Chapter 16 – Endocrine System

Dr. Kim Wilson
York Technical College
Spring 2011
Note: Parts of this presentation were adapted from the lecture
presentations of Mr. John McGill and Mrs. Elizabeth Wyatt of York
Technical College and from Mosby Inc., and affiliate of Elsevier Inc.
 Major
endocrine glands
(Fig. 16-2. pg. 535)
Pituitary, thyroid,
parathyroid, adrenal,
pineal and thymus glands
 Organs
with major
functions outside the
endocrine system
containing endocrine
tissue/cells: pancreas,
gonads, hypothalamus
(neuroendocrine organ)
 Widely
throughout body (Fig.
 Secrete hormones
 “Ductless” glands
Hormones secreted
directly into
 Specific
target cells
receive the hormone
 Function
Sex or anabolic
 Chemical
Made from cholesterol (lipids): Ex.
cortisol, estradiol
Made from amino acids
- amines [epinephrine and
- peptides [oxytocin, ADH]
- proteins [growth hormone, insulin]
- glycoproteins [FSH, TSH]
 Fig.
16-3, pg. 536
Steroid hormones
Steroid hormones (fig. 168, pg. 539)
Detach from a carrier
protein and enter the
plasma membrane
Pass into the nucleus and
bind to a mobile receptor
Complex binds to specific
site on DNA molecule to
trigger transcription
Moves to ribosome →
protein synthesis
Specific effects in target
Nonsteroid hormones
Second messenger model (mechanism)
Hormones can’t penetrate the plasma membrane
and diffuse into cells.
 Target cells have specific receptor for hormone
on cell surface.
 Hormone binds to receptor and causes a second
messenger to be released within the cell.
Exs. of second messengers
cyclic adenosine monophosphate (cAMP)
Calcium calmodulin complex
Calcium (Ca++) channels
 binding of hormone causes Ca channels in cell
membrane to open --> influx of many Ca ions. Ca
ions bind to protein = calmodulin (Fig. 16-10)
Fig 16-9, pg. 540 (G-protein example)
Activates protein kinases
“Tissue hormones”
Effects of PGs
Secretion is produced in a
tissue and diffuses only a
short distance to other
cells within the same
Unique group of lipid
molecules that do not
meet the standard
definition of a hormone
16 different PGs in 9
structural classes
Prostaglandins A – I
Ex. PGEs – role in vascular,
metabolic, and
gastrointestinal functions
 Ex. PGFs – role in reproductive
Image source:
Unique group of lipid hormones (20-carbon fatty
acid with 5-carbon ring) that serve important
and widespread integrative functions in the body
but do not meet the usual definition of a
hormone (Figure 16-13; Table 16-4)
 Called tissue hormones because the secretion is
produced in a tissue and diffuses only a short
distance to other cells within the same tissue;
tend to integrate activities of neighboring cells
 Used
Hypertension, coronary thrombosis, asthma, and
 Some
play a role in autism
 Used
controversy over clinical use
 May
in the treatment of various diseases
to induce labor in women
 Same
as the primary functions of the
nervous system
 Both function to achieve and maintain
stability of the internal environment
 How?
Sending Messages (Cells in the endocrine and nervous
systems send messages to cells in other systems)
Importance: Provides information about changes
occurring in the body  Maintains homeostasis
Communication is part of negative feedback
Regulation of body functions (endocrine and nervous
systems regulate many body functions)
Control is part of negative feedback (Communication
 Control)
Unification of body functions (endocrine and nervous
systems unify body functions to make the body work as
a unit)
These systems unify because they communicate and
Hormone secretion
triggered by an external
stimulus; as hormone
levels rise, the hormones
feed back to the
metabolic pathway that
produces them & inhibit
their further release
Regulates physiological
Regulates the secretion
of almost every hormone.
Maintains physiological
and homeostatic control.
Ex. Negative feedback in
the thyroxine release
Source: Purves et al., Life: The Science of Biology, 4th Edition,
by Sinauer Associates.
