Endocrine system Unit- 13

INTRODUCTION
 The endocrine system refers to the collection of glands of an organism that secrete hormones directly into
the circulatory system to be carried towards distant target organs.
 The endocrine glands act as ductless glands(any glands of endocrine system that secrete hormones directly
into the circulatory system) which interacts with nervous system for regulation and coordination of various
body activities.
 Usually one gland secretes more than one hormone.
 Hormones act as chemical messengers that are released into the blood stream to act on an organ in another
part of the body.
 Although hormones reach all parts of the body, only target cells with compatible receptors are equipped to
respond. Over 50 hormones have been identified in humans and other vertebrates.
 Hormone secretion are influenced by external stimuli, internal rhythmus and usually kept a normal level by
negative feedback system involving other glands and hormones.
 Hormones control or regulate many biological processes and are often produced in exceptionally low amounts
within the body.
 Examples of such processes include:
 Blood sugar control (insulin);
 Differentiation, growth, and function of reproductive organs (testosterone (T) and estradiol); and
 Body growth and energy production (growth hormone and thyroid hormone).
Classification of Hormones:-
a. Depending upon the composition - It is divided into three types:-
a. Amine:- Derived from amino acids tyrosine e.g Thyroid hormone, Catecholamine's, Dopamine
b. Peptide:- Derived from polymers of different amino acids e.g pancretic hormones, pituitary hormones ,
parathyroid hormone, calcitonin.
c. Steroid(fat soluble organic compound):- Derived from cholesterol e.g Mineralocorticoids, glucocorticoids,
Sex hormones.
B. Depending upon the site of production :- Hormones are of two types.
a. Paracrine hormone:-The hormone acts locally by diffusion from its source of target cells in the
neighborhood. Hormone produced from one type of cell acts on adjacent cells. E.g Gastrin hormone
produced by G cells acts on parietal cells.
b. Autocrine hormone :- The hormone act on same the same cell that produced it.(Hormone produced from
one cell acts on the same cell). E.g platelet activating factors from vascular endothelium.

The major endocrine glands are:-

1) Pituitary gland 6) Testes in the male
2) Thyroid gland 7) Pancreas
3) Parathyroid gland 8) Pineal gland
4) Adrenal glands 9) Thymus gland
5) Ovaries glands in female

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 There are two great coordinating system s in our body:-
a. Nervous system and

b. Endocrine system
Cerebral cortex

Hypothalam us

Posterior
pituitary ANS
Anterior pituitary

Other endocrine
glan ds

Target t issue

Hypothalamus(Biological clock)
It is not gland but is a part of nervous system.
It is included in endocrine system because its hormone nervous signal control the secretions from the pituitary
glands.
Anterior pituitary is controlled by “hormone releasing hormones” from the hypothalamus via the hypothalamic
hypophyseal portal vessels.
The posterior pituitary hormones are actually synthesized in hypothalamus and their release is controlled by
nervous signal from hypothalamus.
It synthesis following releasing hormones.
 Thyrotropin-releasing hormone (TRH)  Dopamine (Prolactin-inhibiting hormone)
 Corticotropin-releasing hormone (CRH or PIH
CRF)  Prolactin-releasing hormone
 Growth hormone-releasing hormone  Vasopressin (antidiuretic hormone)ADH
(GHRH)  Oxytocin
 Gonadotropin-releasing hormone (GnRH)

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Hypot halamus

Releasing horm ones

Adenohypophysis of pituitary glands

Trophic hormones to target glands

Hormone secretion by target glands

Raised blood level of target glands hormones

Utilization of hormones

Lowered blood level

D IAGRAM OF THE NEGATIVE FEEDBACK REGULATION OF THE SECRETION OF
HORMONES BY THE ANTERIOR LOBE OF THE PITUITARY GLANDS

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1) Pituitary gland
The pituitary gland (or hypophysis) is an endocrine gland about the size of a pea and weighing 0.5 grams
(500mg) and size 12 × 8 mm² in humans.
It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity
(sella turcica) covered by a dural fold (diaphragma sellae). The pituitary is functionally connected to the
hypothalamus by the median eminence via a small tube called the infundibular stem or pituitary stalk.
It is also known as master glands because it produces a number of hormones , which control the secretion of
many other endocrine glands of the body.
Pituitary glands has 3 distinct parts:-
1. Anterior lobe(adenohypophysis)
2. Intermediate lobe
3. Posterior pituitary lobe (neurohypophysis)

