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Chapter 16
Lecture Outline
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Endocrine System
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Points to ponder
• What is the endocrine system?
• Compare and contrast exocrine and endocrine
glands.
• What are steroid and peptide hormones?
• Name the major glands and their functions in the
endocrine system.
• What is diabetes (type 1 and 2) and how might
you prevent type 1?
• How do the endocrine and nervous systems
work with the rest of the systems in the body to
maintain homeostasis?
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16.1 Endocrine Glands
Endocrine system
• Mostly comprised of glands
• Secretes hormones that move through the
bloodstream to target cells
• Results in a slow but a prolonged response
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16.1 Endocrine Glands
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Hypothalamus
Pituitary Gland
Posterior pituitary
Anterior pituitary
Parathyroids
parathyroid glands
(posterior surface of thyroid)
Thymus
Thyroid
Pancreas
Adrenal Gland
Adrenal cortex
Gonads
Testes
Ovaries
testis
(male)
Figure 16.2 The endocrine system.
ovary (female)
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16.1 Endocrine Glands
What is a target cell?
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nontarget cell
receptors
target cells
hormone
capillary
Figure 16.3 Hormones target
specific cells.
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16.1 Endocrine Glands
Exocrine vs. endocrine glands
• Exocrine glands secrete their products into
ducts that carry these products to other
organs or outside the body.
• Endocrine glands secrete their products
directly into the bloodstream.
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16.1 Endocrine Glands
What are hormones?
• Hormones are chemical signals that promote
communication between cells, body parts,
and even individuals.
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16.1 Endocrine Glands
What are hormones?
• Hormones
– Prostaglandins are local hormones that affect
neighboring cells and thus are not carried in
the bloodstream.
– Pheromones are chemical signals that
influence the behavior of other individuals.
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16.1 Endocrine Glands
What are hormones?
– Peptide hormones bind to a receptor in the
plasma membrane causing the formation of
cAMP which activates a cascade of
enzymes.
– Steroid hormones are lipids that enter a cell
and affect gene activity and thus protein
synthesis.
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16.1 Endocrine Glands
Action of peptide hormones
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capillary
1. Hormone binds to a
receptor in the plasma
membrane.
peptide hormone
(first messenger)
activated
enzyme
receptor protein
2. Binding leads to
activation of an
enzyme that changes
ATP to cAMP.
cAMP
plasma
membrane
ATP
(second messenger)
3. cAM P activates an
enzyme cascade.
Figure 16.4 Action of a peptide
hormone.
4. Many molecules of
glycogen are broken
down to glucose,
which enters the
bloodstream.
glucose
(leaves cell
and goes
to blood)
glycogen
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16.1 Endocrine Glands
Action of steroid hormones
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steroid
hormone
1. Hormone diffuses
through plasma
membrane because
it is lipid soluble.
plasma
membrane
cytoplasm
nucleus
2. Hormone binds
to receptor inside
nucleus.
protein
DNA
receptor
protein
mRNA
Figure 16.5 Action of a steroid
hormone.
3. Hormone-receptor
complex activates
gene and synthesis
of a specific mRNA
molecule follows.
ribosome
mRNA
4. mRNA moves to
ribosomes, and protein
synthesis occurs.
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16.2 Hypothalamus and pituitary gland
Major glands of the endocrine system
1. Hypothalamus
2. Posterior pituitary gland
3. Anterior pituitary gland
4. Thyroid gland
5. Parathyroid glands
6. Adrenal glands
7. Pancreas
8. Testes
9. Ovaries
10.Thymus
11.Pineal gland
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16.2 Hypothalamus and Pituitary Gland
1. Hypothalamus
• Regulates internal environment through the
autonomic nervous system
–
–
–
–
Helps control heartbeat
Helps control body temperature
Helps control water balance
Controls glandular secretions
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16.2 Hypothalamus and Pituitary Gland
2. Posterior pituitary gland
• Stores antidiuretic hormone (ADH) and
oxytocin that are produced by the
hypothalamus
– ADH regulates water balance by reabsorbing
water into the bloodstream.
