Chapter 18

Copyright © John Wiley & Sons, Inc. All rights reserved.
CHAPTER 18
The
Endocrine
System

INTRODUCTION
 The nervous and endocrine systems coordinate all of
the body systems
 The nervous system does so through the action of
neurons, and the neurotransmitters they secrete
 The endocrine
system uses
hormones produced
by endocrine structures
to produce their
effects

 Hormones are simply mediator molecules that have
effects on cells in the local environment, or in a
distant part of the body
 Some hormones, called autocrine hormones are local
hormones that are secreted, and bind to the same
cell.
TYPES OF HORMONES

TYPES OF HORMONES
 Hormones as mediator molecules …
 Paracrine hormones are local hormones that are
secreted into interstitial fluid and act on nearby cells

 Hormones as mediator molecules …
 Endocrine hormones are secreted into interstitial
fluid and then absorbed into the bloodstream to be
carried systemically
to any cell that
displays the
appropriate type
of receptor
TYPES OF HORMONES

SOLUBILITY OF HORMONES
 Hormones can be divided into two broad chemical
classes. This chemical classification is useful because
the two classes exert their effects differently
 Lipid soluble hormones bind to receptors in the
cytoplasm or nucleus of the cell
 Water soluble hormones bind to receptors on the
surface of the cell

 Lipid soluble hormones consist of steroid hormones,
thyroid hormones, and the gas nitric oxide
 Steroid hormones are derived from cholesterol
 Thyroid hormones (T3 and T4) are synthesized by
attaching iodine to the amino acid tyrosine
 The gas nitric oxide (NO) is both a hormone and a
neurotransmitter. Its synthesis is catalyzed by the
enzyme nitric oxide synthase

 Lipid soluble hormones require a carrier protein for
transport in the watery environment of the blood

1 Lipid-soluble
hormone
diffuses into cell
Blood capillary
Target cell
Transport
protein
Free hormone
1 Lipid-soluble
hormone
diffuses into cell
Blood capillary
Activated
receptor-hormone
complex alters
gene expression
Nucleus
Receptor
mRNA
DNA
Cytosol
Target cell
Transport
protein
Free hormone
2
1 Lipid-soluble
hormone
diffuses into cell
Blood capillary
Activated
receptor-hormone
complex alters
gene expression
Nucleus
Receptor
mRNA
Newly formed
mRNA directs
synthesis of
specific proteins
on ribosomes
DNA
Cytosol
Target cell
Transport
protein
Free hormone
Ribosome
2
3
1 Lipid-soluble
hormone
diffuses into cell
Blood capillary
Activated
receptor-hormone
complex alters
gene expression
Nucleus
Receptor
mRNA
Newly formed
mRNA directs
synthesis of
specific proteins
on ribosomes
DNA
Cytosol
Target cell
New proteins alter
cell's activity
Transport
protein
Free hormone
Ribosome
New
protein
2
3
4
Lipid-Soluble
Hormone
Action

 Water soluble hormones include peptide and protein
hormones (and others with an amine group), and a
group of local hormones derived from the arachidonic
acid on our cell membranes called eicosanoids
 Peptide hormones and protein hormones are amino
acid polymers
 The two major types of eicosanoids are prostaglandins
and leukotrienes – both play a role in mediating the
inflammatory response

 Water soluble hormones are easy to transport in the
watery blood. The plasma membrane of target cells,
however, is impermeable to them
 Water soluble hormones exert their effects by
binding to receptors exposed to the interstitial fluid
on the surface of target cells
• the hormone binding to its receptor acts as the
first messenger in a cascade of signal transduction

 The first messenger (the hormone) then causes
production of a second messenger inside the cell, where
specific hormone-stimulated responses take place
 One common second messenger is
cyclic AMP (cAMP). Neuro-
transmitters, neuropeptides, and
several sensory transduction
mechanisms (vision) also act via
second-messenger systems

