Chapter 27.1 Endocrine System

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/[e-mail] is licensed under a Creative Commons Attribution License 4.0 license.

Episode Transcript

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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 seven
point one Endocrine System. All hyperlinks, images and sources can be found at

(00:22):
the link to the book. Inthe description, the specific character of the
greater part of the toxins which areknown to us I need only instant such
toxins as those of tetanus and dietheria, would suggest that the substances produced for
effecting the correliation of organs within thebody through the intermediation of the blood stream
might also belong to this class,since here also specificity of action must be

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a distinguishing characteristic. These chemical messengers, however, or hormones from the Greek
romunu to excite or arouse, aswe might call them, have to be
carried from the organ where they areproduced to the organ which they affect by
means of the blood stream, andthe continually recurring physiological needs of the organism
must determine their repeated production in circulationthroughout the body. Ernest Henry Starling the

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chemical correlation of the functions of thebody the Lancet, nineteen oh five two
three hundred and forty. Hormones,as Starling noted, are produced by one
organ and affect the activities of otherorgans. Unlike nerro transmitters, which you
will learn about later in this module, hormones move via the bloodstream from the
site of production to the site ofaction. But like neurotransmitters, hormones are

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key players in maintaining homeostasis. Beforewe discuss that, however, we need
to review homeostasis and introduce the majorclasses of animal hormones. Types of hormones.
Maintaining homeostasis within the body requires thecoordination of many different systems and organs.
Communication between neighboring cells and between cellsand tissues and distant parts of the

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body occurs through the release of chemicalscalled hormones. Hormones are chemicals that are
released by cell into body fluids,usually blood, and which act on target
cells at some distance from the cellsthat release the hormone. At the target
cells, which are cells that havea receptor for the chemical, the hormones
elicit or response the cells, tissuesand organs that secrete hormones make up the

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endocrine system. Examples of glands ofthe endocrine system include the adrenal glands,
which produce hormones such as epinephrin andnoropinephrin that regulate responses to stress, and
the thyroid gland, which produces thyroidhormones that regulate metabolic rates. Although there
are many different hormones in the humanbody, they can be divided into two

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general classes based on their chemical structureand water solubility. Steroid hormones most are
derivatives of cholesterol, which are notsoluble in water, and peptide peptides and
proteins hormones, which are readily solublein water. One of the key distinguishing
features of lipid derived hormones is thatthey can diffuse across plasma membranes, whereas
the peptide hormones cannot. Lip derivedhormones or lipid soluble hormones, most lipid

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hormones are derived from cholesterol and thusare structurally similar to it, as illustrated
in figure. The primary class oflipid hormones in humans is the steroid hormones.
Examples of steroid hormones include estradiol,which is an estrogen or female sex
hormone, and testosterone, which isan androgen or male sex hormone. These

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two hormones are released by the femaleand male reproductive organs, respectively. Other
steroid hormones include aldosterone and corticol,which are released by the adrenal glands,
along with some other types of androgens. Steroid hormones are insoluble in water and
need to be bound to transport proteinsin order to be transported in the blood.

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As a result, they remain inthe body longer than peptide hormones.
For example, corticol has a halflife of sixty to ninety minutes in humans,
while epinephron, an amino acid derivedhormone, has a half life of
approximately one minute. Part Ace showsthe molecular structure of cholesterol, which has
three six carbon rings attached to afive carbon ring. A hydroxyl group is

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attached to the first six membered ring, and a branched carbon chain is attached
to the five membered ring. Twomethyl groups are attached, each to a
carbon that links the rings together.Part Beach shows the molecular structure of testosterone,
which has a hydroxyl group in placeof the branched carbon chain found on
cholesterol. A ketone instead of ahydroxyl group, is attached to the six

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membered ring. Part C shows themolecular structure of estradiol, which, like
testosterone, as a hydroxyl group inplace of cholesterols branched carbon chain. Estradiol
also lacks one of the methyl groupsfound in cholesterol. The structure is shown
here represent a cholesterol plus the steroidhormones B, testosterone, and C estradiol

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peptide water soluble hormones. The peptidehormones include polypeptides, as well as several
relatively small molecules that are derived fromthe amino acids tyrocine and tryptophan shown in
Figure. Examples of amino acid derivedhormones include epinefrin and norepinephrin, which are
synthesized in the medulla of the adrenalglands, and thyroxine, which is produced

