Chapter 9
The Endocrine
System
Lecture Presentation by
Patty Bostwick-Taylor
Florence-Darlington Technical College
© 2018 Pearson Education, Inc.
The Endocrine System
 Second controlling system of the body
 Nervous system is the fast-control system
 Uses chemical messengers (hormones) that are released into
the blood
 Hormones control several major processes
 Reproduction
 Growth and development
 Mobilization of body defenses
 Maintenance of much of homeostasis
 Regulation of metabolism
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The Endocrine System
 Hormones are produced by specialized cells
 Cells secrete hormones into extracellular fluids
 Blood transfers hormones to target sites
 These hormones regulate the activity of other cells
 Endocrinology is the scientific study of hormones and
endocrine organs
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The
Chemistry
of
Hormones
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 Hormones are classified
chemically as:
 Amino acid–based, which
includes:
 Proteins
 Peptides
 Amines
 Steroids—made from
cholesterol
 Prostaglandins—made from
highly active lipids that act as
local hormones
Hormone
Action
 Hormones affect only certain tissues
or organs (target cells or target
organs)
 Target cells must have specific
protein receptors
 Hormone binding alters cellular
activity
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 Hormones arouse cells or alter cellular
activity
 Typically, one or more of the following
occurs:
1. Change plasma membrane
permeability or membrane
potential by opening or closing
ion channels
2. Activate or inactivate enzymes
3. Stimulate or inhibit cell division
4. Promote or inhibit secretion of a
product
5. Turn on or turn off transcription of
certain genes
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Hormone
Action
Hormone
Action
 Hormones act by two mechanisms
1. Direct gene activation
 Used by steroid hormones
and thyroid hormone
2. Second-messenger system
 Used by protein and peptide
hormones
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 Direct gene activation
1. Steroid hormones diffuse through
the plasma membrane of target
cells
2. Once inside the cell, the hormone
enters the nucleus
3. Then, the hormone binds to a
specific protein within the nucleus
4. Hormone-receptor complex binds
to specific sites on the cell’s DNA
5. Certain genes are activated to
transcribe messenger RNA
6. New proteins are synthesized
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Hormone
Action
Figure 9.1a Mechanisms of hormone action.
Steroid
hormone
Slide 1
Nucleus
Cytoplasm
1
Receptor
protein
2
3
Hormone-receptor
complex
4
DNA
mRNA
5
New
protein
Plasma
membrane
of target
cell
(a) Direct gene activation
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6
 Second-messenger system
1. Hormone (first messenger) binds
to a membrane receptor
2. Activated receptor sets off a
series of reactions that activates
an enzyme
3. Enzyme catalyzes a reaction that
produces a second-messenger
molecule (such as cyclic AMP,
known as cAMP)
4. Oversees additional intracellular
changes to promote a specific
response in the target cell
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Hormone
Action
Figure 9.1b Mechanisms of hormone action.
Slide 1
Cytoplasm
Hormone (first
messenger)
Enzyme
ATP
1
2
3
Second
cAMP messenger
Receptor
protein
Plasma
membrane
of target cell
4
Effect on cellular function,
such as glycogen
breakdown
(b) Second-messenger system
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 Hormone levels in the blood are
maintained mostly by negative
feedback
 A stimulus or low hormone levels in
the blood trigger the release of more
hormone
 Hormone release stops once an
appropriate level in the blood is
reached
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Stimuli for
Control of
Hormone
Release
Stimuli for Control of Hormone Release
 The stimuli that activate endocrine glands fall into three
major categories
1. Hormonal
2. Humoral
3. Neural
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 Hormonal stimuli
 Most common category of
stimulus
 Endocrine organs are activated
by other hormones
 Example:
 Hormones of the
hypothalamus stimulate the
anterior pituitary to secrete
its hormones
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Stimuli for
Control of
Hormone
Release
Figure 9.2a Endocrine gland stimuli.
