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CASE 3: BIOLOGY
● Define the endocrine system and explain its general function.
● Explain; How does the endocrine system maintain the Homeostasis in the body.
● Explain the relationship between nervous system and endocrine system.
● Distinguish Between endocrine and exocrine glands.
● Define the term hormone and explain its function and number its types.
● Describe the mechanisms of steroids and non-steroids hormone action.
● Explain the regulation and transmitters of hormones.
● Describe the types, function, location of the glands, and their effects during
oversecretion or undersecretion on the body.
DEFINITION OF ENDOCRINE SYSTEM
The endocrine system is the collection of glands that produce hormones
that regulate metabolism, growth and development, tissue function, sexual
function, reproduction, sleep, and mood, among other things.
The word endocrine derives from the Greek words "endo," meaning
within, and "crinis," meaning to secrete.
Although the hormones circulate throughout the body, each type
of hormone is targeted toward certain organs and tissues.
➢ The endocrine system gets
some help from organs such as
the kidney, liver, heart and
gonads, which have secondary
○ The kidney, for example,
secretes hormones such as
erythropoietin and renin.
THE GENERAL FUNCTION
How does the endocrine system maintains the
Homeostasis is happening constantly in our bodies. We eat, sweat, drink,
dance, eat some more, have salty fries, and yet our body composition remains
almost the same. If someone were to draw your blood on ten different days of
a month, the level of glucose, sodium, red blood cells and other blood
components would be pretty much constant, regardless of your behavior
(assuming fasting before drawing blood, of course).
How does the endocrine system maintains the
These hormones are sent via the This is the main way we maintain
homeostasis actually, since the endocrine system releases chemicals known as
hormones. These hormones are sent via the blood to specific spots in the body
to control things like blood sugar, heart rate, etc.The Endocrine system is
responsible for homeostasis. The Endocrine system secrete hormones that the
body needs to perform certain functions.
How does the endocrine system maintains the
● When glands create hormones, they get transported through either the
bloodstream or the lymph.
● Hormones help the body to act or react to any threat to homeostasis.
Hormones aid throughout reproduction and birth.
● They help people sleep and wake up.
● The adrenal glands give off adrenaline to help a person perform in potential
danger, and they release dopamine linked with the body's reward system.
● In general, the endocrine system plays a major role in helping the body
maintain homeostasis because it gives off the messengers to help the body to
react to any threats to homeostasis
● The Nervous system & Endocrine system are both essential to
the communication and relay of messages throughout the body.
● They work together to regulate(Homeostasis) the activities of
the other systems.
● Both systems use chemical signals when they respond to
changes that might alter (Homeostasis).
RELATIONSHIP BETWEEN NERVOUS SYSTEM & ENDOCRINE
Feature Nervous System Endocrine System
Signals Electric impulses
Pathways Transmission by neurons Transported by blood
Speed of information fast slow
Duration of effect Short lived Long lived
In a fight or flight response, there is a coordination of both the nervous and endocrine
systems. The nervous system detects stimuli, either inside or out, for example, danger like
an oncoming car about to run someone over, and that in turn sends an impulse to the
endocrine system where a response is carried out. The response in this case is the release
of adrenaline into the bloodstream, by the endocrine glands called adrenal glands. Once
in the bloodstream, this hormone can cause the heart rate to increase, the muscles to
become ready to either react to an emergency situation by fighting or by flight
THE DIFFERENCE BETWEEN
ENDOCRINE AND EXOCRINE GLANDS
ENDOCRINE GLAND: a gland that secretes hormones directly into
the bloodstream; a ductless gland.
EXOCRINE GLAND: a gland that secretes substances into ducts which
then leave the body (i.e. sweat/sebaceous glands) or into an internal
space or lumen (i.e. digestive glands).
★ Exocrine glands are not part of the endocrine system!
