ENDOCRINOLOGY

 Endocrinology is the branch of science that deals with endocrine system, its diseases and
its secretions known as Hormones.
 Hormone is a mediator molecule that is released in one part of body but regulates the
activity of cells in other parts of body.

ENDOCRINE GLANDS:

 Body contains 2 kinds of glands :

1. Exocrine gland

2. Endocrine gland

Exocrine gland Endocrine gland

1. Are glands with ducts Are ductless glands
2. Secretes substances other than Secretes hormones
hormones like enzymes , sweat

3. Secretions reach the target cell via duct Hormones are released into blood
4. Have localized effect of secretions Hormones have widespread effect on body

Based on chemical nature hormones are classified into 3 types

1. Steroid hormones
2. Protein hormones
3. Amino acid derivatives

Steroid hormones –

 are synthesized from cholesterol or its derivatives

 Are secreted by adrenal cortex, gonads and placenta
 Eg- aldosterone, cortisol, testosterone, estrogen and progesterone

Protein hormones-

 Are large or small peptides

 Are secreted by pituitary gland, Parathyroid gland, pancreas and placenta
 Eg: GH, TSH, FSH, LH, Calcitonin, Parathormone, hCG
Amino acid derivatives –

 Thyroid and medullary hormones are derived from amino acid tyrosine.
 Eg: Thyroxine (T4), triiodothyronine (T3), adrenaline, noradrenaline

CONTROL OF HORMONE SECRETION:

1. Hypothalamic control:
 It produces 4 releasing hormones (GHRH, CRH, TRH, GnRH) and 2 inhibiting
hormones (prolactin inhibiting hormone and somatostatin/somatotropin release-
inhibiting hormone)
 The releasing hormones stimulate the anterior pituitary
 For eg: CRH (Corticotropic releasing hormone) – stimulates corticotrophs of anterior
pituitary –> release of ACTH
2. Control of anterior pituitary
 Produces 5 tropic hormones
 Tropic hormones are the hormones that have other endocrine glands as target cells
 They are : GH, ACTH, TSH, Prolactin and Gonadotropin
 These hormones stimulate their target organ
 Eg: CRH from hypothalamus  anterior pituitary  ACTH  stimulates adrenal
cortex  cortisol released
3. Control by Feedback
 Control can be done by negative and positive feedback
 In endocrinology negative feedback control are frequent
 Negative feedback occurs when the rate of process decrease as product concentration
increases
 Positive feedback occurs when rate of process increases as product concentration
increases
 Eg for negative feedback: CRH from hypothalamus  stimulates ACTH of anterior
pituitary ACTH stimulates secretion of cortisol from adrenal cortex  level of
Plasma cortisol increases  cortisol inhibits CRH and ACTH secretion via negative
feedback
 Eg for positive feedback: - LH surge during ovulation:
In late follicular phase estrogen results in increase secretion of GnRH triggers LH
secretion LH causes further secretion of estrogen  which further causes LH
secretion .
4. Neural control:
 Via the autonomic nervous system
Neuroendocrine reflex:

 neuroendocrine cells are cells that receive neuronal input

 neurohormones are hormones secreted by neuroendocrine cells (For Eg, Cells of
adrenal medulla are controlled by sympathetic division of ANS and release
adrenaline which is a neurohormone)
 Neuroendocrine reflex is initiated by stimulation of sensory neurons that cause
release of neurohormones from the neurosecretory (neuroendocrine cells)
 The sensory neurons respond to thermal, tactile or visual stimulus which carry
impulse to spinal cord and then to hypothalamus , where hypothalamic neurons
release neurohormones that reach the target cells and produce desired effect
 Eg:
 i. Milk ejection reflex
Suckling stimulates sensory neurons  stimulate Hypothalamus stimulates
posterior pituitary  release Oxytocin milk ejection

Ii. During labour

Uterine contractionstretch of cervixsensory neurons send impulse to
Hypothalamus stimulate posterior pituitary releases oxytocin induce
labour

