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ENDOCRINE GLANDS
1
...
It consists of two lobes connected by a narrow
band called isthmus
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Hormones of Thyroid Gland:
Cells lining the thyroid follicles secrete two hormones:


Thyroxine/ tetraiodothyronine (T4)



Triiodothyronine (T3)

Both are iodinated tyrosine derivatives
...
The main functions of thyroid
hormones are:


Growth - Thyroid hormones are essential for normal
growth and maturation of most of the tissues of the
body
...




Cardiovascular System - Thyroid hormone increase heart rate and cardiac output
...




Skeletal System - Optimal thyroxine levels are necessary for efficient muscle contraction
...




Reproductive System - The normal functioning of reproductive system requires the hormone
thyroxine at an optimal concentration
...
It is characterized by:
 Stunted growth, mental retardation, low metabolic rate, low body temperature & low heart rate
...
It is also called gull’s disease
...

Simple goitre: It occurs in both children and adults due to the deficiency of iodine
...
Administration of iodine can prevent simple
goitre
...
It is characterized by:
 Bulged eye balls, high metabolic rate, high pulse rate & weight loss
Biosynthesis of Thyroid Hormones:
Thyroid hormones are synthesized by the follicular cells of the thyroid lobes by iodination of aminoacid
tyrosine
...
Thyroid gland has a great avidity for the
iodides in blood
...
Iodide Trapping: The follicular cells take up Iodides from plasma by active transport mechanism
and concentrates the Iodide several folds
...
Oxidation of Iodide to Iodine: The Iodides are oxidized to elemental Iodine by Peroxidase enzyme
...
Iodination of Tyrosine: The Iodine is immediately bound to the Tyrosine to form monoiodotyrosine
(MIT) and diiodotyrosine (DIT)
...

4
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T3 is formed either by coupling of one MIT with one DIT or by deiodination of
T4
...
Deiodination: T3 and T4 are serially de-iodinated by deiodinase to form thyronines and it occurs in
almost all tissues
...
Conjugation of T3 and T4 with acids: T3 and T4 conjugate with glucuronic and sulphuric acids
mainly in liver
...

3
...
These compounds have some biological activity but no physiological role
...
PARATHYROID GLAND
These are four small glands located at the posterior surface of thyroid gland
...
Its function is to regulate blood calcium and phosphate levels
...

Disorders connected with PTH are:
i
...
The effect of this condition is marked by a steep drop in
calcium level in the blood
...

ii
...
It is due to the mobilization
of calcium from the bones
...
The excess
level of calcium in blood gets deposited in kidney, kidney tubules leading to kidney stones
...
ADRENAL GLANDS:
Adrenal glands are two pyramid shaped glands situated on the top of the kidneys
...
Each adrenal gland is formed of an outer layer called adrenal cortex and a central portion
called adrenal medulla
...

I
...

Hormones of Adrenal Cortex:
The hormones of adrenal cortex are broadly classified into three categories based on their function
...

i
...
They regulate mineral ions in blood
...
It regulates the metabolism of Na+ and K+ in the body fluids
...

Aldosterone reduces the elimination of Sodium through urine, saliva, sweat and bile by enhancing the
reabsorption of these ions from body fluids
...
Water is reabsorbed
from the urine by the osmotic effect of Na+ in the blood
...


Glucocorticoids:

Glucocorticoids are secreted from the middle layer of the adrenal cortex
...
These hormones play an important role in carbohydrate, fat and protein
metabolisms
...
Cortisone is involved in combating stress such as heat, cold,
shock, injury, etc
...
Therefore this hormone is also known as anti-stress hormone
...


Sex corticoids:

These are hormones secreted by the middle and inner layers of adrenal cortex
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These hormones include androstenedione and dehydroepiandrosterone
...

Disorders Connected with Cortical Steroids:
1
...
The
symptoms are bronze like pigmentation of skin, low blood sugar, low plasma Na+ and high plasma
K+, Nausea, diarrhea and decreased ability to withstand stress
...
Cushing’s Syndrome: It is due to the hypersecretion of cortisol
...


