ENDOCRINE SYSTEM

Endocrine system
 Endocrine glands consist of groups of secretary cells
surrounded by an extensive network of capillaries that
facilitates diffusion of hormones from the secretary cells in
to the bloodstream.
 They are commonly referred to as ductless glands because
the hormones diffuse directly into the bloodstream.
 The hormones is then carried in the bloodstream to target
tissues and organs that may be quite distant, where they
influence cellular growth and metabolism.
 A hormone is a mediator molecule that is released in one
part of the body but regulates activity of cells in other parts
of the body.

 Homeostasis of the internal environment is maintained
partly by the autonomic nervous system and partly by the
endocrine system. The autonomic nervous system is
concerned with rapid changes, while hormones of the
endocrine system are mainly involved in slower and more
precise adjustment.
The endocrine include :
 The pituitary gland
 Thyroid gland
 Parathyroid gland
 Adrenal gland
 Pineal gland
Endocrine system

 In addition several organs and tissues are not endocrine
glands but contain cells that secrete hormones. These
includes:
 Hypothalamus
 Thymus
 Pancreas
 Ovaries
 Testes
 Kidney
All endocrine glands and hormone – secreting cells
constitute the endocrine system.
The science of the structure and function of the endocrine
glands and diagnosis and treatment of disorders of the
endocrine system is called endocrinology
Endocrine system

 When a hormone arrives at its target cell, it binds
to a specific area, the receptor.
 The receptors for water soluble hormones are
situated on the cell membrane and those for lipid
soluble hormones are inside the cells.
 Basic categories of hormones
 Water soluble hormones-Amino acid based: modified
amino acids (or amines For eg: epinephrine and
norepinephrine), peptides (Insulin and growth hormone),
and proteins (Prostaglandins etc. )
 Lipid soluble hormones-Steroid hormones and thyroid
hormones
Endocrine system

 A hormone is released in response to a specific stimulus
and usually its action reverses the stimulus through a
negative feedback mechanism.
 This may be controlled either indirectly through the release
of hormones by the hypothalamus and the anterior pituitary
gland e.g steroid and thyroid hormones, or directly by blood
levels of the stimulus. E.g Insulin and glucagon.
 The effect of a positive feedback mechanism of the stimulus
and increasing release of the hormone until a particular
process is complete and the stimulus ceases e.g release of
oxytocin during labour.
Endocrine system

 Hormone Transport in the blood
Most water – soluble hormone molecules circulate in the
watery blood plasma in a free form , whereas most lipid-
soluble hormone molecules are bound to transport
proteins. The transport proteins , which are synthesized
by cells in the liver , have three functions:
1. They make lipid-soluble hormones temporarily water
soluble, thus increasing their solubility in blood.
2. They retard passage of small hormone molecule through
the filtering mechanism in the kidneys, thus slowing the
rate of hormones loss in the urine.
3. They provide a ready reserve of hormone, already present
in a the blood stream .
Endocrine system

Control of hormone secretion
When the endocrine gland is stimulated. It release hormone,
increasing the concentration of hormone in the blood. In the
absence of stimulation , the blood level of the hormone
decreases. Regulation of secretion normally prevents
overproduction and underproduction of any given hormone.
Hormone secretion is regulated by
1) Signals from the nervous system
2) Chemical changes in the blood
3) Other hormones
For eg: Nerve impulse to the adrenal medulla regulate the release of
epinephrine
 Blood Ca2+ level regulates the secretion of parathyroid
hormone
 A hormone from the anterior pituitary (ACTH) stimulates the
release of cortisol by the adrenal cortex.
Endocrine system

Pituitary gland and hypothalamus
 The pituitary gland and hypothalamus act as a unit ,
regulating the activity of most of the other endocrine
glands. So ., it is called master endocrine gland .
 The pituitary gland lies in the hypophyseal fossa of the
sphenoid bone below the hypothalamus , to which it is
attached by a stalk.
 It is the size of a pea, weighs about 500 mg and consists
of three distinct parts that originate from different types
of cells.
 The anterior pituitary is an upgrowth of glandular
epithelium from the pharynx and the posterior pituitary is
a downgrowth of nervous tissue from the brain. There is
a network of nerve fibers between the hypothalamus and
the posterior pituitary. Between these lobes there is a
thin strip of tissue called the intermediate lobe and its
function in human is not known.