PITUITARY GLAND

 Pituitary gland or hypophysis or “master gland” is a pea shaped structure that measures
1-1.5cm and lies in hypophyseal fossa of sella turcica of sphenoid bone
 It attaches to hypothalamus by a stalk called infundibulum
 Pituitary gland is divided into: i) Anterior pituitary (Adenohypophysis)
ii) Posterior pituitary ( Neurohypophysis)
 In between the 2 divisions there is an avascular structure called pars intermedia
which later atrophies and forms part of anterior pituitary

ANTERIOR PITUITARY:

 Anterior pituitary (adenohypophysis) is formed by : i) pars distalis

ii) pars tuberalis
iii) pars intermedia
 Release of anterior pituitary hormones is stimulated by releasing hormones and
suppressed by inhibiting hormones from hypothalamus, which are called neurohormones.
 These hormones are transported from hypothalamus through hypothalamo-hypophyseal
portal vessels

Hypothalamo – hypophyseal portal system:

 Generally in a portal system blood flows from one capillary network to a portal vein and
then into a second capillary network
 In hypophyseal portal system blood flows from capillaries in hypothalamus into portal
veins that carry blood to capillaries of anterior pituitary

The hormones secreted by anterior pituitary are :

1. Growth hormone
2. Thyroid stimulating hormone
3. Follicle stimulating hormone from pars distalis
4. Luteinizing hormone
5. Adrenocorticotropic hormone
6. Prolactin
7. Melanocyte stimulating hormone (from pars intermedia)

GROWTH HORMONE (SOMATOTROPIC HORMONE)

Functions:
 skeletal growth- it helps in proliferation of tissues in epiphyseal cartilage of long bones ,
which helps in linear growth. If it is deficient then may cause dwarfism and if it is in
excess then can cause gigantism
 muscle growth- stimulates growth of muscle
 stimulates growth of viscera
 action on metabolism:
i. carbohydrate metabolism – it favors storage of glucose by decreasing peripheral
utilization . Therefore, overaction of GH has diabetogenic effect
ii. protein metabolism – it accelerates synthesis of proteins
iii. fat metabolism – it mobilizes fat from adipose tissue . So, concentration of fatty
acids increases in body fluids which is used for energy production by cells

THYROID STIMULATING HORMONE (TSH):

Function:

- necessary for growth and secretory activity of thyroid gland

- helps in synthesis of T3 and T4 hormones
- Thyrotropin releasing hormone (TRH) from hypothalamus controls TSH secretion
- High levels of T3 and T4 inhibit secretion of TRH via negative feedback.

GONADOTROPIC HORMONES:
- FSH and LH are the gonadotropic hormones
- Their release is controlled by GnRH from hypothalamus

FOLLICLE STIMULATING HORMONE (FSH):

- In females- causes maturation of Graafian follicle

 Helps in estrogen synthesis
- In males – helps in formation of spermatozoa

LUTEINIZING HORMONE (LH):

- In females – helps in ovulation

 Formation and maintenance of corpus luteum which inturn helps in
production of estrogen and progesterone
- In males - synthesis of testosterone from testis

PROLACTIN:

- Causes synthesis of milk in female breast after delivery

- It helps in cell mediated immunity
- Opposes action of gonadotrophins
- High levels of prolactin may cause Hypogonadism/ amenorrhea, that is why, lactating
women do not menstruate
- Its release is controlled by the Prolactin inhibiting factor from hypothalamus
- In males its function is not known but its hypersecretion causes erectile dysfunction/
impotence

ADRENOCORTICOTROPIC HORMONE (ACTH):

- Controls production and secretion of cortisol and other glucocorticoids from adrenal
cortex
- ACTH secretion is stimulated by Corticotropic releasing hormone (CRH) from
hypothalamus
- It causes hyperglycemia and lipolysis
MELANOCYTE STIMULATING HORMONE (MSH):

