ENDOCRINE SYSTEM
The system which studies about the structure and functions of endocrine
glands is called endocrine system.
Special kinds of secretory cells and tissue in our body are called glands.
On the basis of presence or absence of ducts glands can be classified as
a. Exocrine glands
b. Endocrine glands
FUNCTION OF HORMONES
Hormones are specialized substances that coordinate the activities of
specific cells in certain areas of the body.
ENDOCRINE SYSTEM
DIFFERENCE BETWEEN EXOCRINE AND ENDOCRINE GLANDS
EXOCRINE GLANDS ENDOCRINE GLANDS
Glands with ducts Glands without ducts
Exocrine glands produce enzymes Endocrine glands produce hormones
Secretions of exocrine Secretions of endocrine gland[hormones]
gland[enzymes] act locally act away from the site of production
Minimum role in maintaining Major role in maintaining homeostasis
homeostasis
Examples:-salivary gland, gastric Examples:- pituitary gland, thyroid gland,
glands, intestinal glands parathyroid gland
ENDOCRINE SYSTEM
and locate chief endocrine glands
Name Locations
a Pituitary and lies in cranial cavity.
hypothalamus
b Thyroid Each lobe extends from the middle of the anterior part of neck at the
level of C5,C6,C7&T1 vertebra
c Parathyroid Parathyroid gland are small glands of the endocrine system which are
located in the neck behind the thyroid.
d Adrenal Lies on the upper pole of kidney.
e Pancreas Lie more or less transversely across the posterior abdominal wall below
and behind the stomach
f Thymus The thymus gland lies between the sternum and the two large blood
vessels above the heart.
g Ovary Lies in ovarian fossa in pelvic cavity
h Testis Lies in scrotum
j Pineal located above the hypothalamus.
ENDOCRINE SYSTEM
The Hypothalamus
The hypothalamus is located below the thalamus and above the pituitary gland and brain
stem. It is about the size of an almond.
Hypothalmus is actually the part of central nervous system.
The hypothalamus is highly involved in pituitary gland function. When it receives a signal
from the nervous system, the hypothalamus secretes substances known as
neurohormones that start and stop the secretion of pituitary hormones.
FUNCTIONS OF HYPOTHALMUS ( @ SEAT)
Hypothalmus controls
a. sleep wake pattern and sexual activities
b. Endocrine functions and emotions
c. Autonomic function and appetite
d. Thirst and thermoregulation
ENDOCRINE SYSTEM
HORMONES SECRETED BY HYPOTHALAMUS FUNCTIONS
Growth hormone releasing hormone(GHRH) Stimulates pituitary gland to secrete growth hormone.
Growth hormone release inhibiting Inhibits the production of growth hormone from pituitary
hormone(GHRIH) gland.
Thyrotrophin releasing hormone(TRH) Stimulates pituitary gland to produce thyroid stimulating
hormone.
Corticotrophin releasing hormone(CRH) Stimulates pituitary gland to produce ACTCH hormone.
Prolactin releasing hormone(PRH) Stimulates pituitary gland to produce Prolactin
Prolactin inhibiting hormone(PIH) Inhibits the production of prolactin by pituitary gland
Gonadotrophin releasing hormone(GRH) Stimulates pituitary gland to produce follicular stimulating
and leuteinising hormone
Pituitary Gland
ENDOCRINE SYSTEM
The hormones of the pituitary gland help regulate the functions of other endocrine
glands.
The pituitary gland has two parts—the anterior lobe and posterior lobe—that have two
very separate functions.
The hypothalamus sends signals to the pituitary to release or inhibit pituitary hormone
production.
ENDOCRINE SYSTEM
HORMONES PRODUCED BY ANTERIOR FUNCTIONS
PITUITARY GLAND
Growth hormone(GH) Regulates metabolism, promotes tissue growth specially of bones
and muscle.
Thyroid stimulating hormone(TSH) Stimulates growth and activity of thyroid gland and secretion of
T4 &T3.
Adrenocorticotrophic hormone(ACTCH) Stimulates the adrenal cortex to produce glucocorticoids
Prolactin(PRL) Stimulates milk production in breast
Follicle stimulating hormone(FSH) Stimulates production of sperm in testis and stimulates secretion
of oestrogen by ovary, maturation of ovarian follicle
Luteinising hormone(LH) Stimulates secretion of testosterone by testis and stimulates
secretion of progesterone by corpus luteum.
HORMONES PRODUCED BY FUNCTIONS
HYPOTHALAMUS AND STORED
INPOSTERIOR PITUITARY GLAND
Oxytocin Contraction of uterine muscle
Ejection of milk from breast
Antidiuretic hormone(ADH) Retention of water in kidney tubules
ENDOCRINE SYSTEM
ENDOCRINE SYSTEM
Thyroid gland
the thyroid is a butterfly-shaped gland located in front of the windpipe (called the
trachea) and just below the larynx or Adam’s apple in the neck.
It is comprised of two halves, known as lobes, which are attached by a band of thyroid
tissue called the isthmus.