Pituitary gland and hypothalamus

 The anterior pituitary secretes hormones that regulate a
wide range of bodily activities, from growth to
reproduction. Release of anterior pituitary hormones is
stimulated by releasing hormones and suppressed by
inhibiting hormones from the hypothalamus. Thus the
hypothalamus are an important link between the nervous
and endocrine system.
 Hypothalamic hormones reach the anterior pituitary
through a portal system . The heart passes from the heart
through an artery to a capillary to a vein and back to the
heart. In a portal system, blood flows from one capillary
network into a portal vein and then into a second capillary
network without passing through the heart. The name of
the portal system gives the location of the second capillary
network.
Anterior Pituitary gland

 In hypophyseal portal system , blood flows
from capillary in the hypothalamus into
portal veins that carry blood to capillaries of
the anterior pituitary. The Blood transports
releasing and inhibiting hormones secreted
by the hypothalamus. These hormones
influence secretion and release of other
hormones formed in the anterior pituitary.

 The releasing and inhibiting hormones that
stimulate and inhibit secretion of specific
anterior hormones. The whole system is
controlled by a negative feedback
mechanism. When there is a low level of a
hormone in the blood supplying the
hypothalamus , it produces the appropriate
releasing hormone that simulates release of a
trophic hormone by the anterior pituitary. This
in turn stimulates the target gland to produce
and release its hormone. As a result the blood
level of that hormone rises and inhibits the
secretion of releasing factor by hypothalamus.

Hypothalamus Anterior pituitary Target gland /
Tissues
GHRH
(Growth Hormone Releasing Hormone)
GH (Growth Hormone) Most tissues
Many organs
GHRIH
(Growth Hormone Releasing Inhibiting
Hormone
GH inhibition
TSH Inhibition
Thyroid gland
Pancreatic islets
Most Tissues
TRH
(Thyroid releasing Hormone)
TSH
(Thyroid stimulating hormone)
Thyroid gland
CRH
(Corticotrophin releasing Hormone)
ACTH
(Adrenocorticotrophic Hormone)
Adrenal cortex
PRH
(Prolactin releasing Hormone)
PRL
(Prolactin Hormone)
Breast
PIH
(Prolactin Inhibiting Hormone)
PRL inhibition Breast
LHRH / GnRH
(Luteinsing Hormone releasing Hormone)/
(Gonadotrophin releasing Hormone)
FSH, LH
( Follicle stimulating Hormone),
(Luteinsing Hormone)
Ovaries and Testes
Ovaries and Testes
Hormones of the hypothalamus, anterior pituitary and their target tissues

Growth Hormone
 This is the most abundant hormone synthesized by anterior
pituitary.
Functions
 It stimulates growth and division of most body cells specially
in bones and skeletal muscle.
 Growth hormone increases the growth rate of skeleton and
skeletal muscles during childhood and teenage years.
 In adults , growth hormone help to maintain the mass of
muscles and bones
 It promotes healing of injuries and tissue repair.
 It also regulates the metabolism in many organs for eg:
Liver, intestine and pancreas,.
 It stimulates the protein synthesis
 It promotes breakdown of fats and increases blood glucose
levels.

Growth Hormone
 Its release is stimulated by growth hormone releasing
hormone and suppressed by growth hormone release
inhibiting hormone both of which are secreted by the
hypothalamus.
 Secretion of GH is greatest at night during sleep and is also
stimulated by hypoglycemic, exercise and anxiety.
 The daily amount secreted peaks in adolescence and then
declines with age.
 Inhibition of GH secretion occurs by a negative feedback
mechanism when the blood level rises and also when
GHRIH (somatostatin) is released by the hypothalamus
GHRIH also suppresses secretion of TSH and gastro-
intestinal secretion, e.g : gastric juice , gastrin and
cholecystokinin.

 Thyroid stimulating Hormone (TSH)
 This hormone is synthesized by the anterior pituitary and its
release is stimulated by TRH ( Thyrotrophin- releasing hormone)
from the hypothalamus.
 TSH stimulates growth and activity of thyroid gland
 TSH stimulates the synthesis and secretion of the two thyroid
hormone , T3 ( triiodothyronine) and T4 (thyroxine), both are
produced by the thyroid gland.
 TRH ( Thyrotrophin- releasing hormone) from the hypothalamus
controls TSH secretion.
 Release of TRH depends on T3 and T4, which inhibit secretion of
TRH via negative feedback. When the blood level of thyroid
hormone is high , secretion of TSH is reduced and vice- versa.
 There is no thyrotrophin – inhibiting hormone.
 Release its lower in early evening and highest during the night.

