May 29, 2023 • 28 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.
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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 seven
point three How Animals Reproduce. Allhyperlinks, images and sources can be found
(00:22):
at the link to the book.In the description, reproduction is so primitive
and fundamental a function of vital organismsthat the mechanism by which it is assured
is highly complex and not yet clearlyunderstood. It is not necessarily connected with
sex, nor is sex necessarily connectedwith reproduction. Henry Havelock Ellis in Psychology
(00:43):
of Sects nineteen thirty three. Someanimals produce offspring through a sexual reproduction,
while other animals produce offspring through sexualreproduction. Both methods have advantages and disadvantages.
A sexual reproduction produces offspring that aregenetically identical to the parent, because
the offspring are all clones of theoriginal parent. A single individual can produce
(01:07):
offspring a sexually in large numbers ofoffspring can be produced quickly. These are
two advantages that a sexually reproducing organismshave over sexually reproducing organisms. In a
stable or predictable environment, asexual reproductionis an effective means of reproduction because all
the offspring will be adapted to thatenvironment. In an unstable or unpredictable environment,
(01:29):
species that reproduce a sexually may beat a disadvantage because all the offspring
are genetically identical and may not beadapted to different conditions. During sexual reproduction,
the genetic material of two individuals iscombined to produce genetically diverse offspring that
differ from their parents. The geneticdiversity of sexually produced offspring is thought to
(01:51):
give sexually reproducing individuals greater fitness becausemore of their offspring may survive and reproduce
in an unpredictable or changing environment.Species that reproduce sexually and have separate sexes
must maintain two different types of individuals, males and females. Only half the
population females can produce the offspring,so fewer offspring will be produced when compared
(02:15):
to a sexual reproduction. This isa disadvantage of sexual reproduction compared to a
sexual reproduction. A sexual reproduction asexual reproduction occurs in prokaryotic microorganisms bacteria,
Anarchaea and in many eukaryotic single celledand multi celled organisms, both plants and
(02:35):
animals. There are several ways thatanimals reproduce a sexually, the details of
which vary among individual species. Fissionfission, also called binary fission, occurs
in some invertebrate multi celled organisms.It is in some ways analogous to the
process of binary fission of single cellprocaryotic organisms. The term fission is applied
(02:58):
to instances in which an organism appearsto split itself into two parts and,
if necessary, regenerate the missing partsof each new organism. For example,
some flatworms, such as do Gesiaderhotocephala, are able to separate their bodies
into head and tail regions and thenregenerate the missing half in each of the
two new organisms. Sea anemonies Nideria, such as species of the genus Anthoplura
(03:21):
figure, will divide along the oorlaboroaxisand see cucumbers. A Chinodermida of the
genus hall Etheria will divide into twoholfs across the oorlaborolaxis and regenerate the other
half in each of the resulting individuals. Photo shows a larger cream colored seanemony
right next to another anemony of thesame color in shape but smaller. The
(03:42):
Anthoplura artemisia seanemony can reproduce through fissionbudding. Budding is a form of a
sexual reproduction that results from the outgrowthof a part of the body, leading
to a separation of the bud fromthe original organism and the formation of two
individuals, one smaller than the other. Budding occurs commonly in some invertebrate animals,
such as hydras and corals. Inhydras, a bud forms that develops
(04:06):
into an adult and breaks away fromthe main body. Figure Part A.
This shows a hydra which has astocklike body with tentacles growing out the top.
A smaller hydra is budding from theside of the stalk. Part B.
This photo shows branching white coral polyps. A hydra reproduce a sexually through
(04:27):
budding. A bud forms on thetubular body of an adult hydra, develops
a mouth and tentacles, and thendetaches from its parent. The new hydra
is fully developed and will find itsown location for attachment. B Some coral,
such as the Lophelia protusive shown here, can reproduce through budding kretibi modification
of work by ed Bulbi no Aslash Olympic Coast nms no A slash our
(04:51):
slash Office of Ocean Exploration. FragmentationFragmentation is the breaking of an individual into
parts, followed by generation. Ifthe animal is capable of fragmentation and the
parts are big enough, a separateindividual will regrow from each part. Fragmentation
may occur through accidental damage, damagefrom predators, or as a natural form
(05:14):
of reproduction. Reproduction through fragmentation isobserved in sponges, some Nigerians, turbilarians,
echinoderms, and annelids. In someseastars, a new individual can be
regenerated from a broken arm and apiece of the central disc. This sea
star figure is in the process ofgrowing a complete seastar from an arm that
(05:34):
has been cut off. Fisheries workershave been known to try to kill the
sea stars eating their clam or oysterbeds, by cutting them in half and
throwing them back into the ocean.Unfortunately for the workers, the two parts
can each regenerate a new half,resulting in twice as many sea stars to
prey upon. The oysters and clamspart A. The photo shows a brown
(05:56):
seastar with five arms of slightly varyinglengths. Part This is a photo of
a C star with one long armand four very short arms. A Linkiu
multiphora is a species of C starthat can reproduce a sexually via fragmentation.
In this process, be an armthat has been shed grows into a new
C star. Credit a modifiction ofwork by Duane Meadows noah slash nmfs slash
(06:20):
o pr. Parthenogenesis Parthenogenesis is aform of a sexual reproduction in which an
egg develops into an individual without beingfertilized. The resulting offspring can be either
haploid or diploid, depending on theprocess and the particular species. Parthenogenesis occurs
in invertebrates such as water fleas,rhodafers, aphids, stick insects, and
(06:44):
ants, wasps and bees. Ants, bees and wasps use parthenogenesis to produce
haploid males drones. The diploid females, workers and queens are the result of
a fertilized egg. Some vertebrate animals, including some reptiles, amphibians, and
fish, also reproduced through parthenogenesis.Parthenogenesis has been observed in species in which
(07:09):
the sexes were separated. In terrestrialor marine zoos, two female komodo dragons,
a hammerhead shark, and a blacktopshark have produced parthenogenic young even when
the females have been isolated from males. It is possible that these instances of
parthenogenesis occurred in response to unusual circumstancesstemming from captivity and would normally not occur.