Same primary functions (see slides 8 and 9)
Both use chemical messengers but the messengers are
 Mechanisms of carrying out their functions are
different in terms of communication and control
(chemical messengers)
Nervous system
Uses nerve impulses to
Nerve impulses
Produce rapid, shortlasting responses
Control effectors
Endocrine system
Uses hormones to
Produce slow, longlasting responses
Control target organs
Hormone’s specific
destination - Lock & Key
Most organs
Endocrine System
Endocrine gland
Nervous System
Afferent (sensory) neuron(s)
CNS (Reflex Center)
Efferent (motor) neuron(s)
Target organ(s)
 Small (1.2 – 1.5 cm)
but considered the
“master” gland b/c
it controls functions
of other endocrine
 Protected location =
ventral surface of
the brain (Fig 16-14,
pg. 546)
Specifically attached to the
hypothalamus by the
Lies in the Pituitary Fossa of
the Sella Turcica (Sphenoid
bone), covered by Dura Mater
Anterior pituitary (Adenohypophysis)
Develops from upward projection of
pharynx and is made of endocrine tissue
Posterior pituitary (Neurohypophysis)
Develops from downward projection of
brain and is made of neurosecretory
Secretes 7 hormones (Fig. 16-16, pg. 547)
 Cellular
Secrete growth hormone (GH)
Secrete adrenocorticotrophic hormone (ACTH)
Secrete thyroid-stimulating hormone (TSH)
Secrete prolactin (PRL)
Secrete luteinizing hormone (LH) and folliclestimulating hormone (FSH)
Somatotropin (STH)
 Stimulates growth by stimulating the liver and
other tissues to produce insulin-like growth
factor (IGF-1)
 Functions
Stimulates protein anabolism (growth, tissue repair)
Accelerates amino acid transport through IGF-1
Stimulates fat (lipid) metabolism
Indirectly inhibits glucose metabolism
Indirectly increases blood glucose levels
Shifts a cell’s use of nutrients from glucose to catabolism
to towards lipid catabolism
Exerts a hyperglycemic effect in contrast to insulin from
the pancreas, which has a hypoglycemic effect
 Lactogenic
 Produced by acidophils in the pars anterior
 Function: promoting milk secretion during
 Hypersecretion in women = non-nursing
women may lactate and menstral cycle could
be disrupted
 Hypersecretion in men = impotence
 Hyposecretion is not a problem in women
unless a desire to nurse develops
 Have
a stimulating effect on other endocrine
 Stimulate the development of their target
glands and stimulate synthesis of secretion of
the target hormone
 Four main types
Thyroid-stimulating hormone (TSH)
Adrenocorticotrophic hormone (ACTH)
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
 Endocrine
Trophic hormones
Endocrine gland
Endocrine gland
Hormone (trophic)
Target organ(s)
Target organ (endocrine gland)
Response (secretes hormone)
Target organ
 Thyrotropin
 Target
organ thyroid
 Functions
Maintains growth
and development
of thyroid
Stimulates normal
hormone secretion
by thyroid gland
Target Organ:
Adrenal Cortex
 Functions:
 Promotes growth
and development
of adrenal cortex
 Stimulates
by Adrenal Cortex
In the female, stimulates primary graafian follicles
to grow toward maturity and stimulates the follicle
cells to secrete estrogens.
 In the male, stimulates the development of the
seminiferous tubules of the testes and maintains
Stimulates the formation and activity of
the corpus luteum of the ovary
Corpus luteum secretes progesterone and
estrogens when stimulated
Supports follicle-stimulating hormone in
stimulating maturation of follicles
Stimulates interstitial cells in the testes to
develop and secrete testosterone;
Both hormones are called gonadotropins
because they stimulate the growth and
maintenance of the gonads
 Target
Organ: Skin
 Function: Helps Maintain Normal Skin Color
Note: Genes Primarily Control Skin Color; However,
Other Factors (Such as Hormones) Can Modify Skin
Color; If Secretion of MSH Increases (Usually
Abnormal Conditions), Darkens Skin
Controlled in 3 Ways
Hypothalamus secretes releasing
hormones into the blood, which are then
carried to the hypophyseal portal
system (Figure 16-17; Table 16-5)
Hypophyseal portal system carries
blood from the hypothalamus directly to
the adenohypophysis, where the target
cells of the releasing hormones are
located (Figure 16-18)
Releasing hormones influence the
secretion of hormones by acidophils and
Control Release of All APG Hormones
Except MSH
NOTE: GH and PRL Are Only Needed at
Specific Times; Therefore, Controlled by
2 RH's
Through negative feedback, the
hypothalamus adjusts the
secretions of the
adenohypophysis, adjusting the
secretions of the target glands,
which adjust the activity of their
target tissues (Figure 16-19)
 Minute-by-minute variations in
hormone secretion can exhibit
occasional large peaks caused by
pulse in releasing hormone
secretion by the hypothalamus
(Figure 16-20)
 In stress, the hypothalamus
translates nerve impulses into
hormone secretions by endocrine
glands, basically creating a mindbody link
 3.
