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Chapter 10
The Endocrine System
Announcements
• Senses lab- Due Wed!
• Next Monday- Class cancellation a possibility
Lecture Outline
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Function of Endocrine system
Hormones and their mechanisms
Pituitary gland
Pancreas
Other glands
The Endocrine system
Epithelial cells can form glands
• A gland- a
collection of cells
which secrete a
product
• Exocrine- release
substances through
ducts or tubes
Endocrine glands secrete hormones
directly into the body
• Hormone- a signalling
chemical which is
released in one part of
the body and affects
another part of the
body
• Examples- Insulin,
Follicle stimulating
hormone, testosterone
The Endocrine System
• The endocrine system
communicates using
chemical messages
• Hormones influence
growth, development,
metabolism, and
behavior
• Other chemical
messengers act locally
Endocrine System Communication
• Endocrine glands are made up of secretory
cells that release their products called
hormones directly into the adjacent
extracellular fluids where they diffuse directly
into the bloodstream
• Hormones are one of the chemical
messengers of the body
Endocrine System Communication
Figure 10.1
All signals require a receptor
Endocrine System
• Main function of the endocrine system is to
coordinate body systems and maintain
homeostasis
• The major endocrine glands are
– Pituitary
– Thyroid
– Parathyroid
– Adrenals
– Pineal
Endocrine System
Pineal gland
Melatonin
• Reduces jet lag and promotes
sleep
Thymus gland
Thymopoietin, thymosin
• Promote maturation of white
blood cells
Adrenal gland (one on each kidney)
Adrenal cortex
Glucocorticoids (cortisol,
corticosterone,cortisone)
• Stimulate glucose synthesis and
conservation
• Inhibit the inflammatory response
Mineralocorticoids (aldosterone)
• Increase sodium reabsorption by
kidneys
• Increase potassium excretion by
kidneys
Gonadocorticoids (androgens,
estrogens)
• Insignificant effects in adulthood,
relative to secretion by gonads
Adrenal medulla
Epinephrine
• Fight-or-flight response to stress
Norepinephrine
• Fight-or-flight response to stress
Parathyroid glands (two of four)
Parathyroid hormone (PTH)
• Increases blood levels of calcium
Heart
Kidney
Figure 10.2 (1 of 2)
Endocrine System
Stomach
Pancreas
Glucagon
• Increases blood glucose level
Insulin
• Decreases blood glucose level
Testis (one of a pair)
Androgens (testosterone)
• Develop male secondary sex
characteristics
Thyroid gland
Thyroid hormone (TH)
• Regulates metabolism and heat
production
• Promotes development and function
of nervous, muscular, skeletal, and
reproductive systems
Calcitonin (CT)
• Decreases blood levels of calcium
and phosphate
Small intestine
Uterus (contains the
placenta when pregnant)
Ovary (one of a pair)
Estrogens and progesterone
• Develop female secondary sex
characteristics
Figure 10.2 (2 of 2)
Endocrine System Communication
• Hormones circulate throughout the body until
they reach target cells
– They respond to the hormone, influencing growth,
development, metabolism, and behavior
Target Cells
• Target cells have receptors
– Protein molecules that recognize and bind to
specific hormones
• Cells other than target cells lack the correct
receptors and are unaffected by the hormone
Chemical Composition of Hormones
• The mechanism by which hormones influence
target cells depend on the chemical makeup
of the hormones
Chemical Composition of Hormones
• Two types of hormones
– Lipid-soluble
– Water-soluble
Lipid-soluble Hormones
• Lipid-soluble hormones include steroid
hormones
– Derived from cholesterol
• The main organs that secrete steroid
hormones are
– Ovaries
– Testes
– Adrenal glands
Lipidsoluble
Hormones
can freely
pass
through cell
membranes
Extracellular fluid
Steroid hormone
Step 1: The
steroid hormone
diffuses through
the plasma
membrane of
the target cell.
Plasma membrane
of target cell
(lipid bilayer)
Step 7: Enzymes
alter the activity
of the cell.
Step 2: The
steroid hormone
binds to a receptor
in the cytoplasm.