The thyroid gland is situated in the neck in front of the larynx and trachea at the level of
the 5th, 6th and 7th cervical and 1st thoracic vertebrae.
HORMONES SECRETED BY THYROID GLAND FUNCTIONS
a. Tri-iodothyronine(T3) Increase basal metabolic rate.
b. Thyroxine(T4) Bone and brain growth and maturation
Protein anabolism & Fat metabolism
Glycogenesis
Glucose utilization
Calcitonin Decrease blood calcium level by -
Deposition of calcium in bone
Decreasing of calcium reabsorption from kidney
ENDOCRINE SYSTEM
ENDOCRINE SYSTEM
Parathyroid glands
There are four small parathyroid glands, two embedded in the posterior surface of each
lobe of the thyroid gland.
The parathyroid glands secrete parathyroid hormone (PTH, parathormone).
Secretion is regulated by blood calcium levels.
When they fall, secretion of PTH is increased and vice versa.
The main function of PTH is to increase the blood calcium level when it is low.
Parathormone and calcitonin from the thyroid gland act in a complementary manner to
maintain blood calcium levels within the normal range.
ENDOCRINE SYSTEM
ENDOCRINE SYSTEM
ENDOCRINE SYSTEM
HORMONES SECRETED BY FUNCTIONS
ADRENAL CORTEX
Glucocorticoids Increases blood glucose level
it increases the breakdown of protein.
Breakdown of fat into fatty acid and glycerol.
Anti-inflammatory effect.
Blocks the inflammatory response tp allergic reaction.
Decreased immunity of body
Delays wound healing.
Mineralocorticoids It maintains the electrolyte balance in ECF by
It increases the reabsorption of Na and excretion of K from
kidney.
Na reabsorption of Na is also accompanied by retention of
water from kidney tubules.
ENDOCRINE SYSTEM
HORMONES SECRETED BY FUNCTIONS
ADRENAL MEDULLA
Adrenaline Response to stress.
Noradrenaline Increasing heart rate.
Increasing blood pressure.
increase metabolic rate.
dilating the pupil.
ENDOCRINE SYSTEM
ENDOCRINE SYSTEM
Pancreatic islets
ENDOCRINE SYSTEM
The cells that make up the pancreatic islets (islets of Langerhans) are found in
clusters irregularly distributed throughout the substance of the pancreas.
Unlike the exocrine pancreas, which produces pancreatic juice there are no ducts
leading from the clusters of islet cells.
Pancreatic hormones are secreted directly into the bloodstream and circulate
throughout the body.
There are three main types of cells in the pancreatic islets:
• α (alpha) cells, which secrete glucagon
• β (beta) cells, which are the most numerous, secrete insulin
• δ (delta) cells, which secrete somatostatin (GHRIH).
• glucagon increases blood glucose levels
• insulin reduces blood glucose levels.
ENDOCRINE SYSTEM
Pineal gland
The pineal gland is a small body attached to the roof of the third ventricle
and is connected to it by a short stalk containing nerves, many of which
terminate in the hypothalamus.
The gland tends to atrophy after puberty and may become calcified in later
life.
Melatonin is the main hormone secreted by the pineal gland.
Functions of melatonin is believed to be associated with:
coordination of the circadian and diurnal rhythms of many tissues, possibly
by influencing the hypothalamus
inhibition of growth and development of the sex organs before puberty,
ENDOCRINE SYSTEM
Thymus gland:
Lobules containing cortex and medulla
Cortex – densly populated by lymphocytes
Medulla – thin populated by lymphocytes and contains numerous Hassall’s
corpuscles
Thymosin: This is the hormone secreted by the thymus gland and is involved
in the development of T-lymphocytes for cell-mediated immunity.
ENDOCRINE SYSTEM
Testis produce testosterone. The functions of testosterone are
Promotes maturation of sperm.
Initiates development of the secondary sex characteristics:
ENDOCRINE SYSTEM
Local hormones
A number of body tissues not normally described as endocrine glands
secrete substances that act in tissues nearby (locally). Some of these are
described below.
A. Histamine:
This is synthesised and stored by mast cells in the tissues and basophils in
blood.
It is released as part of the inflammatory response, increasing capillary
permeability and causing vasodilation.
B. Serotonin (5-hydroxytryptamine, 5-HT):
This is present in platelets, in the brain and in the intestinal wall.
It causes intestinal secretion and contraction of smooth muscle and its role
in haemostasis (blood clotting).
ENDOCRINE SYSTEM
C. Prostaglandins (PGs):
They act nearby and have potent and wide-ranging physiological effects in:
the inflammatory response, potentiating pain, fever, regulating blood
pressure, blood clotting &uterine contractions during labour.
Other chemically similar compounds include leukotrienes, which are
involved in inflammatory responses, and thromboxanes, e.g. thromboxane
A2, which is a potent aggregator of platelets. All of these active substances
are found in only small amounts, as they are rapidly degraded.
Gastrointestinal hormones
Several local hormones, including gastrin, secretin and cholecystokinin (CCK),
influence the secretion of digestive juices
