Endocrine System Introduction
The endocrine system is made up of glands that produce and
secrete hormones, chemical substances produced in the body that
regulate the activity of cells or organs.
These hormones regulate the body's growth, metabolism (the
physical and chemical processes of the body), and sexual
development and function.
The hormones are released into the bloodstream and may affect
one or several organs throughout the body.
The major glands of the endocrine system are the
hypothalamus, pituitary, thyroid, parathyroids, adrenals, pineal
body, and the reproductive organs (ovaries and testes).
The pancreas is also a part of this system; it has a role in
hormone production as well as in digestion.
The Endocrine System
General Functions of Hormones
• Help regulate:
contraction of cardiac &
– glandular secretion
– some immune functions
• Growth & development
Endocrine Glands Defined
• Exocrine glands
– secrete products into ducts which empty into body
cavities or body surface
– sweat, oil, mucous, & digestive glands
• Endocrine glands
– secrete products (hormones) into bloodstream
– pituitary, thyroid, parathyroid, adrenal, pineal
– other organs secrete hormones as a 2nd function
• hypothalamus, thymus, pancreas,ovaries,testes, kidneys,
stomach, liver, small intestine, skin, heart & placenta
• The endocrine system is a collection of glands
that secrete chemical messages we call
• These signals are passed through the blood to
arrive at a target organ, which has cells
possessing the appropriate receptor.
What Does the Endocrine
System travels from the endocrine
Once a hormone is secreted, it Do?
gland that produced it through the bloodstream to the cells
designed to receive its message. These cells are called target
Along the way to the target cells, special proteins bind to
some of the hormones. These proteins act as carriers that
control the amount of hormone that is available for the cells to
The target cells have receptors that latch onto only specific
hormones, and each hormone has its own receptor, so that
each hormone will communicate only with specific target cells
that have receptors for that hormone.
When the hormone reaches its target cell, it locks onto the
cell's specific receptors and these hormone-receptor
combinations transmit chemical instructions to the inner
workings of the cell.
When hormone levels reach a certain normal amount,
the endocrine system helps the body to keep that level
of hormone in the blood.
Another example of this process is :
parathyroid hormone. Parathyroid hormone
increases the level of calcium in the blood. When the
blood calcium level rises, the parathyroid glands sense
the change and reduce their secretion of parathyroid
hormone. This turnoff process is called a negative
Circulating & Local Hormones
• Circulating hormones
– act on distant targets
– travel in blood
• Local hormones
– paracrines act on
– autocrines act on same
cell that secreted them
General Mechanisms of Hormone Action
• Hormone binds to cell surface or receptor inside
• Cell may then
– synthesize new molecules
– change permeability of membrane
– alter rates of reactions
• Each target cell responds to hormone differently
– liver cells---insulin stimulates glycogen synthesis
– adipose---insulin stimulates triglyceride synthesis
Control of Hormone Secretion
• Regulated by signals from nervous system,
chemical changes in the blood or by other
• Negative feedback control (most common)
– decrease/increase in blood level is reversed
• Positive feedback control
– the change produced by the hormone causes
more hormone to be released
• Disorders involve either hyposecretion or
hypersecretion of a hormone
Overproduction of a hormone
Underproduction of a hormone
Nonfunctional receptors that cause target
cells to become insensitive to hormones
• The hypothalamus contains neurons that control releases
from the anterior pituitary.
• Seven hypothalamic hormones are released into a portal
system connecting the hypothalamus and pituitary, and
cause targets in the pituitary to release eight hormones.