Cytoplasm
Receptor
Nuclear
pore
Nuclear
envelope
Step 6: Proteins,
including enzymes,
are synthesized.
Step 5: Certain
genes are activated.
Step 3: The hormonereceptor complex
enters the nucleus.
Step 4: The hormonereceptor complex
binds to DNA.
Nucleus
Functional groups can radically change the function
of a molecule
Estradiol
Female lion
Testosterone
Male lion
Water-soluble hormones
• Water-soluble hormones are made of amino
acids
• They cannot pass through the lipid bilayer of
the plasma membrane
Water-soluble hormones
• They exert their effects indirectly by binding to
receptors on the surface of the target cell
• This stimulates second messengers within the
cell that carry out the effect of the hormone
• One common second messenger is cyclic
adenosine monophosphate (cAMP)
cAMP is a
common
second
messenger
for watersoluble
hormones
Figure 10.4
This type of hormone characteristically
requires a second messenger.
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A) Lipid-soluble
B) Steroid
C) Water-soluble
D) Prostaglandins
Feedback Mechanisms
• Feedback mechanisms regulate the secretion
of hormones
The
regulation of
blood sugar is
an example of
hormones in
action to
maintain
homeostasis
Figure 10.18 (1 of 2)
Feedback Mechanisms
• Control is usually by a negative feedback
mechanism whereby the increased blood level
of the hormone inhibits its further release
Feedback Mechanisms
• Some hormones are regulated by a positive
feedback mechanism in which the outcome of
a process further stimulates the process
Positive and negative feedback systems regulate
reproduction
Figure 10.5
The Pituitary gland
The pituitary gland is a master control
gland
• Controls other glands
• Secretes many
hormones that affects
systems directly
Hormones
• The anterior pituitary is connected to the
hypothalamus, which synthesizes and secretes
releasing and inhibiting hormones
Hormones
• The anterior pituitary gland synthesizes and
secretes
– Growth hormone (GH)
– Prolactin (PRL)
– Thyroid-stimulating hormone (TSH)
– Adrenocorticotropic hormone (ACTH)
– Follicle-stimulating hormone (FSH)
– Luteinizing hormone (LH)
Hormones
Hypothalamus
Nerve cells in the
hypothalamus produce
antidiuretic hormone
(ADH) and oxytocin (OT).
ADH and OT travel to
the ends of the cells in
the posterior pituitary,
where they are released
into the bloodstream to
influence target tissues.
Posterior
pituitary
Nerve cells in the
hypothalamus secrete
releasing hormones
and inhibiting
hormones.
Anterior
pituitary
Releasing and inhibiting
hormones travel by way
of the bloodstream to
the anterior pituitary
and cause it to modify
secretion of its six
hormones (FSH, LH, GH,
PRL, ACTH, and TSH).
Antidiuretic
hormone (ADH)
Follicle-stimulating
hormone (FSH) and
Luteinizing hormone
(LH)
Growth
hormone (GH)
Oxytocin (OT)
Ovaries, testes
Prolactin (PRL)
Kidney tubules
Thyroidstimulating
hormone (TSH)
Smooth muscle
in uterus
Mammary
glands
Adrenocorticotropic hormone
(ACTH)
Bones, muscles
Mammary
glands
Thyroid gland
Cortex of
adrenal gland
Figure 10.6
Human Growth Hormone
• Two hormones of the hypothalamus regulate
the synthesis and release of GH
– Growth hormone-releasing hormone (GHRH)
stimulates the release of GH
– Growth hormone-inhibitory hormone (GHIH)
inhibits the release of GH
Human Growth Hormone
• Growth hormone (GH) stimulates an increase
in cell size and the rate of cell division in target
cells
• Gigantism
– Abnormally high production of GH in childhood
when the bones are still capable of growing in
length
Human Growth Hormone
Figure 10.7
Human Growth Hormone
• Acromegaly
– High levels of GH in adulthood when the bones
can thicken but not lengthen
