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Chapter 19: Endocrine and
Reproductive System
• Hormones are used when
signals need to be widely distributed.
• Hormones are not
secreted at a uniform rate and
exert their effect at low concentrations.
• Sexual reproduction
involves the development and
fusion of haploid gametes.
I. Hormones and homeostasis
A. Homeostasis: process to keep human
body within certain limits for many
physiological variables
1. Examples:
a) Blood pH
b) Blood CO2 concentration
c) Blood glucose concentration
d) Body temperature
e) Water balance within tissues
2. Each of the variables has an expected value or set
point that is considered normal
3. Negative feedback mechanism: physiological
processes that bring a value back towards to a set
point
a) Like a thermostat that triggers an
action to bring the temperature back into
range
b) Functions to keep a value within the
narrow range that is considered normal
4. Nervous and endocrine system work together to
ensure homeostasis
a) Nervous system: homeostasis control is
usually under the autonomic nervous system
b) Endocrine system: consists of numerous
glands that produce a wide variety of hormones
c) Hormones: chemical messengers that usually
have a physiological effect far from the gland of
origin and are transported by the blood
i) Hormone is secreted into the capillary beds to
be distributed to body cells
ii) Not all body cells are influenced by any one
hormone
iii) Target cells: cells that are affected by the
hormone Hormonal communication
iv) Some hormones have a very specific and
limited target tissue (leptin)
v) Other hormones have a broad range of target
tissues (insulin)
5. Some endocrine glands occur in pairs and some
are singular
6. Pancreas is the only gland that has both exocrine
and endocrine functions
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B. Steroid hormones: made from cholesterol and
classified as lipids
1. Easily pass through cell membrane since the
steroid hormones and cell membrane are nonpolar
2. Receptor-hormone complex: steroid binds with a
receptor protein which then passes into nucleus and
binds to a specific gene
a) May inhibit transcription
b) May promote transcription
3. Steroid hormones control the production or
proteins within the target cell
4. Target cells have their biochemistry
dramatically altered as a result of the steroid
hormone
5. Examples: estrogen and testosterone
Clip
C. Peptide hormones: composed of amino acids
(proteins)
1. Hormone binds to a receptor on the outer
surface of the target cell
2. Presence or absence of the hormone receptor
determines whether or not a cell is a target cell
of that particular hormone
3. Must be a molecular shape and charge fit
between the hormone and receptor
4. Once it has bonded, a secondary messenger is triggered
into action inside the cytoplasm of the cell and starts a
cascade of reactions
a) Final messenger activates an enzyme in the
cytoplasm for a reaction to occur
b) Final messenger activates a transcription factor
that enters the nucleus and either promotes or
inhibits transcription
Summary
Hormone Action
Section 39-1
Nonsteroid hormone
(first messenger)
Steroid Hormone
Receptor
Target cell
membrane
Target cell
membrane
Receptor
cAMP (second
messenger)
Hormonereceptor
complex
Nucleus
Altered
cellular
function
Enzyme
activities
DNA
Altered
cellular
function
Protein
synthesis
Cytoplasm
Cytoplasm
mRNA
Nucleus
II. Selected hormones and their function
A. Thyroxin: produced by the thyroid gland
in the neck
1. Created from an amino acid and
iodine (table salt has iodine added)
a) T3 and T4: forms of thyroxin
and number indicates the number
of iodine atoms within the structure
2. Both forms enter target cells (almost all
cells of the body)
a) T4 is converted to T3
b) T3 enters the nucleus and acts as a
transcription regulatory leading to an
increase in mRNA, which results in an
increase in protein production
3. Proteins lead to an increase in the metabolism
of the cell
4. Cell under the influence of thyroxin will have
a greater need for oxygen and other indicators of
an increased metabolic rate
5. Hyperthyroidism: someone who secretes too much