3
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It is characterized by rise in plasma
Na+, low plasma K+, rise in blood volume and high blood pressure
...
Adrenal Virilism: It is due to the hyper secretion of sex corticoids
...

Biosynthesis of cortical Hormones:
Cortical hormones are synthesized from cholesterol
...
Progesterone
formed from pregnenolone is a precursor of many steroid hormones
...


Adrenal Medulla

It is the central part of adrenal gland
...
These hormones are catecholamines
...

Adrenaline is secreted at time of physical stress, emotion, danger, fear and anger
...
Hence it is also called emergency hormone
...
Nor-adrenaline increases blood pressure by
constricting the peripheral blood vessels
...
The steps
involve hydroxylation and decarboxylation by enzymes
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PITUITARY GLAND
It is a small pea shaped gland attached to the hypothalamus by the pituitary stalk
...
Hence it is also called master gland
...
They are anterior large secretory lobe known as adenohypophysis, and
posterior smaller lobe known as neurohypophysis
...
During foetal development a narrow region appears between the two
lobes known as intermediate lobe or Pars intermedia
...

Hormones of Adenohypophysis:
The anterior lobe secretes four hormones namely:
i
...


Thyroid Stimulating Hormone (TSH)

iii
...


Gonad Stimulating Hormone (GSH)
 Follicle Stimulating Hormone(FSH)
 Luteinizing Hormone (LH)
 Luteotropic Hormone/ Prolactin

Except the growth hormone, all other hormones are tropic hormones
...

i
...

Abnormalities connected with the GH are:
Dwarfism: It is a disorder in children due to hyposecretion of GH
...
It is characterized by:
 Abnormal growth of bones (giving rise to a height of 7-8 feet), long limbs, disproportionately
large muscle & viscera, etc
...
It is characterized by:
 Abnormal elongation of long bones of arms and legs, protruded lower jaw, thickened eye
ridges & lips
...


Thyroid Stimulating Hormone (TSH)

TSH stimulates the growth of thyroid gland and secretion of thyroxine
...


Adrenocorticotropic Hormone(ACTH)

ACTH stimulates the growth of adrenal cortex and secretion of glucocorticoid hormones
...


Gonad Stimulating Hormone (GSH)

GSH include three hormones which influence the growth and development of sex organs, secretion of
sexual hormone and the development of secondary sexual characteristics
...
Follicle Stimulating Hormone (FSH)


In females:
 Influence the development of ovarian follicle, maturation of egg & secretion of oestrogen
...


b
...




In males:
 LH counterpart known as Interstitial Cell Stimulating Hormone (ICSH)
...


c
...

Hormones of Neurohypophysis:
Neurohypophysis is not an endocrine gland because it does not produce any hormones
...

i
...
It can also cause constriction of blood
vessels
...
Hyposecretion of ADH causes a disorder called Diabetes
insipidus
...

A condition called polydipsia is observed in patients with low levels of ADH
...

ii
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It also causes the
rhythmic contraction of uterus at the time of birth facilitating the passage of foetus out of the uterus
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5
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It has an enzyme secreting exocrine part and
hormone secreting endocrine part
...

These are ovoid bodies scattered throughout the pancreas
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

B cells/  cells – These are slightly smaller granular cells and form about 70% of the cells in the islets
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

D cells/  cells – These cells are small granules and secrete somatostatin
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They secrete pancreatic polypeptide
...


Insulin

Insulin is the most important hormone secreted
by the  cells of the pancreatic islets
...

Insulin is a hypoglycemic factor and has the
following functions:
 Lowers blood sugar level by promoting
glycogenesis
 Increases the synthesis of fat from glucose
in the adipose
 Promotes protein synthesis
 Inhibits gluconeogenesis & glycogenolysis
 Reduces oxidation of fat and inhibit ketogenesis
Disorders Connected with Insulin:
Diabetes Mellitus – It is due to the hyposecretion of insulin and is characterized by hyperglycemia,
glycosuria (glucose in urine), polydipsia (excess thirst), polyphagia (excess appetite), etc
...