Human Growth Hormone
Human Growth Hormone
• Pituitary dwarfism
– Insufficient production of GH in childhood
– A genetic disorder treated with growth hormone
produced by recombinant DNA
Human Growth Hormone
Figure 10.9
Prolactin
• Prolactin (PRL)
– Stimulates the mammary glands to produce milk
– Produced during lactation
• Excess may cause infertility and lactation
when there is no pregnancy
• In men
– PRL is involved with the production of mature
sperm in the testes
– Overproduction can lead to sterility
Tropic Hormones
• TSH, ACTH, FSH, and LH are tropic hormones
– Hormones that influence the secretion of
hormones by other glands
Thyroid-Stimulating Hormone
• Thyroid-stimulating hormone (TSH)
– Acts on the thyroid gland to stimulate the
synthesis and release of thyroid hormones
Adrenocorticotropic Hormone
• Adrenocorticotropic hormone (ACTH)
– Controls the synthesis and secretion of
glucocorticoid hormones from the adrenal cortex
Follicle-Stimulating Hormone
• Follicle-stimulating hormone (FSH)
– Promotes development of egg cells and secretion
of estrogen in females
• In males
– FSH promotes the production of sperm
Luteininzing Hormone
• Luteinizing hormone (LH)
– Causes ovulation and the secretion of estrogen
and progesterone
– Prepares the uterus for implantation of a fertilized
ovum and the breasts for the production of milk
• In males
– LH stimulates the production and secretion of
testosterone
Posterior Pituitary
• Cells within the posterior lobe of the pituitary
do not produce any hormones
– Neurons of the hypothalamus manufacture
antidiuretic hormone (ADH) and oxytocin (OT)
– They travel down the nerve cells into the posterior
pituitary, where they are stored and released
Posterior Pituitary
Hypothalamus
Nerve cells in the
hypothalamus produce
antidiuretic hormone
(ADH) and oxytocin (OT).
ADH and OT travel to
the ends of the cells in
the posterior pituitary,
where they are released
into the bloodstream to
influence target tissues.
Nerve cells in the
hypothalamus secrete
releasing hormones
and inhibiting
hormones.
Posterior
pituitary
Anterior
pituitary
Releasing and inhibiting
hormones travel by way
of the bloodstream to
the anterior pituitary
and cause it to modify
secretion of its six
hormones (FSH, LH, GH,
PRL, ACTH, and TSH).
Antidiuretic
hormone (ADH)
Follicle-stimulating
hormone (FSH) and
Luteinizing hormone
(LH)
Growth
hormone (GH)
Oxytocin (OT)
Ovaries, testes
Prolactin (PRL)
Kidney tubules
Thyroidstimulating
hormone (TSH)
Smooth muscle
in uterus
Mammary
glands
Adrenocorticotropic hormone
(ACTH)
Bones, muscles
Mammary
glands
Thyroid gland
Cortex of
adrenal gland
Figure 10.6
Posterior Pituitary Hormones
• Antidiuretic Hormone (ADH)
– Also called vasopressin
– Causes the kidneys to remove water from the fluid
destined to become urine
• A deficiency of ADH results in diabetes
insipidus
– Characterized by excessive urine production and
dehydration
Posterior Pituitary Hormones
• Oxytocin (OT)
– Stimulates uterine contractions of childbirth and
milk ejection from the mammary glands
• In men
– OT may facilitate the transport of sperm and be
involved in male sexual behavior
Posterior Pituitary Hormones
Figure 10.5
Posterior Pituitary Hormones
Figure 10.10
Thyroid Gland Hormones
• Hormones secreted by the thyroid gland
regulate metabolism and decrease blood
calcium
– Thyroxine (T4) and triiodothyrinine (T3),
collectively known as thyroid hormone (TH),
regulate metabolic rate
– Calcitonin
• Decreases blood calcium
Thyroid Gland Hormones
Opening to
trachea
Larynx
Thyroid gland
Parathyroid
glands
Trachea
Back view
Front view
(a) The thyroid gland lies over the trachea, just below the larynx.