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by the thyroid gland. The pennialgland in the brain makes and secretes melatonin,
which regulates sleep cycles. PARTISE showsthe amino acid tyrocine on the left
and epinefron on the right. Epinephrinis similar in structure to tyrocine, with
minor modifications. Part Beach shows theamino acid tryptophan on the left and the

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structurally similar melatonin on the right.A. The hormone epineffrin, which triggers
the phyt or flight response, isderived from the amino acid tyrocine. B.
The hormone melatonin, which regulates circadianrhythms, is derived from the amino
acid tryptophan. Other peptide hormones arepolypeptides chains of amino acids linked by peptide

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bonds. These hormones include molecules thatare quite short polypeptide chains, such as
antidiuretic hormone nine amino acids and oxytocinalso nine amino acids, both of which
are produced in the brain and releasedinto the blood in the posterior pituitary gland.
This class also includes small proteins likethe growth hormones approximate one hundred and

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ninety amino acids produced by the pituitary, and large glycoproteins such as follicle stimulating
hormone, a complex of two differentpolypeptides, each about one hundred amino acids
in length produced by the pituitary.Figure illustrates these peptide hormones secreted peptides like
insulin, are stored within vesicles inthe cells that synthesize them. They are

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then released in response to stimulise suchas high blood glucose levels in a case
of insulin. Amino acid derived andpolypeptide hormones are water soluble. Therefore,
these hormones cannot cross the plasma membranesof cells. Receptors are found on the
surface of the target cells. Oxytocin, growth hormone and follicle stimulating hormone are

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all large with complex three dimensional structures. The structures of peptide hormones A,
oxytocin, B growth hormone, andC follicle stimulating hormone are shown. These
peptide hormones are much larger than thosederived from cholesterol or amino acids. How
hormones work, Hormones mediate changes intarget cells after binding to specific hormone receptors.

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In this way, even though hormonescirculate throughout the body and come into
contact with many different cell types,they only affect cells that possess the necessary
receptors. Receptors for a specific hormonemay be found on many different cells,
or may be limited to a smallnumber of specialized cells. For example,
thyroid hormones act on many different tissuetypes, stimulating metabolic activity throughout the body.

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Testosterone receptors are found in relatively fewcell types. Cells can have many
receptors for the same hormone, butoften also possess receptors for different types of
hormones. The number of receptors thatrespond to a hormone determines the cells sensitivity
to that hormone and the resulting cellularresponse. Receptor binding alter cellular activity and

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results in an increase or decrease innormal body processes, depending on the location
of the protein receptor on the targetcell and the chemical structure of the hormone.
Hormones can mediate changes directly by bindingto intracellular hormone receptors in modulating gene
transcription, or indirectly by binding tocell surface receptors and stimulating signaling pathways.

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Intracellular hormone receptors. Lipid soluble hormones, such as steroid hormones, diffuse across
the membranes of the cells, wherethey are produced Once outside the cell,
they bind to transport proteins that keepthem soluble in the blood stream. At
the target cell, the hormones arereleased from the carrier protein and diffuse across

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the lipid bilayer of the plasma membraneof cells. The steroid hormones pass through
the plasma membrane of a target celland bind to intracellular receptors residing in the
cytoplasm or in the nucleus. Thecell signaling pathways induced by the steroid hormones
regulates specific genes on the cell's DNA. The hormones and receptor complex act as
transcription regulators by increasing or decreasing thesynthesis of mRNA molecules of specific genes.

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The cellular responses are varied, rangingfrom changes in the structure of the cell
to the production of enzymes that catalyzenew chemical reactions. In this way,
the steroid hormone regulates specific cell processes, as illustrated in figure. Illustration shows
a hormone crossing the cellular membrane andattaching to the nr slash HSP complex.

