What is pituitary gland?
The Pituitary Gland : The Pituitary gland is smaller size organ situated in brain and its size is about size of a pea.
The Pituitary gland is located in a bony cavity is called sella tursica and is attached to hypothalamus by a stalk infundibulum. Pituitary gland is also known as master endocrine glands.
It secretes hormones from both size i.e. anterior lobe (Front side) and the posterior lobe (Backside) of the gland.
The main function of pituitary gland is to release hormones in bloodstream.
It is divided anatomically into two Major categories :
2. Nurohypophysis .
Adenohypophysis consists of two portion, pars distalis and pars intermedia.
*Pars Distalis – The Pars distalis region of pituitary commonly called anterior pituitary, produces hormans :
A. Growth Hormons (GH) :
- Single chain peptide comprising of 191 amino acid with molecular weight of 22000.
- Its effects are mediated by somatomedins or insulin like growth factors (IGF).
- Growt hormone secretion is stimulated by Growth hormone releasing hormone (GHRH) and inhibited by Growth hormones release inhibitory hormones (GHRIH).
- GHRH and GHRIH regulates growth hormones secretion by negative feedback mechanism.
- GH release is stimulated by sleep, fasting, stress, exercise, hypoglycemia.
- GH release is inhibited by increase in plasma free fatty acid and high doses of Glucocorticoids.
- Over – secretion of GH stimulates abnormal growth of the body leading to gigantism and low secretion of GH result in stunted growth resulting in pituitary dwarfism.
B. Prolactin (PRL) :-
- Prolactin is also known as lactogenic hormone , mammotropin or luteotropin.
- Single chain peptide comprising of 198 amino acid with molecular weight of 23000.
- Prolactin regulates the growth of the mammary glands and formation of milk in them.
- PRL induces the synthesis of milk protein , lactose production and lipid biosynthesis.
C. Thyroid stimulating hormones (TSH):
- TSH stimulates the synthesis and secretion of thyroid hormones from the thyroid gland.
D. Adrenocorticotropic Hormone: (ACTH )
- ACTH is a 39 amino acid polypeptide with a molecular weight of 4500. It is derived from pro – opiomelanocortin, a larger peptide with a molecular weight of 30000.
- ACTH stimulate the synthesis and secretion of steroids hormones called Glucocorticoids from the adrenal cortex.
- ACTH stimulate lipolysis by activating lipase of adipose tissue.
- ACTH release from pituitary is regulated by hypothalamus through CRH .
corticosteroids exert a negative feedback influence on ACTH production by acting directly on the pituitary and indirectly on hypothalamus.
E. Luteinzing Hormones (LH) –
- LH stimulate gonadal activity , hence are called gonadotrophines.
- LH is a two subunit glycoprotein with 204 amino acid with a molecular weight of 3000.
- In males , LH stimulate the Synthesis and secretion of hormones called androgens from testis.
- In females , LH induces ovulation of fully mature follicles ( graafian follicles ) and maintains the corpus
luteum , formed from the remnants of the graafian follicles after ovulation.
F. Follical stimulating hormones(FSH :
- FSH stimulate gonadal activity, hence are called gonadotrophines.
- FSH is two sub-unit glycoprotein with 204 amino acid with a molecular wieght of 32000.
- FSH stimulates growth and development of the ovarian follicles in females.
- In males FSH induces testosterone production and promotes growth of seminiferous tubules.
- *Pars Intermedia – pars intermedia Secretes only one hormones called melanocytes stimulating hormones (MSH). However, in human the pars intermedia is almost merged with pars distalis.
- *MSH act on the melanocytes (melanin containing cells ) and regulates pigmentation of the skin.
Nurohypophysis (parsnervosa ) also known as posterior pituitary. Store and release two hormones called OXYTOCIN and VASOPRESSIN, Which are actually synthesis by the hypothalamus and are transported axonally to Nurohypophysis.
A. Oxytocin –
Oxytocin is a nonapeptide, which is released from posterior pituitary on stimuli of coitus parturition and swelling.
- Oxytocin acts on the smooth muscles of our body and stimulates their contraction.
- In female, it stimulate a vigorous contraction of uterus at the time of child birth, and milk ejection from the mammary gland.
- Oxytocin increase the force and frequency of uterine contractions
B. Vasopressin –
- Vasopressin is also nonapeptide, which is released from posterior pituitary on stimuli from osmoreceptors and baroreceptors.
- Osmoreceptors and baroreceptors regulate the rate of release of vasopressin governed by body hydration.
- Vasopressin acts mainly at the kidney and Stimulate resorption of water and electrolyte by the distal tubules and thereby reduce loss of water through urine (diuresis).Hence it is also called as anti-diuretic hormones(ADH).
Why is Pituitary gland called as Master gland?
Pituitary gland is also called as master gland because it is very important organ in endocrine system to regulate all other hormones.
Both side of gland (anterior lobe and the posterior lobe) release hormones which different works. Hormone released from Anterior lobe influence the growth, reproduction, sexual development, thyroid and adrenocortical function. Hormone released from posterior (oxytocin) increases uterine contractions and antidiuretic hormone (ADH) which increases re-absorption of water by the tubules of the kidney.