The location and roles of the hypothalamus and
Hypothalamus and Pituitary Gland
• Both are master endocrine glands since their hormones
control other endocrine glands
• Hypothalamus is a section of brain above where pituitary
gland is suspended from stalk (surrounds 3rd ventricle)
• Hypothalamus receives input from cortex, thalamus,
limbic system & internal organs
• Hypothalamus controls pituitary gland with different
releasing & inhibiting hormones (gonadotropin-releasing
hormone, growth hormone-releasing hormone, growth
• Major integrating link between nervous and endocrine
• Anterior and posterior
1. Posterior connected to
2. Anterior connected via
te s ti
(M m o n
Anterior Pituitary & Flow of Blood
• Controlling hormones enter blood
• Travel through portal veins
• Enter anterior pituitary at capillaries
1.Human Growth Hormone (HGH)
• Produced by somatotrophs (somatostatin) of
• Within target cells increases synthesis of insulin
like growth factors that act locally or enter
– common target cells are liver, skeletal muscle,
cartilage and bone
– increases cell growth & cell division
Too much or too
little of any
hormone can be
harmful to your
For example, if the
pituitary gland produces
too much growth
hormone, a teen may
grow excessively tall. If it
produces too little, a teen
may be unusually short.
Doctors can often treat
the problems by
production of hormones
or replacing certain
2.Thyroid Stimulating Hormone (TSH)
• Hypothalamus regulates thyrotroph cells
• Thyrotroph cells produce TSH
• TSH stimulates the synthesis & secretion of T3
• Metabolic rate stimulated
3.Follicle Stimulating Hormone (FSH)
• GnRH from
• Gonadotrophs release
• FSH functions
– initiates the formation of follicles within the ovary
– stimulates follicle cells to secrete estrogen
– stimulates sperm production in testes
4.Luteinizing Hormone (LH)
• GnRH from hypothalamus stimulate gonadotrophs
• Gonadotrophs produce LH
• In females, LH stimulates
– secretion of estrogen
– ovulation of oocyte from ovary
– secretion of progesterone
• In males, stimulates interstitial cells
to secrete testosterone
• Hypothalamus regulates
lactotroph cells (PRH)
• Lactotrophs produce prolactin
• Under right conditions, prolactin
causes milk production
• Suckling reduces levels of hypothalamic
inhibition and prolactin levels rise along
with milk production
6.Adrenocorticotrophic Hormone (ACTH)
• Corticotrophs secrete
ACTH & MSH
• ACTH stimulates cells
of the adrenal cortex that
7.Melanocyte-Stimulating Hormone (MSH)
• Secreted by corticotroph cells
• Releasing hormone from hypothalamus
increases its release from the anterior pituitary
• Function not certain in humans (increase skin
pigmentation in frogs )
Posterior Pituitary Gland
• Does not synthesize
• Consists of axon
terminals of hypothalamic
neurons and pituicytes
• Neurons release two
– antidiuretic hormone
Posterior Pituitary Hormones
• Manufactured in Hypothalamus, released from
– Target = smooth ms. Uterus and Breast (&brain)
– Function = labor and delivery, milk ejection,(pair
• ADH (Vasopressin AVP)
– Target = kidneys
– Function = water reabsorption
• Two target tissues both involved in
• During delivery
– baby’s head stretches cervix
– hormone release enhances
uterine muscle contraction
– baby & placenta are delivered
• After delivery
– suckling & hearing baby’s cry stimulates milk ejection
– hormone causes muscle contraction & milk ejection
• Classic example:
uterine muscle during
2.Antidiuretic Hormone (ADH)
• Known as vasopressin
– decrease urine production
– decrease sweating
– increase BP by retaining
• The pineal gland, or
the pineal body is in
the middle of the
brain. It secretes
regulates when you
sleep at night and
wake up in the
• Pineal gland is a small, cone shaped gland found
in the roof of the third ventricle of the brain.
• Melatonin hormone appears to be secreted in
• It is believed to coordinate the hormones of
fertility and to inhibit the reproductive system
(especially the ovaries of females)
• so that sexual maturation is prevented from
occurring before adult body size has been reached.
• Located in the upper thorax region.
. • Large in infants and children, it decreases in size
throughout adult hood.
• By old age, it is composed mostly of fibrous
connective tissue and fat.