 Adrenocorticotrophic Hormone ( Corticotrophin, ACTH)

 Corticotrophin releasing hormone (CRH) from the hypothalamus
promotes the synthesis and release of ACTH by the anterior
pituitary. And ACTH controls the production and secretion of
cortisol and other glucocorticoids by the cortex of the adrenal
glands.
 ACTH levels are highest at about 8AM and fall to their lower about
midnight, although high levels some times occur at midday and 6
PM.
 It is associated with the sleep pattern and adjustment to changes
takes several days, following e.g ., changing work shifts , traveling
to a different time zone.
 Secretion is also regulated by a negative feedback mechanism . It
is being suppressed when the level of ACTH and CRH is
increased.
 The factor which can stimulate secretion include low blood
glucose , physical trauma, exercise, emotional states, and fever
etc.

Prolactin
 Prolactin , together with other hormones , initiates and
maintains milk secretion by the mammary glands.
 Ejection of milk from the mammary glands depends on the
hormone oxytocin, which is released from the posterior
pituitary.
 Together milk secretion and ejection constitute lactation.
 Prolactin stimulates lactation ( milk production)
 And has a direct effect on the breasts immediately after
parturition( childbirth).
 The hypothalamus secrets both inhibitory and excitatory
hormones that regulates prolactin secretion.
 The blood level of prolactin PRH ( Prolactin releasing hormone)
and is lowered by PIH( prolactin Inhibiting Hormone) (
dopamine).

 After birth suckling stimulates prolactin secretion
and lactation. . High blood level of prolactin reduces
the chances of conception during lactation.
 During the menstruation the blood level of prolactin
decreases.
 Hyper secretion of prolactin in males cause erectile
dysfunction.
 In females hyper secretion of prolactin causes
galactorrhoea ( inappropriate lactation) and
amenorrhea .
 Prolactin secretion is related to sleep i.e it is raised
during any period of sleep, night and day.
 Emotional stress increases the prolactin production.

Gonadotrophins
After puberty two gonadotrophins ( sex hormones)
are secreted by the anterior pituitary in response
to LHRH( luteinsing hormone releasing
hormone), also known as GnRH(gonadotrophin
releasing hormone. In both males and females
these are
 FSH ( Follicle stimulating hormone)
 LH (luteinsing hormone)
 In both the sexes FSH stimulates production of
gametes ( Ova and spermatozoa).

FSH:
In females : The ovaries are targets for follicle
stimulating hormone. FSH stimulates the
secretion of estrogen. During the menstrual
cycle.
IN males: FSH stimulates the production of sperm
in testes.
GnRH from the hypothalamus stimulates the FSH
release. The release of GnRH and FSH is
suppressed by estrogen in females and by
testosterone in males through negative feedback
mechanism. There is no gonadotrophin inhibiting
hormone.

LH ( Luteinizing Hormone):
In females: It triggers ovulation. LH also
stimulate the formation of corpus luteum.
In males: LH stimulates the testes to secrete
the testosterone.
Secretion of LH is also controlled by the
GnRH.
FSH and LH both stimulates the secretion of
estrogen by ovarian cells in females.

Posterior Pituitary.
 Posterior pituitary does not synthesize hormones , it does
stores and release two hormone.
 This is formed nervous tissue and consist of nerve cells
surrounded by supporting cells called pituicytes.
 These neurons have their cell bodies in the supraoptic and
paraventricular nuclei of the hypothalamus and their axons
form a bundle known as hypothalamohypophyseal tract.
 The posterior pituitary secrets one of the two hormones
 Oxytocin
 Antidiuretic hormone.
Posterior pituitary hormones are synthesized in the nerve cell
bodies, transported along the axons and then stored in
vesicles within the axon terminals within the posterior
pituitary. Their release by exocytosis is triggered by nerve
impulses from the hypothalamus.