thyroxin
a) Symptoms: Fatigue or muscle weakness,
nervousness or anxiety, rapid heartbeat, irregular
heartbeat, skin dryness, trouble sleeping, weight loss,
may produce a goiter (enlarged thyroid gland)
b) Graves’ disease: autoimmune disease
6. Hypothyroidism: someone who secretes too little
thyroxin
a) Symptoms: Fatigue, increased sensitivity to cold,
dry skin, weight gain, puffy face
7. Thyroxin helps to regulate internal body
temperature: increase in metabolic rate
produces more heat from the increased
chemical reactions, so increase in thyroxin
will lead to an increase in body temperature
Clip
B. Leptin: produced by adipose (fat) tissue in the body
1. More fat stored in the body, the more leptin is
produced and secreted into the bloodstream
2. Leptin’s target cell: hypothalamus of the
brainstem to lower your appetite
a) Evolutionary if someone has enough fat
reserves, that person doesn’t need to eat as
much
b) Simple logic doesn’t hold true today
since people who are obese have a higher
level of leptin
3. Researchers are working on why they have
appeared to be come desensitized to the high
level of leptin
4. Other researchers suggest that function of leptin
is related to increasing appetite when fat
reserves are low
Leptin video
C. Melatonin: produced in the pineal gland and
helps to regulate the daily 24-hour cycle of activity
(circadian rhythm)
1. Little melatonin is produced during the day
and peak production is after dark with
maximum between 2am-4am
2. Natural circadian rhythm is altered when a
person alters his or her period of exposure to
light over a short period of time and
disruption of their normal sleep schedule
a) Jet lag: disorientation symptoms occur
when traveling between time zones disrupts
normal sleep patterns
b) Working temporary night shifts can cause
same disruption
c) Melatonin pills can be taken
for jet lag until normal circadian
rhythm has naturally reset
Clip
D. Insulin and glucagon: produced and secreted by
pancreas and regulate blood glucose levels
1. Cells rely on glucose for cell respiration and
lowers the blood glucose level
2. Glucose is absorbed into the bloodstream
from the capillary beds of the villi of the small
intestines after eating and increases the blood
glucose level
3. Increase and decrease in blood glucose levels
goes on 24 hours a day, every day
4. The homeostatic normal level must be maintained
reasonably close and a negative feedback
mechanisms is used
5. Glucose from villi travels through the hepatic portal
vein to the liver ( concentration varies on the time
of last meal and is the only blood vessel in which
blood levels fluctuate to a large degree)
6. Hepatocytes are trigged into action by the two
hormones: insulin and glucagon
7. Antagonistic hormones: have opposite effects on
blood glucose concentrations
8. Blood glucose begins to increase
a) Beta (ß) cells of pancreases produce insulin
b) Insulin is secreted into bloodstream and all cells are
exposed to it
c) Insulin effects on cells: opens protein channels in
their plasma membranes and allows glucose to diffuse
into the cell by facilitated diffusion
d) Insulin stimulates the hepatocytes in the liver to
take in glucose and convert it to glycogen (also occurs in
muscle cells)
e) Blood glucose level is reduced
9. Blood glucose begins to decrease
a) Decreases when a person has not eaten in many
hours or exercises vigorously
b) Body needs to use the glycogen in the liver and
muscle cells
c) Alpha (α) cells of pancreas produce and secrete
glucagon
d) Glucagon stimulates the hydrolysis of the glycogen
stored in hepatocytes and muscle cells to make glucose
e) Glucose enters the blood and blood glucose levels
increase Clip
E. Diabetes: disease characterized by hyperglycemia (high
blood glucose) too much glucose in blood and not in cells
1. Type I: caused when the ß cells of pancreas don’t
produce sufficient insulin
a) Usually controlled by injections of insulin
at certain times
b) Autoimmune disease: body’s own immune
system attacks and destroys the ß cells so little
or no insulin is produced
c) Develops in children or at any age
d) Only 10% of diabetics have this type
2. Type II: caused by body cell receptors that do