– Oxytocin causes uterine contractions during
childbirth and allows milk to be released
during nursing.
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16.2 Hypothalamus and Pituitary Gland
3. Anterior pituitary gland
• Controlled by hypothalamic-releasing and
hypothalamic-inhibiting hormones
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16.2 Hypothalamus and Pituitary Gland
3. Anterior pituitary gland
• Hormones produced by the anterior pituitary
1. Thyroid-stimulating hormone (TSH) stimulates
the thyroid to produce thyroid hormones.
2. Adrenocorticotropic hormone (ACTH)
stimulates the adrenal cortex to produce
cortisol.
3. Gonadotropic hormones stimulate gonads to
produce sex cells and hormones.
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16.2 Hypothalamus and Pituitary Gland
3. Anterior pituitary gland
4. Prolactin (PRL) stimulates mammary glands
to develop and produce milk only after
childbirth.
5. Melanocyte-stimulating hormone (MSH)
causes skin-color changes in many fishes,
amphibians, and reptiles having
melanophores, special skin cells that produce
color variations.
6. Growth hormone (GH) promotes skeletal and
muscular growth.
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16.2 Hypothalamus and Pituitary Gland
The hypothalamus and pituitary
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hypothalamus
1.Neurosecretory cells produce
hypothalamic-releasing and
hypothalamic-inhibiting hormones.
2. These hormones are secreted into
a portal system.
1. Neurosecretory cells produce
ADH and oxytocin.
optic
chiasm
3. Each type of hypothalamic
hormone either stimulates or
inhibits production and secretion
of an anterior pituitary hormone.
2. These hormones move down
axons to axon terminals.
portal system
3. When appropriate, ADH and
oxytocin are secreted from axon
terminals into the bloodstream.
Posterior pituitary
Figure 16.6
Hormones
produced by the
hypothalamus and
pituitary.
Kidney tubules:
antidiuretic
hormone (ADH)
Smooth muscle
in uterus:
oxytocin
Mammary glands:
oxytocin
Anterior pituitary
Mammary glands:
prolactin (PRL)
4. The anterior pituitary secretes
its hormones into the bloodstream,
which delivers them to specific
cells, tissues, and glands.
Thyroid:
thyroid-stimulating
hormone (TSH)
Adrenal cortex:
adrenocorticotropic
hormone (ACTH)
Bones, tissues:
growth hormone
(GH)
Ovaries, testes:
gonadotropic
hormones (FSH, LH)
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16.2 Hypothalamus and Pituitary Gland
What happens when the body
produces too much or too little GH?
• Pituitary dwarfism – too little GH is produced
during childhood; results in small stature
• Gigantism – too much GH is produced during
childhood; results in poor health
• Acromegaly – overproduction of GH as an
adult; results in larger than normal feet, hands,
and face
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16.2 Hypothalamus and Pituitary Gland
What happens when plentiful GH is
produced during childhood?
Figure 16.8 Growth hormone
influences height.
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16.2 Hypothalamus and Pituitary Gland
What happens when GH is produced
in high amounts during adulthood?
Figure 16.9 Overproduction of growth hormone in adults leads to acromegaly.
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16.3 Thyroid and Parathyroid Glands
4. Thyroid gland
• It is a large gland located below the larynx.
• Iodine is needed in the diet to allow the
thyroid gland to produce its hormones.
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16.3 Thyroid and Parathyroid Glands
4. Thyroid gland
• It produces
– thyroid hormone (TH) which regulates
metabolism.
– calcitonin which helps lower blood Ca2+ levels
by stimulating the deposition of calcium in the
bones.