Oxytocin:
 During and after delivery of a baby, oxytocin affects two target
tissues : The mother’s uterus and breasts.
 During delivery , oxytocin enhances contraction of smooth
muscle cells in the wall of the uterus, after delivery , it
stimulates milk ejection.
 The function of oxytocin in males and non pregnant females is
not clear.
Milk Ejection: The process of milk ejection also involve a positive
feed back mechanism . Suckling generates sensory impulses
that are transmitted from the breasts to the hypothalamus . The
impulse trigger the release of oxytocin from the posterior
pituitary and oxytocin stimulates contraction of lactating
breasts, ejecting milk. Suckling also inhibits the release of PIH (
Prolactin Releasing Hormone), prolonging prolactin secretion
and lactation.

 Antidiuretic Hormone:
Antidiuretic hormone that decrease urine production. ADH
secretion causes the kidneys to return more water to the blood
, and decreasing the urine volume. In the absence of ADH, urine
output is increased from the normal. ADH also decreases the
water loses through sweating and cause the constriction of
arterioles, which increases blood pressure.
As the osmotic pressure rises, the secretion of ADH increases.
More water is therefore reabsorbed and the urine output is
reduced. This means that the body retains more water and the
rise in osmotic pressure is reversed. Conversely, when the
osmotic pressure of the blood is low, for example: After a large
fluid intake, secretion of ADH is reduced, less water is
reabsorbed and more urine is produced.
At high concentration , for example after severe blood loss, ADH
causes smooth muscle contraction, especially vasoconstriction
in the blood vessels of the skin and abdominal organs. This
cause raise in systemic blood pressure.

 Thyroid Gland
The butterfly shaped thyroid gland is located just inferior to
the larynx. It is composed of right and left lobes, one on
either side of the thyroid cartilage. It is highly vascular
that weighs about 25g and is surrounded by a fibrous
capsule. The lobes are joined by a narrow isthmus, lying
in front of the trachea.
Microscopic spherical sacs called thyroid follicles make up
most of the thyroid gland. The wall of each follicle
consists primarily of cells called follicular cells. Between
the follicles there are other cells found singly or in small
groups : parafollicular cells, also called C-cells, which
secrete the hormone calcitonin.
Two parathyroid gland lie against the posterior surface of
each lobe and sometimes embedded in thyroid tissue.
The follicular cells produce two hormones
 Thyroxine ( T4 or tetraiodothyronine)
 Triiodothyronine (T3)
Parafollicular cells produce hormone:
Calcitonin ( help to regulate calcium homeostasis)

Thyroxine and tri-iodothyronine:
 Iodine is essential for the formation of thyroid gland
hormones, thyroxine ( T4) and tri-
iodothyronine(T3).
 The body’s main source of iodine are seafood ,
vegetables grown in iodine-rich soil and iodinated
table salt in the diet.
 The thyroid gland selectivity takes up iodine from
the blood, a process called iodine trapping.
 The thyroid hormones are synthesized as large
precursor molecule called thyroglobulin, the major
constituent of colloid . The release of T3 and T4
into blood is regulated by TSH (thyroid stimulating
hormone) from the anterior pituitary.

When the supply of
iodine is deficient,
Excess TSH is secreted
and there is proliferation
of thyroid gland and
enlargement of the gland.
Secretion of T3 and T4
begins about the third
month of fetal life and is
increased at puberty and
in women during the
reproductive years.
Otherwise it remains,
constant throughout life.,

 Thyroid hormones enter the target cells and regulate the
expression of genes in the nucleus, i.e they increase or
decrease the synthesis of some proteins including enzymes.
They combine with specific receptor sites and enhance the
effects of other hormones. E.g- adrenaline and noradrenaline.
T3 and T4 affect most cells of the body by:
 Increasing the basal metabolic rate and heat production
 Regulating metabolism of carbohydrate , proteins and fats.
Uses
 T3 and T4 are essential for normal growth and development of
the skeleton and nervous system.
 Other uses see in table

Calcitonin:
 This hormone is secreted by the parafollicular cells
or C- cells in the thyroid gland. It acts on bone and
the kidneys to reduce the blood calcium level when it
is raised and reduces the reabsorption of calcium
from the bones and inhibits reabsorption of calcium
by the renal tubules.
 Its effect is opposite to that of parathyroid hormone,
the hormone secreted by the parathyroid glands.
 Release of calcitonin is stimulate by increase in the
blood calcium level.
 This hormone is important during childhood when
bones undergo considerable changes in size and
shape.