• Thymus produces a hormone called thymosin.
• During childhood, it acts as an incubator for the
maturation of a special group of whiteblood
cells(T lymphocytes or T cells).
• T cells are play a great role in immune respose.
• On each side of trachea is lobe of thyroid
• Weighs 1 oz & has rich blood supply
• Location: Located close to thyroid cartilage. Has two
lateral lobes connected by thyroid isthmus medially.
Isthmus covers cricoid cartilage in ventral view.
• Development: first endocrine gland to apear during
development. Develops from endodermal thickening in floor
of early pharynx and epithelium of 3rd and 4th gill slit pouches
as early as 24 days after fertilization. Starts out caudal to
tongue, but ultimately comes to be wrapped around laryngeal
Actions of Thyroid
• T3 & T4 = thyroid
hormones responsible for
our metabolic rate,
synthesis of protein,
breakdown of fats, use of
glucose for ATP production
• Calcitonin = responsible for
building of bone & stops
reabsorption of bone (lower
blood levels of Calcium)
Iodine deficiency causes
thyroid to enlarge as it
tries to produce thyroxine
• Goiters A thyroid goiter is a dramatic
enlargement of the thyroid gland.
•Very small (less than 5 mm).
•Called parathyroid glands because of their position on
posterior margins outer surface of thyroid gland.
•More superior of each pair usually near middle of margin of
•More inferior of each pair usually at inferior apex of lobe.
Development: Like thyroid gland, develop from endodermal
thickening in floor of early pharynx and epithelium of 3rd and
4th gill slit pouches.
• 4 pea-sized glands found on back of thyroid gland
• Raise blood calcium levels
– increase activity of osteoclasts
– increases reabsorption of Ca+2 by kidney
– promote formation of calcitriol (vitamin D3) by
kidney which increases absorption of Ca+2 and
Mg+2 by intestinal tract
Regulation of Calcium Blood Levels
• High or low blood levels of Ca+2 stimulate the release of
different hormones --- PTH or CT
• Hyperthyroidism Hyperthyroidism means too
much thyroid hormone.
• Hypothyroidism Hypothyroidism means too little
thyroid hormone and is a common problem.
• Thyroid Cancer Thyroid cancer is a fairly
common malignancy, however, the vast majority
have excellent long term survival.
• Solitary Thyroid Nodules There are several
characteristics of solitary nodules of the thyroid
which make them suspicious for malignancy.
• Thyroiditis Thyroiditis is an inflammatory
process ongoing within the thyroid gland.
• Adrenal gland located atop kidney
• Outer part = cortex
– Secretes Cortisol (stress), Androgens,
• Inner part = medulla
– SNS control
– Secretes EPI & NEPI (fight or flight)
• Each kidney has an adrenal gland located above it.
• The adrenal gland is divided into an inner medulla and
an outer cortex.
• The medulla synthesizes amine hormones, the cortex
secretes steroid hormones.
• The adrenal medulla consists of modified neurons that
secrete two hormones: epinephrine and
• Stimulation of the cortex by the sympathetic nervous
system causes release of hormones into the blood to
initiate the "fight or flight" response.
• The adrenal cortex produces several steroid hormones
in three classes: mineralocorticoids, glucocorticoids,
and sex hormones.
Mineralocorticoids maintain electrolyte balance.
Glucocorticoids produce a long-term, slow
response to stress by raising blood glucose levels
through the breakdown of fats and proteins; they
also suppress the immune response and inhibit the
The structure of the kidney as relates to hormones
Two diseases associated with
the adrenal cortex:
1. Cushing’s Disease :
Cushing's disease refers to a pituitary-dependent cause of Cushing's
syndrome: a tumor (adenoma) in the pituitary gland produces large
amounts of ACTH, causing the adrenal glands to produce elevated
levels of cortisol
2. Addison’s disease
Addison’s disease (also chronic adrenal
insufficiency, hypocortisolism, and hypoadrenalism) is a
rare, chronic endocrine disorder in which the adrenal glands do
not produce sufficient steroid hormones (glucocorticoids and
often mineralocorticoids). It is characterised by a number of
relativelynonspecific symptoms, such as abdominal pain and
The pancreas is an elongated organ located toward the
back of the abdomen behind the stomach.