(a) Hormonal stimulus
1 The hypothalamus secretes
hormones that…
Hypothalamus
2 …stimulate
the anterior
pituitary
gland to
secrete
hormones
that…
Thyroid
gland
Anterior
pituitary
gland
Adrenal
cortex
Gonad
(testis)
3 …stimulate other endocrine
glands to secrete hormones
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 Humoral stimuli
 Changing blood levels of certain
ions and nutrients stimulate
hormone release
 Humoral indicates various body
fluids, such as blood and bile
 Examples:
 Parathyroid hormone and
calcitonin are produced in
response to changing levels of
blood calcium levels
 Insulin is produced in response
to changing levels of blood
glucose levels
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Stimuli for
Control of
Hormone
Release
Figure 9.2b Endocrine gland stimuli.
(b) Humoral stimulus
1 Capillary blood contains low
concentration of Ca2+, which
stimulates…
Capillary
(low Ca2+
in blood)
Thyroid gland
(posterior view)
Parathyroid
glands
Parathyroid
glands
PTH
2 …secretion of parathyroid
hormone (PTH) by parathyroid
glands
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 Neural stimuli
 Nerve fibers stimulate hormone
release
 Most are under the control of the
sympathetic nervous system
 Examples:
 Sympathetic stimulation of
the adrenal medulla to
release epinephrine and
norepinephrine
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Stimuli for
Control of
Hormone
Release
Figure 9.2c Endocrine gland stimuli.
(c) Neural stimulus
1 Preganglionic sympathetic
fiber stimulates adrenal medulla
cells…
CNS (spinal cord)
Preganglionic
sympathetic fibers
Medulla of
adrenal
gland
Capillary
2 …to secrete catecholamines
(epinephrine and norepinephrine)
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The Major
Endocrine
Organs
 Hypothalamus
 Pituitary gland
 Pineal gland
 Thyroid gland
 Parathyroid glands
 Thymus
 Adrenal glands
 Pancreas
 Gonads (testes and ovaries)
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Figure 9.3 Location of the major endocrine organs of the body.
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
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The Major Endocrine Organs
 Some glands have purely endocrine functions
 Anterior pituitary, thyroid, adrenals, parathyroids
 Endocrine glands are ductless glands
 Hormones are released directly into blood or
lymph
 Other glands are mixed glands, with both
endocrine and exocrine functions (pancreas,
gonads)
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 Pituitary gland
 Pea-sized gland that hangs
by a stalk from the
hypothalamus in the brain
 Often called the “master
endocrine gland”
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Pituitary Gland
and
Hypothalamus
 Hypothalamus produces releasing
hormones and inhibiting hormones
 These hormones are released
into portal circulation, which
connects hypothalamus to
anterior pituitary
 Hypothalamus also makes two
hormones: oxytocin and antidiuretic
hormone
 Carried to posterior pituitary via
neurosecretory cells for storage
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Pituitary Gland
and
Hypothalamus
Figure 9.4 Hormones released by the posterior pituitary and their target organs.
Optic
chiasma
Axon
terminals
Hypothalamic
neurosecretory
cells
Hypothalamus
Arterial blood supply
Posterior lobe
Capillary bed
Venous drainage
Anterior lobe
of the pituitary
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ADH
Oxytocin
Kidney tubules
Mammary glands
Uterine muscles
 Posterior pituitary
 Does not make the hormones it
releases
 Stores hormones made by the
hypothalamus
 Two hormones released
 Oxytocin
 Antidiuretic hormone (ADH)
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Pituitary Gland
and
Hypothalamus
 Posterior pituitary (continued)
 Oxytocin
 Stimulates contractions of
the uterus during labor,
sexual relations, and
breastfeeding
 Causes milk ejection (letdown reflex) in a
breastfeeding woman
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Pituitary Gland
and
Hypothalamus
 Posterior pituitary (continued)
 Antidiuretic hormone (ADH)
 Inhibits urine production
(diuresis) by promoting water
reabsorption by the kidneys
 Urine volume decreases, blood
pressure increases
 In large amounts, causes
constriction of arterioles,
leading to increased blood
pressure (the reason why ADH
is known as vasopressin)
 Alcohol inhibits ADH secretion
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Pituitary Gland
and
Hypothalamus
 Six anterior pituitary hormones
 Two hormones affect
nonendocrine targets
1. Growth hormone
2. Prolactin
 Four are tropic hormones
1. Follicle-stimulating
hormone
2. Luteinizing hormone
3. Thyrotropic hormone
4. Adrenocorticotropic
hormone
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Pituitary Gland
and
Hypothalamus
Figure 9.5 Hormones of the anterior pituitary and their major target organs.