Stress stimulates the secretion of APG hormones
(mind/body link)
cortex (mind)
secretion of
release of APG
Target organs (body) → response
 Note:
In the mind/body link, stress not only
turns on the autonomic and somatic nervous
systems, it also activates the APG
 Neurohypophysis
 Serves
as storage and
release site for
antidiuretic hormone
and oxytocin, which
are synthesized in the
hypothalamus (Figure
16-21; Table 16-6)
Release into the blood
is controlled by
nervous stimulation
Target organ: Kidney (tubules)
 Function: Maintains Water Balance (Promotes
Water Retention  Prevents Dehydration
(“Against Diuresis”)
Prevents the formation of a large volume of urine,
thereby helping the body conserve water
Causes a portion of each tubule in the kidney to
reabsorb water from the urine being formed
Dehydration triggers its release
Also called arginine vasopressin because it
stimulates a rise in blood pressure, partly by
increasing contraction in small arteries
Target Organs: Uterus
(Smooth Muscle);
Mammary Glands
Stimulates Uterine
Contractions (Labor;
Post Delivery)
Stimulates Milk
Ejection (into
Mammary Ducts) From
Lactating Breasts
Note: Prolactin’s Function
is Lactation, Oxytocin’s
Function is Milk Ejection
from Lactating Breasts
See Negative
Feedback Mechanism:
 Water deprivation
stimulates ADH
secretion, decreases
free-water clearance,
and enhances water
 ADH and water form a
negative feedback
 Stimulus for the
Production/Release of
ADH: Water Loss
ADH and Negative
Dehydration and low blood pressure
ADH secretion increases
More water absorbed by kidney
Blood pressure rises
ADH secretion decreases
Unusual since most hormones are
controlled by negative feedback
General mechanism: blood level
hormone & increased response by
target organ(s)  stimulates
hormone secretion
Cycle broken when job completed
Once job is completed,
hormone is no longer needed
Stimulus for the
production/release of oxytocin
During labor: Movement of baby
(Places pressure on receptors in
the lining of the uterus
After delivery: Nursing infant
Tiny, pine cone–shaped
Location: In the cranial
cavity on the dorsal surface
of the brain
Specific: dorsal aspect of the
brain’s diencephalon: Above
the superior and inferior
colliculi that form the roof of
the midbrain
Member of the nervous
system because it receives
visual stimuli
Member of the endocrine
system because it secretes
Supports the body’s
biological clock:
Principal pineal secretion is
melatonin (Table 16-10)
Structure of the thyroid gland
Composed of two large lateral lobes and a narrow connecting isthmus
(Figure 16-22)
A thin, wormlike projection of thyroid tissue often extends upward from the
Weight of the thyroid in an adult is approximately 30 g (1 oz)
Location: Neck, on the anterior and lateral surfaces of the trachea, just
below the larynx
Composed of follicles (Figure 16-23)
Small, hollow spheres
Filled with thyroid colloid that contains thyroglobulins
 Thyroid hormone (Figure 16-24;
 Actually two different hormones
Triiodothyronine (T3):
 Contains three iodine atoms
 Considered the principal thyroid hormone
 Binds efficiently to nuclear receptors in target cells
 Tetraiodothyronine (T4), or thyroxine:
 Contains four iodine atoms
 Approximately 20 times more abundant than T3
 Major importance is as a precursor to T3
Thyroid gland stores considerable amounts of a
preliminary form of its hormones before secreting them
Before being stored in the colloid of follicles, T3 and T4
are attached to globulin molecules, forming thyroglobin
Table 16-7)
Before release, T3 and T4 detach from globulin
and enter the bloodstream
Once in the blood, T3 and T4 attach to a plasma
protein called thyroid-binding globulins and
travel as a hormone-globulin complex
T3 and, to a lesser extent, T4 detach from plasma
globulin as they near the target cells
Thyroid hormone helps regulate the metabolic
rate of all cells and cell growth and tissue
differentiation; said to have a “general” target
Calcitonin (Table 16-7)
Produced by thyroid gland
in the parafollicular cells
 In human beings,
calcitonin may subtly
influence the processing
of calcium by bone cells
by decreasing blood
calcium levels and
promoting conservation of
hard bone matrix
 Parathyroid hormone acts
as antagonist to calcitonin
to maintain calcium
Structure of the parathyroid glands
Four or five parathyroid glands embedded in the
posterior surface of the thyroid’s lateral lobes (Figure
 Tiny, rounded bodies within thyroid tissue formed by
compact, irregular rows of cells (Figure 16-26)
 Parathyroid hormone (Table 16-7)
 An antagonist to calcitonin and the primary
hormone to maintain calcium homeostasis (Figure
Acts on bone and kidney
Causes more bone to be dissolved, yielding calcium
and phosphate, which enter the bloodstream
Causes phosphate to be secreted by the kidney cells
into the urine to be excreted
Causes increased intestinal absorption of calcium by
stimulating the kidney to produce active vitamin D,
which increases calcium absorption in the gut
Structure of the
adrenal glands