not respond properly to insulin
a) Insulin resistance: body
cells no longer respond to insulin
b) Pancreas may start to produce less insulin
c) More common form: 90% and associated
with genetic history, obesity, lack of exercise,
age, and certain ethnic groups
3. Serious effects of untreated diabetes
a) Damage to retina, leading to blindness
b) Kidney failure
c) Nerve damage
d) Increased risk of cardiovascular disease
e) Poor wound healing/amputations needed
Clip
F. Pituitary gland and hypothalamus
1. Pituitary gland: made up of two different lobes
(anterior and posterior) that produce many different
hormones and some of the hormones influence the
production of other hormones
2. Hypothalamus: controls the actions of the
pituitary gland and communicate with the two lobes
differently
3. Posterior lobe of pituitary gland: contains axons
of neurosecretory cells ( long cells whose dendrites
and cell bodies are in the hypothalamus and axons
are in posterior pituitary)
a) Hormones (oxytocin and ADH) produced
in the cell body ends of the neurosecretory
cells (inside hypothalamus) and the hormones
move down the axon into the posterior
pituitary gland
b) Hormones are secreted in a similar way to
the release of neurotransmitters
4. Anterior pituitary gland: releases hormones after being
targeted by hormones from the hypothalamus (produced
in neurosecretory cells)
a) Hypothalamus produces hormones called
releasing hormones into a capillary bed that joins
together to form a portal vein which extends into the
anterior pituitary
i) Example: gonadotropin-releasing hormone
(GnRH)
b) Portal vein branches into a second capillary
bed that allows the releasing hormone to leave
blood and enter the target cells of the anterior pituitary
c) Releasing hormones stimulates the anterior
pituitary cells to secrete specific hormones
i) GnRH stimulates the secretion of
follicle-stimulating hormone (FSH) and
luteinizing hormone (LH) into the blood
Clip
PituitaryPituitary 2
G. Prolactin and oxytocin: pituitary hormones involved in
lactation (production of milk for baby)
1. Prolactin: increases during pregnancy and result in the
development of milk-producing cells within the breast
2. Oestrogen (estrogen) levels during pregnancy
inhibit the cells from releasing the milk
3. After birth, two events stimulate the secretion of milk
a) Lowering of estrogen
b) High levels of oxytocin (stimulates contractions
during labor)
4. Without the inhibiting effect of estrogen, prolactin
stimulates the milk producing cells to release the
milk
5. Oxytocin results in the contraction of smooth
muscle tissue surrounding the ducts carrying the
milk, so the milk can be ejected
6. Positive feedback: both hormones increase by the
stimulation of the nipple by a suckling infant
7. Colostrum: first milk right after birth is high in
carbohydrates, proteins, and antibodies and low in
fat, decreases after the first few days
H. Other pituitary gland hormones
1. Nine different peptide hormones are
secreted from the pituitary gland
III. Human reproductive system: male gamete
fertilizes a female gamete to produce an
offspring with half the genetic makeup of each
parent (ensures genetic variation) and hormones
play a key role
A. Male reproductive system: adapted for the
production and release of gametes (sperm)
1. Testis: gland that produces sperm
and hormone testosterone
a) Testosterone functions include
i) Determine the development of male
genitalia during embryonic development
ii) Ensures development of secondary
sex characteristics during puberty
iii) Ensures sperm production
2. Epididymis: location where sperm mature and
are capable of swimming by use of their flagella
3. Scrotum: sacs that hold testes outside the body
so sperm production can occur at a temperature
cooler than body temperature
4. Vas deferens: muscular tube that carries mature
sperm from epididymis to urethra
5. Seminal vesicles: small glands that produce and
add seminal fluid to the semen
6. Prostate gland: gland that produces much of the
seminal fluid including carbohydrates for the
sperm
7. Penis: organ that fills with blood to facilitate
ejaculation of sperm