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The complex associates releasing the heat shockprotein and nr slash hormone complex. The
complex dimerizes, enters the nucleus andattaches to an HRI element on DNA,
triggering transcription of certain genes. Anintracellular nuclear receptor NR is located in the
cytoplasm bound to a heat shock proteinHSP. Upon hormone binding, the receptor

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dissociates from the heat shock protein andtranslocates to the nucleus. In the nucleus,
the hormone receptor complex binds to aDNA sequence called the hormone response element
HRI, which triggers gene transcription andtranslation. The corresponding protein product can then
mediate changes in self function. Otherlipid soluble hormones that are not steroid hormones,

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such as vitamin D and thyroxine Areceptors located in the nucleus. The
hormones diffuse across both the plasma membraneand the nuclear envelope, then bind to
receptors in the nucleus. The hormonereceptor complex stimulates transcription of specific genes plasma
membrane hormone receptors. Peptide hormones arenot lipid soluble and therefore cannot diffuse through

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the plasma membrane of cells. Lipidinsoluble hormones bind to receptors on the outer
surface of the plasma membrane. Unlikesteroid hormones, lipid insoluble hormones do not
directly affect the target cell because theycannot enter the cell and act directly on
DNA. Binding of these hormones toa cell surface receptor results in activation of

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a signaling pathway. This triggers intracellularactivity and carries out the specific effects associated
with the hormone. In this way, nothing passes through the plasma membrane.
The hormone that binds at the surfaceremains at the surface of the cell,
while the intracellular product remains inside thecell. The hormone that initiates the signaling
pathway is called a first messenger,which activates a second messenger in a cytoplasm.

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As illustrated in figure. Illustration showsepinephrin bound to the extracellular surface of
a betadrinergic receptor. A G proteinassociated with the intracellular surface of the receptor
is activated when the GDP associated withit is replaced with GTP. The G
protein activates the enzymodenyl cyclase, whichconverts ATP to CMP, triggering a cellular

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response. The amino acid derived hormonesepinefron and noropineffrin bind to beatadrinergic receptors on
the plasma membrane of cells. Hormonebinding to receptor activates a G protein,
which in turn activates a dentyl cyclase, converting ATP to CMP. CMP is
a second messenger that mediates a cellspecific response. An enzyme called phosphodiasterase breaks

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down CMP, terminating the signal.The specific response of a cell to a
lipid insoluble hormone depends on the typeof receptors that are present on the plasma
membrane and the substrate molecules present inthe cell cytoplasm. Cellular responses to hormone
binding of a receptor include altering membranepermeability in metabolic pathways, stimulating synthesis of

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proteins and enzymes, and activating hormonerelease. Hormonal regulation of body systems.
Hormones have a wide range of effectsand modulate many different body processes. Two
regulatory processes that will be examined hereas examples are regulation of the functions of
the reproductive system and regulation of carbohydratemetabolism hormonal regulation of the reproductive system.

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Regulation of the reproductive system is aprocess that requires the action of hormones from
the pituitary gland, the adrenal cortex, and the gonads. During puberty,
in both males and females, thehypothalamus produces gonadotropin releasing hormone GnRH, which
stimulates the production and release of folliclestimulating hormone FSH and luteinizing hormone LH from

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the anterior pituitary gland. These hormonesregulate the gonads testes in males and ovaries
in females, and therefore are calledgonadotropins. In both males and females,
FSH stimulates gammet production in LH stimulatesproduction of hormones by the gonads. An
increase in gonad hormone levels inhibits GnRHproduction DROUGH, a negative feedback loop regulation

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of the male reproductive system. Inmales, FSH stimulates the maturation of sperm
cells. FSH production is inhibited bythe hormone in hibbon, which is released
by the testes. LH stimulates productionof the sex hormones androgens by the interstitial
cells of the tests and therefore isalso called interstitial cell stimulating hormone. The

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most widely known androgen in males istestosterone. Testosterone promotes the production of sperm
and masculine characteristics everyday. Connection thedangers of synthetic hormones. Photo shows baseball
player Jason Giomby at a game.Professional baseball player Jason Giomby publicly admitted to

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and apologized for is use of anabolicsteroids supplied by a trainer credit Bryce Words.
Some athletes attempt to boost their performanceby using artificial hormones that enhance muscle
performance. Anabolic steroids, a formof the male sex hormone testosterone, are
one of the most widely known performanceenhancing drugs. Steroids are used to help

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build muscle mass. Other hormones thatare used to enhance athletic performance include erythropoatin,
which triggers the production of red bloodcells, and human growth hormone,
which can help in building muscle mass. Most performance enhancing drugs are illegal for
non medical purposes. They are alsobanned by national and international governing bodies,

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including the International Olympic Committee, theUS Olympic Committee, the National Collegiate Athletic
Association, the Major League Baseball andthe National Football League. The side effects
of synthetic hormones are often significant andnon reversible, and in some cases fatal.
Androgens produce several complications, such asliver dysfunctions and liver tumors, prostate

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gland enlargement and difficulty urinating, prematureclosure of epiphesial cartilages, testicular atrophy,
infertility, and immune system depression.The physiological strain caused by these substances is
often greater than what the body canhandle, leading to unpredictable and dangerous effects
and linking their use to heart attacks, strokes, and impaired cardiac function.