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16.3 Thyroid and Parathyroid Glands
Thyroid abnormalities
• Simple goiter – thyroid enlarges due to lack
of iodine in the diet
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16.3 Thyroid and Parathyroid Glands
Thyroid abnormalities
• Hypothyroidism – low blood levels of thyroid
hormones
A. Congenital hypothyroidism: thyroid does not
develop properly and is characterized in a
short, stocky person who may have mental
retardation
B. Myxedema: hypothyroidism in adults
characterized by lethargy, weight gain, loss of
hair, cold intolerance, and thick, puffy skin
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16.3 Thyroid and Parathyroid Glands
Thyroid abnormalities
• Hyperthyroidism – excess thyroid hormones
in the blood
A. Exophthalimic goiter: characterized by
enlargement of the thyroid gland, protrusion
of the eyes, hyperactivity, and insomnia
B. Thyroid tumor: can also cause
hyperthyroidism
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16.3 Thyroid and Parathyroid Glands
Thyroid abnormalities
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
affected eye
a. Simple goiter
b. Congenital hypothyroidism
c. Exophthalmic goiter
a: © Bruce Coleman, Inc./Alamy; b: © Medical-on- Line/Alamy; c: © Dr. P. Marazzi/Photo Researchers,Inc.
Figure 16.10 Effects of insufficient dietary iodine, hypothyroidism, and hyperthyroidism.
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16.3 Thyroid and Parathyroid Glands
5. Parathyroid glands
• Small glands embedded in the surface of the
thyroid gland
• Produces parathyroid hormone (PTH)
– Causes blood Ca2+ level to increase by
promoting osteoclast activity
– Promotes reabsorption of Ca2+ by the kidneys
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16.3 Thyroid and Parathyroid Glands
Regulation of blood calcium
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calcitonin
Thyroid gland
secretes
calcitonin
into blood.
Bones
take up Ca2+
from blood.
Blood Ca2+
lowers.
Homeostasis (normal blood Ca2+)
Blood Ca2+
rises.
Parathyroid
glands
release PTH
into blood.
activated
vitamin D
parathyroid
hormone
(PTH)
Figure 16.11 Blood calcium
homeostasis.
Intestines
Kidneys
absorb Ca2+ reabsorb Ca2+
from digestive from kidney
tract.
tubules.
Bones
release Ca2+
into blood.
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16.4 Adrenal Glands
6. Adrenal glands
• Glands that sit on top of the kidneys
• Two parts of each gland
– Adrenal medulla: controlled by the nervous
system
– Adrenal cortex: portions are controlled by
ACTH from the anterior pituitary
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16.4 Adrenal Glands
The adrenal glands
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adrenal gland
kidney
adrenal cortex
connective
tissue capsule
zona
glomerulosa
adrenal medulla
adrenal cortex
(a)
zona
fasciculata
zona
reticularis
adrenal medulla
(b)
Figure 16.12 The adrenal glands.
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16.4 Adrenal Glands
Adrenal medulla
• Inner portion of the adrenal glands
• Hypothalamus initiates stimulation of hormone
secretion in the adrenal medulla
• Produces hormones that allow a short-term
response to stress (“fight or flight” response)
– Epinephrine (adrenaline)
– Norepinephrine
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16.4 Adrenal Glands
Adrenal cortex
• Outer portion of the adrenal glands
• Produces hormones that provide a long-term
response to stress
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16.4 Adrenal Glands
Adrenal cortex
• Two major types of hormones
– Glucocorticoids
• regulate carbohydrate, protein, and fat
metabolism.
• suppress the body’s inflammatory response.
• e.g., cortisol and cortisone
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16.4 Adrenal Glands
Adrenal cortex
– Mineralocorticoids
• regulate salt and water balance.
• e.g., aldosterone (targets the kidney)
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16.4 Adrenal Glands
Summary of the adrenal glands
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stress
hypothalamus
Neurosecretory
cells produce
hypothalamicreleasing
hormone.
path of nerve
impulses
Stress Response:
Long Term
Glucocorticoids
Protein and fat metabolism
instead of glucose
breakdown.
neuron
cell body
Anterior
pituitary
secretes
ACTH.
sympathetic fibers
spinal cord
(cross section)
ACTH
epinephrine
Reduction of inflammation;
immune cells are
suppressed.
Mineralocorticoids
Sodium ions and water
are reabsorbed by kidney.
norepinephrine
Blood volume and
pressure increase.