DEFINITION OF HORMONES
Hormones are chemical substances that act like messenger molecules in
the body. After being made in one part of the body, they travel to other
parts of the body where they help control how cells and organs do their
Important Functions of hormones include
● Growth and development of Prompting cell or tissue
● Food metabolism
● Initiating and maintaining sexual development and reproduction
● Maintaining body temperature
● Controlling thirst
● Regulating mood and cognitive functioning
TYPES OF HORMONES
Hormones are classified by various criteria:
•By Proximity of their site of synthesis to their site of action.
•By their chemical structure.
•By their degree of solubility in aqueous medium.
3 classes of hormones based on proximity of site of
Synthesis to Site of Action:
1. Autocrine Hormones: those that act on the same cells that
2. Paracrine Hormones: those that are synthesized very close to
their site of action.
3. Endocrine Hormones: those that are synthesized by endocrine
glands and transported in the blood to target cells that
contain the appropriate receptors.
4 classes of hormones based on chemical structure:
1. Peptides or Protein hormones:
made of amino acids joined by peptide bonds.
most hormones belong to this group except hormones secreted by the gonads
(testis and ovary) and the adrenal cortex.
•Thyrotropin Releasing Hormone (TRH), made up of three amino acid
•Insulin, made up of 51 amino acid residues.
2. Steroid hormones.
● made of fatty acids using cholesterol as a functional group.
● only hormones secreted by the gonads and adrenal cortex
belong to this group .
3. Amino acid derivatives.
4. Fatty acid derivatives.
Two classes of hormones based on solubility in aqueous
1. Hydrophilic Hormones.
•Hormones that are soluble in aqueous medium.
•They cannot cross the cell membrane.
Examples: Insulin, Glucagon, Epinephrine.
2. Lipophilic Hormones.
● Hormones that are not soluble in aqueous medium, but soluble in
● They can easily cross the cell membrane,
Examples: Thyroid hormones, Steroid hormones
● Location of receptors for each class of hormone is different.
MECHANISM OF HORMONES
As there are huge variety of hormones , there are two mechanism by which
hormone trigger changes in cells.They are :
● Direct Gene Activation
● Second-Messenger System
Direct Gene Activation .
● Steroid hormones use the mechanism of direct gene expression because they are
● First, they diffuse through the plasma membranes of their target cells into their
● Then they binds to a specific hormone receptor it then further binds to specific
sites on the cell's DNA
● Which activates certain genes to transcribe messenger RNA . it then translates in
● Resulting in the synthesis of new protein .
● Water soluble and non-steroid hormones are unable to enter targeted cells so they
bind to hormone receptor.
● Which is situated on target cell's plasma membrane and utilize a second
● The hormone binds to the membrane receptor and activated receptor sets off a
series of reaction that activates an enzyme
● The enzyme in turn, catalyze reactions that produce second messenger molecules
also known as cAMP.
● This promotes typical response of the target cell to hormone.
Most hormones are regulated by feedback mechanisms. A
feedback mechanism is a loop in which a product feeds back to
control its own production
Negative feedback occurs when a product feeds back to
.decrease its own production
Positive feedback occurs when a product feeds back to increase
its own production
CONTROL OF HORMONE RELEASE
Endocrine Gland Stimuli
The stimuli that activate the endocrine organs fall into three
major categories—hormonal, humoral, and neural
The most common stimulus
is a hormonal stimulus, in which endocrine
organs are prodded into action by other hormone
Changing blood levels of certain ions
and nutrients may also stimulate
In isolated cases, nerve fibers stimulate hormone release, and
the target cells are said to respond to neural stimuli. The
classic example is sympathetic nervous system stimulation of
the adrenal medulla to release norepinephrine and
epinephrine during periods of stress
HORMONE TRANSPORT IN BLOOD
Hormones flow through the blood and then bind to their
receptors within the capillaries or diffuse out to reach the
receptors at the target cell.
Water insoluble hormones must bind to plasma protein to be
carried into the plasma, hormones remain bind to these protein
for some time which act as a reservoir for the hormones.
Water soluble hormones which can dissolve into the plasma by
itself and can easily diffuse out to their site of action. Water
soluble hormones act faster in a short period of time.