Location: Top of
the kidneys, fitting
like caps (Figure
 Composed of two
portions (Figure
16-29; Table 16-8)
Adrenal cortex:
made of endocrine
tissue (Figure 1630)
Adrenal medulla:
made of
Adrenal cortex: all cortical
hormones are steroids and
are known as
corticosteroids (Figure 1631)
Composed of three distinct
layers of secreting cells
Zona glomerulosa: outermost
layer, directly under the outer
connective tissue capsule of
the adrenal gland; secretes
Zona fasciculata: middle
layer; secretes glucocorticoids
Zona reticularis: inner layer;
secretes small amounts of
glucocorticoids and
Composed of 3 groups
1. Mineralocorticoids
Have an important role in the regulatory process of
sodium in the body
Only physiologically important mineralocorticoid in the
body; primary function is maintenance of sodium
homeostasis in the blood by increasing sodium
reabsorption in the kidneys
 Aldosterone also increases water retention and promotes
the loss of potassium and hydrogen ions
 Aldosterone secretion is controlled by the reninangiotensin-aldosterone system and by blood potassium
concentration (Figure 16-32)
System helps control blood pressure
Decreased BP  Detected by
kidney sensors 
Kidney sensors secrete renin into
blood 
Renin participates In chemical
reactions that occur in blood that
convert a blood protein into
Angiotensin I, then Angiotensin II
Angiotensin II targets adrenal
cortex, causes increased secretion
of Aldosterone 
Result: Sodium retention,
followed by water retention,
potassium and hydrogen loss 
Causes blood volume to increase
Causes BP to increase (back into
homeostatic range)
2. Glucocorticoids
Main glucocorticoids secreted by the zona fasciculata
are cortisol, cortisone, and corticosterone, with
cortisol the only one secreted in significant quantities
Affect every cell in the body
Are protein mobilizing, gluconeogenic, and
Tend to cause a shift from carbohydrate catabolism to
lipid catabolism as an energy source
Essential for maintaining normal blood pressure by
aiding norepinephrine and epinephrine to have their
full effect, causing vasoconstriction
High blood concentration causes eosinopenia and
marked atrophy of lymphatic tissues
Act with epinephrine to trigger normal recovery from
injury produced by inflammatory agents
Secretion increases in response to stress
Except during stress response, secretion is mainly
controlled by a negative feedback mechanism
involving adrenocorticotropic hormone from the
Secretion is characterized by several large pulses of
increased hormone levels throughout the day, the
largest occurring just before waking (Figure 16-33)
3. Gonadocorticoids: sex hormones (androgens)
released from the adrenal cortex for both males
and females
Female hormones appear to have no physiological
significance in males
Male hormones do appear to have physiological
significance in females
Exact functions haven’t been determined (may contribute to sex
characteristics in females)
 Adrenal medulla
 Neurosecretory tissue:
composed of neurons that
secrete their products into the blood
Adrenal medulla secretes two important
epinephrine (adrenaline) (80% excretion)
Norepinephrine (catecholamines)
Part of the class of nonsteroid hormones called
Both hormones bind to the receptors of
sympathetic effectors to prolong and enhance
the effects of sympathetic stimulation by the
autonomic nervous system (Figure 16-34)
 Functions
“Flight or fight response”
Location: Abdominal
cavity (mostly behind
the stomach)
 Hormones )Endocrine
portion: Pancreatic
 Secretes 2 major
hormones: glucagon
and insulin
 Dual gland:
Endocrine and
exocrine properties
Structure (Figure 16-35)
 Elongated gland weighing
approximately 100 g (3.5
 Location: head lies in the
duodenum, extends
horizontally behind the
stomach, and then touches
the spleen
 Composed of endocrine and
exocrine tissues
 Pancreatic islets (islets
of Langerhans):
endocrine portion
 Acini: exocrine portion;
secretes a serous fluid
containing digestive
enzymes into ducts
draining into the small
Pancreatic islets
Each islet contains four primary types of endocrine
glands joined by gap junctions:
Alpha cells (A cells) secrete glucagon (Figure 16-36)
Beta cells (B cells) secrete insulin; account for up to 75%
of all pancreatic islet cells
Delta cells (D cells) secrete somatostatin
Pancreatic polypeptide cells (F, or PP, cells) secrete
pancreatic polypeptides
 Pancreatic
hormones: work as a team to
maintain homeostasis of food molecules
(Figure 16-37; Table 16-9)
Glucagon: produced by A cells; tends to increase
blood glucose levels; stimulates gluconeogenesis
in liver cells
Insulin: produced by B cells; lowers blood
concentration of glucose, amino acids, and fatty
acids and promotes their metabolism by tissue
Somatostatin: produced by D cells; primary role
is regulating the other endocrine cells of the
pancreatic islets
Pancreatic polypeptide: produced by F cells;
influences the digestion and distribution of food
molecules to some degree
Glucagon and insulin work together to maintain blood
glucose levels.