Anterior lobe(adenohypophysis)
 Growth hormone:- Release under the influence of hypothalamic growth hormone releasing hormone (GHRH)
- Stimulates growth and cell reproduction.
 Thyroid-stimulating hormone (thyrotropin)(TSH):- Release under the influence of hypothalamic thyrotropin
releasing hormone(TRH) - Stimulates thyroxine (T4) and triiodothyronine (T3) synthesis and release from
thyroid gland, Stimulates iodine absorption by thyroid gland.
 Adrenocorticotropic hormone(corticotropin)ACTH:- Release under the influence of hypothalamic
corticotropin releasing hormone(CRH):- Stimulates corticosteroid (glucocorticoid and mineralcorticoid) and
androgen synthesis and release from adrenocortical cells.
 Prolactin(PRL):- Stimulates milk synthesis and release from mammary glands, Mediates sexual gratification
 Luteinizing hormone(LH):-
 In females: Stimulates ovulation , Stimulates formation of corpus luteum
In males: Stimulates testosterone synthesis from Leydig cells (interstitial cells)
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 Follicle-stimulating hormone(FSH):- Release under the influence of Gonadotropin releasing hormone.
 In females: Stimulates maturation of ovarian follicles in ovary
In males: Stimulates maturation of semiferous tubules, Stimulates spermatogenesis, Stimulates production
of androgen-binding protein from Sertoli cells of the testes.
Intermediate lobe
The intermediate lobe is prominent in the embryonic period of human life.
It synthesis and secretes melanocytes- stimulating hormones (MSH) that helps in growth and development of
melanocytes which gives the colour to skin.
It is formed in Rakthe’s pouch
Posterior pituitary lobe (neurohypophysis)
It develops from neuro- ectoderm.
It has neural connection with the hypothalamus.
a. Vasopressin(antidiuretic hormone)ADH :- Increases water permeability in the distal convoluted tubule and
collecting duct of nephrons, thus promoting water reabsorption and increasing blood volume. And Blood
pressure is maintain.
When concentration of ADH is very high in blood ,the ADH causes arteriolar smooth muscle contraction
tending to vasoconstriction and elevation of arterial blood pressure. Threfore ADH is also called vasopressin.
b. Oxytocin:- In females: uterine contraction during birthing, It causes ejection of milk(lactation )
Blood supply:- The pituiary gland is suplied by superior and inferior hypophyseal artery, which is branches of
internal carotid artery.
Venous drainage:- Short veins emerge on the surface of the gland and drain into neighboring dural venous
sinuses.

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1) Thyroid gland
Thyroid gland is situated in the lower part of the front and sides of the neck.
Location :- On anterior aspect of the neck from the middle of anterior surface of the thyroid cartilage (C5) of the
larynx to 6th tracheal ring (T1)
It has a fibrous capsule and is highly vascular gland.
It has two lobes joined by isthmus (Butterfly shape)
Size of each 5 × 3 ×cm 2
Total weight :- 25 gm

Thyroid gland has two part

a. Folicles b. Parafollicular cells(C cells)
It is functional unit of the thyroid glands. It is present between the follicles.
It has single layer of follicular cells(Cuboidal cells) It secrete calcitonin.
Follicles secrete and store colloid (which is a thick Function:- Regulation of blood calcium level.
sticky substance containing thyroglobulin and Decrsese calcium and phosphate absorption from
iodine), kidney.
It secrete thyroid hormone. Decrease release of calcium and phosphate from
bone by decreasing osteoclastic activity.
There are two types of thyroid hormone.
i. Tri-iodo –thyronine(T3) – 10%
ii. Tetra iodo thyronine (T4) or thyroxine – (90%)

Functions of thyroid hormones are:-

 Stimulates oxygen consumption and energy consumption, thereby increasing the basal metabolic rate
 Stimulate protein breakdown in tissue.
 Stimulate absorption of glucose from intestine so blood glucose level increase.
 Increase cardiac output by combination action of thyroid and catecholamine on the heart.
 Thyroid hormone is required for cerebral cortex and basal ganglia development.
 Effect on cholesterol metabolism , decreasing cholesterol level in blood
 Enhance the normal growth by potentialing the GH secretion.
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 T4 cause loss of calcium via urine.
Calcitonine:- It reduces the reabsorption of calcium from bone and inhibits reabsorption of  Ca2+ by the renal
tubules.
Arterial blood supply:- Superior thyroid artery and branch of external carotid artery and inferior thyroid artery,
branch of the subclavian artery.
Venous drainage:- Superior , middle and inferior thyroid veins. Superior and middle veins drain into internal
jugular vein and inferior thyroid vein drains into left brachiocephalic vein.
Nerve supply:- Superior , middle and inferior sympathetic ganglia.