- When present in excess can cause darkening of skin

- Exact role in humans not known
- It may influence brain activity

POSTERIOR PITUITARY
 Also called as neurohypophysis
 It consists of neuroglial cells and nerve fibers but no glandular cells
 It consists of 3 parts – pars nervosa
-infundibular stem
- median eminence
 Hormones of posterior pituitary are synthesized in hypothalamus and are then transported
via nerve fibers and stored in posterior pituitary.
 2 hormones released from posterior pituitary are – i. ADH/Vasopressin

-ii. Oxytocin

OXYTOCIN:
In females: -2 major functions – uterine contraction during labour
- milk ejection after delivery
a) Uterine contraction :- during delivery oxytocin enhances uterine wall
contraction
- It helps in expulsion of fetus and placenta
- After expulsion of placenta though raw area is present in endometrium ,
minimum bleeding is seen due to powerful oxytocin induced contraction

b) Milk ejection:- oxytocin causes contraction of myoepithelial cells around

mammary gland which drives out milk by pumping action

In males – oxytocin may help in ejaculation of semen

- Or facilitate release of sperm into urethra by causing contraction of smooth muscle fibers
in vas deferens

ADH (ANTI DIURETIC HORMONE/ VASOPRESSIN):

- Has 2 major effects- i. conservation of body water

ii. Contraction of vascular smooth muscle

 a) Retention of water:- it conserves water by acting on nephrons and increasing
reabsorption of water from DCT and collecting duct. Hence due to ADH action there is
conservation of water and concentration of urine

b) Vasopressor action:- in large amount ADH shows vasoconstrictor action

THYROID GLAND
FUNCTIONAL ANATOMY:

 Thyroid= shield
 It weighs 15-20 gms
 Situated at root of neck around trachea below larynx.
 It has 2 lobes which are connected in the middle by Isthmus
 On the posterior side of thyroid there are 4 parathyroid glands
 Microscopically, Thyroid gland is composed of large number of closed follicles which
are lined by follicular cells
 Follicular cavity is filled with colloidal substance known as thyroglobulin which is
secreted by the follicular cells.
 Follicular cells also secrete T3 ( Tri-iodothyronine) and T4 (Thyroxine)
 In between the follicles, parafollicular cells are present which secrete Calcitonin

Hormones of Thyroid Gland:

 Tetraiodothyronine ( T4 or Thyroxine)
 Tri iodothyronine (T3)
 Calcitonin
Formation of Thyroid hormones

1. Iodide trapping- the follicular cells trap iodide ions by actively transporting them from
blood to cell. As a result thyroid gland contains most of iodide.
2. Synthesis of thyroglobulin- while follicular cells are trapping iodide, they are also
synthesizing thyroglobulin which is released into the lumen of follicle.
3. Oxidation of iodide- For the iodide ions to bind to thyroglobulin they must be oxidized
and converted to iodine. They are oxidized in presence of peroxidase enzyme and are
released into the follicular lumen.
4. Iodination of tyrosine – the formed iodine then react with tyrosine that are part of
thyroglobulin. Binding of one iodine atom yields T1 (monoiodotyrosine) and second
iodination produces T2 (diiodotyrosine). This bound thyroglobulin forms a sticky
material in lumen called colloid.
5. Coupling of T1 and T2 – 2 molecules of T2 may join to form T4 or T1 and T2 may join
to form T3.
6. Pinocytosis and digestion of colloid – droplets of colloid re-enter follicular cells ,
whenever required, by Pinocytosis and merge with lysosomes. Digestive enzymes in the
lysosomes break down thyroglobulin separating T3 and T4.
7. Secretion of thyroid hormone – As T3 and T4 are lipid soluble they diffuse through
plasma membrane and into blood.
8. Transport in blood – most of T3 and T4 combine with transport proteins in blood mainly
thyroxine binding globulin and reach the target cells

Storage of thyroid hormones:

- Thyroid hormones are stored in the form of thyroglobulin

- Most of the hormones released from thyroid is in form of T4 . but in tissues especially
liver and kidney T4 is converted to T3 which is the active form of T4 which acts on the
target cells.