THE PITUITARY GLAND
The main endocrine gland. It is a small structure in the
head. The pituitary gland is about the size of a bean,
and it hangs by a stalk from the hypothalamus.It is
called the master gland because it produces hormones
that control other glands and many body functions
including growth. The pituitary consists of the anterior
and posterior pituitary.
The pituitary glands are made of the anterior lobe
and posterior lobe. The anterior lobe produces and
releases hormones. The posterior lobe does not
produce hormones per se—this is done by nerve cells
in the hypothalamus—but it does release them into the
The Anterior Pituitary
The anterior lobe releases hormones upon receiving releasing or inhibiting
hormones from the hypothalamus. These hypothalamic hormones tell the anterior
lobe whether to release more of a specific hormone or stop production of the
Anterior Lobe Hormones:
● Growth hormone (GH): GH is essential in early years to maintaining a
healthy body composition and for growth in children. In adults, it aids
healthy bone and muscle mass (increases bone and muscle growth) . It also
affects fat distribution and increases protein synthesis.
● Prolactin (PRL): Prolactin stimulates breast milk production after
● Follicle-stimulating hormone (FSH): FSH works with LH to ensure
normal functioning and development of the ovaries and testes. It stimulates
the production of egg and sperm.
● Luteinizing hormone (LH): LH works with FSH to ensure normal
functioning of the ovaries and testes. It triggers ovulation in females and
stimulates testosterone production in male.
● Adrenocorticotropic hormone (ACTH): ACTH stimulates the adrenal
glands to produce hormones.
● Thyroid-stimulating hormone (TSH): TSH stimulates the thyroid gland
to produce hormones.
The Posterior Pituitary
The posterior pituitary (or neurohypophysis) comprises the posterior lobe of the
pituitary gland and is part of the endocrine system.
The posterior lobe contains the ends of nerve cells coming from the
hypothalamus. The hypothalamus sends hormones directly to the posterior lobe
via these nerves, and then the pituitary gland releases them.
Posterior Lobe Hormones:
● Antidiuretic hormone (ADH): Antidiuretic hormone, also known as
vasopressin, acts to maintain blood pressure, blood volume and tissue water
content by controlling the amount of water and hence the concentration of
urine excreted by the kidney.This hormone prompts the kidneys to increase
water absorption in the blood.
● Oxytocin: Oxytocin is involved in a variety of processes, such as contracting
the uterus during childbirth and stimulating breast milk production.
Hypersecretion- Too much of any hormone secreted into the body is usually
caused by a secretory pituitary gland tumor.
● Secretory tumors produce too much prolactin (the hormone that triggers
milk production in new mothers), which leads to infertility, discharge
from breasts and menstrual abnormality.
● Some tumors may affect the adrenal glands, due to oversecretion of
hormones, which stimulates them and cause a hormone imbalance.
● Tumors can also make excess of growth hormone which stimulate the
thyroid gland, leading to overproduction of the thyroid
hormone.Oversecretion of the pituitary hormone human growth hormone
can cause gigantism if it occurs before growth of the long bones is
complete, or acromegaly if it begins during adulthood.
● Hormones secreted in less amount in the body are commonly
caused by a non-secretory pituitary gland tumor, which interferes
with the ability of the normal pituitary gland to create hormones.
● It can, however, also be caused by a large secretory tumor.
● Hyposecretion can also happen with surgery or radiation therapy
for a pituitary gland tumor.
● Undersecretion of human growth hormone can lead to dwarfism if
experienced during childhood, and decreased endocrine function
accompanied by lethargy and loss of sexual capacity in the adult.
THE PINEAL GLAND
The pineal gland, also known as the "pineal
body," is a small endocrine gland.
It is located on the back portion of the third
cerebral ventricle of the brain, which is a
fluid-filled space in the brain. This gland lies
in-between the two halves of the brain. The
gland is named for its shape, which resembles a
pinecone (in Latin, "pinea").
THE PINEAL GLAND
The pineal gland's function in the body is not clearly understood yet.