2) Parathyroid gland
There are usually four parathyroid glands
The glands are named according to their position as the superior and inferior parathyriod glands.
Size :- 6×4 ×2 mm² (Size of apple seed )
Weight :- about 30 mg in men and 35 mg in women.
There are small glands embedded in the posterior surface of the thyroid gland (2 in each lobe) and surrounded by
fine connective tissue capsule.
It has two types of cells:
Chief cells :- it secrete parathyriod hormone (PTH)/ parathormone.
Oxyphill cells:- It is develop stage of chief cells.
- Regulation of PTH is by blood calcium level(Decreasing Ca+ causes increase secretion of PTH and vice versa)
Arterial supply:- Internal thoracic and inferior thyroid areteries
Venous drainage:- Left branchio- cephalic, internal thoracic and inferior thyroid vein.
Nerve supply:- sympathetic trunks.

Function
1. PTH causes rise of ionized fraction of serum calcium. This is done by:-
Increasing rate of reabsorption of bone.
Reducing the renal clearance or excretion of calcium and
Increasing the efficiency of calcium absorption from intestine by promoting the synthesis of calcitriol.
2. PTH increases renal phosphate excretion so phosphate level in blood decreases.

3) Adrenal glands/ Suprarenal gland

There is a pair of adrenal or superior gland. One adrenal gland is situated on the upper pole of each kidney,
behind the peritoneum and is enclosed within the renal fascia.
Weight :- 5gm
Size:- 5× 3× 1 cm
Each glands has outer cortex secreting steroids hormones , called adrenocorticosteroid or cortocoids and inner
medulla secreting catecholamine.

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Low blood pressure

Decrease renal blood flow

Renin secretion by kidney

Angiotensinogen from liver under influence of rennin

Converts
Angiotensin I
Under the influence of angiotensin
converting enzyme in lungs
Angiotensin II Vasocnstriction increase BP
Stimulates
Adrenal cortex

To secrete aldosterone

Increase reabsorption of sodium & water into blood from kidney tubules & excretion of potassium
(To maintain electrochemical balance)

Rises blood sodium & volume of extracellular fluid

Increase blood volume & blood pressure

Flow chart showing rennin Angiotensin – aldosterone system

Adrenal cortex
Adrenal cortex produces 3 types of hormones:-
Glucocorticoids
Mineralocorticoids
Androgens

Glucocorticoids:-
 Its secretion is increase mainly by sterss, ACTH, head/ cold , surgery, Trauma or infections.
 It helpa in regulation of metabolism of glucose and immune system suppression.
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 It maintain blood glucose level by gluconeogenesis by decreasing peripheral utilization of glucose by
deposition of glycogen in liver.
Catabolism of protein for gluconeogenesis.
Lipolysis in adipose tissue.
 It inhibits ACTH secretion.
 Maintain normal behaviour.
 Also helps in mineral metabolism – promotion of sodium and water reabsorption from renal tubule and
excretion of potassium from renal tubule.
 It inhibits all inflamatory responses and delay wound healing & suppresses manifestations of allergic from
tissue.
 It increase RBC , neutrophils & platelets and decreasing lymphocytes ,eosinophils & basophils.
 It stimulates secretion of HCL so leading to peptic ulcer.
Mineralocorticoids
 It helps in regulation of blood pressure and electrolyte balance by renin – angiotensin – aldosterone
system.
 Mineralocorticoids are aldosterone , fludrocortisone and desoxycorticosterone acetate (DOCA).
Androgens
 The Androgens are the hormones that exert masculinizing(Give a masculine apperence) effects and they
promotes protein anabolism and growth.
Secretion of adrenal androgen is controlled by ACTH & causes same suppression of feminine characters in
female & causes appearance of acne vulgaris & sexual hair.
Excess of these steroids , they can cause hirsutism.

Adrenal medulla
Medulla is completely surrounded by the cortex.
Secretion of adrenal medulla called medullary hormones is very closed to sympathetic system. It secrete
hormones called adrenaline and noradrenalin(Catacholamines) which are the neurotransmiters in sympathetic
nervous system.
It is responsible for “Fight and flight” response.
It is the part of the sympathetic division of the ANS.
The main function of the nor adrenalin is maintenance of blood pressure by causing general vasoconstriction :
except of the coronory arteries.
Adrenaline affects the nervous system , which controls function such as heart rate, dilatation of the pupils &
secretion of sweat & saliva.
Function of adrenaline and aoradrenaline:-
 They increase heart and force of cardic contraction.
 Constrict blood vessels of skin.
 Dilated blood vessels of muscles , Brain and , heart
 Dilate bronchi (Bronchodilator , Not noradrenalin)
 Pupils dilatation.
 Gut relaxation (slowing down the peristalsis in the GI tract),

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 Inhibits micturation by relaxing detrusor muscle and constricting trigone of bladder.
 Contraction of non pregnant uterus and Relaxation of pregnant uterus
 Increasing the metabolic state Hyperglycaemia, Calorigenesis and hyperkalemia.
 Increase the activity of the sweat glands and contraction of the skin muscles causing “Goose flesh ”
 Reduction in the secretion of saliva and other digestive juices.

