
In low humidity environments. The secretionof sebum is stimulated by hormones,
(33:28):
many of which do not become activeuntil puberty. Thus, sebacious glands are
relatively inactive during childhood. Functions ofthe skin. The skin in accessory structures
perform a variety of essential functions,such as protecting the body from invasion by
microorganisms, chemicals, and other environmentalfactors, preventing dehydration, acting as a
(33:50):
sensory organ, modulating body temperature andelectrolyte balance, and synthesizing vitamin D.
The underlying hypodermis has important roles instoring facts, forming a cushion over underlying
structures, and providing insulation from coldtemperatures. Protection the skin protects the rest
of the body from the basic elementsof nature, such as wind, water,
(34:12):
and UV sunlight. It acts asa protective barrier against water loss due
to the presence of layers of keratinand glycolipids in the stratum corneum. It
also is the first line of defenseagainst abrasive activity due to contact with grit
microbes or harmful chemicals. Sweat excretedfrom sweat glands deeters microbes from overcolonizing the
(34:32):
skin surface by generating dermocytin, whichhas antibiotic properties sensory function. The fact
that you can feel an ant crawlingon your skin, allowing you to flick
it off before it bites is becausethe skin, and especially the hair's projecting
from hair follicles in the skin,can sense changes in the environment. The
hair root plexus surrounding the base ofthe hair follicle senses of disturbance and then
(34:55):
transmits the information to the central nervoussystem, brain and spinal cord, which
can then respond by activating the scalvalmuscles of your eyes to see the ant
and the scalaval muscles of the bodyto act against the ant. The skin
acts as a sense organ because theepidermis, dermis, and the hypodermis contains
specialized sensory nerve structures that detect touch, surface temperature, and pain. These
(35:19):
receptors are more concentrated on the tipsof the fingers, which are most sensitive
to touch, especially the Meisener corpusaltactyle corpusoal figure, which responds to light
touch, and the Picinian corpusal lamellatedcorpusol, which responds to vibration. Mercle
cells scenes scattered in the straight andbio are also touch receptors. In addition
to these specialized receptors, there aresensory nerves connected to each hair follicle,
(35:45):
pain and temperature receptors scattered throughout theskin, and motor nerves innervate the erector,
pyli, muscles, and glands.This reach innervation helps us sense our
environment and react accordingly. Light micrographof a Meisener corpusal. This micrograph shows
a skin cross section at low magnification. The Meisner's corpusal is a large oval
(36:06):
shaped structure located in the papillary layerof the dermis, under the lowest deepest
layer of the epidermis. The corpusalcontains a dark staining oval. Within the
outer light staining oval, several horizontalbars are arranged vertically within the inner oval.
Also, several cells with dark purplenuclei can be seen scattered throughout the
(36:27):
corpusal. In this micrograph of askin cross section, you can see a
Meisner corpusal arrow, a type oftech receptor located in a dermal papilla adjacent
to the basement membrane and straight andbile of the overlying epidermis alm times one
hundred credit Ben Smith slash Wikimedia Commons. Thermoregulation, the integumentary system helps regulate
(36:49):
body temperature through its tight association witha sympathetic nervous system, the division of
the nervous system involved in our fightor flight responses. The sympathetic nervous system
is continuously monitoring body temperature and initiatingappropriate motor responses. Recall that sweat glands,
accessory structures to the skin, secretewater, salt, and other substances
(37:12):
to cool the body when it becomeswarm, even when the body does not
appear to be noticeably sweating, Approximatelyfive hundred millimeters of sweat insensible perspiration are
secreted a day. If the bodybecomes excessively warm due to high temperatures,
vigorous activity figure EEK, or acombination of the two, sweat glands will
be stimulated by the sympathetic nervous systemto produce large amounts of sweat, as
(37:35):
much as zero point seven to onepoint five all per hour for an active
person. When the sweat evaporates fromthe skin surface, the body is cooled
as body heat is dissipated. Inaddition to sweating, arterials in the dermist
dilate so that excess heat carried bythe blood can dissipate through the skin and
into the surrounding environment Figure EBB.This accounts for the skin redness that many
(37:59):
people experience one exercising thermoregulation. PartA is a photo of a man skiing
with several snow covered trees in thebackground. Part B is a diagram with
a right and left half. Theleft half is tidled heat is retained by
the body, while the right halfis tidled heat loss through radiation and convection.
(38:19):
Both show blood flowing from an arterythrough three capillary beds within the skin.
The beds are arranged vertically, withthe topmost bed located along the boundary
of the dermis and epidermis. Thebottomost bed is located deep in the hypodermis.
The middle bed is evenly spaced betweenthe topmost and bottomost beds. In
each bed, oxygenated blood red entersthe bed on the left, and deoxygenated
(38:45):
blood blue leaves the bed on theright. The left diagram shows a picture
of snow flicks above the capillary beds, indicating that the weather is cold.