(07:30):
Sexual reproduction. Sexual reproduction is thecombination of reproductive cells from two individuals,
each contributing a haploid gamete to generategenetically unique offspring. The nature of
the individuals that produce the two kindsof gametes can vary, having, for
example, separate sexes or both sexesin each individual. Hermaphroditism. Hermaphroditism occurs
(07:55):
in animals in which one individual hasboth male and female reproductive systems. Invertebrates
such as earthworms, slugs, tapeworms, and snails, figure are often hermaphroditic.
Hermaphrodites may self fertilize, but typicallythey will mate with another of their
species, fertilizing each other and bothproducing offspring. Self fertilization is more common
(08:16):
in animals that have limited mobility orare not motal, such as barnacles and
clams. Many species have specific mechanismsin place to prevent self fertilization because it
is an extreme form of inbreeding andusually produces less fit offspring. Part A
the photo shows a land snail.Part B the photo shows two snails mating.
(08:39):
Many A snails are hermaphrodites. Whentwo individuals b mate, they can
produce up to one hundred eggs each. Credit A modification of work by a
soft stillman. Credit B modification ofwork by scristious slash flicker. Fertilization,
the fusion of a sperm and anegg, is a process called fertilization.
(09:01):
This can occurr their inside internal fertilizationor outside external fertilization. The body of
the female humans provide an example ofthe former, whereas frog reproduction is an
example of the ladder external fertilization.External fertilization usually occurs in aquatic environments,
where both eggs and sperm are releasedinto the water. After the sperm reaches
(09:26):
the egg, fertilization takes place.Most external fertilization happens during the process of
spawning where one or several females releasetheir eggs and the males release sperm in
the same area at the same time. The spawning may be triggered by environmental
signals such as water temperature or thelength of daylight. Nearly all fish spawn,
(09:46):
as do crustaceans such as crabs andshrimp, molluscs such as oysters,
squid, and echinoderms such as seaurchins and sea cucumbers. Frogs, corals,
mayflies, and mosquitoes also spawn.Figure photo shows mating toads. The
larger female carries the smaller male onher back during sexual reproduction. In toads,
(10:09):
the male grasps the female from behindand externally fertilizes the eggs as they
are deposited. Credit Burnie Coal internalfertilization. Internal fertilization occurs most often in
terrestrial animals, although some aquatic animalsalso use this method. Internal fertilization may
occur by the male directly depositing spermin the female during mating. It may
(10:33):
also occur by the male depositing spermin the environment, usually in a protective
structure, which a female picks upto deposit the sperm. In her reproductive
tract. There are three ways thatoffspring are produced following internal fertilization. In
oviparity, fertilized eggs are laid outsidethe female's body and developed there, receiving
(10:54):
nourishment from the yoke that is apart of the egg figure A. This
occurs in insects, some bony fish, some reptiles, a few cartilaginous fish,
some amphibians, a few mammals,and all birds. Most non avian
reptiles and insects produce leathery eggs,while birds and some turtles produce eggs with
high concentrations of calcium carbonate in theshell, making them hard. Chicken eggs
(11:16):
are an example of a hard shell. The eggs of the egg laying mammals,
such as the platypus and Echidna,are leathery. In ovoviparity, fertilized
eggs are retained in the female andthe embryo obtains its nourishment from the eggs
yolk. The eggs are retained inthe female's body until they hatch inside of
her where she lays the eggs rightbefore they hatch. This process helps protect
(11:39):
the eggs until hatching. This occursin some bony fish, like the platyfish
Siphophrous Maculatus figure EBB, some sharks, lizards, some snakes, garter snake,
thamnoficer talus, some vipers, andsome invertebrate animals Matta, gascar hisssing
cockroche Gronfiterina portentosa. In viviparity,the young are born alive. They obtain
(12:03):
their nourishment from the female, andare born in varying states of maturity.
This occurs in most mammals figure AC, some cartilaginous fish, and a few
reptiles. Part A. The photoshows small yellow eggs on a leaf with
tiny beetles hatching out of some.Part B. The photo shows of fish
in an aquarium with a pale bulgingbelly parts. The photo shows a hairless
(12:26):
baby squirrel with closed eyes. Ina oviparity, young developed in eggs outside
the female body, as with theseHarmoniaxidritis beetles hatching. Some aquatic animals,
like this b pregnant Sypopherus maculatus,are oviviparous, with the egg developing inside
the female and nutritions applied primarily fromthe yoke. In mammals, nutrition is
(12:50):
supported by the placenta, as wasthe case with this see newborn squirrel credit
be modification of work by Gurmy Watchercredit ce modification of work by Autrum five
twenty nine slash flicker. Hormonal controlof reproduction in the animal kingdom. There
are many interesting examples of reproductive strategies, and hormones are involved in regulating all
(13:11):
of those. Rather than attempt tocover the wide diversity of strategies and hormones,
we will concentrate on the hormonal controlof reproduction in a single species,
Homo sapiens. The human male andfemale reproductive cycles are controlled by the interaction
of hormones from the hypothalamus and anteriorpituitary with hormones from reproductive tissues and organs.
(13:33):
In both sexes, the hypothalamus monitorsand causes the release of hormones from
the anterior pituitary gland. When thereproductive hormone is required, the hypothalamus sends
a gonadotropin releasing hormone GnRH to theanterior pituitary. This causes the release of
follicles stimulating hormone FSH and luteonizing hormoneLH from the anterior pituitary into the blood.