However, it is known to play a role in regulating female reproduction
and sexual maturation. It also has a part in controlling circadian
rhythms (biological processes), the body’s internal clock that affects
such actions as when we wake and sleep. The pinealocytes create and
secrete melatonin, a hormone that helps maintain the body’s internal
clock. Melatonin also helps regulate female reproductive hormones,
including when women menstruate.
THE PINEAL GLAND
The main consequences of swallowing large amounts of
melatonin are drowsiness and reduced core body
temperature. Very large doses have effects on the
performance of the human reproductive system (delay in
Reduced melatonin production is not known to have any
effect on health.
The thyroid gland is located at the base of the throat,
just inferior to the Adam’s apple.
It is a fairly large gland consisting of two lobes joined
by a central mass, or isthmus .
● Thyroid hormone (thyroxine [T4] and
triiodothyronine [T3]) .
Thyroid gland is composed of hollow structures
called follicles , which store a sticky colloidal
Thyroid hormone is derived from this colloid. But
calcitonin hormone is made by the parafollicular
cells found in the connective tissue between the
Thyroxine (T4): is the major hormone secreted by the thyroid follicles.
Triiodothyronine (T3): is formed at the target tissues by conversion of thyroxine to
Each is constructed from two tyrosine amino acids linked together, but thyroxine has
four bound iodine atoms, whereas triiodothyronine has three .
● It is the body’s metabolic hormone
● Thyroid hormone controls the rate at which glucose is “burned,” or oxidized, and
converted to body heat and chemical energy.
● necessary for normal growth and development.
Excessive levels of thyroid hormones in the blood
Graves' disease : is an immune system disorder where the thyroid gland
enlarges and the eyes may bulge, or protrude anteriorly , high basal
metabolic rate, intolerance of heat, rapid heartbeat, weight loss, nervous
and agitated behavior, and a general inability to relax.
low levels of thyroid hormones in the blood
goiter :It is an enlargement of
the thyroid gland that results
when the diet is deficient in
Cretinism : it results in
dwarfism in which adult body
proportions remain childlike.
which is characterized by both
physical and mental sluggishness
,Other signs are puffiness of the
face, fatigue, poor muscle tone,
low body temperature (the
person is always cold), obesity,
and dry skin. (in adult ).
Calcitonin hormone :
● made by the so-called parafollicular cells found in the connective tissue between the
● decreases blood calcium levels by causing calcium to be deposited in the bones.
● It acts antagonistically to parathyroid hormone,
● It is released directly to the blood in response to increasing levels of blood calcium.
● The parathyroid glands are four small
glands located on the posterior aspect of
the thyroid gland.
● Low blood levels of calcium stimulate the
parathyroid glands to release parathyroid
hormone (PTH). It causes bone calcium to
be liberated into the blood.
● PTH also stimulates the kidneys and
intestine to absorb more calcium
● Hyposecretion of PTH results in:
If blood calcium levels fall too low, neurons become
extremely irritable and overactive. They deliver
impulses to the muscles so rapidly that the muscles go
into uncontrollable spasms (tetany), which may be
● Hypersecretion leads to extreme bone wasting
The hypothalamus is a secretion of the brain responsible for the production of
many of the body's essential hormones .It's not an endocrine gland but regulates
the secretion of some pituitary gland hormones.
The hypothalamus is located below the thalamus and above the
pituitary gland and brain stem
Functions of hypothalamus
● The primary function of the hypothalamus is homeostasis
● The hypothalamus govern temperature regulation
● The hypothalamus also governs thirst and hunger
● It also governs sleep, mood, and blood pressure
The pancreas is a large gland that lies alongside the stomach and the small bowel.It is
divided into the head, body and tail.
Functions of the pancreas
It makes digestive juices, which consists of powerful enzyme.
It makes hormones that control blood glucose levels
Primary hormones secreted by the pancreas include:
● Gastrin: this hormone aids digestion by stimulating certain cells
● Glucagon: this helps insulin maintain normal blood glucose by working in the
opposite way of insulin
● Insulin: this hormone regulates blood glucose by allowing many of your body's
cell to absorb and use glucose
Diseases and disorders of the pancreas
● Type 1 diabetes
● Type 2 diabetes
● The female and male gonads produce sex cells (an exocrine
● They also produce sex hormones that are identical to those
produced by adrenal cortex cells.