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Regulation of the female reproductive system infemales FSH stimulates development of egg cells called
OVA, which develop in structures calledfollicles. Follicle cells produce the hormone in
hibbon, which inhibits FSH production.LH also plays a role in the development
of OVA, induction of ovulation andstimulation of estradiol and progesterone production by the

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ovaries, as illustrated in figure.Estradiol and progesterone are steroid hormones that prepare
the body for pregnancy. Estradiol producessecondary sex characteristics in females, while both
estradiol and progesterone regulate the innstrual cycle. The hypothalamus secretes GnRH, which stimulates
secretion of FSH and LH from thepituitary. The hypothalamus and pituitary are both

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found in the brain. FSH andLH stimulate follicle growth in the ovaries,
and a surge in LH triggers ovulation. The two ovaries, which are located
on either side of the uterus,secrete estradiol, progesterone, and inhibbon.
Estradiol and progesterone regulate female sex characteristicsand the menstrual cycle. In Hibbon inhibits

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FSH production by the pituitary in anegative feedback loop. Hormonal regulation of the
female reproductive system involves hormones from thehypothalamus, pituitary, and ovaries. In
addition to producing FSH and LH,the anterior portion of the pituitary gland also
produces the hormone prolactin PRL. Infemales, Prolactin stimulates the production of milk

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by the mammary lands following childbirth.Prolactin levels are regulated by the hypothalamic hormones
prolactin releasing hormone PR and prolactin inhibitinghormone pH, which is now known to
be dopamine. PRH stimulates the releaseof prolactin and pH inhibits it. This
is a classic negative feedback loop.The posterior pituitary releases the hormone oxytocin,

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which stimulates uterine contractions during childbirth.The uterine smooth muscles are not very sensitive
to oxytocin until late in pregnancy,when the number of oxytocin receptors in the
uterus peaks. Stretching of tissues inthe uterus and cervix stimulates oxytocin release.
During childbirth, contractions increase in intensityas blood levels of oxytocin rise via positive

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feedback mechanism until the birth is complete. Oxytocin also stimulates the contraction of myoepithelial
cells around the milk reducing mammary glands. As these cells contract, milk is
force from the secretory alveolite into milkducts and is ejected from the breasts in
milk ejection let down reflex. Oxytocinrelease is stimulated by the suckling of an

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infant, which triggers the synthesis ofoxytocin in the hypothalamus and its release into
circulation at the posterior pituitary. Hormonalregulation of carbohydrate metabolism. Blood glucose levels
vary widely over the course of aday as periods of food consumption alternate with
periods of fasting. Insulin and glucagonare the two hormones primarily responsible for maintaining

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homeostasis of blood glucose levels. Additionalregulation is mediated by the thyroid hormones.
Regulation of blood glucose levels by insulinand glucagon. Cells of the body require
nutrients in order to function, andthese nutrients are obtained through feeding. In
order to manage nutrient intake, storingexcess intake, and utilizing reserves when necessary,

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the body uses hormones to moderate energystores. Insulin is produced by the
beta cells of the pancreas, whichare stimulated to release insulin as blood glucose
levels rise. For example, aftera meal is consumed. Insulin lowers blood
glucose levels by enhancing the rate ofglucose uptake and utilization by target cells,
which use glucose for ATP production.It also stimulates the liver to convert glucose

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to glycogen, which is then storedby cells for later use. Insulin also
increases glucose transport into certain cells,such as muscle cells, fat cells,
and liver cells. This results froman insulin mediated increase in the number of
glucose transporter proteins in plasma membranes,which remove glucose from circulation by facilitated diffusion.