(13:58):
Although the hormones are named after theirfunctions in female reproduction, they are
produced in both sexes and play importantroles in controlling reproduction. Other hormones have
specific functions in the male and femalereproductive systems. Male hormones at the onset
of puberty, the hypothalamus causes therelease of FSH and LH into the male
(14:20):
system for the first time. FSHenters the tests and stimulates the Sertoli cells
located in the walls of the seminiferoustubules to begin promoting spermatogenesis. Figure LH
also enters the testes and stimulates theinterstitial cells of LYDIG located in between the
walls of the seminiferous tubules, tomake in release testosterone into the testes and
(14:41):
the blood. Testosterone stimulates spermatogenesis.This hormone is also responsible for the secondary
sexual characteristics that develop in the maleduring adolescence. The secondary sex characteristics in
males included deepening of the voice,the growth of facial, axillary and pubic
(15:01):
hare, an increase in muscle bulk, and the beginnings of the sex drive.
Hormonal control of the male reproductive systemis mediated by the hypothalamus, anterior
pituitary, and testes. The hypothalamusreleases gnrn, causing the anterior pituitary to
release LH and fsh. FSH andLH both act on the testes. FSH
(15:24):
stimulates the sertole cells and the testesto facilitate spermatogenesis and to secrete in hibbin.
LH causes the lydic cells and thetestes to secrete testosterone. Testosterone further
stimulates spermatogenesis by the sertole cells,but inhibits GnRH, LH, and FSH
production by the hypothalamus and anterior pituitary. In Hibbons secreted by sertol cells also
(15:48):
inhibits FSH and LH production by theanterior pituitary. Hormones control sperm production in
a negative feedback system. A negget a feedback system occurs in the mail
with rising levels of testosterone acting onthe hypothalamus and anterior pituitary to inhibit the
release of GnRH, FSH, andLH. In addition, the sertoli cells
(16:11):
produce the hormone in hibbon, whichis released into the blood when the sperm
count is too high. This inhibitsthe release of GnRH, and FSH,
which will cause spermatogenesis to slow down. If the sperm count reaches a low
of twenty million slash EML, thecyrtoli cells cease, the release of inhibbon,
and the sperm count increases female hormones. The control of reproduction in females
(16:36):
is more complex. The female reproductivecycle is divided into the ovarian cycle and
the menstrul cycle. The ovarian cyclegoverns the preparation of endocrine tissues and release
of eggs, while the menstrual cyclegoverns the preparation and maintenance of the uterine
lining figure. These cycles are coordinatedover a twenty two to thirty two day
(16:56):
cycle, with an average length oftwenty days. As with the male,
the g n r H from thehypothalamus causes the release of the hormones FSH
and LH from the anterior pituitary.In addition, estrogen and progesterone are released
from the developing follicles. As withtestosterone in males, estrogen is responsible for
(17:18):
the secondary sexual characteristics of females.These include breast development, flaring of the
hips, and a shorter period forbone growth. The ovarian cycle and the
menstrual cycle the ovarian and menstrual cyclesare regulated by hormones of the hypothalamus,
pituitary, and ovaries. Figure Theebb and flow of the hormones causes the
(17:41):
ovarian and menstrual cycles to advance.The ovarian and menstrual cycles occur concurrently.
The first half of the ovarian cycleis the follicular phase, slowly rising levels
of FSH because the growth of follicleson the surface of the ovary. This
process prepares the egg for ovulation.As the follicles grow, they begin releasing
(18:03):
estrogen. The first few days ofthis cycle coincide with menstruation, or the
slowing off of the functional layer ofthe endometrium in the uterus. After about
five days, estrogen levels rise andthe menstrual cycle enters the proliferative phase.
The endometrium begins to regrow, replacingthe blood vessels and glands that deteriorated during
(18:25):
the end of the last cycle.Hormone levels during the follicular phase ovulation and
the luteal phase are compared. Duringthe follicular phase, LH and FSH secreted
from the pituitary stimulate several follicles togrow. The follicles produce low levels of
estrogen that inhibit GnRH secretion by thehypothalamus, keeping LH and FSH levels low.
(18:48):
Low levels of estrogen also cause theendometrio arteries to constrict, resulting in
men'struation. During the time leading upto ovulation, LH and FSH stimulate maturation
of one of the follicles. Thegrowing follicle begins to produce high levels of
estrogen, which stimulates GnRH secretion bythe hypothalamus. As a result, LH
(19:11):
and FSH levels rise, resulting inovulation about a day later. Estrogen also
causes the endometrium to thicken. Afterovulation, the ovarian cycle enters the luteal
phase. LH from the pituitary stimulatesgrowth of the corpus lutium from the ruptured
follicle. The corpus lutium secretes estrogenand progesterone that block GnRH production by the
(19:34):
hypothalamus. In LH and FSH productionby the pituitary. Estrogen and progesterone also
cause the endometrium to further develop.The ovarian and menstrual cycles of female reproduction
are regulated by hormones produced by thehypothalamus, pituitary, and ovaries just prior
(19:55):
to the middle of the cycle,approximately day fourteen. The high level of
estrogen causes FSH and especially LH torise rapidly then fall. The spike in
LH causes the most mature follical torupture and release its egg. This is
ovulation. The follicles that did notrupture degenerate, and their eggs are lost.
(20:15):
The level of estrogen decreases when theextra follicles degenerate. Following ovulation,
the ovarian cycle enters its luteal phaseand the menstrual cycle enters its secretory phase,
both of which run from about dayfifteen to twenty eight. The ludeal
and secretory phases refer to changes inthe ruptured follicle. The cells in the
(20:36):
follicle undergo physical changes and produce astructure called a corpus lutium. The corpus
lutium produces estrogen and progesterone. Theprogesterone facilitates the regrowth of the uterine lining
and inhibits the release of further FSHand LH. The uterus is being prepared
to accept a fertilized egg should itoccurred during the cycle. The inhibition of
(21:00):
FSH and LH prevents any further eggsand follicles from developing. While the progesterone
is elevated, the level of estrogenproduced by the corpus lutium increases to a
steady level for the next few days. If no fertilized egg is implanted into
the uterus, the corpus lutium degeneratesin the levels of estrogen and progesterone decrease.