● The major differences from the adrenal sex hormone
production are the source and relative amounts of hormones
● The female sex organ that serves as an endocrine gland
● The female gonads or ovaries, are paired, almond-sized
organs located in the pelvic cavity.
● Ovaries produce female sex cells ( ova or eggs) and two
groups of steroids hormones estrogens and progesterone.
● An ovarian follicle (and ovum) start to mature each month following
puberty under the influence of FSH (Follicle-stimulating hormone ) .The
developing follicle secretes estrogen
● Luteinizing hormone (LH) causes the follicle to rupture and release the
ovum (ovulation); the follicle becomes the corpus luteum. The corpus
luteum secretes progesterone
a) The estrogens are responsible for the development of sex characteristics in
women (primarily growth and maturation of the reproductive organs)and the
appearance of secondary sex characteristics (hair in the pubic and axillary
b) Acting with progesterone, estrogens promote breast development and cyclic
changes in the uterine lining (the menstrual cycle).
a) Progesterone as already noted, acts with estrogen to bring about the
b) During pregnancy, it quiets the muscles of the uterus so that an implanted
embryo will not be aborted and helps prepare breast tissue for lactation
HYPOSECRETION AND HYPERSECRETION OF OVARIAN
❖ Hyposecretion of the ovarian hormones severely hampers a
woman’s ability to conceive and bear children
❖ Extreme hypersecretion of ovarian hormones by the ovaries is a rare
clinical entity, because excessive secretion of estrogens automatically
decreases the production of gonadotropins by the pituitary, and this
limits the production of ovarian hormones.
● The male sex organ that also serves as an endocrine gland
● The paired oval testes of the male are suspended in a sac, the scrotum, outside
the pelvic cavity.
● Testes produce male sex cells or sperm and male sex hormones testosterone
● FSH( follicle-stimulating hormone) causes the production of sperm
● LH causes the production of testosterone
● At puberty, testosterone promotes the growth and maturation of the
reproductive system organs to prepare the young man for reproduction.
● It also causes the male’s secondary sex characteristics (growth of facial hair,
development of heavy bones and muscles, and lowering of the voice) to
appear and stimulates the male sex drive.
● In adults, testosterone is necessary for continuous production of sperm.
HYPOSECRETION OF TESTOSTERONE
Leads to a lack of male sex characteristics.There are two types:
This type of hypogonadism (also known as primary testicular failure) originates from a
problem in the testicles.
Examples: Klinefelter Syndrome, Mumps Orchitis, hemachromatosis
This type indicates a problem in the Hypothalamus or the pituitary gland.
In cases of hyposecretion, the man becomes sterile; such cases are usually treated by
Location: They are flat pyramidal shaped, curved over the top of each kidney.
Structure: Although it looks like a single organ, they are actually two endocrine organs;
Adrenal Medulla and Adrenal Cortex.
● Epinephrine and norepinephrine are released by adrenal medulla.
● 3 classes of hormones are released by the adrenal cortex; Mineralocorticoids,
Glucocorticoids and sex hormones.
Function of Adrenal cortex hormones
Hormones of Adrenal cortex are collectively called corticosteroids.
1. Mineralocorticoids: (mainly Aldosterone).
● Regulares the mineral ( or salt) content of the blood.
● Their target is the kidney tubules.
● When aldosterone is released, Na+
ions are reabsorbed and K+
are released into the
● When Na+
are reabsorbed, water is reabsorbed too(osmosis).
● In this way, blood volume and B.P are adjusted.
2. Glucocorticoids:(corticosterone, cortisone but mainly cortisol)
● Maintain normal cell metabolism.
● Promote Protein breakdown, lipolysis and gluconeogenesis.
● Helps the body fight long term stressors.