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As insulin binds to its target cellvia insulin receptors and signal transduction,
it triggers the cell to incorporate glucosetransport proteins into its membrane. Insulin also
stimulates the conversion of glucose to fatin adipocytes and a synthesis of proteins.
These actions mediated by insulin cause bloodglucose concentrations to fall, called a hypoglycemic

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low sugar effect, which inhibits furtherinsulin release from beta cells through a negative
feedback loop. When blood glucose levelsdecline below normal levels, for example,
between meals or when glucose is utilizedrapidly during exercise, the hormone glucagon is
released from the alpha cells of thepancreas Glucagon raises blood glucose levels, eliciting
what is called a hyperglycemic effect bystimulating the breakdown of glycogen to glucose in

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scleval muscle cells, and liver cellsin a process called glycogenolysis. Glucose can
then be utilized as energy by musclecells and released into circulation by the liver
cells. Glucagon also stimulates absorption ofamino acids from the blood by the liver,
which then converts them to glucose.This process of glucosynthesis is called gluconeogenesis.

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Glucagon also stimulates adipose cells to releasefatty acids into the blood. These
actions mediated by glucagon result in anincrease in blood glucose levels to normal homeostatic
levels. Rising blood glucose levels inhibitfurther glucagon release by the pancreas via negative
feedback mechanism. In this way,insulin and glucagon work together to maintain homeostatic

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glucose levels, as shown in link. When blood glucose levels fall, the
pancreas secretes the hormone glucagon. Glucagoncauses the liver to break down glycogen,
releasing glucose into the blood. Asa result, blood glucose levels rise.
In response to high glucose levels,the pancreas releases insulin. In response to

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insulin, target cells take up glucose, and the liver converts glucose to glycogen.
As a result, blood glucose levelsfall. Insulin and glucagon regulate blood
glucose levels via negative feedback mechanisms.Impaired insulin function can lead to a condition
called diabetes mallatis, the main symptomsof which are illustrated in figure. This

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can be caused by low levels ofinsulin production by the beta cells of the
pancreas, or by reduced sensitivity oftissue cells to insulin. This prevents glucose
from being absorbed by cells, causinghigh levels of blood glucose or hyperglycemia high
sugar. High blood glucose levels makeit difficult for the kidneys to recover all

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the glucose from nascent urine, resultingin glucose being lost in urine. High
glucose levels also result in less waterbeing reabsorbed by the kidneys, causing high
amounts of urine to be produced.This may result in dehydration over time.
High blood glucose levels can cause nervedamage to the ice and peripheral body tissues,
as well as damage to the kidneysand cardiovascular system. Over secretion of

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insulin can cause hypoglycemia low blood glucoselevels. This causes insufficient glucose availability to
cells, often leading to muscle weakness, and can sometimes cause unconsciousness or death
if left untreated. Symptoms of diabetesinclude excessive thirst, excessive hunger, lethargy
and stupor blurred vision, weight loss, breath that smells like acetone, hyperventilation,

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nausea, vomiting, abdominal pain,frequent urination, and glucose in the
urine. The main symptoms of diabetesare shown credit modification of Work by Michael
Hackstrom. Endocrine glands. Both theendocrine and nervous systems use chemical signals to
communicate and regulate the body's physiology.The endocrine system releases hormones that act on

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target cells to regulate development, growth, energy, metabolism, reproduction, and
many behaviors. The nervous system releasesneurotransmitters or neurohormones that regulate neurons, muscle
cells, and endocrine cells. Becausethe neurons can regulate the release of hormones.
The nervous and endocrine systems work ina coordinated manner to regulate the body's

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physiology. Hypothalamic pituitary axis the hypothalamusinvertebrates integrates the endocrine and nervous systems.
The hypothalamus is an endocrine organ locatedin the diencephalon of the brain. It
receives input from the body and otherbrain areas and initiates endocrine responses to environmental
changes. The hypothalamus acts as anendocrine organ, synthesizing hormones and transporting them

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along axons to the posterior pituitary gland. It synthesizes and secretes regulatory hormones that
control the endocrine cells in the anteriorpituitary gland. The hypothalamus contains autonomic centers
that control endocrine cells in the adrenalmedulla via neural control. The pituitary gland,