Releasing hormones
secreted into portal
circulation
Hypothalamus
Anterior pituitary
Posterior pituitary
Hypophyseal
portal system
Adrenocorticotropic
hormone (ACTH)
Growth hormone (GH)
Bones and muscles
Prolactin (PRL) Follicle-stimulating Thyrotropic
hormone (TH)
hormone (FSH)
and luteinizing
Mammary
hormone (LH)
glands
Thyroid
Testes or ovaries
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Adrenal cortex
 All anterior pituitary hormones:
 Are proteins (or peptides)
 Act through second-messenger
systems
 Are regulated by hormonal
stimuli
 Are regulated mostly by
negative feedback
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Pituitary Gland
and
Hypothalamus
 Growth hormone (GH)
 General metabolic hormone
 Major effects are directed to
growth of skeletal muscles and
long bones
 Plays a role in determining final
body size
 Causes amino acids to be built
into proteins
 Causes fats to be broken down
for a source of energy
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Pituitary Gland
and
Hypothalamus
Pituitary Gland
and
Hypothalamus
 Prolactin (PRL)
 Stimulates and maintains milk
production following childbirth
 Function in males is unknown
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 Gonadotropic hormones
 Regulate hormonal activity of the
gonads
 Follicle-stimulating hormone
(FSH)
 Stimulates follicle
development in ovaries
 Stimulates sperm
development in testes
 Luteinizing hormone (LH)
 Triggers ovulation of an
egg in females
 Stimulates testosterone
production in males
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Pituitary Gland
and
Hypothalamus
 Thyrotropic hormone (TH), also
called thyroid-stimulating hormone
(TSH)
 Influences growth and activity of
the thyroid gland
 Adrenocorticotropic hormone
(ACTH)
 Regulates endocrine activity of
the adrenal cortex
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Pituitary Gland
and
Hypothalamus
 Hangs from the roof of the third
ventricle of the brain
 Secretes melatonin
 Believed to trigger the body’s
sleep/wake cycle
 Believed to coordinate the
hormones of fertility in humans
and to inhibit the reproductive
system until maturity occurs
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Pineal
Gland
 Found at the base of the throat,
inferior to the Adam’s apple
 Consists of two lobes and a
connecting isthmus
 Follicles are hollow structures that
store colloidal material
 Produces two hormones
1. Thyroid hormone
2. Calcitonin
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Thyroid
Gland
Figure 9.6a The thyroid gland.
Thyroid cartilage
Epiglottis
Common carotid
artery
Isthmus of
thyroid gland
Trachea
Brachiocephalic
artery
Left subclavian
artery
Left lobe of
thyroid gland
Aorta
(a) Gross anatomy of the thyroid gland, anterior view
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 Thyroid hormone
 Major metabolic hormone
 Controls rate of oxidation of
glucose to supply body heat and
chemical energy
 Needed for tissue growth and
development
 Composed of two active iodinecontaining hormones
 Thyroxine (T4)—secreted by
thyroid follicles
 Triiodothyronine (T3)—
conversion of T4 at target
tissues
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Thyroid
Gland
 Calcitonin
 Decreases blood calcium levels
by causing calcium deposition
on bone
 Antagonistic to parathyroid
hormone
 Produced by parafollicular cells
found between the follicles
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Thyroid
Gland
 Tiny masses on the posterior of the
thyroid
 Secrete parathyroid hormone (PTH)
 Most important regulator of
calcium ion (Ca2+) homeostasis
of the blood
 Stimulates osteoclasts to
remove calcium from bone
 Hypercalcemic hormone
(increases blood calcium levels)
 Stimulates the kidneys and
intestine to absorb more calcium
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Parathyroid
Glands
Figure 9.7 Hormonal control of the level of calcium ions in the blood.