Figure 10.11a
Thyroid Gland Hormones
Figure 10.11b
Thyroid Gland Hormones
• Thyroid hormone (TH)
– Produced in the follicular cells
– Stimulates protein synthesis, the breakdown of
lipids, and the use of glucose for the production of
ATP
Thyroid Gland Hormones
• Simple goiter
– An enlarged thyroid gland
– May be produced by a diet deficient in iodine,
which is needed for the production of TH
– Can be treated by iodine supplements or
administration of TH
Thyroid Gland Hormones
Figure 10.12a
Thyroid Gland Hormones
• Cretinism
– Too little TH during fetal development or infancy
– Characterized by dwarfism and delayed mental
and sexual development
• Myxedema
– Too little TH in adulthood
– Causes a condition in which fluid accumulates in
facial tissues and a decrease in alertness, body
temperature, and heart rate
Thyroid Gland Hormones
Figure 10.12b
Thyroid Gland Hormones
• Graves’ disease
– Oversecretion of TH
– Results in an autoimmune disorder due to the
production of antibodies that mimic the action of
TSH
• Symptoms include
– Increased metabolic rate and heart rate
accompanied by sweating, nervousness, and
weight loss
– Many also have exopthalmos
Thyroid Gland Hormones
Figure 10.12c
Thyroid Gland Hormones
• Calcitonin (CT)
– Helps regulate calcium concentration in the blood
by either
• Stimulating the absorption of calcium by bone
• Increasing the excretion of calcium in the urine
Thyroid Gland Hormones
Figure 10.13
Thyroid Gland Hormones
Figure 10.13 (1 of 2)
Thyroid Gland Hormones
Figure 10.13 (2 of 2)
Parathyroid Gland Hormones
• Parathyroid glands
– Four small round masses lateral to the thyroid
gland
– Secrete parathyroid hormone (PTH), or
parathormone, which increases the blood calcium
level
Parathyroid Gland Hormones
• PTH
– Stimulates
• Osteoclasts to break down bone-releasing calcium into
the blood
• Removal of calcium from the urine, returning it to the
blood
• Rate calcium is absorbed from the gastrointestinal tract
– Inhibits
• Osteoblasts
Parathyroid Gland Hormones
• Undersecretion of PTH
– Can result in nervousness and muscle spasms
• Oversecretion
– Pulls calcium from bone tissue, causing weakened
bones and elevated blood calcium levels
• Might lead to kidney stones, calcium deposits in the
soft tissue, and decreased activity of the nervous
system
Adrenal Gland Hormones
• The adrenal glands
– Located at the top of the kidneys
– Composed of two regions
• Adrenal cortex
• Adrenal medulla
Adrenal Gland Hormones
• The adrenal cortex (outer region) secretes
– Gonadocorticoids
– Glucocorticoids
– Mineralcorticoids
• The adrenal medulla (inner region) secretes
– Epinephrine (adrenaline)
– Norepinephrine (noradrenaline)
Adrenal Gland Hormones
Figure 10.14a
cortex
Adrenal GlandAdrenal
Hormones
Adrenal
gland
• Mineralocorticoids
• Gonadocorticoids
• Glucocorticoids
Adrenal medulla
• Epinephrine
• Norepinephrine
(b) A section through the adrenal gland
reveals two regions, the outer
adrenal cortex and the inner adrenal
medulla. These regions secrete
different hormones.
Figure 10.14b
Adrenal Gland Hormones
• Gonadocorticoids
– Androgens and estrogens
– Secreted by the adrenal cortex in both males and
females
Adrenal Gland Hormones
• Mineralocorticoids
– Affect mineral homeostasis and water balance
• Aldosterone
– Acts on cells of the kidneys to
• Increase reabsorption of sodium ions into the blood
• Promote the excretion of potassium ions in the urine
Adrenal Gland Hormones
• Addison’s disease
– Caused by the undersecretion of cortisol and
aldosterone
– Appears to be an autoimmune disorder in which
the cells of the adrenal cortex are perceived as
foreign
– Results in bronzing of the skin, weight loss,
fatigue, electrolyte imbalance, poor appetite, and
resistance to stress
– May be caused by inadequate secretion of ACTH
Adrenal Gland Hormones
Figure 10.15
Adrenal Gland Hormones
• Glucocorticoids
– Affect glucose homeostasis
– Act on the liver to promote the conversion of fat
and protein into intermediate substances available
to the body’s cells
– Inhibit the inflammatory response
Adrenal Gland Hormones
• Cushing’s syndrome
– May be caused by the oversecretion of
glucocorticoids or a tumor on either the adrenal
cortex or anterior pituitary
– Results in redistribution of body fat and
accumulation of fluid in the face, fatigue, high
blood pressure, and elevated glucose levels
Adrenal Gland Hormones
Figure 10.16
Adrenal Gland Hormones
• The adrenal medulla
– Produces epinephrine (adrenaline) and
norepinephrine (noradrenaline)
– Both of these hormones are used in our response
to danger, preparing us for fight-or-flight
Pancreas Gland Hormones
• Hormones of the pancreas
– Secreted from the pancreatic islets
– Regulate blood glucose levels through glucagon
and insulin
Pancreas Gland Hormones
Stomach
Common bile duct
(from gallbladder and liver)
Pancreas
Pancreatic
duct
Duodenum
(first part of
small intestine)
(a) Structure of the pancreas and associated ducts. Exocrine cells of the pancreas
secrete digestive enzymes into the pancreatic duct, which unites with the
common bile duct before entering the small intestine.
