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CHAPTER
9
The
Endocrine
System
© 2012 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
© 2012 Pearson Education, Inc.
Hormone Overview
•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  the scientific study of
hormones and endocrine organs
© 2012 Pearson Education, Inc.
The Chemistry of Hormones
•Hormones  chemical substances that are
secreted by endocrine cells into the
extracellular fluids and regulate the metabolic
activity of other cells in the body
•Classified chemically as:
•Amino acid–based, which includes proteins,
peptides, and amines
•Steroids  made from cholesterol
•Prostaglandins  made from highly active
lipids
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Mechanisms of 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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Effects Caused by Hormones
•Changes in plasma membrane permeability or
electrical state
•Synthesis of proteins, such as enzymes
•Activation or inactivation of enzymes
•Stimulation of mitosis
•Promotion of secretory activity
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The Chemistry of Hormones
•Two mechanisms in which hormones act
•Direct gene activation
•Second-messenger system
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Direct Gene Activation (Steroid Hormone
Action)
•Diffuse through the plasma membrane of
target cells
•Enter the nucleus
•Bind to a specific protein within the nucleus
•Bind to specific sites on the cell’s DNA
•Activate genes that result in synthesis of new
proteins
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Steroid
hormone
Cytoplasm
Nucleus
1
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Figure 9.1a, step 1
Steroid
hormone
1
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Nucleus
Cytoplasm
2
Receptor
protein
Figure 9.1a, step 2
Steroid
hormone
Nucleus
Cytoplasm
1
Receptor
protein
2
3
Hormonereceptor complex
© 2012 Pearson Education, Inc.
Figure 9.1a, step 3
Steroid
hormone
Nucleus
Cytoplasm
1
Receptor
protein
2
3
Hormonereceptor complex
4
DNA
© 2012 Pearson Education, Inc.
Figure 9.1a, step 4
Steroid
hormone
Nucleus
Cytoplasm
1
Receptor
protein
2
3
Hormonereceptor complex
4
DNA
mRNA
© 2012 Pearson Education, Inc.
5
Figure 9.1a, step 5
Steroid
hormone
Nucleus
Cytoplasm
1
Receptor
protein
2
3
Hormonereceptor complex
4
DNA
mRNA
5
New
protein
Plasma
membrane
of target
cell
© 2012 Pearson Education, Inc.
6
Figure 9.1a, step 6
Second-Messenger System (Nonsteroid
Hormone Action)
•Hormone binds to a membrane receptor
•Hormone does not enter the cell
•Sets off a series of reactions that activates an
enzyme
•Catalyzes a reaction that produces a secondmessenger molecule (such as cAMP)
•Oversees additional intracellular changes to
promote a specific response
© 2012 Pearson Education, Inc.
Nonsteroid
hormone (first
messenger)
Cytoplasm
1
Receptor
protein
© 2012 Pearson Education, Inc.
Figure 9.1b, step 1
Nonsteroid
hormone (first
messenger)
Cytoplasm
Enzyme
1
2
Receptor
protein
© 2012 Pearson Education, Inc.
Figure 9.1b, step 2
Nonsteroid
hormone (first
messenger)
Cytoplasm
Enzyme
ATP
3
1
2
Second
cAMP messenger
Receptor
protein
© 2012 Pearson Education, Inc.
Figure 9.1b, step 3
Nonsteroid
hormone (first
messenger)
Cytoplasm
Enzyme
ATP
3
1
2
Receptor
protein
Plasma
membrane
of target cell
© 2012 Pearson Education, Inc.
Second
cAMP messenger
4
Effect on cellular function,
such as glycogen
breakdown
Figure 9.1b, step 4
Control of Hormone Release
•Hormone levels in the blood are mostly
maintained by negative feedback
•A stimulus or low hormone levels in the
blood triggers the release of more hormone
•Hormone release stops once an appropriate
level in the blood is reached
© 2012 Pearson Education, Inc.
Hormonal Stimuli of Endocrine Glands
•Most common stimuli
•Endocrine glands are activated by other
hormones
•Examples:
•Anterior pituitary hormones travel to target
glands, such as the thyroid gland, to prompt
the release of a particular hormone, such as
thyroid hormone
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(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 Gonad
cortex (Testis)
3 …stimulate other endocrine
glands to secrete hormones
© 2012 Pearson Education, Inc.
Figure 9.2a
Humoral Stimuli of Endocrine Glands
•Changing blood levels of certain ions 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
© 2012 Pearson Education, Inc.
(b) Humoral stimulus
1 Capillary blood contains low
concentration of Ca2+, which
stimulates…
Capillary
(low Ca2+
in blood)
Thyroid gland
(posterior view)
Parathyroid
Parathyroid
glands
PTH glands
2 …secretion of parathyroid
hormone (PTH) by parathyroid
glands
© 2012 Pearson Education, Inc.