8. Urethra: tube via which the semen leaves the
penis
Clip
B. Female reproductive system: adapted for the
production and release of gametes (egg) and for
fertilization and growth of fetus until birth
1. Ovary: gland (organ) that produces and
secretes estrogen and ovum (egg)
a) Location where ovulation occurs
b) Grows into the corpus luteum which
produces the hormone progesterone
2. Fallopian tubes: ducts that carry the ovum (or early
embryo) to the uterus
3. Uterus: muscular structure where the early embryo
implants and develops if a pregnancy occurs
4. Endometrium: highly vascular lining of the uterus
5. Cervix: lower muscular portion of the uterus which has an
opening to the vagina that allows sperm to enter and
pathway for childbirth
6. Vagina: muscular tube that leads from outside of body to
cervix, where sperm enters the female reproductive system
C. How does a person become male or female
1. Receive X chromosome from mother
2. Receive either X or Y chromosome from father
a) XX-female
b) XY-male
3. Embryos of both sexes are virtually identical until the
8th week after fertilization
4. Alleles that interact on both of the X chromosomes
results in higher levels of estrogen and progesterone
production resulting in the prenatal development of
reproductive structures
5. Genes located on the Y chromosome are
responsible for early testes development and
higher levels of testosterone resulting in male
reproductive structures
6. Same embryonic tissue that becomes the ovaries
gives rise to the testes, so they the male and
female reproductive structures are homologous.
D. Role of sex hormones during puberty
1. Same hormones that first determined
gender are secreted during puberty in higher
amounts
2. Increased production of hormones results
secondary sex characteristics
3. Female secondary characteristics
a) Enlargement of breasts
b) Growth of pubic and underarm hair
c) Widening of hips
4 Male secondary characteristics
a) Growth of facial, underarm, chest, and pubic hair
b) Enlargement of the larynx and deepening of voice
c) Increased muscle mass and size of penis
E. Menstrual cycle: female hormonal cycle that begins at puberty
and lasts an average of 28 days
1. Purpose of cycle: to time the release of an egg (ovum)
for possible fertilization and later implantation into the
inner lining of the uterus
a) Follicular phase: maturing of ovum in follicle
b) Ovulation: release of egg from follicle
c) Luteal phase: egg travels down Fallopian tube
and fertilization can occur
d) Menstruation: no fertilization, then the blood
vessels of the endometrium lining is broken down
and released Clip
2. Hormones from hypothalamus and pituitary gland
a) Hypothalamus: regulatory center of the
menstrual cycle
b) Gonadotropin-releasing hormone (GnRH):
that targets the anterior pituitary gland to produce
and secrete 2 hormones that target the ovaries
i) Follicle-stimulating hormone (FSH)
ii) Luteinizing hormone (LH)
3. Effects of FSH and LH on ovaries
a) Increase the production and secretion of
estrogen
i) Estrogen targets the endometrium of
uterus to increase blood vessels
ii) Estrogen stimulates the pituitary
gland to release more FSH and LH
(positive feedback loop)
b) Production of Graafian follicles within the ovaries
i) Follicle cells: cells within ovaries
ii) Oocytes: reproductive cells in follicles
iii) FSH and LH stimulate follicle cells and oocytes
to take on a cellular arrangement called
Graafian follicles
c) Spike in FSH and LH lead to ovulation (release of oocyte
from Graafian follicle)
i) Oocyte is surrounded by the inner ring of follicle
cells (entire structure called a follicle) and enters
Fallopian tube
ii) Corpus luteum: outer ring of the follicle that
remains in the ovary that begins to divide and fill in
the area left by ovulation and produces progesterone
form 10-12 days after ovulation
iii) Progesterone: hormone that maintains the
thickened and high vascular endometrium so embryo
can implant
iv) High levels of estrogen and progesterone provide a
negative feedback to the hypothalamus to not secrete
more GnRH so another follicle is not produced during
a pregnancy
v) No pregnancy established: corpus luteum begins to