The pancreas has digestive and hormonal functions.
One part of the pancreas, the exocrine pancreas, secretes
The other part of the pancreas, the endocrine pancreas,
secretes hormones called insulin and glucagon. These
hormones regulate the level of glucose (sugar) in the
Pancreatic Endocrine Hormones and Their
1.Glucagon : Assist insulin in regulating blood glucose
(sugar) in the normal range (actions are opposite of
• Disease due to deficient action: Some times nothing,
Disease due to excess action: Hyperglycemia
Disease due to excess action: Hyperglycemia
2.Somatostatin: Regulate the production and excretion of
other endocrine tumors
• Disease due to excess action: Diabetes (inhibits
insulin production), gallstones, and dietary fat intolerance.
• Diabetes results from inadequate levels of insulin.
• Type I diabetes is characterized by inadequate levels of
insulin secretion, often due to a genetic cause.
• Type II usually develops in adults from both genetic
and environmental causes.
• Loss of response of targets to insulin rather than lack of
insulin causes this type of diabetes.
• Diabetes causes impairment in the functioning of the
eyes, circulatory system, nervous system, and failure of
• Diabetes is the second leading cause of blindness in the
• Treatments involve daily injections of insulin,
monitoring of blood glucose levels and a controlled diet.
Regulation of Glucagon & Insulin Secretion
• Low blood glucose
stimulates release of
• High blood glucose
stimulates secretion of
Travel in blood w/carrier
Cytoplasmic or nuclear receptors
change protein synthesis
The reproductive glands are the main source of sex hormones.
In males, the testes, located in the scrotum, secrete hormones
called androgens; the most important of which is testosterone.
These hormones affect many male characteristics (for example,
sexual development, growth of facial hair and pubic hair) as well
as sperm production.
In females, the ovaries, located on both sides of the uterus,
produce estrogen and progesterone as well as eggs.
These hormones control the development of female
characteristics (for example, breast growth), and they are also
involved in reproductive functions (for
Growth hormone (GM)
Stimulates contraction of uterus
and mammary gland cells
Promotes retention of water
Stimulates growth (especially
bones) and metabolic functions
Stimulates milk production
Stimulates production of
ova and sperm
Stimulates ovaries and testes
Stimulates thyroid gland
Stimulates adrenal cortex
to secrete glucocorticoids
made by hypothalamus)
Glucose in blood
Glucose in blood
Lowers blood glucose
Raises blood glucose
Raise blood glucose level;
increase metabolic activities;
constrict certain blood
Raise blood glucose level
FSH arid LH
Support sperm formation;
promote development and
maintenance of male
Stimulate uterine lining
promote development and
maintenance of female
secondary sex characteristics
Promotes uterine lining
ESH and LH
ESH and LH
Drugs Affecting the Pituitary
↓GH = pituitary dwarfism
• BRAND NAME(S):
• Genotropin, Norditropin, Nutropin,
• Somatropin is also used to increase height in
children with a certain genetic disorder
• Side effectHeadache, nausea,vomiting, fatigue,
• Other drugs- Humatrope Inj, Somatropin
Gigantism is abnormally large growth due to
an excess of growth hormone during
childhood, before the bone growth plates
Symptoms: The child will grow in height, as
well as in the muscles and organs.
Stopping or reducing the overproduction of
growth hormone is not easy; thus, doctors
may need to use a combination of surgery,
radiation therapy, and drug therapy.
Drugs Affecting the Parathyroid &
•Typically a result of tumors
•Most common cause is Grave’s Disease
•Surgical removal of the diseased gland