Calcitonin:

- is secreted by parafollicular cells of thyroid gland

- it can decrease the level of calcium in blood by inhibiting the action of osteoclasts ,
which help in bone resorption, and by accelerating uptake of calcium and phosphate into
bone extra cellular matrix.

Functions of Thyroid Hormone:

 Thyroid hormones increases BMR. When BMR increases cellular metabolism of

carbohydrates, lipids and proteins also increases
 It has Calorigenic effect- Thyroid hormones increase body temperature by increased
BMR and increased production and use of ATPs
  Regulation of metabolism- thyroid hormones stimulate protein synthesis and also protein
catabolism
 Increases gluconeogenesis, glycogenolysis, due to which there
will be elevation of blood sugar level
 It also increases lipolysis and enhance cholesterol excretion , thus
reducing blood cholesterol level.
 Along with growth hormone and insulin thyroid hormones accelerate body growth
 Thyroxine increases appetite and GIT movements
 It accelerates erythropoietic activity and increases blood volume
 Normal thyroxine level is necessary for normal sleep pattern
 Is required for normal functioning of all systems
 Calcitonin secreted by parafollicular cells can regulate the level of Calcium in the body
by inhibiting the action of osteoclasts

Regulation of thyroid hormone secretion:

 Main regulators of T4 and T3 secretion are :

i) TRH - Thyrotropin releasing hormone from hypothalamus stimulates anterior pituitary

to secrete TSH

ii) TSH – Thyroid Stimulating hormone from anterior pituitary stimulate synthesis and
release of thyroid hormones

iii)Feedback – Elevated hormone levels of T3 & T4 inhibit release of TRH and TSH by
negative feed back mechanism and low levels of T3 & T4 stimulate hypothalamus to
secrete TRH

iv)Autoregulation – is done by the thyroid gland via Iodide trapping mechanism. Iodide is
necessary for hormone synthesis. When dietary level of iodine is moderate , blood level
of thyroid hormone is normal. When its uptake is high the enzymes necessary for
hormone synthesis are inhibited by iodide itself, resulting in suppression of hormone
synthesis. This effect of iodide is called Wolff-Chaikoff effect.
APPLIED ASPECTS:

A normally functioning thyroid is called Euthyroid.

GOITER:

- is enlargement of thyroid gland which may occur in both hyper and hypothyroidism
- Goiter in hyperthyroidism is called as toxic goiter and in hypothyroidism called as non
toxic goiter
a) Toxic Goiter – there is enlargement of gland with increased hormone secretion

b) Non toxic Goiter - can be classified as Iodine deficiency Goiter and Idiopathic non
toxic Goiter
- Iodine deficiency goiter / endemic colloid goiter – due to deficiency of iodine in diet
there is no synthesis of thyroid hormones , but increased TSH secretion takes place which
causes gland to enlarge due to increased thyroglobulin formation.
- Idiopathic non toxicGoiter- some food stuffs contain goitrogenic substance such as
Goitrin which suppress the synthesis of thyroid hormones . Eg: Turnip, cabbage

PARATHYROID GLANDS
 Are 4 in number and are located in posterior surface of thyroid gland
 They contain 2 kinds of cells : Chief cells that produce parathyroid hormone
(Parathormone) and Oxyphil cells, which may be depleted chief cells.

Parathormone /Parathyroid hormone (PTH):

 Is essential for maintenance of blood calcium levels and phosphate levels
 Its specific action is to increase the number and activity of osteoclasts.