break down and this leads to a decline in progesterone
and estrogen and highly vascular endometrium can no
longer be maintained (menstruation)
vi) Low progesterone and estrogen signals the
hypothalamus to begin secreting GnRh for another
menstrual cycle to begin Clip
F. In Vitro fertilization (IVF) IVF
1. Natural fertilization: occurs in Fallopian
tube 24-48 hours after ovulation resulting in a
zygote that begins to divide by mitosis and
takes several days to reach the uterus
a) Blastocyst: embryo at 100 cells that
reaches the uterus and implants into the
endometrium
2. Infertility: couples that are unable to bear
children and is due to many possible reasons
a) Males with low sperm counts
b) Males with impotence
c) Females who don’t ovulate normally
d) Females with blocked Fallopian tubes
3. In vitro fertilization: reproductive technology that helps to
overcome these reasons for infertility
a) Female is given hormones for a month to stimulate
ovaries to produce eggs
i) First 2 weeks using an injected drug or nasal
spray that suspends her natural hormones with the
menstrual cycle
ii) Next 12 days she takes hormone injections
including FSH to produce many follicles in each
ovary and provide many oocytes (superovulation)
b) Egg are harvested surgically and sperm is
ejaculated into a container
c) Sperm is injected into an egg or large
number of sperm can be placed in dish with
the egg
d) Zygotes develop in a cultured medium and
are observed using a microscope to determine
if they are growing (cleavage stage)
e) Growing zygotes can be placed in medium
to grow into a blastocyst
f) Embryo is transferred on either Day 3
during the cleavage stage or Day 5 as a
blastocyst
g) Embryo(s) are loaded in a soft catheter and
are placed in the uterine cavity through the cervix.
h) Healthy remaining embryos can be frozen and
used later
William Harvey 1628
• Did experiments to show how blood is circulated
through the body by doing animal experimentation
and human cadaver dissections to determine that
the heart was a double pump.
• Did experiments on embryology and sought to
find an ovum in a dissected deer
• First to suggest that humans and other mammals
reproduced by joining of an egg and sperm
IV. Spermatogenesis: production of male gametes by meiosis
within testes
A. Spermatozoa: sperm cells that are made in the
testis inside the seminiferous tubules
1. Near the outer wall of the seminiferous
tubules lie germinal epithelial cells called
spermatogonia (undergoes mitosis or meiosis)
a) Mitosis: to replenish numbers that become
spermatozoa ( millions of spermatozoa can be
produced in one day starting at puberty)
b) Meiosis: spermatogonia undergo meiosis to
produce spermatozoa (haploid gamete)
2. Spermatogonia first replicate the DNA within their
diploid nucleus and prepare for cell division
a) Mitosis: two cells results and are capable of
growing and dividing later
b) Meiosis: 4 spermatozoa are the result
3. Steps of meiosis/spermatogenesis
a) Spermatogonia are diploid and contain 23
homologous pairs (46 chromosomes)
b) DNA replication occurs and doubles the number of
chromosomes (pairs of chromatids)
c) Meiosis I: 2 cells each with haploid number of
chromosomes (23) because the homologues pairs have
been separated, but each chromosome still exists as a
pair of chromatids
d) Meiosis II: Chromatids are separated and 4 haploid
cells are formed each with 23 chromosomes
4. Steps for forming a functioning motile spermatozoa
a) Haploid cells remain in seminiferous tubules to
develop flagellum and an acrosome (enzymes to
break through egg)
b) Need nutrients during this time and are
connected to Sertoli cells
c) Each of the stages has moved the cell closer to
the interior of the seminiferous tubules (lumen in the
center)
d) Completed differentiation, detach from Sertoli
cells, move through lumen, to storage area (epididymis)
V. Oogenesis: production of female gametes by
meiosis
A. Similar steps to spermatogenesis for the
chromosomes
1. Produces 4 cells as the end product of
meiosis
2. Polar bodies: 3 of the cells are not used
as gametes because they are too small to
produce a viable zygote
3. Ovum: one of the cells that is very large