(21:21):
The endometrium begins to degenerate as theprogesterone levels drop, initiating the next
menstrual cycle. The decrease in progesteronealso allows the hypothalamus to send GnRH to
the anterior pituitary, releasing FSH andLH and starting the cycles again. Gestation
pregnancy begins with the fertilization and implantationof an egg and continues through to the
(21:45):
birth of the individual. The lengthof time of gestation, or the gestation
period, in humans, is twohundred and sixty six days and is similar
in other grade apes. Gestation periodsin other animals range from twelve to thirteen
days in the America an apossum tothe six hundred and sixty day gestation period
of the African elephant. Within twentyfour hours of fertilization, the egg nucleus
(22:07):
has finished myosis and the egg andsperm nuclei fuse. With fusion. The
cell is known as a zygote.The zygode initiates cleavage and the developing embryo
travels through the oviduct to the uterus. The developing embryo must implant into the
wall of the uterus within seven daysor it will deteriorate and die. The
(22:29):
outer layers of the developing embryo orblastocyst, grow into the endometrium by digesting
the endometrial cells, and healing ofthe endometrium closes up the blastocyst into the
tissue. Another layer of the blastocyst, the chorean, begins releasing a hormone
called human beta choreonic gonadotropin beta hCG, which makes its way to the corpus
lutium and keeps that structure active.This ensures adequate levels of progesterone that will
(22:53):
maintain the endometrium of the uterus forthe support of the developing embryo. Pregnant
sea tests determine the level of betahCG in urine or serum. If the
hormone is present, the test ispositive. The gestation period is divided into
three equal periods or trimesterors. Duringthe first two to four weeks of the
(23:15):
first trimester, nutrition and waste arehandled by the endometrio lining through diffusion.
As the trimester progresses, the outerlayer of the embryo begins to merge with
the endometrium, and the placenta forms. The placenta takes over the nutrient and
waste requirements of the embryo and fetus, with the mother's blood passing nutrients to
the placenta and removing waste from it. Chemicals from the fetus, such as
(23:40):
bilirubin are processed by the mother's liverfor elimination. Some of the mother's aminoglobulins
will pass through the placenta, providingpassive immunity against some potential infections. Internal
organs and body structures begin to developduring the first trimester. By five weeks,
limbbuds, eye, the heart,and liver have been basically formed.
(24:03):
By eight weeks, the term fetusapplies and the body is essentially formed Figure
A. The individual is about fivecentimeters two inches in length, and many
of the organs such as the lungsand liver are not yet functioning. Exposure
to any toxins is especially dangerous duringthe first trimester, as all of the
bodies, organs, and structures aregoing through initial development. Anything that interferes
(24:27):
with chemical signaling during that development canhave a severe effect on the fetus survival.
Part A photo shows a human fetuswith a large bent head and a
dark eye, fingers on its arm, and a leg bud. The spine
is visible through the back and theabdomen protrudes out as far as the leg
bud. Part B, the secondtrimestor fetus, has long arms and legs
(24:49):
and is attached to the placenta,which is round and larger than the fetus
parts. This illustration shows a thirdtrimestra fetus, which is a fully developed
baby. The fetus is upside downand pressing on the cervix. The thick
umbilical cord extends from the fetus bellyto the placenta. A fetal development is
(25:11):
shown at nine weeks gestation B.This fetus is just entering the second trimester,
when the placenta takes over more ofthe functions performed as the baby develops
C. There is rapid fetal growthduring the third trimester. Credit A modification
of work by Edethman. Credit B. Modification of work by National Museum of
(25:32):
Health and Medicine. Credits modification ofwork by Gray's anatomy. During the second
trimester, the fetis grows to aboutthirty centimeters about twelve inches Figure B.
It becomes active and the mother usuallyfeels the first movements. All organs and
structures continue to develop. The placentahas taken over the functions of nutrition and
(25:55):
waste elimination and the production of estrogenand progesterone from the corpus lutium, which
has degenerated. The placenta will continuefunctioning up through the delivery of the baby.
During the third trimester, the fetusgrows to three to four kilograms six
point five to eight point five poundsand about fifty centimeters nineteen to twenty inches
(26:15):
long Figure C. This is theperiod of the most rapid growth during the
pregnancy, as all organ systems continueto grow and develop. Labor is the
name given to the muscular contractions thatexpel the fetus and placenta from the uterus
Toward the end of the third trimester, estrogen causes receptors on the uterine wall
(26:36):
to develop and bind the hormone oxytocin. At this time, the fetus usually
reorients facing forward and down, withthe back or crown of the head pushing
on the cervix uterine opening. Thiscauses the cervix to stretch and nerve.
Impulses are sent to the hypothalamus,which signals the release of oxytocin from the
posterior pituitary. Oxytocin causes smooth musclein the uterine wall to cause contract At
(27:00):
the same time, the placenta releasesprostaglandins into the uterus, increasing the contractions.
A positive feedback relay occurs between theuterus, hypothalamus, and the posterior
pituitary to assure an adequate supply ofoxytocin. As more smooth muscle cells are
recruited, the contractions increase in intensityand force. As noted previously, this
(27:23):
is a good example of a positivefeedback loop. The stimulus causes the production
of a hormone that increases the stimulus. There are three stages to labor.
During stage one, the cervix thinsand dilates. This is necessary for the
baby and placenta to be expelled.During birth, the cervix will eventually dilate
(27:45):
to about ten centimeters. During stagetwo, the baby is expelled from the
uterus, The uterus contracts and themother pushes as she compresses her abdominal muscles
to aid the delivery. The laststage is the passage of the placenta after
the baby has been born and theorgan has completely disengaged from the uterine wall.
(28:06):
If labor should stop before stage twois reached, synthetic oxytocin known as
potocin can be administered to restart andmaintain labor. This podcast will be released
episodically and follow the sections of thetextbook in the description. For a deeper
understanding, we encourage you review thetext version of this work voice by voicemaker
(28:27):
Dotaan. This was produced by BrandonCasturo as a Creative Common Sense production.