Figure 10.17a
Pancreas Gland Hormones
Figure 10.17b
Pancreas Gland Hormones
• Glucagon
– Increases glucose in the blood by converting
glycogen to glucose in the liver
Pancreas Gland Hormones
Figure 10.18 (2 of 2)
Pancreas Gland Hormones
• Insulin
– Decreases blood glucose levels
– Stimulates transport of glucose into muscle cells,
white blood cells, and connective tissue cells
– Inhibits the breakdown of glycogen to glucose
– Prevents conversion of amino and fatty acids into
glucose
Pancreas Gland Hormones
• Diabetes mellitus
– A group of metabolic disorders characterized by
an abnormally high level of glucose in the blood
Pancreas Gland Hormones
• Type 1 diabetes mellitus
– Usually develops in people younger than 25 years
of age
– An autoimmune disease
– A person’s own immune system attacks the cells
of the pancreas responsible for insulin production
Pancreas Gland Hormones
• Type 2 diabetes mellitus
– Usually develops after age 40, but has begun
showing up in younger people recently
– Characterized by a decreased sensitivity to insulin
(insulin resistance)
Thymus Gland Hormones
• Thymus gland
– Secretes hormones, such as thymopoietin and
thymosin, which are involved in the maturation of
T lymphocytes
– These hormones and the thymus gland play a very
important role in immunity
Pineal Gland Hormones
• The pineal gland
– Contains secretory cells that produce melatonin
– Levels of circulating melatonin are greater at night
than during daylight hours
• Due to the input the pineal gland receives from the
visual pathways
Pineal Gland Hormones
Pineal gland
Cerebrum
Hypothalamus
Skull
Pituitary gland
Figure 10.19
Pineal Gland Hormones
• Melatonin is linked to sleep, fertility, and aging
• Too much melatonin can result in seasonal
affective disorder (SAD), which is associated
with winter
• Treatment includes repeated exposure to very
bright light
Pineal Gland Hormones
PLAY
Animation—The Hypothalamus and the Pituitary
Other Chemicals Act Locally
• Local signaling molecules act very quickly on
adjacent cells
– Neurotransmitters
– Growth factors
– Nitric oxide (NO)
– Prostaglandins
Other Chemicals Act Locally
• Prostaglandins
– Lipid molecules continually released by the
plasma membranes of most cells
– At least 16 different prostaglandin molecules
function within the human body
Other Chemicals Act Locally
• Although they act locally, prostaglandins can
have very diverse effects including
– Actions on the reproductive system
– Fertility
– Blood clotting
– Body temperature
Hormonal Response to Stress
• General adaptation syndrome (GAS)
– A series of physiological adjustments made by our
bodies in response to extreme stress
– Has three phases
• Alarm
• Resistance
• Exhaustion
Hormonal Response to Stress
• Alarm
– Fight-or-flight response
• Resistance
– Glucocorticoids from adrenal cortex are the main
hormones
– Body’s protein and fat reserves mobilized
– Body fluids conserved
• Exhaustion
– Organs are unable to meet the heavy demands of
the resistance phase, and they begin to fail
Hormonal Response to Stress
PLAY
| Fighting Stress