Glucagon

It is a protein hormone secreted by  cells of pancreatic islets
...
It promotes
glycogenolysis by which glycogen is broken down into glucose
...
A
proper balance between insulin and glucagon production is necessary to maintain constant blood sugar
level
...


Somatostatin

It is an inhibitory hormone secreted by  cells of pancreatic islets
...

iv
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Its function is
to self regulate pancreatic secretion (both exocrine and endocrine) & activities
...

6
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The thymus is enclosed in a
connective tissue capsule which sends septa into the gland dividing it into lobules
...
The cortex is composed of closely packed cells called lymphocytes or
thymocytes
...

The main function of thymus is the processing of T lymphocytes
...

i
...

ii
...

7
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It is covered by pia matter and
connective tissue septa divide the gland into alveoli & cords of cells
...

Tryptophan

Serotonin

N- acetyl serotonin

Melatonin

Melatonin is the most potent melanophore contracting substance which can cause aggregation of melanin
granules and blanching of skin
...

The mammalian pineal gland may act as a biological clock as melatonin synthesis is cyclical in nature and
depends upon the environmental lighting
...
Circadian rhythm is the physical, mental,
behavioral changes that follow a roughly 24-hour cycle
...
GONADS
Gonads have dual functions such as gametogenic and hormonal
...
The
male gonad is called testes and the female gonad is called ovary
...


Testes:

The endocrine part of testes is known as Leydig cells or interstitial cells
...
Androgens include androsterone & testosterone
...
Therefore LH is also called interstitial cell stimulating hormone (ICSH)
...

ii
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The
oestrogen include three hormones namely - estradiol, estriol, and estrone
...

The secretion of oestrogen is stimulated by FSH from the anterior pituitary
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It appears 1-2 days after ovulation
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HYPOTHALAMUS – Regulation of Endocrine System
The hypothalamus is a part of the brain consisting of grey masses called hypothalamic nuclei
...
The secretions of these hypothalamic nuclei control the
pituitary gland
...
These hormones reach the pituitary through the portal blood
...
The releasing hormones include:
 Thyrotropin Releasing Hormone (TRH)

TSH

 Corticotropin Releasing Hormone (CRH)

ACTH

 Gonadotropin Releasing Hormone ( GnRH)

Anterior
Pituitary

GTH

The inhibiting hormone secreted by the hypothalamic nuclei is called somatostatin
...
The other two hormones secreted by the hypothalamic nuclei
are - vasopressin and oxytocin
...

HYPOPHYSIAL AXIS
Hypothalamic-Pituitary-Adrenal axis (HPA) is a complex set of direct influence and feed-back interactions
among three endocrine glands – the hypothalamus, pituitary gland and adrenal gland
...

HPA is the major part of neuroendocrine system that controls and regulates many body processes including
digestion, immune system, emotions, reactions to stress, energy storage, and metabolism
...


The Hypothalamic Nuclei: It contains neuroendocrine neuron that synthesizes and secretes
vasopressin and Corticotropin Releasing Hormone (CRH)
...


ii
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Anterior Pituitary: CRH & Vasopressin stimulate the secretion of ACTH or corticotropin
...
Glucocorticoids in
turn act back on the hypothalamus and pituitary to suppress CRH and ACTH production in a
negative feed-back cycle
...
Even though they regulate
all other endocrine glands, the secretion of a hormone by a gland at the time of need is not the only action of
master glands
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Hypothalamus
TRH
Pituitary
Gland
Positive feed-back
Low level of thyroxine

TSH Negative feed-back
High level of thyroxine

Thyroid Gland

Thyroxine

Eg: secretion of thyroxine
If thyroxine level is lowered in blood, it stimulates the hypothalamus to secrete a releasing factor known as
Thyrotropin Releasing Factor/ Thyrotropin Releasing Hormone (TRH)
...
This hormone acts upon
the thyroid gland and stimulates the production of thyroxine
...
This slows down the activity of pituitary gland and
secretion of TSH
...




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