Blood is only flowing through the deepestof the three capillary beds, as the
upper beds are closed off to reduceheat loss from the outer layers of the
skin. The right diagram shows apicture of the sun above the capillary beds,
(39:07):
indicating that the weather is hot.Blood is flowing through all three capillary
beds, allowing heat to radiate outof the blood, increasing heat loss.
Parts is a photo of a manrunning through a forested trail on a summer
day. During strenuous physical activities suchas skiing, a or running see,
the dermal blood vessels dilate and sweatsecretion increases B. These mechanisms prevent the
(39:31):
body from overheating. In contrast,the dermal blood vessels constrict to minimize heat
loss in response to low temperatures Bcredit a tricyle slash flicker credit c Ralph
Daily. When body temperatures drop,the arterials constrict to minimize heat loss,
particularly in the ends of the digitsand tip of the nose. This reduced
(39:53):
circulation can result in the skin takingon a whitish hue. Although the temperature
or of the skin drops as aresult, passive heat loss is prevented and
internal organs and structures remain warm.If the temperature of the skin drops too
much, such as environmental temperatures belowfreezing, the conservation of body core heat
can result in the skin actually freezing, a condition called frostbite. Aging and
(40:19):
the integumentary system. All systems inthe body accumulate subtle and some not so
subtle changes as a person ages.Among these changes are reductions in cell division,
metabolic activity, blood circulation, hormonallevels, and muscle strength. Figure
in the skin, These changes arereflected in decreased mitosis in the straight and
(40:40):
bio leading to a thinner epidermis.The dermis, which is responsible for the
elasticity and resilience of the skin,exhibits a reduced ability to regenerate, which
leads to slower wound healing. Thehypodermis, with its fat stores, loses
structure due to the reduction and redistributionof fat, which in turn contributes to
the thinning and sagging of skin aging. This figure consists of two photos.
(41:07):
One photo shows a young woman onthe phone. Her skin is smooth and
unwrinkled. The other photo shows anelderly woman in the same posture while on
the phone. The skin of herhands and forearms is wrinkled. Generally,
skin, especially on the face andhands, starts to display the first noticeable
(41:27):
signs of aging as it loses itselasticity over time. Credit Janet Ramsden.
The accessory structures also have lowered activity, generating thinner hair and nails and reduced
amounts of sebum and sweat. Areduced sweating ability can cause them elderly to
be intolerant to extreme heat. Othercells in the skin, such as melanocytes
(41:49):
and dendritic cells, also become lessactive, leading to a paler skin tone
and lowered immunity. Wrinkling of theskin occurs due to break down of its
structure, which results from decreased oologenand elastin production in the dermis, weakening
of muscles lying under the skin,and the inability of the skin to retain
adequate moisture. Many antiaging products canbe found in stores today. In general,
(42:13):
these products try to rehydrate the skinand thereby fill out the wrinkles,
and some stimulate skin growth using hormonesand growth factors. Additionally, invasive techniques
include collagen injections to plump the tissueand injections of Botox, registered the name
brand of the bachelinum neurotoxin that paralyzethe muscles that crease the skin and cause
wrinkling. Vitamin D synthesis The epidermallayer of human skin synthesizes vitamin D when
(42:39):
exposed to UV radiation. In thepresence of sunlight, a form of vitamin
D three called colcalciphril is synthesized froma derivative of the steroid cholesterol. In
the skin, The liver converts colicalcipherlto calcidiol, which is then converted to
calcitriol, the active chemical form ofthe vitamin and the kidneys. Vitamin D
(43:00):
is essential for normal absorption of calciumand phosphorus, which are required for healthy
bones. The absence of sun exposurecan lead to a lack of vitamin D
in the body, leading to acondition called rickets, a painful condition in
children where the bones are misshapen dueto a lack of calcium, causing bolagidness.
Elderly individuals who suffer from vitamin Ddeficiency can develop a condition called osteomolasia,
(43:24):
a softening of the bones. Inpresent day society, vitamin D is
added as a supplement to many foods, including milk and orange juice, compensating
for the need for sun exposure.In addition to its essential role in bone
health, vitamin D is essential forgeneral immunity against bacterial, viral, and
fungal infections. Recent studies are alsofinding a link between insufficient vitamin D and
(43:50):
cancer. This podcast will be releasedepisodically and follow the sections of the text
book in the description. For adeeper under standing, We encourage you review
the text version of this work voiceby voicemaker Donayane. This was produced by
Brandon Castiro as a creative Common Senseproduction.
Popular Podcasts
Stuff You Should Know
If you've ever wanted to know about champagne, satanism, the Stonewall Uprising, chaos theory, LSD, El Nino, true crime and Rosa Parks, then look no further. Josh and Chuck have you covered.
Dateline NBC
Current and classic episodes, featuring compelling true-crime mysteries, powerful documentaries and in-depth investigations. Follow now to get the latest episodes of Dateline NBC completely free, or subscribe to Dateline Premium for ad-free listening and exclusive bonus content: DatelinePremium.com
The Bobby Bones Show
Listen to 'The Bobby Bones Show' by downloading the daily full replay.