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 three How Animals Reproduce. Allhyperlinks, images and sources can be found
(00:22):
at the link to the book.In the description, reproduction is so primitive
and fundamental a function of vital organismsthat the mechanism by which it is assured
is highly complex and not yet clearlyunderstood. It is not necessarily connected with
sex, nor is sex necessarily connectedwith reproduction. Henry Havelock Ellis in Psychology
(00:43):
of Sects nineteen thirty three. Someanimals produce offspring through a sexual reproduction,
while other animals produce offspring through sexualreproduction. Both methods have advantages and disadvantages.
A sexual reproduction produces offspring that aregenetically identical to the parent, because
the offspring are all clones of theoriginal parent. A single individual can produce
(01:07):
offspring a sexually in large numbers ofoffspring can be produced quickly. These are
two advantages that a sexually reproducing organismshave over sexually reproducing organisms. In a
stable or predictable environment, asexual reproductionis an effective means of reproduction because all
the offspring will be adapted to thatenvironment. In an unstable or unpredictable environment,
(01:29):
species that reproduce a sexually may beat a disadvantage because all the offspring
are genetically identical and may not beadapted to different conditions. During sexual reproduction,
the genetic material of two individuals iscombined to produce genetically diverse offspring that
differ from their parents. The geneticdiversity of sexually produced offspring is thought to
(01:51):
give sexually reproducing individuals greater fitness becausemore of their offspring may survive and reproduce
in an unpredictable or changing environment.Species that reproduce sexually and have separate sexes
must maintain two different types of individuals, males and females. Only half the
population females can produce the offspring,so fewer offspring will be produced when compared
(02:15):
to a sexual reproduction. This isa disadvantage of sexual reproduction compared to a
sexual reproduction. A sexual reproduction asexual reproduction occurs in prokaryotic microorganisms bacteria,
Anarchaea and in many eukaryotic single celledand multi celled organisms, both plants and
(02:35):
animals. There are several ways thatanimals reproduce a sexually, the details of
which vary among individual species. Fissionfission, also called binary fission, occurs
in some invertebrate multi celled organisms.It is in some ways analogous to the
process of binary fission of single cellprocaryotic organisms. The term fission is applied
(02:58):
to instances in which an organism appearsto split itself into two parts and,
if necessary, regenerate the missing partsof each new organism. For example,
some flatworms, such as do Gesiaderhotocephala, are able to separate their bodies
into head and tail regions and thenregenerate the missing half in each of the
two new organisms. Sea anemonies Nideria, such as species of the genus Anthoplura
(03:21):
figure, will divide along the oorlaboroaxisand see cucumbers. A Chinodermida of the
genus hall Etheria will divide into twoholfs across the oorlaborolaxis and regenerate the other
half in each of the resulting individuals. Photo shows a larger cream colored seanemony
right next to another anemony of thesame color in shape but smaller. The
(03:42):
Anthoplura artemisia seanemony can reproduce through fissionbudding. Budding is a form of a
sexual reproduction that results from the outgrowthof a part of the body, leading
to a separation of the bud fromthe original organism and the formation of two
individuals, one smaller than the other. Budding occurs commonly in some invertebrate animals,
such as hydras and corals. Inhydras, a bud forms that develops
(04:06):
into an adult and breaks away fromthe main body. Figure Part A.
This shows a hydra which has astocklike body with tentacles growing out the top.
A smaller hydra is budding from theside of the stalk. Part B.
This photo shows branching white coral polyps. A hydra reproduce a sexually through
(04:27):
budding. A bud forms on thetubular body of an adult hydra, develops
a mouth and tentacles, and thendetaches from its parent. The new hydra
is fully developed and will find itsown location for attachment. B Some coral,
such as the Lophelia protusive shown here, can reproduce through budding kretibi modification
of work by ed Bulbi no Aslash Olympic Coast nms no A slash our
(04:51):
slash Office of Ocean Exploration. FragmentationFragmentation is the breaking of an individual into
parts, followed by generation. Ifthe animal is capable of fragmentation and the
parts are big enough, a separateindividual will regrow from each part. Fragmentation
may occur through accidental damage, damagefrom predators, or as a natural form
(05:14):
of reproduction. Reproduction through fragmentation isobserved in sponges, some Nigerians, turbilarians,
echinoderms, and annelids. In someseastars, a new individual can be
regenerated from a broken arm and apiece of the central disc. This sea
star figure is in the process ofgrowing a complete seastar from an arm that
(05:34):
has been cut off. Fisheries workershave been known to try to kill the
sea stars eating their clam or oysterbeds, by cutting them in half and
throwing them back into the ocean.Unfortunately for the workers, the two parts
can each regenerate a new half,resulting in twice as many sea stars to
prey upon. The oysters and clamspart A. The photo shows a brown
(05:56):
seastar with five arms of slightly varyinglengths. Part This is a photo of
a C star with one long armand four very short arms. A Linkiu
multiphora is a species of C starthat can reproduce a sexually via fragmentation.
In this process, be an armthat has been shed grows into a new
C star. Credit a modifiction ofwork by Duane Meadows noah slash nmfs slash
(06:20):
o pr. Parthenogenesis Parthenogenesis is aform of a sexual reproduction in which an
egg develops into an individual without beingfertilized. The resulting offspring can be either
haploid or diploid, depending on theprocess and the particular species. Parthenogenesis occurs
in invertebrates such as water fleas,rhodafers, aphids, stick insects, and
(06:44):
ants, wasps and bees. Ants, bees and wasps use parthenogenesis to produce
haploid males drones. The diploid females, workers and queens are the result of
a fertilized egg. Some vertebrate animals, including some reptiles, amphibians, and
fish, also reproduced through parthenogenesis.Parthenogenesis has been observed in species in which
(07:09):
the sexes were separated. In terrestrialor marine zoos, two female komodo dragons,
a hammerhead shark, and a blacktopshark have produced parthenogenic young even when
the females have been isolated from males. It is possible that these instances of
parthenogenesis occurred in response to unusual circumstancesstemming from captivity and would normally not occur.