Figure 9.2b
Neural Stimuli of Endocrine Glands
•Nerve impulses stimulate hormone release
•Most are under the control of the sympathetic
nervous system
•Examples:
•The release of norepinephrine and
epinephrine by the adrenal medulla
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(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)
© 2012 Pearson Education, Inc.
Figure 9.2c
Major Endocrine Organs
•Pituitary gland
•Thyroid gland
•Parathyroid glands
•Adrenal glands
•Pineal gland
•Thymus gland
•Pancreas
•Gonads (Ovaries and Testes)
•Hypothalamus
© 2012 Pearson Education, Inc.
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
© 2012 Pearson Education, Inc.
Figure 9.3
Pituitary Gland
•Size of a pea
•Hangs by a stalk from the hypothalamus in the
brain
•Protected by the sphenoid bone
•Has two functional lobes
•Anterior pituitary  glandular tissue
•Posterior pituitary  nervous tissue
•Often called the “master endocrine gland”
© 2012 Pearson Education, Inc.
Hormones of the Anterior Pituitary
•Six anterior pituitary hormones
•Two affect non-endocrine targets
•Growth hormone  major effects are
directed to the growth of skeletal muscles
and long bones of the body
•Prolactin  stimulates and maintains milk
production by the mother’s breasts. No
known function in men
© 2012 Pearson Education, Inc.
Hormones of the Anterior Pituitary
•Growth hormone
•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
© 2012 Pearson Education, Inc.
Hormones of the Anterior Pituitary
•Growth hormone (GH) disorders
•Pituitary dwarfism  results from
hyposecretion of GH during childhood
•Body proportions are fairly normal, but the
person is a living minaiture (4 ft. max)
•Gigantism  results from hypersecretion of
GH during childhood
•Anywhere between 8 and 9 ft. is common
•Acromegaly  results from hypersecretion
of GH during adulthood
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Pituitary dwarf (left), Giant (center), Normal height woman (right)
© 2012 Pearson Education, Inc.
Figure 9.5
Acromegaly  the facial bones,
particularly the lower jaw and the boy
ridges underlying the eyebrows, enlarge
tremendously, and do the feet and hands
© 2012 Pearson Education, Inc.
Hormones of the Anterior Pituitary
•Four stimulate other endocrine glands (tropic
hormones)
•Thyroid-stimulating hormone (thyrotropic
hormone)  influences the growth and
activity of the thyroid gland
•Adrenocorticotropic hormone  regulates
the endocrine activity of the cortex portion of
the adrenal gland
•Two gonadotropic hormones
© 2012 Pearson Education, Inc.
Hormones of the Anterior Pituitary
•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
© 2012 Pearson Education, Inc.
Hormones of the Anterior Pituitary
•Characteristics of all anterior pituitary
hormones
•Proteins (or peptides)
•Act through second-messenger systems
•Regulated by hormonal stimuli, mostly
negative feedback
© 2012 Pearson Education, Inc.
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
Adrenal cortex
Testes or ovaries
© 2012 Pearson Education, Inc.
Figure 9.4
Pituitary–Hypothalamus Relationship
•Hormonal release is regulated by releasing
and inhibiting hormones produced by the
hypothalamus
•Hypothalamus produces two hormones
•These hormones are transported to
neurosecretory cells of the posterior pituitary
•Oxytocin
•Antidiuretic hormone
•The posterior pituitary is not strictly an
endocrine gland, but does release hormones
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Hormones of the Posterior Pituitary
•Oxytocin
•Stimulates contractions of the uterus during
labor, sexual relations, and breastfeeding
•Causes milk ejection in a nursing woman
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Hormones of the Posterior Pituitary
•Antidiuretic hormone (ADH)
•Inhibits urine production by promoting water
reabsorption by the kidneys
•In large amounts, causes vasoconstriction
leading to increased blood pressure
•Also known as vasopressin
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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
Figure 9.6
Thyroid Gland
•Found at the base of the throat
•Consists of two lobes and a connecting
isthmus
•Produces two hormones
•Thyroid hormone
•Calcitonin
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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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Figure 9.7a
Thyroid Gland
•Thyroid hormone
•Major metabolic hormone
•Composed of two active iodine-containing
hormones
•Thyroxine (T4)—secreted by thyroid
follicles
•Triiodothyronine (T3)—conversion of T4 at
target tissues
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Colloid-filled
Follicle cells
follicles
Parafollicular cell
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(b) Photomicrograph of thyroid gland
follicles (125×)
Figure 9.7b
Thyroid Gland
•Thyroid hormone disorders
•Goiters
•Thyroid gland enlarges due to lack of
iodine in the diet
•Salt is iodized to prevent goiters
•Cretinism
•Caused by hyposecretion of thyroxine
•Results in dwarfism during childhood
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© 2012 Pearson Education, Inc.