and is the gamete cell
B. Events occurring before birth
1. Oogonia: cells within ovaries that undergo
mitosis to build up the numbers of oogonia and
grew into larger cells (oocytes) both types of
cells are diploid
2. Oocytes begin the early stages of meiosis but
stops at prophase I
3. Primary follicle: Follicle cells undergo mitosis
and a single layer of follicle cells surrounds each
oocyte
it
4. Female child is born her ovaries contain
nearly a half million primary follicles and
they remain unchanged until puberty
C. Events occurring with the menstrual cycle
1. Few primary follicles finish meiosis I
a) Secondary oocyte: one large haploid
cell
b) Polar body: small haploid cell that is
not used
2. Single ring of follicle cells begins to divide and form
fluid
3. Graafian follicle: Two rings of follicle cells are are
formed with a fluid-filled cavity separating them with
the first inner ring surrounding the oocyte
4. Increase in fluid between the two follicle cell layers
creates a bulge on the surface of the ovary and leads to
ovulation
5. Secondary oocyte with the inner ring of follicle cells
that is released at ovulation
6. Meiosis II does not occur until fertilization
a) If fertilization does not occur, the gamete
remains a secondary oocyte and dies
b) If fertilization does occur, the events
stimulate the secondary oocyte to complete
meiosis II
c) It is a true ovum for a very brief period
between the spermatozoa starting to fertilize
the secondary oocyte and the haploid nuclei
fusing to form the zygote
D. Mature spermatozoa and ova: haploid cells
1. Spermatozoon: very small cell
a) Flagellum for movement
b) Mitochondria for ATP
c) Acrosome: organelle contains
hydrolytic enzymes to help with
fertilization
d) No extra organelles and small size
helps it swim great distances
2. Ovum: (secondary oocyte) largest cell in most
animals due to the unequal division of the
cytoplasm during meiosis to ensure that one cell
receives all the cytoplasm, nutrients, and
organelles necessary to start a new life
a) Yolk: contain nutrients
b) Cortical granules: small vesicles that
release contents at fertilization to prevent
more than one sperm from entering
c) Zona pellucida: layer of glycoproteins
outside the plasma membrane to help with
sperm binding
VI. Fertilization and early development
A. External fertilization: females lay eggs to
allow the male to fertilize the eggs outside the
female’s body
1. Female fish will lay hundreds of eggs
and male fish will swim above the eggs and
release milt
2. Milt: contains millions of spermatozoa
3. Animals that use this method rarely
provide parental care and a large number of
eggs are laid since many don’t survive
B. Internal fertilization: female and males engage in
some form of intercourse in which spermatozoa are
deposited into the female in order to fertilize one or
more ovum
1. Number of ova is far less then external
fertilization since reproductive success is high
2. High level of parental care of the young
3. Alligators have internal fertilization and lay
eggs in a nest, incubates them, and protects
young from predators
C. Fertilization in humans
1. Millions of spermatozoa are ejaculated into
the female’s vagina
2. Motile spermatozoa absorb fructose sugar
in semen in order to have fuel for journey
3. Some spermatozoa enter cervical opening
and gain access to uterus
4. Swim up the endometrial lining and some
enter the openings to the two Fallopian tubes
5. Only a small percentage of spermatozoa will
reach the location of the second oocyte if it is
present
6. Fertilization occurs in the Fallopian tube
7. Takes many spermatozoa to penetrate the follicle
cell layer and the zona pellucida
8. Several spermatozoa gain access to the zona
pellucida and release the hydrolytic enzymes
(acrosome reaction)
9. One spermatozoon will reach the plasma membrane first and
will use the hydrolytic enzymes to penetrate the egg
10. Plasma membranes of the two gametes fuse together
11. Cortical reaction: designed to prevent more than one
spermatozoon from fertilizing the ovum (polyspermy)
a) Cortical granules: located around the interior of the
plasma membrane of the ovum