(07:30):
Sexual reproduction. Sexual reproduction is thecombination of reproductive cells from two individuals,
each contributing a haploid gamete to generategenetically unique offspring. The nature of
the individuals that produce the two kindsof gametes can vary, having, for
example, separate sexes or both sexesin each individual. Hermaphroditism. Hermaphroditism occurs
(07:55):
in animals in which one individual hasboth male and female reproductive systems. Invertebrates
such as earthworms, slugs, tapeworms, and snails, figure are often hermaphroditic.
Hermaphrodites may self fertilize, but typicallythey will mate with another of their
species, fertilizing each other and bothproducing offspring. Self fertilization is more common
(08:16):
in animals that have limited mobility orare not motal, such as barnacles and
clams. Many species have specific mechanismsin place to prevent self fertilization because it
is an extreme form of inbreeding andusually produces less fit offspring. Part A
the photo shows a land snail.Part B the photo shows two snails mating.
(08:39):
Many A snails are hermaphrodites. Whentwo individuals b mate, they can
produce up to one hundred eggs each. Credit A modification of work by a
soft stillman. Credit B modification ofwork by scristious slash flicker. Fertilization,
the fusion of a sperm and anegg, is a process called fertilization.
(09:01):
This can occurr their inside internal fertilizationor outside external fertilization. The body of
the female humans provide an example ofthe former, whereas frog reproduction is an
example of the ladder external fertilization.External fertilization usually occurs in aquatic environments,
where both eggs and sperm are releasedinto the water. After the sperm reaches
(09:26):
the egg, fertilization takes place.Most external fertilization happens during the process of
spawning where one or several females releasetheir eggs and the males release sperm in
the same area at the same time. The spawning may be triggered by environmental
signals such as water temperature or thelength of daylight. Nearly all fish spawn,
(09:46):
as do crustaceans such as crabs andshrimp, molluscs such as oysters,
squid, and echinoderms such as seaurchins and sea cucumbers. Frogs, corals,
mayflies, and mosquitoes also spawn.Figure photo shows mating toads. The
larger female carries the smaller male onher back during sexual reproduction. In toads,
(10:09):
the male grasps the female from behindand externally fertilizes the eggs as they
are deposited. Credit Burnie Coal internalfertilization. Internal fertilization occurs most often in
terrestrial animals, although some aquatic animalsalso use this method. Internal fertilization may
occur by the male directly depositing spermin the female during mating. It may
(10:33):
also occur by the male depositing spermin the environment, usually in a protective
structure, which a female picks upto deposit the sperm. In her reproductive
tract. There are three ways thatoffspring are produced following internal fertilization. In
oviparity, fertilized eggs are laid outsidethe female's body and developed there, receiving
(10:54):
nourishment from the yoke that is apart of the egg figure A. This
occurs in insects, some bony fish, some reptiles, a few cartilaginous fish,
some amphibians, a few mammals,and all birds. Most non avian
reptiles and insects produce leathery eggs,while birds and some turtles produce eggs with
high concentrations of calcium carbonate in theshell, making them hard. Chicken eggs
(11:16):
are an example of a hard shell. The eggs of the egg laying mammals,
such as the platypus and Echidna,are leathery. In ovoviparity, fertilized
eggs are retained in the female andthe embryo obtains its nourishment from the eggs
yolk. The eggs are retained inthe female's body until they hatch inside of
her where she lays the eggs rightbefore they hatch. This process helps protect
(11:39):
the eggs until hatching. This occursin some bony fish, like the platyfish
Siphophrous Maculatus figure EBB, some sharks, lizards, some snakes, garter snake,
thamnoficer talus, some vipers, andsome invertebrate animals Matta, gascar hisssing
cockroche Gronfiterina portentosa. In viviparity,the young are born alive. They obtain
(12:03):
their nourishment from the female, andare born in varying states of maturity.
This occurs in most mammals figure AC, some cartilaginous fish, and a few
reptiles. Part A. The photoshows small yellow eggs on a leaf with
tiny beetles hatching out of some.Part B. The photo shows of fish
in an aquarium with a pale bulgingbelly parts. The photo shows a hairless
(12:26):
baby squirrel with closed eyes. Ina oviparity, young developed in eggs outside
the female body, as with theseHarmoniaxidritis beetles hatching. Some aquatic animals,
like this b pregnant Sypopherus maculatus,are oviviparous, with the egg developing inside
the female and nutritions applied primarily fromthe yoke. In mammals, nutrition is
(12:50):
supported by the placenta, as wasthe case with this see newborn squirrel credit
be modification of work by Gurmy Watchercredit ce modification of work by Autrum five
twenty nine slash flicker. Hormonal controlof reproduction in the animal kingdom. There
are many interesting examples of reproductive strategies, and hormones are involved in regulating all
(13:11):
of those. Rather than attempt tocover the wide diversity of strategies and hormones,
we will concentrate on the hormonal controlof reproduction in a single species,
Homo sapiens. The human male andfemale reproductive cycles are controlled by the interaction
of hormones from the hypothalamus and anteriorpituitary with hormones from reproductive tissues and organs.
(13:33):
In both sexes, the hypothalamus monitorsand causes the release of hormones from
the anterior pituitary gland. When thereproductive hormone is required, the hypothalamus sends
a gonadotropin releasing hormone GnRH to theanterior pituitary. This causes the release of
follicles stimulating hormone FSH and luteonizing hormoneLH from the anterior pituitary into the blood.