Figure 9.8
Thyroid Gland
•Myxedema
•Caused by hypothyroidism in adults
•Results in physical and mental
sluggishness, puffiness of the face, fatigue,
low body temp., obesity, dry skin
•Graves’ disease
•Caused by hyperthyroidism (generally
results from a tumor of the thyroid gland)
•Results in increased metabolism, heat
intolerance, rapid heartbeat, weight loss,
and exophthalmos  eyes bulge
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
Figure 9.9
Thyroid Gland
•Calcitonin
•Decreases blood calcium levels by causing
its deposition on bone
•Antagonistic to parathyroid hormone
•Produced by parafollicular cells
•Parafollicular cells are found between the
follicles
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Colloid-filled
Follicle cells
follicles
Parafollicular cell
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(b) Photomicrograph of thyroid gland
follicles (125×)
Figure 9.7b
Parathyroid Glands
•Tiny masses on the posterior of the thyroid
•Secrete parathyroid hormone (PTH)
•Stimulate osteoclasts to remove calcium
from bone
•Stimulate the kidneys and intestine to
absorb more calcium
•Raise calcium levels in the blood
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Calcitonin
Calcitonin
stimulates
calcium salt
deposit in bone.
Thyroid gland
releases calcitonin.
Stimulus
Rising blood
Ca2+ levels
Calcium homeostasis of blood: 9–11 mg/100 ml
BALANCE
BALANCE
Stimulus
Falling blood
Ca2+ levels
Thyroid
gland
Osteoclasts
degrade bone
matrix and
release Ca2+
into blood.
Parathyroid
glands
PTH
© 2012 Pearson Education, Inc.
Parathyroid
glands release
parathyroid
hormone (PTH).
Figure 9.10
Adrenal Glands
•Sit on top of the kidneys
•Two regions
•Adrenal cortex—outer glandular region has
three layers
•Mineralocorticoids secreted by outermost
layer
•Glucocorticoids secreted by middle layer
•Sex hormones secreted by innermost
layer
•Adrenal medulla—inner neural tissue region
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Adrenal
gland
Capsule
Mineralocorticoidsecreting area
Kidney
Adrenal gland
• Medulla
• Cortex
Cortex
Glucocorticoidsecreting area
Sex hormone
secreting area
Medulla
Kidney
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Adrenal
cortex
Adrenal
medulla
Figure 9.11
Hormones of the Adrenal Cortex
•Mineralocorticoids (mainly aldosterone)
•Produced in outer adrenal cortex
•Regulate mineral content in blood
•Regulate water and electrolyte balance
•Target organ is the kidney
•Production stimulated by renin and
aldosterone
•Production inhibited by atrial natriuretic
peptide (ANP)
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Decreased Na+ or
increased K+ in
blood
Stress
Hypothalamus
Decreased
blood volume
and/or blood
pressure
Corticotropinreleasing hormone
Anterior pituitary
Increased
ACTH blood pressure
or blood volume
Kidney
Renin
Indirect
stimulating
effect via
angiotensin
Angiotensin II
Direct
stimulating
effect
Heart
Atrial natriuretic
peptide (ANP)
Inhibitory
effect
Mineralocorticoidproducing part of
adrenal cortex
Enhanced secretion
of aldosterone targets
kidney tubules
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Increased absorption
of Na+ and water;
increased K+ excretion
Increased blood
volume and
blood pressure
Figure 9.12
Hormones of the Adrenal Cortex
•Glucocorticoids (including cortisone and
cortisol)
•Produced in the middle layer of the adrenal
cortex
•Promote normal cell metabolism
•Help resist long-term stressors
•Released in response to increased blood
levels of ACTH
© 2012 Pearson Education, Inc.
Short term
Stress
More prolonged
Hypothalamus
Releasing hormones
Nerve impulses
Spinal cord
Corticotropic cells of
anterior pituitary
Preganglionic
Adrenal sympathetic
medulla fibers
ACTH
Adrenal
cortex
Mineralocorticoids Glucocorticoids
Short-term stress response
Catecholamines 1. Increased heart rate
2. Increased blood pressure
(epinephrine and
3. Liver converts glycogen
norepinephrine)
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
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Long-term stress response
1. Retention of sodium 1. Proteins and fats
converted to
and water by kidneys
glucose or broken
2. Increased blood
down for energy
volume and blood
2. Increased blood
pressure
sugar
3. Suppression of
immune system
Figure 9.13
Hormones of the Adrenal Cortex
•Sex hormones
•Produced in the inner layer of the adrenal
cortex
•Small amounts are made throughout life
•Mostly androgens (male sex hormones) are
made but some estrogens (female sex
hormones) are also formed
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Adrenal Glands
• Adrenal cortex disorders
• Addison’s disease
• Results from hyposecretion of all adrenal
cortex hormones
• Bronze skin tone, muscles are weak,
burnout, susceptibility to infection
• Hyperaldosteronism
• May result from an ACTH-releasing tumor
• Excess water and sodium are retained
leading to high blood pressure and edema
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© 2012 Pearson Education, Inc.