Calcitonin
Calcitonin
stimulates
calcium salt
deposit in bone.
Thyroid gland
releases calcitonin.
Stimulus
Rising blood
Ca2+ levels
BALANCE
Calcium homeostasis of blood:
9–11 mg/100 ml
BALANCE
Stimulus
Falling blood
Ca2+ levels
Thyroid
gland
Osteoclasts
degrade bone
matrix and release
Ca2+ into blood.
Parathyroid
glands
PTH
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Parathyroid
glands release
parathyroid
hormone (PTH).
 Located in the upper thorax,
posterior to the sternum
 Largest in infants and children
 Decreases in size throughout
adulthood
 Produces a hormone called
thymosin
 Matures some types of white
blood cells
 Important in developing the
immune system
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Thymus
 Sit on top of the kidneys
 Two regions
1. Adrenal cortex—outer glandular
region has three layers that
produce corticosteroids
 Mineralocorticoids are secreted
by outermost layer
 Glucocorticoids are secreted by
middle layer
 Sex hormones are secreted by
innermost layer
2. Adrenal medulla—inner neural
tissue region
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Adrenal
Glands
Figure 9.8 Microscopic structure of the adrenal gland.
Adrenal
gland
Capsule
Mineralocorticoidsecreting area
Kidney
Adrenal gland
•Medulla
•Cortex
Cortex
Glucocorticoidsecreting area
Sex hormonesecreting area
Medulla
Kidney
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Adrenal
cortex
Adrenal
medulla
 Hormones of the adrenal cortex
 Mineralocorticoids (mainly
aldosterone)
 Produced in outer adrenal
cortex
 Regulate mineral (salt)
content in blood, particularly
sodium and potassium ions
 Regulate water and
electrolyte balance
 Target organ is the kidney
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Adrenal
Glands
Adrenal Glands
 Hormones of the adrenal cortex (continued)
 Release of aldosterone is stimulated by:
 Humoral factors (fewer sodium ions or too many
potassium ions in the blood)
 Hormonal stimulation (ACTH)
 Renin and angiotensin II in response to a drop in blood
pressure
 Aldosterone production is inhibited by atrial natriuretic
peptide (ANP), a hormone produced by the heart when
blood pressure is too high
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Figure 9.9 Major mechanisms controlling aldosterone release from the adrenal cortex.
Decreased Na+ or
increased K+ in
blood
Stress
Hypothalamus
Corticotropinreleasing
hormone
Decreased
blood volume
and/or blood
pressure
Anterior pituitary
ACTH
Kidney
Renin
Indirect
stimulating
effect via
angiotensin
Increased
blood pressure
or blood volume
Heart
Atrial natriuretic
peptide (ANP)
Angiotensin II
Direct
stimulating
effect
Inhibitory
effect
Mineralocorticoidproducing part of
adrenal cortex
Enhanced secretion
of aldosterone targets
kidney tubules
Increased absorption
of Na+ and water;
increased K+ excretion
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Increased blood
volume and
blood pressure
 Hormones of the adrenal cortex
(continued)
 Glucocorticoids (including cortisone
and cortisol)
 Produced by middle layer of
adrenal cortex
 Promote normal cell metabolism
 Help resist long-term stressors
by increasing blood glucose
levels (hyperglycemic hormone)
 Anti-inflammatory properties
 Released in response to
increased blood levels of ACTH
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Adrenal
Glands
 Hormones of the adrenal cortex
(continued)
 Sex hormones
 Produced in the inner layer
of the adrenal cortex
 Small amounts are made
throughout life
 Most of the hormones
produced are androgens
(male sex hormones), but
some estrogens (female sex
hormones) are also formed
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Adrenal
Glands
 Adrenal medulla
 Produces two similar hormones
(catecholamines)
1. Epinephrine (adrenaline)
2. Norepinephrine
(noradrenaline)
 These hormones prepare the body
to deal with short-term stress (“fight
or flight”) by:
 Increasing heart rate, blood
pressure, blood glucose levels
 Dilating small passageways of
lungs
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Adrenal
Glands
Figure 9.10 Roles of the hypothalamus, adrenal medulla, and adrenal cortex in the stress response.
