Pituitary gland | Master gland | hypophysis

 [PITUITARY GLAND]

- Hypophysis

- Master gland

Introduction-

 Master endocrine gland
 situated in sella turcica, a depression present in  at the base of Skull.
 it is connected with hypothalamus by the pituitary stalk or hypophyseal stalk.

Divisions of pituitary gland-
Pituitary gland is divided in two divisions-
1. Adenohypophysis / anterior pituitary
2. Neurohypophysis / posterior pituitary

Pars intermedia-
 A small and relatively avascular structure between the two divisions of pituitary gland.

Development of pituitary gland-

Anterior pituitary-
Ectodermal in origin.
Arises from the pharyngeal epithelium as an upward growth known as rathke pouch.

Posterior pituitary-
Neuroectodermal in origin.
Arises from hypothalamus as a downward diverticulum.

Rathke pouch and diverticulum grow towards each other and meet in the midway between the roof of the buccal cavity and base of brain.

Hypothalamo-hypophyseal relationship-
Regulation of secretion-

Relationship between hypothalamus and pituitary gland is called hypothalamo-hypophyseal relationship.

Hormones from hypothalamus are transported to anterior pituitary through hypothalamo hypophyseal portal blood vessels.
but the hormones from hypothalamus to posterior pituitary are transported by nerve fibres of hypothalamo hypophyseal tract.

hormone secreted by hypothalamus are transported to anterior pituitary and posterior pituitary what is the mode of transport of these hormones is different.

Anterior pituitary
Adenohypophysis

anterior pituitary is also called master gland because it regulate many other endocrine glands through its hormones.
Parts of anterior pituitary-
Three parts
1. Pars diatalis
2. Pars tuberalis
3. Pars intermedia

Histology of anterior pituitary-
Ant. Pituitary has 2 types of cells-
1. Chromophobe cells
2. Chromophil cells

Chromophobe cells-
Do not possess granules.
Poorly stain.
Form 50% of total cells in ant. Pituitary.
Not secretory in nature.
But, precursors of chromophil cells.

Chromophil cells-
Contain large number of granules.
Darkly stained.

Types of chromophil cells-
Classified by two methods
A. On the basis of staining property
B. On the basis of secretory nature

A. On the basis of staining property-
2types
1. Acidophilic cells / alpha cells- (forms 35%)
Somatotropes
Lactotropes

2. Basophilic cells / beta cells- (forms 15%)
Corticotropes
Thyrotropes
Gonadotropes

B. On the basis of secretory nature-
5 types
1. Somatotropes-
Secrete growth hormone (GH)

2. Corticotropes-
Secrete adrenocorticotropic hormone

3. Thyrotropes-
Secrete TSH ( thyroid stimulating hormone)

4. Gonadotropes-
Secrete FSH and LH

5. Lactotropes-
Secrete prolactin.


somatotrophs forms about 30% to 40% of the chromophil cells so 52 tumors that secret large quantities of human growth hormones are called acidophilic tumors.

Regulation of anterior pituitary secretion-
Neurohormones-
hypothalamus controls anterior pituitary by security the releasing and inhibitory hormones which are called neurohormones.

neurohormones from hypothalamus are transported anterior pituitary through hypothalamo hypophyseal portal vessels.

*Releasing and inhibitory hormones secreted by hypothalamus.
1. GHRH
 (growth hormone releasing hormone)
Stimulates the release of growth hormone

2. GHRP
(Growth hormone releasing polypeptide)
Stimulate the release of GHRH and growth hormone.

3. GHIH / somatostatin
(Growth hormone inhibitory hormone)

4. TRH
(Thyrotropic releasing hormone)
Stimulates the release of thyroid stimulating hormone.

5. CRH
(Corticotropin-releasing hormone)
Stimulate the release of adrenocorticotropin.

6. GnRH
(Gonadotropin-releasing hormone)
Stimulates the release of gonadotropins FSH and LH.

7. PIH
(Prolactin inhibitiory hormone)
Inhibits prolactin hormone secretion.

*recently the hormone beta lipoprotein is found to be secreted by anterior pituitary.

Hormone secreted by anterior pituitary-
1. GH
2. TSH
3. ACTH
4. FSH
5. LH
6. Prolactin

Tropic hormones
- GH
- TSH
- ACTH
- FSH
- LH
Gonadotropic hormones
- FSH
- LH

POSTERIOR PITUITARY
NEUROHYPOPHYSIS

Parts of posterior pituitary-
3 parts

1. Pars nervosa / infundibular process
2. Neural stalk / infundibular stem
3. Median eminence

Hypophyseal stalk-
pars tuberalis of anterior pituitary and the neural stalk of posterior pituitary together form the Hypophyseal stalk.

Histology of posting pituitary-
ok pituitary is made up of neural type of cells called pituicytes and unmyelinated nerve fibres.

Pituicytes-
Fusiform cells derived from glial cells.
Pituicytes act as supporting cells.
Do not secrete any hormone.
Pituicytes have several processes and brown pigment granules.

Unmyelinated nerve fibres-
they come from supraoptic and paraventricular nucleus of the hypothalamus through the pituitary stalk.

Hormone secreted by posterior pituitary-

1. ADH / vasopressin
Antidiuretic hormone

2. Oxytocin

Source of secretion of pituitary hormones-
The posterior pituitary does not secrete any hormone.
ADH and Oxytocin are synthesized in the hypothalamus.
from hypothalamus they are transported to the posterior pituitary through the nerve fibre of hypothalamo-hypophyseal tract.
Neurophysin-
proteins involved in transport of these hormones are called neurophysin-.
neurophysin are the binding proteins which transport vasopressin and Oxytocin from hypothalamus to posterior pituitary via hypothalamo-hypophyseal tract and storage of these hormones in posterior pituitary.

Neurophysin 1 or oxytocin- neurophysin is the binding proteins for oxytocin.

Neurophysin 2 or ADH-neurophysin is the binding proteins for ADH.


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