Adrenal Glands
• Adrenal cortex disorders
• Cushing’s syndrome
• Results from a tumor in the middle cortical
area of the adrenal cortex
• “Moon face,” “buffalo hump” on the upper
back, high blood pressure, hyperglycemia,
weakening of bones, depression
• Masculinization
• Results from hypersecretion of sex hormones
• Beard and male distribution of hair growth
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
Hormones of the Adrenal Medulla
•Produces two similar hormones
(catecholamines)
•Epinephrine  adrenaline
•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
gland
Capsule
Mineralocorticoidsecreting area
Kidney
Adrenal gland
• Medulla
• Cortex
Cortex
Glucocorticoidsecreting area
Sex hormone
secreting area
Medulla
Kidney
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Adrenal
cortex
Adrenal
medulla
Figure 9.11
Pancreatic Islets
•The pancreas is a mixed gland and has both
endocrine and exocrine functions
•The pancreatic islets produce hormones
•Insulin  allows glucose to cross plasma
membranes into cells from beta cells
•Glucagon  allows glucose to enter the
blood from alpha cells
•These hormones are antagonists that
maintain blood sugar homeostasis
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Homeostatic Imbalance
•Diabetes Mellitus
•A lack of insulin in the blood leads to
increasingly high blood glucose levels
•Glucose begins to spill into the urine
because kidney tubules cannot reabsorb it
fast enough
•As glucose flushes from the system, water
follows which leads to dehydration
•Fats and proteins are broken down for to
meet energy requirements
© 2012 Pearson Education, Inc.
Homeostatic Imbalance
•Type 2 – Adult onset diabetes
•Insulin is produced, by for some reason their
insulin receptors are unable to respond to it
•Treated with special diets or oral
hypoglycemic medications
•Type 1 – Juvenile diabetes
•Insulin is not produced
•Treated by an insulin pump or insulin
injections throughout the day
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Stomach
Pancreas
(a)
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Figure 9.14a
Exocrine
cells of
pancreas
(b)
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Pancreatic
islets
Figure 9.14b
Exocrine
cells of
pancreas
Alpha (α)
cells
Capillaries
Cord of beta (β) cells secreting
insulin into capillaries
(c)
© 2012 Pearson Education, Inc.
Figure 9.14c
Uptake of glucose
from blood is
enhanced in most
body cells
Insulin-secreting cells
of the pancreas
activated; release
insulin into the blood
Insulin
Pancreas
Elevated blood
sugar level
Tissue cells
Glucose Glycogen
Liver takes up
glucose and stores
as glycogen
Stimulus
Blood
glucose level
(e.g., after
eating four
jelly doughnuts)
Stimulus
Blood glucose
level (e.g., after
skipping a meal)
Blood glucose rises
to homeostatic
set point; stimulus
for glucagon
release diminishes
Glucose Glycogen
Liver breaks
down glycogen
stores and
Liver
releases
glucose to the
blood
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Blood glucose
falls to homeostatic
set point; stimulus
for insulin release
diminishes
Low blood sugar level
Glucagon-releasing
cells of pancreas
activated; release
glucagon into blood
Glucagon
Figure 9.15
Pineal Gland
•Found on the third ventricle of the brain
•Secretes melatonin
•Helps establish the body’s wake and sleep
cycles
•Believed to coordinate the hormones of
fertility in humans
© 2012 Pearson Education, Inc.
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
© 2012 Pearson Education, Inc.
Figure 9.3
Thymus Gland
•Located posterior to the sternum
•Largest in infants and children
•Produces thymosin
•Matures some types of white blood cells
•Important in developing the immune system
© 2012 Pearson Education, Inc.
Gonads
•Ovaries
•Produce eggs
•Produce two groups of steroid hormone
•Estrogens
•Progesterone
•Testes
•Produce sperm
•Produce androgens, such as testosterone
© 2012 Pearson Education, Inc.
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
© 2012 Pearson Education, Inc.
Figure 9.3
Hormones of the Ovaries
•Estrogens
•Stimulate the development of secondary
female characteristics
•Mature female reproductive organs
•With progesterone, estrogens also
•Promote breast development
•Regulate menstrual cycle
© 2012 Pearson Education, Inc.
Hormones of the Ovaries
•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
© 2012 Pearson Education, Inc.
Hormones of the 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
© 2012 Pearson Education, Inc.