Short term
More prolonged
Stress
Hypothalamus
Releasing hormones
Nerve impulses
Spinal cord
Corticotropic cells of
anterior pituitary
ACTH
Preganglionic
Adrenal sympathetic
medulla fibers
Adrenal
cortex
Mineralocorticoids Glucocorticoids
Shor t-term stress response
Catecholamines
(epinephrine and
norepinephrine)
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1. Increased heart rate
2. Increased blood pressure
3. Liver converts glycogen to
glucose and releases glucose
to blood
4. Dilation of bronchioles
5. Changes in blood flow patterns,
leading to increased alertness
and decreased digestive and
kidney activity
6. Increased metabolic rate
Long-term stress response
1. Retention of sodium
and water by kidneys
2. Increased blood
volume and blood
pressure
1. Proteins and fats
converted to glucose
or broken down for
energy
2. Increased blood sugar
3. Suppression of
immune system
 Pancreas
 Located in the abdomen, close to
stomach
 Mixed gland, with both endocrine
and exocrine functions
 The pancreatic islets (islets of
Langerhans) produce hormones
 Insulin—produced by beta cells
 Glucagon—produced by alpha cells
 These hormones are antagonists
that maintain blood sugar
homeostasis
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Pancreatic
Islets
Figure 9.11a Pancreatic tissue.
Stomach
Pancreas
(a)
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 Insulin
 Released when blood glucose
levels are high
 Increases the rate of glucose
uptake and metabolism by body
cells
 Effects are hypoglycemic
 Glucagon
 Released when blood glucose
levels are low
 Stimulates the liver to release
glucose to blood, thus
increasing blood glucose levels
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Pancreatic
Islets
Figure 9.12 Regulation of the blood glucose level by a negative feedback mechanism involving pancreatic hormones.
Uptake of glucose
from blood is
enhanced in most
body cells.
Insulin-secreting cells
of the pancreas
activated; release
insulin into
the blood.
Pancreas
Insulin
Glucose
Elevated blood
sugar level
Stimulus
Blood glucose
level (e.g., after
eating four jelly
doughnuts)
Tissue cells
Glycogen
Liver takes up
glucose and stores
as glycogen.
BALANCE: Normal blood glucose level
(about 90 mg/100 ml)
Blood glucose rises
to homeostatic
set point; stimulus
for glucagon
release diminishes.
Liver breaks
down glycogen
stores and
releases glucose
to the blood.
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Blood glucose
falls to homeostatic
set point; stimulus
for insulin release
diminishes.
Glucose
Stimulus
Blood glucose
level (e.g., after
skipping a meal)
Low blood sugar level
Glucagon-releasing
cells of pancreas
activated; release
glucagon into blood.
Glycogen
Liver
Glucagon
Gonads
 Gonads
 Produce sex cells
 Produce sex hormones
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 Ovaries
 Female gonads located in the pelvic
cavity
 Produce eggs
 Produce two groups of steroid
hormones
1. Estrogens
2. Progesterone
 Testes
 Male gonads suspended outside the
pelvic cavity
 Produce sperm
 Produce androgens, such as
testosterone
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Gonads
Figure 9.3 Location of the major endocrine organs of the body.
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
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Gonads
 Estrogens
 Stimulate the development of
secondary female
characteristics
 Mature the female reproductive
organs
 With progesterone, estrogens also:
 Promote breast development
 Regulate menstrual cycle
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Gonads
 Progesterone
 Acts with estrogen to bring
about the menstrual cycle
 Helps in the implantation of an
embryo in the uterus
 Helps prepare breasts for
lactation
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 Testes
 Produce several androgens
 Testosterone is the most
important androgen
 Responsible for adult male
secondary sex
characteristics
 Promotes growth and
maturation of male
reproductive system
 Required for sperm cell
production
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Gonads