(13:58):
Although the hormones are named after theirfunctions in female reproduction, they are
produced in both sexes and play importantroles in controlling reproduction. Other hormones have
specific functions in the male and femalereproductive systems. Male hormones at the onset
of puberty, the hypothalamus causes therelease of FSH and LH into the male
(14:20):
system for the first time. FSHenters the tests and stimulates the Sertoli cells
located in the walls of the seminiferoustubules to begin promoting spermatogenesis. Figure LH
also enters the testes and stimulates theinterstitial cells of LYDIG located in between the
walls of the seminiferous tubules, tomake in release testosterone into the testes and
(14:41):
the blood. Testosterone stimulates spermatogenesis.This hormone is also responsible for the secondary
sexual characteristics that develop in the maleduring adolescence. The secondary sex characteristics in
males included deepening of the voice,the growth of facial, axillary and pubic
(15:01):
hare, an increase in muscle bulk, and the beginnings of the sex drive.
Hormonal control of the male reproductive systemis mediated by the hypothalamus, anterior
pituitary, and testes. The hypothalamusreleases gnrn, causing the anterior pituitary to
release LH and fsh. FSH andLH both act on the testes. FSH
(15:24):
stimulates the sertole cells and the testesto facilitate spermatogenesis and to secrete in hibbin.
LH causes the lydic cells and thetestes to secrete testosterone. Testosterone further
stimulates spermatogenesis by the sertole cells,but inhibits GnRH, LH, and FSH
production by the hypothalamus and anterior pituitary. In Hibbons secreted by sertol cells also
(15:48):
inhibits FSH and LH production by theanterior pituitary. Hormones control sperm production in
a negative feedback system. A negget a feedback system occurs in the mail
with rising levels of testosterone acting onthe hypothalamus and anterior pituitary to inhibit the
release of GnRH, FSH, andLH. In addition, the sertoli cells
(16:11):
produce the hormone in hibbon, whichis released into the blood when the sperm
count is too high. This inhibitsthe release of GnRH, and FSH,
which will cause spermatogenesis to slow down. If the sperm count reaches a low
of twenty million slash EML, thecyrtoli cells cease, the release of inhibbon,
and the sperm count increases female hormones. The control of reproduction in females
(16:36):
is more complex. The female reproductivecycle is divided into the ovarian cycle and
the menstrul cycle. The ovarian cyclegoverns the preparation of endocrine tissues and release
of eggs, while the menstrual cyclegoverns the preparation and maintenance of the uterine
lining figure. These cycles are coordinatedover a twenty two to thirty two day
(16:56):
cycle, with an average length oftwenty days. As with the male,
the g n r H from thehypothalamus causes the release of the hormones FSH
and LH from the anterior pituitary.In addition, estrogen and progesterone are released
from the developing follicles. As withtestosterone in males, estrogen is responsible for
(17:18):
the secondary sexual characteristics of females.These include breast development, flaring of the
hips, and a shorter period forbone growth. The ovarian cycle and the
menstrual cycle the ovarian and menstrual cyclesare regulated by hormones of the hypothalamus,
pituitary, and ovaries. Figure Theebb and flow of the hormones causes the
(17:41):
ovarian and menstrual cycles to advance.The ovarian and menstrual cycles occur concurrently.
The first half of the ovarian cycleis the follicular phase, slowly rising levels
of FSH because the growth of follicleson the surface of the ovary. This
process prepares the egg for ovulation.As the follicles grow, they begin releasing
(18:03):
estrogen. The first few days ofthis cycle coincide with menstruation, or the
slowing off of the functional layer ofthe endometrium in the uterus. After about
five days, estrogen levels rise andthe menstrual cycle enters the proliferative phase.
The endometrium begins to regrow, replacingthe blood vessels and glands that deteriorated during
(18:25):
the end of the last cycle.Hormone levels during the follicular phase ovulation and
the luteal phase are compared. Duringthe follicular phase, LH and FSH secreted
from the pituitary stimulate several follicles togrow. The follicles produce low levels of
estrogen that inhibit GnRH secretion by thehypothalamus, keeping LH and FSH levels low.
(18:48):
Low levels of estrogen also cause theendometrio arteries to constrict, resulting in
men'struation. During the time leading upto ovulation, LH and FSH stimulate maturation
of one of the follicles. Thegrowing follicle begins to produce high levels of
estrogen, which stimulates GnRH secretion bythe hypothalamus. As a result, LH
(19:11):
and FSH levels rise, resulting inovulation about a day later. Estrogen also
causes the endometrium to thicken. Afterovulation, the ovarian cycle enters the luteal
phase. LH from the pituitary stimulatesgrowth of the corpus lutium from the ruptured
follicle. The corpus lutium secretes estrogenand progesterone that block GnRH production by the
(19:34):
hypothalamus. In LH and FSH productionby the pituitary. Estrogen and progesterone also
cause the endometrium to further develop.The ovarian and menstrual cycles of female reproduction
are regulated by hormones produced by thehypothalamus, pituitary, and ovaries just prior
(19:55):
to the middle of the cycle,approximately day fourteen. The high level of
estrogen causes FSH and especially LH torise rapidly then fall. The spike in
LH causes the most mature follical torupture and release its egg. This is
ovulation. The follicles that did notrupture degenerate, and their eggs are lost.
(20:15):
The level of estrogen decreases when theextra follicles degenerate. Following ovulation,
the ovarian cycle enters its luteal phaseand the menstrual cycle enters its secretory phase,
both of which run from about dayfifteen to twenty eight. The ludeal
and secretory phases refer to changes inthe ruptured follicle. The cells in the
(20:36):
follicle undergo physical changes and produce astructure called a corpus lutium. The corpus
lutium produces estrogen and progesterone. Theprogesterone facilitates the regrowth of the uterine lining
and inhibits the release of further FSHand LH. The uterus is being prepared
to accept a fertilized egg should itoccurred during the cycle. The inhibition of
(21:00):
FSH and LH prevents any further eggsand follicles from developing. While the progesterone
is elevated, the level of estrogenproduced by the corpus lutium increases to a
steady level for the next few days. If no fertilized egg is implanted into
the uterus, the corpus lutium degeneratesin the levels of estrogen and progesterone decrease.