Stress Response:
Short Term
Heartbeat and blood
pressure increase.
Blood glucose level rises.
glucocorticoids
Muscles become
energized.
adrenal medulla
adrenal cortex
Figure 16.13 Response of the adrenal medulla and the adrenal cortex to stress.
mineralocorticoids
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16.4 Adrenal Glands
Adrenal glands can malfunction
•
Addison disease – hyposecretion of glucocorticoids by
the adrenal cortex, characterized by bronzing of the skin
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a.
Figure 16.15 Addison disease.
b.
a: © Custom Medical Stock Photo; b: © NMSB/Custom Medical Stock Photo
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16.4 Adrenal Glands
Adrenal glands can malfunction
•
Cushing syndrome – hypersecretion of glucocorticoids
by the adrenal cortex, characterized by weight gain in
the trunk of the body but not the arms and legs
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(both): Courtesy Shannon Halverson
Figure 16.16
Cushing syndrome.
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16.5 Pancreas
7. Pancreas
•
Fish-shaped organ behind the stomach
•
Composed of two tissues
– Exocrine: produces and secretes digestive
juices
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16.5 Pancreas
7. Pancreas
– Endocrine (islets of Langerhans): produces
and secretes hormones
1. Insulin – secreted when blood glucose is high;
stimulates the uptake of glucose by cells
(muscle and liver)
2. Glucagon – secreted when blood glucose is
low; stimulates the breakdown of glycogen in
the liver
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16.5 Pancreas
Regulation of blood glucose
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inslin
Liver stores
glucose from
blood as
glycogen.
80x
B cells in
pancreatic islet
Muscle cells
store glycogen
and build protein.
After eating,
pancreas
secretes insulin
into blood.
Adipose tissue
uses glucose
from blood to
form fat.
Glucose level
drops.
Homeostasis (normal blood glucose)
Glucose level
rises.
Between eating,
pancreas secretes
glucagon into
blood.
Liver breaks
down glycogen
to glucose.
Glucose enters
blood.
A cells in 80x
Pancreatic islet
Figure 16.18 Blood glucose
homeostasis.
Adipose tissue
breaks down fat.
glucagon
(both): © Victor P. Eroschenko
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16.5 Pancreas
What is diabetes?
• It is the inability to control blood glucose
levels.
• There are two types: type 1 and type 2.
• 25.8 million people in the US have diabetes.
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16.5 Pancreas
What is diabetes?
• General symptoms include
–
–
–
–
–
–
frequent urination.
unusual hunger and/or thirst.
unexplained change in weight.
blurred vision.
sores that heal slowly or not at all.
excessive fatigue.
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16.5 Pancreas
What is diabetes?
• Long-term effects are blindness, loss of
limbs, nerve deterioration, kidney, and
cardiovascular disease.
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16.5 Pancreas
Diabetes: Understanding the 2 types
• Type 1
– It is normally early-onset.
– Type 1 is an autoimmune disorder that
tends to run in families.
– Pancreatic cells are attacked and cannot
produce insulin.
– Need insulin injections are needed.
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16.5 Pancreas
Diabetes: Understanding the 2 types
• Type 2
– Type 2 is normally adult-onset and is the
most common type.
– It tends to occur in obese, sedentary people.
– Cells do not respond to insulin.
– Usually diet and exercise are important for
controlling this and may even prevent this.
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16.6 Other Endocrine Glands
8. Testes
• Gonads found in males
• Produce androgens (e.g., testosterone)
– Stimulates growth of the penis and testes
– Responsible for male sex characteristics
such as facial, underarm, and pubic hair
– Prompts the larynx and vocal cords to
enlarge, resulting in a lower voice
– Promotes muscular strength
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16.6 Other Endocrine Glands
9. Ovaries
• Gonads found in females
• Produce estrogen and progesterone
– Stimulate growth of the vagina and uterus
– Responsible for secondary sex
characteristics such as female body hair, fat
distribution, and breast development
– Responsible for egg maturation
– Regulate the uterine cycle
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16.6 Other Endocrine Glands
Hormones produced by the
testes and ovaries
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Stimulates the female
secondary sex
characteristics and
maturation of eggs
Stimulates the male
secondary sex
characteristics and
maturation of sperm
hypothalamus
anterior
pituitary
FSH,
LH
testosterone
Figure 16.20 The hormones
produced by the testes and the
ovaries.
testis
estrogen and
progesterone
FSH,
LH
ovary
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16.6 Other Endocrine Glands
10. Thymus
• The thymus lies beneath the sternum.