Water-soluble
hormone
Receptor
G protein
Blood capillary
Binding of hormone (first messenger)
to its receptor activates G protein,
which activates adenylate cyclase
Adenylate cyclase
Target cell
1
Water-soluble
hormone
Receptor
G protein
cAMP
Second messenger
Activated adenylate
cyclase converts
ATP to cAMP
Blood capillary
Adenylate cyclase
Target cell
ATP
1
2
Water-soluble
hormone
Receptor
cAMP serves as a
second messenger
to activate protein
kinases
G protein
Protein kinases
cAMP
Second messenger
Activated adenylate
cyclase converts
ATP to cAMP
Blood capillary
Adenylate cyclase
Target cell
ATP
1
2
3 Activated
protein
kinases
Water-soluble
hormone
Receptor
cAMP serves as a
second messenger
to activate protein
kinases
G protein
Protein kinases
cAMP
Activated
protein
kinases
Second messenger
Activated adenylate
cyclase converts
ATP to cAMP
Activated protein
kinases
phosphorylate
cellular proteins
Blood capillary
Adenylate cyclase
Target cell
ATP
1
2
4
3
Protein— P
ADP
Protein
ATP
Water-soluble
hormone
Receptor
cAMP serves as a
second messenger
to activate protein
kinases
G protein
Protein kinases
cAMP
Activated
protein
kinases
Protein—
Second messenger
Activated adenylate
cyclase converts
ATP to cAMP
Activated protein
kinases
phosphorylate
cellular proteins
Millions of phosphorylated
proteins cause reactions that
produce physiological responses
Blood capillary
Adenylate cyclase
Target cell
P
ADP
Protein
ATP
ATP
1
2
4
3
5
Water-soluble
hormone
Receptor
cAMP serves as a
second messenger
to activate protein
kinases
G protein
Protein kinases
cAMP
Activated
protein
kinases
Protein—
Second messenger
Phosphodiesterase
inactivates cAMP
Activated adenylate
cyclase converts
ATP to cAMP
Activated protein
kinases
phosphorylate
cellular proteins
Millions of phosphorylated
proteins cause reactions that
produce physiological responses
Blood capillary
Adenylate cyclase
Target cell
P
ADP
Protein
ATP
ATP
1
2
6
4
3
5
Water-Soluble
Hormone
Action

EFFECTS OF HORMONES
 Prostaglandins (PGs) and leukotrienes are eicosanoid
hormones with local control. They are synthesized
from membrane lipids and have widespread effects
 PG’s mediate pain, platelet aggregation, fever, and
inflammation. They regulate smooth muscle
contraction, gastric acid secretion, and airway size
• aspirin is a drug that works by inhibiting an enzyme
necessary for synthesis of certain PGs: the ones that
facilitate pain and the inflammatory response

EFFECTS OF HORMONES
 Endocrine hormones control a variety of
physiological processes. Among other things, they:
 Balance the composition and volume of body fluids
 Regulate metabolism and energy production
 Direct the rate and timing of growth and
development
 Exert emergency control during physical and
mental stress (trauma, starvation, hemorrhage)
 Oversee reproductive mechanisms

EFFECTS OF HORMONES
(Interactions Animation)
o Introduction to endocrine hormones:
Regulation, secretion and concentration
You must be connected to the internet to run this animation

ENDOCRINE SYSTEM GLANDS
 Glands that secrete endocrine hormones into the
bloodstream are called endocrine glands
 They are one of two major types of glands in the
body, the other being exocrine glands (which
secrete their products into ducts )
 In this chapter we will focus our
study on the endocrine glands
and the widespread effects of
endocrine hormones

CONTROL OF HORMONES
 When stimulated, an endocrine gland will release its
hormone in frequent bursts, increasing the
concentration of the hormone in the blood
 Hormone secretion is regulated by signals from the
nervous system, chemical changes in the blood, and
other hormones
• Most hormonal regulatory systems work via
negative feedback, but a few operate via positive
feedback

CONTROL OF HORMONES
 This example shows how PTH and calcitonin have
negative feedback influence on one another

CONTROL OF HORMONES
 In a positive feedback system the
hormone output reinforces and
encourages the stimulus. For
example, during childbirth, the
hormone oxytocin stimulates
contractions of the uterus, and
uterine contractions in turn
stimulate more oxytocin release,
a positive feedback effect

CONTROL OF HORMONES
o Hormones Summary

THE ENDOCRINE SYSTEM
 The endocrine system consists of the pituitary,
thyroid, parathyroid, adrenal and pineal glands
 Some of the most important glands of the
endocrine system are not exclusively endocrine
glands: The hypothalamus, thymus, pancreas,
ovaries, and testes are paramount;
the kidneys, stomach, liver,
small intestine, skin, heart,
and placenta also contribute

THE ENDOCRINE SYSTEM

THE HYPOTHALAMUS
 The hypothalamus is the major link between the
nervous and endocrine systems
 It receives input from several regions in the brain
including the
thalamus, the
RAS, and
the limbic
system