Parathyroid Gland
 There are four small
parathyroid glands,
embedded in the
posterior surface of
the lobe of thyroid
gland and are small
, rounded mass of
tissue called
parathyroid glands.
 Each gland has a
mass of about 40
mg.
 One superior and
one inferior
parathyroid gland
are attached to each
lateral lobe.

Function
 The parathyroid glands secrete parathyroid hormone
(PTH).
 Secretion is regulated by the blood level of calcium. When
this falls, secretion of PTH is increased and vice versa.
 To increase the blood calcium level when it is low.( The
level is increased by indirectly increasing the amount of
calcium absorbed from the small intestine and reabsorbed
from the renal tubules. If it is inadequate , then PTH
stimulates osteoclast and reabsorption of calcium from
bones.
PTH and calcitonin is needed for:
 Muscle contraction
 Blood clotting
 Nerve impulse transmission.

Adrenal Glands
 There are two adrenal glands, one situated on each
kidney. In an adult, each adrenal gland is 3-5cm in
height, 2-3cm in width, and a little less than 1 cm thick.
 The glands are composed of two parts which have
different structures and functions. The outer part is the
cortex and the inner part the medulla. The adrenal cortex
is essential to life because it produces steroid hormones.
Complete loss of adrenocortical hormones leads to
death due to dehydration and electrolyte imbalances ,
unless hormone replacement therapy begins.
 The adrenal medulla produces three catecholamine :
Norepinephrine , epinephrine and small amount of
dopamine.

Adrenal cortex
The adrenal cortex produces three steroids called
adrenocorticocoids. They are:
a) Glucocorticoids
b) Mineralocorticoids
c) Sex Hormones ( androgens)
a) Glucocorticoids
 The Glucocorticoids, regulates metabolism and resistance to
stress, include cortisol ( hydrocortisone), corticostrone and
cortisone. Out of three , cortisol is the most abundant, and
accounting for 95% of glucocorticoid activity.
 Control of glucocorticoid secretion is by negative feedback
system. Low blood levels of Glucocorticoids, mainly cortisol
stimulate hypothalamus to secrete corticotrophin- releasing
hormone (CRH)
Adrenal Glands

 CRH promotes the release of ACTH from the anterior pituitary.
Stress and ACTH flows in the blood to the adrenal cortex, where
it stimulates Glucocorticoids secretion . To a much smaller
extent, ACTH also stimulates secretion of aldosterone.
 In non-stressful conditions, secretion has marked circadian
variations. The highest level of hormones occurs between 4AM
and 8AM and the lowest, between midnight and 3AM. When the
sleeping and waking pattern is changed , it takes several days
for adjustment of the ACTH/ cortisol secretion to take place.
Glucocorticoids has the following effects:
1. Gluconeogenesis and hyperglycemia
2. LIpolysis
3. Stimulating breakdown of proteins
4. Promoting absorption of sodium and water from renal tubules.
5. Anti-inflammatory actions
6. Suppression of immune responses
7. Delayed wound healing.

Mineralocorticoids
 Aldosterone is the major mineralocorticoids. It
regulates homeostasis of two mineral ions, namely
sodium and potassium, and helps adjust blood
pressure and blood volume.
 Its functions are mainly maintenance of water and
electrolyte balance in the body.
 It stimulates reabsorption of sodium and excretion of
potassium in the urine.
 The blood potassium level regulates the amount of
aldosterone produced by adrenal cortex.
 When the potassium level rises, the secretion of
aldosterone is more.
 Renin-angiotensin system also play an important
role in release of aldosterone. (See diagram )

Sex Hormones:
In both males and females, the adrenal
cortex secrets small amount of
androgen and the quantity is so low
that their effects are insignificant.
This hormone is secreted in large
quantity after puberty.

Adrenal medulla
 The medulla is completely surrounded by the adrenal cortex. It
develops from nervous tissue in the embryo and is a part of
sympathetic division of the autonomic nervous system.
 It produce the hormones adrenaline and noradrenaline.
Adrenaline and Noradrenaline
 Noradrenaline is the postgangoilinic neurotransmitter of the
sympathetic division of the autonomic nervous system. Adrenaline
and some noradrenaline are released into the blood from the
adrenal medulla during stimulation of the sympathetic nervous
system. They together potentiate the fight and flight response by
Increasing heart rate
Increasing blood pressure
Increasing metabolic rate
Dilating the pupil
Adrenaline has a greater effect on the heart and metabolic processes
whereas noradrenaline has more influence on blood vessels.