Functions of PTH:
It has 4 major functions:
- It increases bone resorption by intensifying osteoclastic activity
- It facilitates conversion of Vitamin D into its active form Calcitriol.
- It facilitates absorption of Calcium from jejunum via Calcitriol.
- It acts on renal tubules to increase calcium reabsorption and phosphate excretion
 ENDOCRINE PANCREAS
 Pancreas is both an endocrine and exocrine gland
 Is located in curve of duodenum
 Has a head, body and tail
 Pancreas is composed of 2 types of tissues: acini and islet of Langerhans
 Acini - secrete digestive juice and flow out through a duct forming the exocrine portion
 In between the acini are tiny clusters of endocrine tissue called islet of Langerhans
o Each pancreatic islet includes 4 types of cells:
 = alpha or A cells- secretes Glucagon
 = Beta or B cells- secretes Insulin
 = Delta or D cells- secretes Somatostatin
 = F cells – secretes pancreatic polypeptide
INSULIN:
 Is an anti- diabetic hormone
 Its effect on carbohydrate metabolism:
o it decreases blood glucose level and increases storage in form of glycogen
o it promotes glycogenesis and increases peripheral utilization of glucose
o it inhibits gluconeogenesis and glycogenolysis
 on protein metabolism:
o helps in storage of proteins
o helps in protein synthesis
o prevents degradation of proteins
 on fat metabolism:
o helps in storage of fat in adipose tissue
o promotes synthesis of lipids
o inhibits lipolysis
 major target organs of insulin are liver, muscle and adipocytes.
 Effect on liver:
o it promotes glycogenesis and protein synthesis
o inhibits gluconeogenesis
 on skeletal muscle:
o allows glucose and amino acid uptake by muscles
o promotes protein synthesis and glycogenesis
 on adipocytes:
o inhibits lipolysis
o allows synthesis and storage of fat
 GLUCAGON:
 its action is opposite to insulin
 it increases blood glucose level,by peripheral utilization of lipids and conversion of
proteins to glucose
 major target cell is hepatocyte
 On hepatocytes:
o It promotes hepatic glycogenolysis and increases blood glucose level (by
breaking glycogen)
o Promotes gluconeogenesis (formation of glucose from non carbohydrate source)
 It promotes lipolysis

Regulation of glucagon and insulin secretion:

 Level of blood glucose controls secretion of insulin and glucagon by negative feedback
mechanism
 Low blood glucose stimulates glucagon secretion from alpha cells resulting in
glycogenolysis in liver, and gluconeogenesis
 This leads release of glucose into blood leading to raise in blood glucose level
 As blood glucose level rises, hyperglycemia may occur which results in inhibition of
glucagon secretion by negative feedback mechanism
 The high blood glucose causes stimulation of insulin secretion resulting in lowering
blood glucose level.
 If blood glucose level drops below normal then by negative feedback mechanism insulin
secretion is inhibited

SOMATOSTATIN:

- Inhibits secretion of insulin and glucagon

- slows absorption of nutrients from GIT

PANCREATIC POLYPEPTIDE

- Inhibits somatostatin secretion

- increases secretion of glucagon

-decreases pancreatic juice secretion

APPLIED ASPECT:

1. DIABETES MELLITUS:

 Is a metabolic disorder characterized by high blood glucose level and other symptoms
 Diabetes= polyuria and mellitus= honey
 2 types: Type I and Type II

Type I Diabetes mellitus:

 Is due to deficiency of insulin because of destruction of B cells
 Can occur at any age , usually before 40 years
 Also called as insulin dependant DM (IDDM) as the person affected requires insulin
injections
 In childhood if it occurs it is called as juvenile onset DM

Type II DM:
 Is due to insulin resistance (failure of insulin receptors to give response to insulin)
 Usually occurs after 40 years
 Most of the time can be controlled by oral hypoglycemic drugs rarely requires insulin
 So also called as non insulin dependant DM (NIDDM)

Signs and symptoms of Diabetes Mellitus:

 Glycosuria- loss of glucose in blood
 Polyuria and polydipsia
 Polyphagia
 Asthenia- loss of strength due to protein depletion
 Acidosis- as glucose not used up by body , fat is digested for energy causing excess
formation of keto acids leading to acidosis

2. HYPERINSULINISM:

- hypersecretion of insulin

- Develops hypoglycemia due to which neurological symptoms develop like tremors, convulsions and
coma
 ADRENAL GLANDS
 Adrenal glands (supra renal glands) lie superior to each kidney and have
flattened pyramidal shape
 It is structurally divided into peripheral adrenal cortex and central adrenal
medulla
 A connective tissue capsule covers the gland
 Adrenal medulla is functionally related to sympathetic nervous system; it
secretes hormones epinephrine and nor epinephrine in response to sympathetic
stimulation
 Adrenal cortex secretes an entirely different group of hormones called
corticosteroids which are essential for life.