THE PITUITARY GLAND
 The hypothalamus mainly controls the pituitary
gland, which is also called the hypophysis
 The pituitary hangs down from the hypothalamus
on a stalk called the infundibulum
 The gland is divided into an anterior
adenohypophysis and a posterior neurohypophysis -
the anterior pituitary accounts
for about 75% of the total
weight of the gland

THE ADENOHYPOPHYSIS
 The anterior pituitary (adenohypophysis) is
anatomically and functionally connected to the
hypothalamus by blood vessels that form a portal
system called the hypophyseal portal system
 In a portal system, blood flows from one capillary
network into a portal vein, and then into a second
capillary network before returning to the heart
• The name of the portal system indicates the
location of the second capillary network

 Specialized neurosecretory cells in the
hypothalamus secrete releasing hormones
into the hypophyseal portal system
that supplies blood to the
anterior pituitary
gland
THE ADENOHYPOPHYSIS

THE ADENOHYPOPHYSIS
 The second capillary system of the hypophyseal portal
system delivers the hypothalamic releasing hormones
to the anterior pituitary
 5 types of anterior pituitary cells secrete seven
hormones

ANTERIOR PITUITARY HORMONES
Hypothalamus
Hormone
Hormone released
from
Adenohypophysis
Major Function/ Target
Growth hormone
releasing hormone
(GHRH)
Human Growth
Hormone (hGH)
Also called somatostatin,
stimulates secretion of
insulin-like growth factors
(IGFs) that promote growth
Thyrotropin
releasing hormone
(TRH)
Thyroid Stimulating
Hormone (TSH)
Stimulates synthesis and
secretion of thyroid
hormones by the thyroid
gland
Prolactin releasing
hormone
(PRH)
Prolactin (PRL)
Stimulates breast growth,
and development of the
mammary glands

Hypothalamus
Hormone
Hormone released
from
Adenohypophysis
Gonadotropic
releasing hormone
(GnRH)
Follicle Stimulating
hormone (FSH)
Ovaries initiate development
of oocytes; testes initiate
development of spermatozoa
Gonadotropic
releasing hormone
(GnRH)
Luteinizing hormone
(LH)
Ovaries stimulate ovulation;
testes stimulate testosterone
production

Hypothalamus
Hormone
Hormone released
from
Adenohypophysis
Corticotropin
releasing hormone
(CRH)
Adrenocorticotropic
Hormone (ACTH)
Stimulates release of
mineralocorticoid,
glucocorticoid, and androgen
hormones from the adrenal
cortex
Corticotropin
releasing hormone
(CRH)
Melanocyte
Stimulating hormone
(MSH)
Stimulate the production and
release of melanin by
melanocytes in skin and hair.
MSH signals to the brain have
effects on appetite and sexual
arousal

 hGH Stimulating
Glycogenolysis
 hGH Growth and
Development

 Cortisol
 ACTH and Cortisol

 TRH and TSH

 Tropic hormones are hormones produced and
secreted by the anterior pituitary that target other
endocrine glands
 All hormones in the previous lists target other
endocrine glands (are trophic hormones) except
hGH, Prolactin, and MSH, which directly target
the end organs

THE NEUROHYPOPHYSIS
 The posterior pituitary (neurohypophysis) is
embryologically derived from and anatomically
connected to the hypothalamus – it releases, but does
not synthesize any hormones
 When stimulated, neurosecretory
cells in the hypothalamus
release oxytocin and
ADH from their axon
terminals located in
the posterior pituitary

THE NEUROHYPOPHYSIS
 Oxytocin targets smooth muscle in the uterus and
breasts. In the uterus, oxytocin stimulates uterine
contractions, and in response to the sucking from an
infant, oxytocin stimulates “milk letdown” in the
breasts
 ADH targets the collecting ducts in the kidney and
sweat glands in the skin to minimize water loss. It
also directly causes arterioles to constrict thereby
increasing blood pressure

THE NEUROHYPOPHYSIS
 This graphic
demonstrates the
regulation of ADH
secretion

POSTERIOR PITUITARY
HORMONES
 Antidiuretic Hormone Animation

PITUITARY GLAND DISORDERS
 Acromegaly occurs as a result of excess HGH during
adulthood. This disease is marked by enlargement and
elongation of the bones of the face, jaw, cheeks, and
hands (the long bones of
the extremities are
unaffected because the
growth plates have
already closed)