● When glucocorticoids are released, fats and even proteins are broken down to
● Anti-Inflammatory: Inhibit WBC hence they slow down wound healing.
● Depression of Immune system: High doses can depress immune response hence
they are prescribed during organ transplant.
3. Sex hormones: (or Androgens)
● In both male and female Androgens are released but in relatively small quantities.
● Mainly testosterone, but some estrogen is also produced.
● In females after menopause, ovarian secretion of estrogen ceases and all estrogen is
derived from adrenal androgens.
Function of Adrenal Medulla hormones
1. Epinephrine: (Adrenaline) and Norepinephrine (noradrenaline)
● Enhances and prolongs the effects of “ fight or flight” response of the sympathetic
● Increases Heart rate, B.P, Blood glucose level and dilate small passageways of the
● These events result in more oxygen and faster circulation of blood, mainly to brain,
heart and muscles.
● Epinephrine and norepinephrine are released when adrenal medulla is stimulated by
the sympathetic nervous system during “fight or flight” response.
● Glucocorticoids are released from adrenal cortex in response to rising levels of
ACTH in blood. Acth is secreted from the anterior pituitary lobe by the release of
CRF from hypothalamus, which is controlled by steroid level in blood.
● Aldosterone release is stimulated by humoral factors, such as fewer Na+
-Renin from kidneys also causes release of aldosterone when Blood pressure drops.
-A hormone of heart ANP prevents aldosterone release, to reduce blood pressure.
Deficiency of Adrenal cortex hormones
Under-secretion of all adrenal cortex hormones leads to Addison’s
Because of low aldosterone, Na+ and water all lost from the body, leading to:
● Electrolyte and water imbalance
● Muscle weakness
● Lessened ability to, cope with stress. Eg.cold, which is normally easy to
overcome, become life threatening.
Oversecretion of Adrenal cortex hormones:
Hypersecretion may results from a tumor of Pituitary of Adrenal cortex.
Hyperactivity of the outermost cortical area results in
When tumor is in the middle cortical area, Cushing’s syndrome
results.Excessive glucocorticoids results in:
● ‘Buffalo hump’ on the upper back
● High blood pressure
● Bone weakness
● Severe depression of immune system.
Oversecretion of Adrenal Medulla hormones:
Hypersecretion of epinephrine and norepinephrine leads to a prolonged
“ fight or flight response” including:
● High Blood pressure
● Increased heart rate
● High metabolism
● High Glucose.
Location:The thymus gland is located in the
behind the sternum.
Hormones:Thymosin and other hormones:
Thymic humoral factor,
thymic factor and Thymopoietin.
Function of Thymus gland:
Promotes the maturation of T-cells WBCs.
Other endocrine Tissues and Organs:
● Human Chorionic Gonadotrophin.
● Estrogen and progesterone.
•Renin -restore normal blood pressure,
thereby increasing filtration rates of
water and solutes in the kidney tubules.
•Erythropoietin –stimulates the
production of red blood cells,
Calcitriol- stimulates active transport of
dietary calcium across intestinal cell
membranes in the intestine
•Gastrin –stimulates glands to release hydrochloric acid.
•Secretin-Pancreas: stimulates release of bicarbonate-rich juice.
Liver: increases release of bile.
Stomach: reduces secretions and motility.
•Cholecystokinin-Pancreas: stimulates release of enzyme-rich juice.
Gallbladder: stimulates expulsion of stored bile.
Duodenal papilla: causes sphincter to relax, allowing bile and pancreatic juice
to enter duodenum.
•Atrial natriuretic peptide (ANP)-Kidney: inhibits sodium ion
reabsorption and renin release.
Adrenal cortex: inhibits secretion of aldosterone, thereby
decreasing blood volume and blood pressure.
•Leptin-suppresses appetite and increases energy expenditure
in the brain.
•Resistin-causes resistance of peripheral tissues to insulin.
● Essentials of human anatomy & physiology , Elaine N. Marieb , Eleventh Edition ,
chapter 9 :The endocrine System , pages 312-314 & 317-319.