4) Ovaries glands in female

Ovaries is ovum producing female reproductive organ found in pairs. Each ovaries is whitish in colour and
located alongside the lateral wall of uetrus called ovarian fossa. The main function of ovaries is gamate
production.
Ovaries secrete estrogen and progesterone
Estrogen :- Estrogen is collective name for a group of steroid compounds (Osteradial, oestriol, oestrone)
Function:-
 Developes secondary sexual character in female.
 Feminine fat deposition in breast , hip and thigh.
 Voice change
 Shyness
 Development and maturity of female genitalial organs.
 Maintenance of vaginal flora.
 Regulation of endometrium after menstruation(pre-ovulation).
 Increase watery cervical secretion (For easy sperm penetration).
 Increase fallopin tube motility, Blood coagubility, bone formation , bone reabsorption.
Progesterone :- It affects only those tissue which have already been influenced by estrogen.
Function:-
 It helps in thickening of endometrium .
 Bring about decidual changes in endometrium after pregnancy occurs.
 Decrease sensitivity of endometrium to oxytocin.
 Converts the watery cervical secretion induced by estrogen to viscid, scanty and cellular secretion which
is hostile to sperm penetration.
 Causes proliferation of acini in mammary glands & prepare breast for lactation.
 Leads to slight rise in temperature (0.5 c) when progesterone is at high level.
 Inhibits growth hormones secretion.
 Prolonged use causes impairs glucose intolerance.
 High circulating concentration of progesterone leads to sedative effects.

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Different between estrogen and progesterone

Estrogen progesterone

It causes proliferative changes of menstrual phase in It causes secretory changes of menstrual phases in the
the endometrium. endometrium.
Induces watery secretion in the cervix favorable for It converts the watery secretion into viscid, scanty
sperm penetration and cellular , hostile to sperm penetration.
It causes secondary sexual changes It causes decidual changes, breast and uterine
(pubertal changes) changes for pregnancy
It sensitizes the uterus to oxytocin and ripens the It decreases sensitivity of the endometrium to
cervix. oxytocin

5) Testes in the male

Testes are the male gonads one on each side lying in the scrotum being suspended by spermatic cords.
It secrete testosterone hormone.
Function:-
 It helps in spermatogenesis(i.e production of sperm)
 LH inhibition.
 Development of epididymis, vas deferens, seminal vesicles.
 It helps skeletal and muscular growth.
 Formation of scorum , penis, male urethra.
 Male pubertal changes, sexual maturity, male behaviour.

6) Pancreas(Islets of Langerhans)
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Islets of Langerhans: Known as the insulin-producing tissue, the islets of Langerhansdo more than that. They
are groups of specialized cells in the pancreas that make and secrete hormones.
The pancreas is a glandular organ in the digestive system and endocrine system of vertebrates. In humans, it is
located in the abdominal cavity behind the stomach.
It is an endocrine gland producing several important  hormones including:-
 Alpha (α) cells secrete glucagons
 Betta (β) cells secrete  insulin
 Delta (δ ) cell secrete somatostatin and 
 F cell secrete pancreatic polypeptide
Function of glucagons
It tends to increase the blood glucose level.
Stimulates liver to breakdown glycogen to be released in blood as glucose.(Glycogenolysis)
Activates glyconeogenesis – Conversion of amino acid into glucose.Breakdown stored fat into fatty acids for use
as fuel by cells (lypolysis)

Function insulin
Insuline reduces blood glucose level.
It converts glucose to glycogen in liver for storage.
Increase lipid (Fatty acids) synthesis.
Decrease release of glucogenic amino acids.
Increase protein synthesis & decrease protein catabolism.
Decrease glucose output from the liver.
Function of somatostatin
It inhibits secretion of several hormones like growth hormones , thyroid stimulating hormones, cholecystokinin &
insulin.
It inhibits rapid reproduction of normal & tumours cells.