The short term or
immediate response
is prepared for fight
and flight. In the
longer term , ACTH
from the anterior
pituitary stimulates
the release of
glucocorticoids and
mineralocorticoids
from the adrenal
cortex and a more
prolong response to
stress.

Pancreatic Islet
The pancreas is both an endocrine gland and an exocrine
gland.
Unlike the exocrine pancreas, which produces pancreatic
juices, there are no ducts .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 secrets glucagon
 β( beta) cells , which secrets insulin.
 δ ( delta) cells, which secrete somatostatin (GHRIH)
The normal blood glucose level is between 3.5 an 8mmol/litre
(63to 144mg/100ml). Blood glucose levels are controlled
mainly by the opposing actions of insulin and glucagon:
 Glucagon increases blood glucose levels
 Insulin reduces blood glucose levels.

Insulin:
Insulin is a polypeptide consisting of about 50 amino acids.
Glucagon raises blood glucose level, insulin lowers it.
Somatostatin inhibits both insulin and glucagon release .

 Regulation of glucagon and insulin secretion

Insulin
 Insulin is a polypeptide consisting of about 50 amino acids. The
main functions of insulin is to lower raised blood nutrient
levels, especially glucose but also amino acids and fatty acids.
When these nutrients are in excess , insulin promotes their
storage by:
 Acting on the cell membrane and stimulating uptake and use of
glucose by muscle and connective tissue cells.
 Increasing conversion of glucose to glycogen, especially in the
liver and skeletal muscle.
 Accelerating uptake of amino acids by cells, and the synthesis
of protein
 Promoting synthesis of fatty acids and storage of fat in adipose
tissue.
 Decreasing glycogenolysis
 Preventing the breakdown of protein and fat and help in
gluconeogenesis.

Secretion is stimulated by :
 Increased blood glucose levels
 Parasympathetic stimulation
 Raised blood amino acids and fatty acid level
 Gastrointestinal hormones ( gastrin, secretin etc.)
Secretion is decreased by:
 Sympathetic stimulation
 Glucagon
 Adrenaline
 Cortisol
 Somatostatin
Insulin

Glucagon
 The glucagon increased blood glucose level by
stimulating:
 Conversion of glycogen to glucose in the liver
and skeletal muscle
 Gluconeogenesis
Secretion is stimulated by:
 Low blood glucose level
 Exercise
Secretion is decreased by:
 Somatostatin
 Insulin

Somatostatin
 This hormone inhibit the secretion of both
insulin and glucagon in addition to
inhibiting the secretion of GH from the
anterior pituitary.

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
 The pineal Gland is about 10mm long, is reddish brown in colour
and is surrounded by a capsule.
Melatonin
 This is a hormone secreted by the pineal gland.
 Secretion is controlled by daylight and level fluctuate during
each 24 hours period, being highest at night and lower around
midday.
 Secretion is influenced by the number of daylight hours i.e
seasonal variations.
Its function are not known but associated with
 coordination of circadian rhythm
 Inhibition of growth and development of the sex organ before
puberty, possibly by preventing synthesis and releases of
gonadotrophins.

Thymus gland
 The thymus gland is located behind the
sternum between the lungs.
 The hormone secreted by this gland is
thymosin and which is required for the
development of T- lymphocyte for cell
mediate immunity.

Some Local Hormones secreted by
endocrine gland
Endocrine gland secrets substances that act locally .
Some are
 Histamine: This hormone is synthesized by the
mast cells in the tissues and the basophils in blood.
It plays a role in inflammation. It causes contraction
of bronchi, GIT and stimulates the secretion of
gastric juice.
 Serotonin: This is present in platelets, in the brain
and in the intestinal wall. It causes intestinal
secretion and contraction of smooth muscle.

 Prostaglandins: These are lipid substances and found in most
tissues that act as a local hormone and the effects are:
 The inflammatory response
 Potentiating pain
 Fever
 Regulating blood pressure
 Blood clotting
 Uterine contraction during labour.
Some other prostaglandins are leukotrienes and thromboxanes
(platelet aggregator).
Gastrointestinal Hormones: Some hormone such as gastrin ,
secertin and cholecystokinin influence the secretion of digestive
juices and their functions.
Some Local Hormones secreted by
endocrine gland

ENDOCRINE SYSTEM

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