PITUITARY GLAND DISORDERS
 Diabetes Insipidus (DI) is very different from the
disease called sugar diabetes (diabetes mellitus)
 DI is caused by the insufficient release of ADH from
the neurohypophysis. Without ADH acting on the
collecting ducts in the kidneys, the normal urine
output of 1–1.5 liters per day increases to over 2.5
liters per day and dehydration and hypernatremia
results

THE THYROID GLAND
 The butterfly-shaped thyroid gland is located inferior
to the larynx and anterior to the trachea. It has two
laterally placed lobes separated by a bridge-like
isthmus

THE THYROID GLAND
 Most of the thyroid gland is composed of spherical
groups of follicular cells called thyroid follicles
 The follicles store
a 100-day supply
of its two hormones
in an inactive
gel-like substance
called TGB (for
thyroglobulin)

 Thyroid-stimulating hormone (TSH) is released by the
anterior pituitary gland in response to TRH secreted
into the portal system
 The hypothalamus
responds to higher
circulating levels of
T3 and T4 via negative
feedback to inhibit
TRH secretion
THYROID HORMONES

Low blood levels of T3
and T3 or low metabolic
rate stimulate release of
Hypothalamus
TRH
Actions of Thyroid Hormones:
Increase basal metabolic rate
Stimulate synthesis of Na+/K+ ATPase
Increase body temperature (calorigenic effect)
Stimulate protein synthesis
Increase the use of glucose and fatty acids for ATP production
Stimulate lipolysis
Enhance some actions of catecholamines
Regulate development and growth of nervous tissue and bones
1
Anterior
pituitary
TRH, carried
by hypophyseal
portal veins to
anterior pituitary,
stimulates
release of TSH
by thyrotrophs
Hypothalamus
TSH
TRH
Stimulate lipolysis
1
2
Anterior
pituitary
TRH, carried
by hypophyseal
portal veins to
anterior pituitary,
stimulates
release of TSH
by thyrotrophs
TSH released into
blood stimulates
thyroid follicular cells
Thyroid
follicle
Hypothalamus
Anterior
pituitary
TSH
TRH
Stimulate lipolysis
1
2
3
T3 and T4
released into
blood by
follicular cells
TRH, carried
by hypophyseal
portal veins to
anterior pituitary,
stimulates
release of TSH
by thyrotrophs
TSH released into
blood stimulates
Thyroid
follicle
Hypothalamus
Anterior
pituitary
TSH
TRH
Stimulate lipolysis
1
2
3
4 T3 and T4
released into
blood by
follicular cells
Elevated
T3inhibits
release of
TRH and
TSH
(negative
feedback)
TRH, carried
by hypophyseal
portal veins to
anterior pituitary,
stimulates
release of TSH
by thyrotrophs
TSH released into
blood stimulates
Thyroid
follicle
Hypothalamus
Anterior
pituitary
TSH
TRH
Stimulate lipolysis
1
2
3
5
4
Thyroid Hormone
Regulation

 A goiter is an enlargement of the thyroid gland and
may be associated with hyperthyroidism,
hypothyroidism, or euthyroidism
 In many third-word countries
dietary iodine intake is inadequate;
the resultant low level of thyroid
hormone in the blood stimulates
secretion of TSH, which causes
thyroid gland enlargement
THYROID HORMONES

THE PARATHYROID GLANDS
 The parathyroid glands are small, round masses of
tissue attached to the posterior surface of the lateral
lobes of the thyroid gland
 There are usually two
parathyroid glands
attached to each
lobe of the thyroid,
one superior and one inferior

PARATHYROID HORMONES
 Calcitonin (Thyrocalcitonin) is made by the
parafollicular (C-cells) of the thyroid gland and
when secreted lowers the blood calcium level
 An increase in blood calcium will stimulate the C-cells
of the thyroid to secrete calcitonin
 Increased calcitonin will cause a negative feedback
inhibition of parathyroid hormone (PTH) which
causes a decrease in blood calcium and an increase
in blood phosphate levels

 Calcitonin

 Parathyroid hormone (PTH) is made by the more
numerous chief (principal) cells of the gland
 PTH increases absorption
of Ca2+
from the GI tract
and stimulates osteoclastic
activity so that Ca2+
is
released from bone into
the blood