Function of pancreatic polypeptide

The function of PP is to self-regulate pancreatic secretion activities (endocrine and exocrine); it also has effects
on hepatic glycogen levels and gastrointestinal secretions.
Its secretion in humans is increased after a protein meal, fasting, exercise, and acute hypoglycemia and is
decreased bysomatostatin and intravenous glucose.
Plasma PP has been shown to be reduced in conditions associated with increased food intake and elevated
in anorexia nervosa.
Artery :- Inferior pancreaticoduodenal artery,  anterior superior pancreaticoduodenal artery, posterior superior
pancreaticoduodenal artery, splenic artery
Vein:- Pancreaticoduodenal veins, pancreatic veins
Nerve:- Pancreatic plexus, celiac ganglia , vagus nerve
Lymph:- Splenic lymph nodes,  celiac lymph nodes and superior mesenteric lymph nodes

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7) Pineal gland
It is also known as the pineal body.
The pineal glands is a small glands situated under
the brain behind the third ventricles.
It is approximately 10mm in length . It is connected
to the brain by a short stalk.
There are nerve fibers in the stalk, but they
apparently do not reach the gland.
In young and infant, the pineal glands is large.
It produces melatonin, which affects the modulation
of sleep patterns.
They also inhibits the onset of puberty in human.
The glands tends to atrophy after puberty and may
become calcifies in later life.

8) Thymus gland
Thymus gland is located behind the sternum and
between lungs & is active until puberty. After
puberty thymus starts to slowly shrink & become
replased by fat.
Thymosin is secreted by the thymus gland, and its
mainly important because it stimulates the
development of T lymphocytes. (T lymphocytes,
also known as killer T blood cells,
function in the immune system to recognize foreign antigens on the surface of invading cells.

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LOCAL HORMONES
A number of body tissue not normally describe as endocrine glands secrete substances that act locally.
The term local hormones usually means the following chemical are secreted by the cells not in glands E.g
Histamine, 5HT, Bradykinin, Prostaglandin etc
Heart:-
 It secrete Atrial – natriuretic factors in Small intestine:-
response to hypervolaemia.  Gastrin
 It increase Na+ excretion through kidney and  Secretin
inhibits further secretion of ADH (Maintain  Cholecystokinin
fluid volume in the body).  Enterokinin
Kidney:-  Vasoactive intestinal peptide (VIP)
 Erythropoietin Placenta
 Renin  It secrete estrogen. Progesterone, Human
 Calcitriol(Vitamin D3) chorionic gonadotropin hormone (HCG)
 Human placental lactogen(HPL)
Histamine:- It is synthesized by mast cells in tissues and basophils in blood

Function:-
It increase capillary permibility and dilatation of capillaries.
Cause contraction of smooth muscles of bronchi and alimentary tract.
Stimulates the secretion of gastric juice.
It is also related to the pain and itching sensation.

Serotonin(5 – hydroxy - tryptamine):- It is present in platelates , brain and intestinal wall

Function:-
 Haemostasis  Vasoconstriction
 Contraction of smooth muscle  Also act as neurotransmitter in the CNS.
 Intestional secretion
Bradykinin:- It is powerful vasodilator. So it may cause local vasodilator and emigration of leucocytes during
inflammation .
It is also one of the pain producing substance.
Eicosanoids:- Prostaglandins, Thromboxanes, prostacycline, Lipoxin and leukotroenes are collectively called
Eicosanoids.
Prostaglandins:-They act on blood vessels to cause increase cellular permeability, Vasodilatation and broncho-
dilatation and also inhibits inflamatory cell function.
Thromboxanes:-It is vasoconstrictor and bronchoconstrictor and enhance inflammatory cells function by causing
platelet aggregation.
Prostacycline:- It is synthesized by endothelial and smooth muscles cells in the wall of the blood vessels . It
induces vasodilatation broncho-constriction and inhibits inflammatory cells function by acting as anti-
aggregating agent for platelets.

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Leukotroenes:- they cause broncho constriction, increase capillary permeability , vasoconstriction and attact
neutrophils and eosinophils to the inflammatory site.

Question
o Define endocrine glands and list out the hormone release from these glands with its function.
o Name the hormone produced by the pituitary glands and explain the function of them.
o Name the hormone produced by the thyroid glands and explain the function of them.
o Name the hormone produced by parathyroid gland and explain the function of them.
o Name the hormone produced by the female ovaries glands and explain the function of them.
o Name the hormone produced by the male testes glands and explain the function of them.
o Name the hormone produced by the pineal gland and explain the function of them.
o Name the hormone produced by the thymus glands and explain the function of them.
o Name the hormone produced by the cortex and medulla of the adrenal glands and explain the function of
them.
o Name the hormone produced by pancreas and explain the function of them.
o Define local hormone and write short notes about local hormone.

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