The Pituitary Gland and its hormones

b. 

The Pituitary Gland:

Endocrine tissue is made up of cells that produce secretions which are poured directly into blood. Endocrine cells lie in close apposition to blood capillaries or sinusoids. Secretions of endocrine cells are called hormones. Hormones travel through blood to target cells and influence their function

 

The Endocrine Glands (Ductless glands)

1.     Pituitary (hypophysis)

2.     Adrenal gland (suprarenal)

3.     Thyroid gland

4.      Parathyroid gland

 

The Pituitary Gland: also called as “Master endocrine gland”.

The pituitary gland has the following two major Parts:

a. Adenohypophysis

b.  Neurohypophysi

 

a. Adenohypophysis:-(Anterior Pituitary): consist of the following parts

1.     pars distalis,

2.     pars intermedia

3.     pars tuberalis.

 Neurohypophysis :-  (Posterior Pituitary): consist of pars nervosa, infundibular stalk & median eminence.

 a. Adenohypophysis

1.  Pars Distalis:

Cells are arranged as irregular cords in between thin-walled fenestrated sinusoids.

Consists of 2 major group of cells: chromophils & chromophobes.

Chromophils are of 2 types: basophils & acidophils.

2. Pars Intermedia: Poorly developed in humans. Consists mainly of basophils.

Presence of colloid filled vesicles. Some cells produce melanocyte stimulating hormone (MSH).

3. Pars Tuberalis: Consists of chromophilic (mostly basophilic) & chromophobic cells.

 b. Neurohypophysis

Consists of:  Numerous non-myelinated nerve

Produce 2 hormones:

1.     Oxytocin

2.     Vasopressin

 

Hormones of Adenohypophysis

Type of chromophil	Class	Secretory Product	Target Organ
Acidophil	Somatotrophs (about 50%)	growth hormone (GH, also known as somatotrophin, STH)	General, but a major target is the chondrocytes in epiphyseal growth plates. Promotes growth (together with insulin like growth factors)
	Mammotrophs (about 20%)	prolactin (PRL)	Milk producting tissue (alveolar cells) in the breast
Basophil	Corticotrophs (about 20%)	ACTH (Adrenocorticotrophic hormone,) also known as corticotrophin. Melanocyte-stimulating hormone (MSH)	Trophic (trophic - from the greek - to nourish)- general action - promote growth and secretory activity in other endocrine glands. ACTH target is the corticosteroid cells of the adrenal cortex. MSH target is the melanocytes. TSH target is the follicular epithelial cells of the thyroid. FSH target is the follicular cells of the ovaries, to promote growth of follicles, or the sertoli cells of the testes to promote spermatogenesis. LH target is developing follicles - promotes ovulation, or the Leydig cells of the testes - where it promotes secretion of adrogenens, aiding spermatogenesis. Three of these trophic hormones (TSH, FSH and LH) are glycoproteins, so they can be stained up by the technique PAS.
	Thyrotrophs (about 5%)	TSH (thyroid stimulating hormone), also known as thyrotrophin
	Gonadotrophs (about 5%)	gonadotrophins: FSH (follicle stimulating hormone) and LH (Lutenising hormne).

 

Posterior  lobe of Pituitary. gland- Neurohypophysis

The posterior pituitary looks very different to the anterior pituitary.  It contains non-myelinated axons which are the neurosecretory cells. The cell bodies of these cells are located in the hypothalamus.

It only secretes two hormones:

Antidiuretic hormone (ADH) which acts on the kidney, and oxytocin, which acts on the uterus.