 Parathyroid Hormone

1 High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT.
release more CT.
CALCITONIN inhibits
osteoclasts, thus decreasing
blood Ca2+ level.
2
release more CT.
Low level of Ca2+ in blood
stimulates parathyroid
gland chief cells to release
more PTH.
CALCITONIN inhibits
blood Ca2+ level.
3
2
release more CT.
more PTH.
CALCITONIN inhibits
blood Ca2+ level.
PARATHYROID HORMONE (PTH)
promotes release of Ca2+ from
bone extracellular matrix into
blood and slows loss of Ca2+
in urine, thus increasing blood
Ca2+ level.
3
4 2
1
PTH also stimulates
the kidneys to release
CALCITRIOL.
High level of Ca2+ in blood
release more CT.
more PTH.
CALCITONIN inhibits
blood Ca2+ level.
Ca2+ level.
3
4 2
5
1
CALCITRIOL stimulates
increased absorption of
Ca2+ from foods, which
increases blood Ca2+ level.
PTH also stimulates
the kidneys to release
CALCITRIOL.
High level of Ca2+ in blood
release more CT.
more PTH.
CALCITONIN inhibits
blood Ca2+ level.
Ca2+ level.
3
4 2
5
6
Calcium Regulation

THE ADRENAL GLANDS
 There are two adrenal glands, one superior to each
kidney (also called the suprarenal glands). During
embryonic development, the adrenal glands
differentiate into two structurally and functionally
distinct regions
• the adrenal cortex
• the adrenal medulla Catecholamines like
norepinephrine
Steroid hormones
like cortisol

THE ADRENAL GLANDS

THE ADRENAL CORTEX
 The adrenal cortex is peripherally located and makes
up 80-90% of the total weight of the gland
 The cortex is subdivided into three zones, each of
which secretes a different group of steroid
hormones, all formed
from the cholesterol
molecule

 Just deep to the CT capsule, the cells of the zona
glomerulosa synthesize mineralocorticoid hormones
 The middle zone, or zona fasciculata, secrete mainly
glucocorticoid hormones,
primarily cortisol
 The inner zona reticularis
is the site of synthesis
of weak androgens
(masculinizing hormones)
ADRENOCORTICAL HORMONES

 Mineralocorticoids regulate the concentrations of Na+
and K+
in the blood (affects blood volume/pressure)
 Aldosterone is the major hormone in this group
 Glucocorticoids influence glucose metabolism and the
ability to resists the effects of stress
 Cortisol is the major hormone in this group
 Weak androgens (masculinizing sex hormones) have
little effect in men, but play an important role in
promoting libido in women
ADRENOCORTICAL HORMONES

 The most important effects of aldosterone is seen in
the renin-angiotensin-aldosterone system (RAAS)
 The RAAS is stimulated by a decrease in blood
volume and/or blood pressure – as in cases of
dehydration or hemorrhage. Low BP stimulates
juxtaglomerular cells
in the kidney to
secrete the
enzyme renin
RAAS

RAAS
 Renin converts the plasma protein angiotensinogen
(produced in the liver) into angiotensin I. As
angiotensin I circulates to the lungs, an enzyme called
angiotensin converting enzyme (ACE) converts
angiotensin I to angiotensin II
 Angiotensin II stimulates the adrenal cortex to
secrete aldosterone (salt and H20 resorption
indirectly increases BP), and it is a
potent vasoconstrictor (which
directly increases BP)

RAAS

GLUCOCORTICOIDS
 Glucocorticoids (mainly cortisol) regulate metabolism
by promoting the breakdown of proteins and fats to
form glucose (gluconeogenesis). Increased blood sugar
levels assist the body to cope with stress
 Their inflammatory effects result from inhibiting
white blood cells. Unfortunately they also retard
tissue repair and slow wound healing
• glucocorticoids are very useful in the treatment of
chronic inflammatory disorders such as Lupus,
though long term side-effects are severe

GLUCOCORTICOIDS
 High levels of circulating cortisol, as seen with
corticosteroid drugs (prednisone), or tumors (adrenal
cortex, pituitary gland) is called Cushing’s syndrome
 Manifestations include hyper-
glycemia, poor wound healing,
osteoporosis, dermatitis, fat
redistribution (spindly arms and
legs, moon face, buffalo hump at
the neck), and truncal obesity

GLUCOCORTICOIDS
 In adults, hyposecretion of glucocorticoids and
aldosterone, usually as a result of an autoimmune
disorder, is called Addison’s disease
 The physiologic effects include
hypoglycemia, Na+
loss, low BP,
dehydration, and muscle weakness
• only after his death did the world
learn that President Kennedy
suffered from Addison’s disease