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sometimes called the hypothesis or master gland, is located at the base of
the brain in a celltersica, agroove of the sphenoid bone of the skull
illustrated in figure. It is attachedto the hypothalamus via stock called the pituitary
stalk or infindibulum. The anterior portionof the pituitary gland is regulated by releasing
or release inhibiting hormones produced by thehypothalamus, and the posterior pituitary receives signals

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via neuro secretary cells to release hormonesproduced by the hypothalamus. The pituitary has
two distinct regions, the anterior pituitaryand the posterior pituitary, which between them
secrete nine different peptide or protein hormones. The posterior lobe of the pituitary gland
contains axons of the hypothalamic neurons.The pituitary gland sits at the base of

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the brain, just above the brainstem. It is lobe shaped and hangs
down from the hypothalamus, to whichit is connected to via a narrow stalk.
The anterior part of the pituitary istoward the front and the posterior end
is toward the back. The pituitarygland is located at A the base of
the brain end b connected to thehypothalamus by the pituitary stalk. Credit a

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modification of work by NZI. CreditBYE modification of work by Gray's anatomy thyroid
gland. The thyroid gland is locatedin the nack, just below the larynx
and in front of the trachea.As shown in figure. It is a
butterfly shaped gland with two lobes thatare connected by the isthmus. It has
a dark red color due to itsextensive vascular system. When the thyroid swells

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due to dysfunction, it can befelt under the skin of the nac.
The thyroid is located in the nack, beneath the larynx and in front of
the trachea. It consists of rightand left lobes and a narrow central region
called the isthmus of thyroid. Abovethe isthmus of thyroid is the pyramidal lobe.
This illustration shows the location of thethyroid gland. Thyroid follical cells synthesize

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the hormone thyroxine, which is alsoknown as tphord because it contains four atoms
of iodine and triodothyronine, also knownas T three because it contains three atoms
of iodine. Follical cells are stimulatedto release stored T three in T four
by thyroid stimulating hormone TSH, whichis produced by the anterior pituitary. These

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thyroid hormones increase the rates of mitochondrialATP production. A third hormone, calcitonin,
is produced by parafulicular cells of thethyroid, either releasing hormones or inhibiting
hormones. Chalcitonine release is not controlledby TSH, but instead is released when
calcium ion concentrations in the blood rise. Chalcitonin functions to help regulate calcium concentrations

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in body fluids. It acts inthe bones to inhibit osteoclast activity and in
the kidneys to stimulate excretion of calcium. The combination of these two events lowers
body fluid levels of calcium. Parathyroidglands. Most people have four parathyroid glands,
however the number can vary from twoto six. These glands are located

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on the posterior surface of the thyroidgland, as shown in figure. Normally,
there is a superior gland and aninferior gland associated with each of the
thyroids two lobes. Each parithyroid glandis covered by connective tissue and contains many
secretory cells that are associated with acapillary network the parathyroid glands around structures located

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on the surface of the right andleft lobes of the thyroid gland. In
the illustration shown, there are twoparathyroid glands on each side, and one
is located above the other. Theparathyroid glands are located on the posterior of
the thyroid gland credit modification of workby NZI. The parathyroid glands produce parathyroid

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hormone PT. PTH increases blood calciumconcentrations when calcium ion levels fall below normal.
PTH one enhances reabsorption of C Atwo plus by the kidneys, two
stimulates osteoclast activity and inhibits osteoblast activity, and three it stimulates synthesis and secretion
of calcitriol by the kidneys, whichenhances C A two plus absorption by the

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digestive system. PTH and chalcitonin workin opposition to one another to maintain HOMEOSTATICA
two plus levels in body fluids.Adrenal glands. The adrenal glands are associated
with the kidneys. One gland islocated on top of each kidney, as
illustrated in figure. The adrenal glandsconsist of an outer adrenal cortex and an

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inner adrenal medulla. These regions secretedifferent hormones. The adrenal glands are lumpy,
irregular structures located on top of thekidneys. The location of the adrenal
glands on top of the kidneys isshown credit modification of work by NZI Adrenal
cortex. The adrenal cortex is madeup of layers of epithelial cells and associated

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capillary networks. This gland produces mineralcorticoids, glucocorticoids, and androgens. The
main mineral lolocorticoid, a class ofsteroid hormones that regulate salt and water balance,
is aldosterone, which regulates the concentrationof nonplus ions in urine, sweat,
pancreas, and saliva. Aldosterone releasefrom the adrenal cortex is stimulated by