ADRENAL CORTEX:
 is subdivided into 3 zones , each of which secretes different hormones
-i) The outer zone – zona glomerulosa secretes mineralocorticoids
-ii) Middle- zona fasciculata- secretes glucocorticoids
- iii) Inner zone- zona reticularis- secretes androgens

Mineralocorticoids
 are the corticosteroids that affect mineral homeostasis (electrolytes)
- Aldosterone is the major mineralocorticoid.
- It regulates homeostasis of 2 mineral ions, namely sodium ions and potassium
ions and helps adjust BP and blood volume
-it increases reabsorption of Na+ and water from renal tubules and increases
excretion of K+ through renal tubules
- It also promotes H+ ion excretion in urine and maintains pH of blood

Glucocorticoids
 Are the corticosteroids which affect glucose homeostasis
 hormones include cortisol(hydrocortisone), corticosterone and cortisone,
amongst which cortisol is abundant
Effects of glucocorticoids:
- increases protein breakdown
- stimulates gluconeogenesis and lipolysis
- provides resistance to stress. It provides additional glucose to tissues in
conditions of fasting, exercise, bleeding etc
- reduces inflammation and depress immune responses (hence prescribed after
organ transplantation to avoid tissue rejection by immune system)
 Androgens
 are steroid hormones that have masculinizing effects
 mainly secreted is DHEA (dehydroepiandrosterone)
 - in females, they promote libido, and are converted to estrogen (which are main
source of estrogen after menopause)
 -stimulates growth of axillary and pubic hair in both sexes

ADRENAL MEDULLA:
 Is a modified sympathetic ganglion of ANS.
 The hormone producing cells- Chromaffin cells- are innervated by sympathetic
preganglionic neurons of ANS
 2 major hormones synthesized are epinephrine and nor epinephrine

 Functions:
 In stressful situations hypothalamus stimulates the sympathetic preganglionic
neurons which stimulate the chromaffin cells to secrete epinephrine and nor
epinephrine. These 2 hormones carry out the fight and flight response
 On metabolism- Adrenaline increases BMR
- Increases blood levels of glucose by glycogenolysis
- Also causes fat mobilization
 On Blood vessels- They also increase blood flow to heart, liver, skeletal muscles
 On Heart- They increase the cardiac output by increasing heart rate and force of
contraction
 On respiration- Adrenaline increases rate of respiration and causes
bronchodilation

GONADS- OVARIES AND TESTES

 Gonads are the organs that produce gametes – sperm in males and oocytes in females
 Gonads also secrete hormones

OVARIES

The hormones secreted by ovaries are :

o estrogen and progesterone
o relaxin and inhibin
Estrogen:

- during childhood estrogen is secreted in small quantity

- during puberty the secretion increases sharply resulting in changes in sexual organs
1. effect on ovarian follicles – it promotes the growth of ovarian follicles
2. effect on uterus –
a. enlargement of uterus
b. increase in blood supply to endometrium
c. proliferation of endometrial glands and vessels
d. increase in contractility of uterine muscles
these changes prepare uterus for pregnancy
3. effect on fallopian tube –
a. acts on mucosal lining of fallopian tube and increases number of ciliated epithelial
cells
b. increases activity of cilia to promote movement of ovum
c. enhances proliferation of glandular tissue
these changes are necessary for fertilization of ovum
4. effect on vagina –
a. reduces pH of vagina
b. increases vaginal epithelium proliferation
these changes prevent vaginal infections
5. effect on secondary sexual characters-
a. distribution of hair in pubic region and axilla
b. skin vascularity increases and becomes soft and smooth
c. shoulders become narrow and hip broadens
d. fat deposition increases in breast and buttocks
e. voice becomes high pitched
6. effect on breast-
a. growth and development of ductile system of breast
b. these changes prepare breast for lactation
7. effect on bones-
a. increases osteoblastic activity, so, growth rate increases at puberty
8. effect on metabolism-
a. induces anabolism of proteins
b. causes deposition of fat in subcutaneous tissues, breast, buttocks and thighs