• This gland is largest and most active during
childhood.
• T lymphocytes mature here.
• It secretes hormones called thymosins that aid in
differentiation of lymphocytes.
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16.6 Other Endocrine Glands
11. Pineal gland
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•
Located in the brain
•
Secretes melatonin
that regulates the
sleep/wake cycle
(circadian rhythm)
•
May also regulate
sexual
development
a. Experimental
b. Winter
6 P.M. 6 A.M.
c. Summer
© The McGraw-Hill Companies, Inc./Evelyn Jo Johnson, photographer
Figure 16.21 Melatonin production changes by season.
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16.6 Other Endocrine Glands
Hormones from other tissues
• Erythropoietin is secreted by the kidneys to
increase red blood cell production.
• Leptin is produced by fat cells, and acts on
the hypothalamus to give a feeling of being
satiated.
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16.6 Other Endocrine Glands
Hormones from other tissues
• Prostaglandins
– Groups of potent chemicals that are not
carried in the bloodstream work locally on
neighboring cells.
– Some cause smooth muscle contraction.
– They have a major impact on reproductive
organs.
– They have many other roles in the body.
– Aspirin and ibuprofen block the synthesis of
these.
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16.7 Hormones and Homeostasis
Homeostasis
• The nervous and endocrine systems are
important in maintaining homeostasis.
– The hypothalamus bridges regulatory
functions of both systems.
– The nervous system is able to respond to
changes in the external environment.
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16.7 Hormones and Homeostasis
How the nervous and endocrine
systems work with other body systems
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The nervous and endocrine systems
work together to maintain homeostasis
The systems listed here in particular.
also work with these two systems.
Nervous and Endocrine Systems
The nervous and endocrine systems
coordinate the activities of the other systems.
The brain receives sensory input and controls
the activity of muscles and various glands.
The endocrine system secretes hormones
that influence the metabolism of cells, the
growth and development of body parts, and
homeostasis.
Cardiovascular System
Nerves and epinephrine regulate contraction
of the heart and constriction/dilation of blood
vessels. Hormones regulate blood glucose
and ion levels. Growth factors promote blood
cell formation. Blood vessels transport
hormones to target cells.
Respiratory System
The respiratory center in the brain regulates
the breathing rate. The lungs carry on gas
exchange for the benefit of all systems,
including the nervous and endocrine systems.
Urinary System
Nerves stimulate muscles that permit
urination. Hormones (ADH and aldosterone)
help kidneys regulate the water-salt balance
and the acid-base balance of the blood.
Digestive System
Nerves stimulate smooth muscle and permit
digestive tract movements. Hormones help
regulate digestive juices that break down food
to nutrients for neurons and glands.
Muscular System
Nerves stimulate muscles, whose contractions
allow us to move out of danger. Androgens
promote growth of skeletal muscles. Sensory
receptors in muscles and joints send
information to the brain. Muscles protect
neurons and glands.
Figure 16.22 The nervous system and
endocrine system interact to control homeostasis.
Reproductive System
Nerves stimulate contractions that move
gametes in ducts, and uterine contraction that
occurs during childbirth. Sex hormones
influence the development of the secondary
sex characteristics.
Integumentary System
Nerves activate sweat glands and arrector pili
muscles. Sensory receptors in skin send
information to the brain about the external
environment. Skin protects neurons and
glands.
Skeletal System
Growth hormone and sex hormones regulate
the size of the bones; parathyroid hormone
and calcitonin regulate their Ca 2+ content and
therefore bone strength. Bones protect nerves
and glands.
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