THE ADRENAL MEDULLA
 The inner region of the adrenal gland, the adrenal
medulla, is a modified sympathetic ganglion that
develops from the same embryonic tissue as all other
sympathetic ganglia of the ANS and is innervated by
sympathetic preganglionic neurons
 The catecholamines epinephrine (80%), and
norepinephrine (20%), are secreted at the adrenal
medulla and serve to prolong the sympathetic
response

ADRENAL MEDULLA HORMONES
 Epinephrine/Norepinephrine

THE PANCREAS
 The pancreas is both an endocrine and an exocrine
gland. It is located posterior and inferior to the
stomach. We will discuss its endocrine functions here
and its exocrine functions
in detail in chapter 24

 Most of the exocrine cells of the pancreas are
arranged in clusters called acini and produce digestive
enzymes which flow through ducts into the GI tract
 Distributed among the acini are clusters of
endocrine tissue
called pancreatic
islets (islets of
Langerhans)
THE PANCREAS

 Each pancreatic islet contains four types of hormone-
secreting cells: alpha (A), beta (B), delta (D), and F cells
 Alpha cells secrete glucagon which increases blood
glucose levels by acting
on hepatocytes to
convert glycogen
to glucose
 Beta cells secrete
insulin
PANCREATIC HORMONES

PANCREATIC HORMONES
 Insulin is an anabolic hormone - it decreases blood
glucose levels by acting on
hepatocytes to convert glucose
to glycogen and then facilitating
diffusion of glucose into the cells
 Insulin and glucagon are counter-
regulatory hormones in that
their actions act to balance one
another in terms of blood glucose

 Somatostatin acts in a paracrine manner to inhibit
both insulin and glucagon release from neighboring
beta and alpha cells. It
also inhibits the secretion
of hGH
 The interactions of the
four pancreatic hormones
are complex and not
completely understood
PANCREATIC HORMONES

Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
1
GLUCAGON
Glucagon acts on
hepatocytes
(liver cells) to:
• convert glycogen
into glucose
(glycogenolysis)
• form glucose from
lactic acid and
certain amino acids
(gluconeogenesis)
Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
GLUCAGON
1
2 Glucagon acts on
hepatocytes
(liver cells) to:
into glucose
(glycogenolysis)
lactic acid and
certain amino acids
(gluconeogenesis)
Glucose released
by hepatocytes
raises blood glucose
level to normal
Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
GLUCAGON
1
2
3
Glucagon acts on
hepatocytes
(liver cells) to:
into glucose
(glycogenolysis)
lactic acid and
certain amino acids
(gluconeogenesis)
Glucose released
by hepatocytes
level to normal
If blood glucose
continues to rise,
hyperglycemia inhibits
release of glucagon
Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
GLUCAGON
1
2
3
4
Glucagon acts on
hepatocytes
(liver cells) to:
into glucose
(glycogenolysis)
lactic acid and
certain amino acids
(gluconeogenesis)
Glucose released
by hepatocytes
level to normal
If blood glucose
continues to rise,
release of glucagon
Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
High blood glucose
(hyperglycemia)
stimulates beta cells
to secrete
GLUCAGON
1 5
2
3
4
INSULIN
Insulin acts on various
body cells to:
• accelerate facilitated
diffusion of glucose
into cells
• speed conversion of
glucose into glycogen
(glycogenesis)
• increase uptake of
amino acids and increase
protein synthesis
• speed synthesis of fatty
acids (lipogenesis)
• slow glycogenolysis
• slow gluconeogenesis
Glucagon acts on
hepatocytes
(liver cells) to:
into glucose
(glycogenolysis)
lactic acid and
certain amino acids
(gluconeogenesis)
Glucose released
by hepatocytes
level to normal
If blood glucose
continues to rise,
release of glucagon
Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
High blood glucose
(hyperglycemia)
to secrete
INSULINGLUCAGON
1 5
2
3
4
6 Insulin acts on various
body cells to:
into cells
(glycogenesis)
protein synthesis
acids (lipogenesis)
Blood glucose level falls
Glucagon acts on
hepatocytes
(liver cells) to:
into glucose
(glycogenolysis)
lactic acid and
certain amino acids
(gluconeogenesis)
Glucose released
by hepatocytes
level to normal
If blood glucose
continues to rise,
release of glucagon
Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
High blood glucose
(hyperglycemia)
to secrete
INSULINGLUCAGON
1 5
2
3
4
6
7
Insulin acts on various
body cells to:
into cells
(glycogenesis)
protein synthesis
acids (lipogenesis)
If blood glucose continues
to fall, hypoglycemia
inhibits release of
insulin
Blood glucose level falls
Glucagon acts on
hepatocytes
(liver cells) to:
into glucose
(glycogenolysis)
lactic acid and
certain amino acids
(gluconeogenesis)
Glucose released
by hepatocytes
level to normal
If blood glucose
continues to rise,
release of glucagon
Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
High blood glucose
(hyperglycemia)
to secrete
INSULINGLUCAGON
1 5
2
3
4
6
7
8
Glucose/Insulin
Regulation