 Testes (Figure 16-2;
 Sex glands
 Paired organs within
Table 16-10)
the scrotum in
the male
Composed of seminiferous tubules
and a scattering of interstitial cells
Testosterone is produced by the
interstitial cells and responsible for
the growth and maintenance of
male sexual characteristics
Testosterone secretion is mainly
regulated by gonadotropin levels in
the blood
 Ovaries (Figure 16-2; Table 16-10)
 Primary sex organs in the female
 Set of paired glands in the pelvis that
several types of sex hormones
Estrogens: steroid hormones secreted by ovarian
follicles; promote development and maintenance of
female sexual characteristics
Progesterone: secreted by corpus luteum; maintains
the lining of the uterus necessary for successful
Ovarian hormone secretion depends on the changing
levels of follicle-stimulating hormone and luteinizing
hormone from the adenohypophysis
Tissues that form on the
lining of the uterus as a
connection between the
circulatory systems of
the mother and
developing child
 Serves as a temporary
endocrine gland that
produces human
chorionic gonadotropin
(hCG), estrogens, and
progesterone (Table 1610)
Signals the ovaries of the mother to
maintain the corpus luteum, which
maintains the lining of the uterus in
No pregnancy
 Corpus luteum (secretes
progesterone) becomes corpus
albicans (scar tissue); lining of the
uterus is shed in menstration
 Placenta (developing embryo)
secretes hCG; corpus luteum
remains, continues to secrete
progesterone, maintains uterine
lining for successful pregnancy
NOTE: hCG is secreted in high levels in
early pregnancy, pregnancy tests check
for the presence of this hormone
Gland located in the
mediastinum just beneath the
sternum (Figure 16-2)
 Large in children; begins to
atrophy at puberty and, by old
age, is a vestige of fat and
fibrous tissue
 Considered primarily a
lymphatic organ, but the
hormone thymosin has been
isolated from thymus tissue
(Table 16-10)
 Thymosin stimulates
development of T cells
The mucous lining of the
gastrointestinal tract contains
cells that produce both
endocrine and exocrine
secretions (Table 16-10)
Gastrointestinal hormones
 Gastrin, secretin, and
cholecystokinin, play
regulatory roles in
coordinating the secretory
and motor activities involved
in the digestive process
 Ghrelin: hormone secreted
by endocrine cells in gastric
mucosa; stimulates
hypothalamus to boost
appetite; slows metabolism
and fat burning; may
contribute to obesity
The heart has a secondary
endocrine role
Hormone-producing cells
produce several atrial
natriuretic peptides,
including atrial natriuretic
hormone (Table 16-10)
Function: to oppose increases
in blood volume or blood
Promotes sodium and water
Antagonist to antidiuretic
hormone and aldosterone
Other antagonists
For calcium: CT/PTH
For glucose: insulin/GH,
glucocorticords, glucagon
 Endocrine
regulation begins in the womb
 Many hormones are active from birth
Evidence that a hormonal signal from fetus to
mother signals the onset of labor
 Hormones
related to reproduction begin at
 Secretion of male reproductive hormones is
continuous from puberty, slight decline in
late adulthood
 Secretion of female reproductive hormones
declines suddenly and completely in middle
 Nearly
every process in the human organism
is kept in balance by the intricate interaction
of different nervous and endocrine
regulatory chemicals
 The endocrine system operates with the
nervous system to finely adjust the many
processes they regulate
 Neuroendocrine system adjusts nutrient
 Calcitonin, parathyroid hormone, and
vitamin D balance calcium ion use
 The nervous system and hormones regulate

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