b) When two plasma membranes fuse the cortical granules
fuse with the ovum’s plasma membrane and release their
enzymes to the outside
c) Enzymes result in a chemical change in the zone
pellucida making it impermeable to any more spermatozoa
d) Takes place within a few seconds of the
first spermatozoon gaining access
12. Spermatozoon donates its paternal set of
haploid chromosomes to the maternal set in the
ovum
13. Zygote: newly fertilized ovum that is diploid
D. Early development: implantation into the
endometrium by the blastocyst
1. Fertilization stimulates the zygote to begin
mitosis and first division occurs in 24 hours
after fertilization
a) Rate of mitosis division increases with
subsequent divisions
b) Early embryo continues to move
down the Fallopian tube
2.Blastocyst: embryo is 100 cells in size when it implants
and is characterized by
a) Trophoblast: surrounding layer of cells which
help form the fetal portion of the placenta
b) Inner cell mass: group of cells on the interior
and located on one end of the blastocyst,
will become the body of the embryo
c) Fluid-filled cavity
3. Implantation: blastocysts embeds its self in the
endometrium layer of the uterus
4. Ovum is large because it contains the nutrients
needed for early embryonic development
a) No true growth of the embryo since the
100 cells embryo is the same size as the original
ovum
b) Nutrients used for metabolism
c) By the time the blastocyst implants it is
running out of stored nutrients in the yolk
E. Role of the placenta
1. Placenta: forms from the trophoblast layer of
the blastocyst and forms from tissue from both
the embryo and mother
2. Pancake shaped structure
a) Side further into the uterine wall is made of
the mother
b) Side closer to the embryo is formed by
embryo and contains connective tissue and small
blood vessels
3. Umbilical cord: protective sheath that develops
and covers three fetal blood vessels
a) Two fetal vessels carry fetal blood to the
placenta and is deoxygenated and carries
waste products and exchanges materials with
the maternal bloodstream
b) Third fetal vessel returns the blood to the
fetus which is oxygenated and has nutrients
that have been added to it when it passed
through the placenta
c) There is an exchange of molecules, but no
exchange of blood, at no time does the blood
from the fetus and mother mix Clip
F. Early embryo and placenta secrete hormones
1. Embryo secretes human chorionic
gonadotropin hormone (HCG) and can be
detected by pregnancy tests
2. HCG enters the mother’s blood and
maintains the corpus luteum of her ovary in
order to secrete progesterone to maintain the
endometrium, so the embryo can implant
3. Placenta takes over the production of
progesterone during the pregnancy and estrogen
which inhibits the production of any further
oocyte development
Ultrasound at 23 weeks
G. Hormonal events associated with birth
1. Birth (parturition): process that is not a normal part
of homeostasis
a) Characterized by uterine contractions
that start at a low intensity and occur
infrequently
b) As the birth continues the contractions
become more intense and more frequent
c) Positive feedback: previous event results in a
more forceful and frequent future event. There
is no homeostatic factor being controlled and
the series of events will only end when birth
occurs
2. Oxytocin: hormone involved in positive feedback
mechanism
a) Estrogen produced by the placenta induces the
production of oxytocin protein receptors in the
uterine muscle
b) Oxytocin is produced by the hypothalamus
and secreted by the posterior pituitary gland and
it is released at the time of birth
c) Oxytocin receptors respond to oxytocin with
the first contraction
d) First contraction signals the hypothalamus to signal
the posterior pituitary to release more oxytocin
e) Continues to happen as the uterine contractions
become very intense and frequent
f) Ends with the birth since the uterine muscle will no
longer have anything to contract upon
Note: Pitocin is a chemical given to induce labor and it
is recognized by the receptors of the uterus as oxytocin
and it starts the positive feedback loop
5 Minutes after birth
10 Minutes after birth
Chimera Video