PANCREATIC HORMONES
 Insulin

GONADAL HORMONES
 The ovaries are paired oval bodies located in the
female pelvic cavity. They produce several steroid
hormones including two estrogens (estradiol and
estrone), progesterone, relaxin, and inhibin
 Estrogens, along with FSH and
LH from the anterior pituitary,
regulate the menstrual cycle,
maintain pregnancy, and prepare
the mammary glands for lactation

GONADAL HORMONES
 Ovarian hormones also promote enlargement of the
breasts and widening of the hips at puberty, and help
maintain these female secondary sex characteristics
 Progesterone prepares the uterus lining for
implantation of a fertilized ovum

OVARIAN HORMONES
 Hormonal Regulation of Female
Reproductive System

GONADAL HORMONES
 The male gonads, the testes, are oval glands that lie in
the scrotum. The main hormone produced and
secreted by the testes is testosterone, an androgen
(male sex hormone)
 Testosterone is needed for
production of sperm and
maintenance of male
secondary sex characteristics

TESTICULAR HORMONES
 Hormonal Regulation of Male
Reproductive Function

THE PINEAL GLAND
 The pineal gland is a small
endocrine gland
attached to the roof of the
third ventricle – it is part of
the epithalamus
 The pineal gland secretes the hormone melatonin,
which contributes to maintaining the biological
clock (seasonal and daily cycles)
• more melatonin is secreted in darkness; the pineal
gland is very developed in nocturnal animals

THE THYMUS GLAND
 The thymus gland secretes thymosin, which promotes
the proliferation and maturation of T cells
 T cells are a type of white blood cell (lymphocyte)
that destroys microorganisms
and foreign substances
through direct
cellular contact

GENERAL ADAPTATION SYNDROME
 The general adaptation syndrome (GAS) or stress
response refers to the consequences of failure to
respond appropriately to emotional or physical
threats, whether actual or imagined
 Interestingly, stressful situations can be events
normally considered to be “good”, as well as bad
• for instance, a marriage can be as stressful as a
divorce, a birth as stressful as a death, etc.

 It is impossible to remove all of the stress from our
everyday lives, and some levels of stress actually help
us perform well and be productive. Regardless, the
body’s homeostatic mechanisms attempt to counteract
stress, and maintain a constant internal environment
whenever possible
 If stress is extreme, unusual, or long lasting, the
normal mechanisms may not be enough, and they
may elicit a series of changes called the stress
response or GAS

 There are three stages to a prolonged stress response:
alarm reaction, resistance reaction, and exhaustion
 The alarm reaction is the short-lived fight-or-flight
response initiated by the hypothalamus and
mediated by the sympathetic division of the ANS
• it brings huge amounts of glucose and oxygen to
the brain, the lungs, and skeletal muscles
• the RAAS is also activated to maintain blood
volume and BP

THE ALARM REACTION
 The Alarm Reaction

 The three stages to the GAS continued…
 The resistance reaction is initiated in large part by
hypothalamic releasing hormones and is a longer-
lasting response. The release of high levels of
cortisol and thyroid hormones assures that the
tissues of the body can sustain necessary metabolic
needs

The alarm reaction leads to a resistance response.

 The three stages to the GAS continued…
 Exhaustion occurs when the body’s reserves become
so depleted that they cannot sustain the resistance
stage
• Prolonged exposure to high levels of cortisol and
other hormones causes wasting of muscle,
suppression of the immune system, ulceration of
the GI tract, and failure of pancreatic beta cells…
disease often ensues

THE GAS
 General Adaptation Syndrome

Chapter 18

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Chapter 18