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a decrease in blood concentrations of sodiumions, blood volume, or blood pressure,
or by an increase in blood potassiumlevels. The three main glucocorticoids steroid
hormones that regulate glucose metabolism, arecorticol corticosterone, and cortisone. The glucocorticoids
stimulate the synthesis of glucose and canalso enhance gluconeogenesis conversion of a non carbohydrate

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to glucose by liver cells. Theyalso promote the release of fatty acids from
adipose tissue. These hormones increase bloodglucose levels to maintain levels within a normal
range between meals. These hormones aresecreted in response to act and levels are
regulated by negative feedback. Androgens aresex hormones that promote masculinity. They are

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produced in small amounts by the adrenalcortex in both males and females. They
do not affect sexual characteristics and maysupplement sex hormones released from the gonads adrenal
medulla. The adrenal medulla contains twotypes of secretory cells, one that produces
epineffrin adrenaline and another that produces norabinefrinnor adrenaline. Epineffrin is the primary adrenal

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medulla hormone, accounting for seventy fiveto eighty percent of its secretions. Epinephrin
and noropineffrin increase heart rate, breathingrate, cardiac muscle contractions, blood pressure,
and blood glucose levels. They alsoaccelerate the breakdown of glucose in skeletal
muscles and stored fats in adipose tissue. The release of epinephrin and norabineffrin is

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stimulated by neural impulses from the sympatheticnervous system. Neural impulses originating from the
hypothalamus in respets distress release these hormonesto prepare the body for the phyd or
flight response. Pancreas the pancreas illustratedin figure is an elongated organ that is
located between the stomach and the proximalportion of the small intestine. It contains

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both exocrine cells that excrete digestive enzymesand endocrine cells that release hormones. It
is sometimes referred to as a heterocrinegland because it has both endocrine and exocrine
functions. The pancreas is a grainy, teardrop shaped organ tucked between the stomach
and intestine. The pancreas is foundunderneath the stomach and points toward the spleen.

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Credit modification of work by NZI,the endocrine cells of the pancreas form
clusters called pancreatic islets or the isletsof longer hans, as visible in the
micrograph shown in figure. The pancreaticislets contain two primary cell types, alpha
cells, which produce the hormone glucagon, and beta cells, which produce the

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hormone insulin. These hormones regulate bloodglucose levels. As blood glucose levels decline,
alpha cells release glucagon to raise theblood glucose levels by increasing rates of
glycogen breakdown and glucose release by theliver. When blood glucose levels rise,
such as after a meal, betacells release insulin to lower blood glucose levels

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by increasing the rate of glucose uptakein most body cells and by increasing glycogen
synthesis in skeletal muscles and the liver. Together, glucagon and insulin regulate blood
glucose levels. Micrograph shows purple stainedcells in a white tissue. The white
tissue is surrounded by tissue that stainspink. The islets of langerhons are clusters

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of endocrine cells found in the pancreasthey stain lighter than surrounding cells. Credit
modification of work by Mohammed Tea Tabian, Christopher P. White, Grant,
Morhin and bernard E touch scale Bardettafrom Matt Russell pennial gland. The pennial
gland produces mel melatonin. The rateof melatonin production is affected by the photoperiod

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amount of light in a twenty fourhour period. Nerves from the visual pathways
innervate the pineal gland. During theday light, little melatonin is produced.
However, melatonin production increases during thenight dark. In some mammals, melatonin
has an inhibitory effect on reproductive functionsby decreasing production and maturation of sperm oocytes

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and reproductive organs. Lastly, melatoninis involved in biological rhythms, particularly circadian
rhythms such as the sleep wake cycleand eating habits. Gonads. The gonads,
the male testes, and female ovariesproduce steroid hormones. The testes produce
androgens, testosterone being the most prominent, which allow for the development of secondary

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sex characteristics and the production of spermcells. The ovaries produce estradiol and progesterone,
which cause secondary sex characteristics and preparethe body for childbirth. This podcast
will be released episodically and follow thesections of the textbook in the description for
a deeper understanding. We encourage youreview the text version of this work voice

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by voicemaker Dotaane. This was producedby Brandon Casturo as a creative Common Sense Production