(21:21):
The endometrium begins to degenerate as theprogesterone levels drop, initiating the next
menstrual cycle. The decrease in progesteronealso allows the hypothalamus to send GnRH to
the anterior pituitary, releasing FSH andLH and starting the cycles again. Gestation
pregnancy begins with the fertilization and implantationof an egg and continues through to the
(21:45):
birth of the individual. The lengthof time of gestation, or the gestation
period, in humans, is twohundred and sixty six days and is similar
in other grade apes. Gestation periodsin other animals range from twelve to thirteen
days in the America an apossum tothe six hundred and sixty day gestation period
of the African elephant. Within twentyfour hours of fertilization, the egg nucleus
(22:07):
has finished myosis and the egg andsperm nuclei fuse. With fusion. The
cell is known as a zygote.The zygode initiates cleavage and the developing embryo
travels through the oviduct to the uterus. The developing embryo must implant into the
wall of the uterus within seven daysor it will deteriorate and die. The
(22:29):
outer layers of the developing embryo orblastocyst, grow into the endometrium by digesting
the endometrial cells, and healing ofthe endometrium closes up the blastocyst into the
tissue. Another layer of the blastocyst, the chorean, begins releasing a hormone
called human beta choreonic gonadotropin beta hCG, which makes its way to the corpus
lutium and keeps that structure active.This ensures adequate levels of progesterone that will
(22:53):
maintain the endometrium of the uterus forthe support of the developing embryo. Pregnant
sea tests determine the level of betahCG in urine or serum. If the
hormone is present, the test ispositive. The gestation period is divided into
three equal periods or trimesterors. Duringthe first two to four weeks of the
(23:15):
first trimester, nutrition and waste arehandled by the endometrio lining through diffusion.
As the trimester progresses, the outerlayer of the embryo begins to merge with
the endometrium, and the placenta forms. The placenta takes over the nutrient and
waste requirements of the embryo and fetus, with the mother's blood passing nutrients to
the placenta and removing waste from it. Chemicals from the fetus, such as
(23:40):
bilirubin are processed by the mother's liverfor elimination. Some of the mother's aminoglobulins
will pass through the placenta, providingpassive immunity against some potential infections. Internal
organs and body structures begin to developduring the first trimester. By five weeks,
limbbuds, eye, the heart,and liver have been basically formed.
(24:03):
By eight weeks, the term fetusapplies and the body is essentially formed Figure
A. The individual is about fivecentimeters two inches in length, and many
of the organs such as the lungsand liver are not yet functioning. Exposure
to any toxins is especially dangerous duringthe first trimester, as all of the
bodies, organs, and structures aregoing through initial development. Anything that interferes
(24:27):
with chemical signaling during that development canhave a severe effect on the fetus survival.
Part A photo shows a human fetuswith a large bent head and a
dark eye, fingers on its arm, and a leg bud. The spine
is visible through the back and theabdomen protrudes out as far as the leg
bud. Part B, the secondtrimestor fetus, has long arms and legs
(24:49):
and is attached to the placenta,which is round and larger than the fetus
parts. This illustration shows a thirdtrimestra fetus, which is a fully developed
baby. The fetus is upside downand pressing on the cervix. The thick
umbilical cord extends from the fetus bellyto the placenta. A fetal development is
(25:11):
shown at nine weeks gestation B.This fetus is just entering the second trimester,
when the placenta takes over more ofthe functions performed as the baby develops
C. There is rapid fetal growthduring the third trimester. Credit A modification
of work by Edethman. Credit B. Modification of work by National Museum of
(25:32):
Health and Medicine. Credits modification ofwork by Gray's anatomy. During the second
trimester, the fetis grows to aboutthirty centimeters about twelve inches Figure B.
It becomes active and the mother usuallyfeels the first movements. All organs and
structures continue to develop. The placentahas taken over the functions of nutrition and
(25:55):
waste elimination and the production of estrogenand progesterone from the corpus lutium, which
has degenerated. The placenta will continuefunctioning up through the delivery of the baby.
During the third trimester, the fetusgrows to three to four kilograms six
point five to eight point five poundsand about fifty centimeters nineteen to twenty inches
(26:15):
long Figure C. This is theperiod of the most rapid growth during the
pregnancy, as all organ systems continueto grow and develop. Labor is the
name given to the muscular contractions thatexpel the fetus and placenta from the uterus
Toward the end of the third trimester, estrogen causes receptors on the uterine wall
(26:36):
to develop and bind the hormone oxytocin. At this time, the fetus usually
reorients facing forward and down, withthe back or crown of the head pushing
on the cervix uterine opening. Thiscauses the cervix to stretch and nerve.
Impulses are sent to the hypothalamus,which signals the release of oxytocin from the
posterior pituitary. Oxytocin causes smooth musclein the uterine wall to cause contract At
(27:00):
the same time, the placenta releasesprostaglandins into the uterus, increasing the contractions.
A positive feedback relay occurs between theuterus, hypothalamus, and the posterior
pituitary to assure an adequate supply ofoxytocin. As more smooth muscle cells are
recruited, the contractions increase in intensityand force. As noted previously, this
(27:23):
is a good example of a positivefeedback loop. The stimulus causes the production
of a hormone that increases the stimulus. There are three stages to labor.
During stage one, the cervix thinsand dilates. This is necessary for the
baby and placenta to be expelled.During birth, the cervix will eventually dilate
(27:45):
to about ten centimeters. During stagetwo, the baby is expelled from the
uterus, The uterus contracts and themother pushes as she compresses her abdominal muscles
to aid the delivery. The laststage is the passage of the placenta after
the baby has been born and theorgan has completely disengaged from the uterine wall.
(28:06):
If labor should stop before stage twois reached, synthetic oxytocin known as
potocin can be administered to restart andmaintain labor. This podcast will be released
episodically and follow the sections of thetextbook in the description. For a deeper
understanding, we encourage you review thetext version of this work voice by voicemaker
(28:27):
Dotaan. This was produced by BrandonCasturo as a Creative Common Sense production.
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