Progesterone:

- is concerned mainly with preparation of uterus for pregnancy and breasts for lactation
1. effect on fallopian tube –
a. promotes secretory activity of mucosal liming
these secretions are necessary for nutrition of fertilized ovum
 2. effect on uterus-
a. promotes secretory activity of uterine endometrium during secretory phase of
menstrual cycle
b. increases thickness of endometrium
c. increases blood supply to endometrium
d. decreases frequency of uterine contraction
e. these prepare uterus for implantation of fertilized ovum
3. effect on cervix-
a. increases thickness of cervical mucosa and thereby inhibits the entry of sperm
4. effect on mammary glands-
a. promotes the development of lobules and alveoli of mammary glands by
proliferating and enlarging the alveolar cells
5. effect on hypothalamus –
a. it inhibits secretion of LH by negative feedback, this helps in contraceptive
action

Hormones functions
3. Relaxin Increases flexibility of symphysis pubis during
pregnancy and helps cervix dilatation
4. Inhibin Inhibits secretion of FSH

TESTES

 Main hormones produced are - testosterone and inhibin

= Testosterone-

i) In fetal life –
a. Helps in sex differentiation
b. Development of accessory sex organs
c. Descent of the testes

ii) In adult life

a. Effect on sex organs
1. Increases size of the penis, scrotum and testes after puberty

b. Effect on secondary sexual characters

1. Development of musculature
 2. Increases thickness of bone matrix
3. Causes broadening of shoulders and narrowing of pelvic outlet
4. Increases thickness of skin , quantity of melanin pigement and
secretory action of sebaceous glands
5. Causes male type of hair distribution in the body – hair growth
over pubis, on face, chest , backs and limbs
6. Change in voice – low pitched voice
7. Increases basal metabolic rate
8. Has got erythropoietic action

= Inhibin-

- inhibits secretion of FSH

 These hormones are regulated by the GnRH released by hypothalamus which stimulate
anterior pituitary to release Gonadotropic hormones – namely LH and FSH which inturn
act on Ovaries and Testes to release estrogen, progesterone and testosterone

PINEAL GLAND
 Pineal gland or epiphysis is a small endocrine gland attached to roof of third ventricle
at midline
 Has 2 types of cells : parenchymal cells and neuroglial cells
 In adult pineal gland is calcified but the parenchymal cells exist and secrete the
hormonal substance

Functions of pineal gland:

 - controls sexual activities in animals
 - secretes hormonal substance called melatonin

Melatonin:
 Is secreted by parenchymal cells of pineal gland
 It acts mainly on gonads
 In humans it inhibits the onset of puberty by inhibiting the gonads
 Its secretion is more in darkness (night) than day
 As it is liberated during darkness, it is thought to promote sleep
 In response to visual impulse sent from retina there is stimulation of pineal
gland for secretion of melatonin
 THYMUS
 Is a bilobed organ located behind sternum in the mediastinum.
 Each thymic lobule consists of outer cortex and inner medulla
 Outer cortex is composed of large number of T cells and macrophages. Immature T cells
migrate from red bone marrow to thymic cortex and begin to mature here
 The medulla consists of more mature T cells
 In infants thymus is large but after puberty thymic tissue is replaced by adipose and
areolar connective tissue . by the time person reaches maturity gland is atrophied

Functions of Thymus:
 It plays an important role in lymphoid function and endocrine function
 =Lymphoid function:
o It helps in processing T lymphocytes and hence helps in development of
immunity
 =Endocrine function:
o secretes 2 hormones thymosin and thymin
o Thymosin accelerates lymphopoiesis and proliferation of T lymphocytes
o Thymin suppresses neuromuscular activities by inhibiting acetylcholine release