pituitary gland (anatomy)

Pituitary GlandDANISH HASSANLECTURER, UNIVERSITY OF SARGODHA

Pituitary Gland (Anatomy)

Also called the hypophesis Measures about 1 centimeter in diameter and 0.5 to

1 gram in weight Lies in the sella turcica, connected to the

hypothalamus by the pituitary/hypophysial stalk.

Physiologically, divided into two distinct portions: 1. Anterior pituitary (Adenohypophysis) 2. Posterior pituitary (Neurohypophysis)

Between these is a small, relatively avascular zone called the pars intermedia

Almost absent in the human being but is much larger and much more functional in some lower animals

1. Anterior Pituitary/Adenohypophysis

Also known as the master gland because it regulates many other endocrine glands through its hormones.

Anterior pituitary consists of three parts:

1. Pars distalis2. Pars tuberalis3. Pars intermedia

Anterior pituitary has two types of cells, which have different staining properties:

1. Chromophobe cells2. Chromophil cells

1. Chromophobe Cells Do not possess granules and stain poorly. Form 50% of total cells in anterior Are not secretory in nature, but are the precursors

of chromophil cells

2. Chromophil Cells Contain large number of granules and are darkly

stained Form rest of 50% of anterior pitutary.

Types:1. Basis of staining property2. Basis of secretory nature

Based on Staining Property

1. Acidophilic cells / alpha cells Form 35%

2. Basophilic cells / beta cells, Form 15%.

Based on the Secretory Nature1. Somatotropes (GH)2. Corticotropes (AcTH)3. Thyrotropes (TSH)4. Gonadotropes (FSH &

LH)5. Lactotropes

(Prolactin)

30 to 40 per cent of the anterior pituitary cells are somatotropes that secrete growth hormone,

20 per cent are corticotropes that secrete ACTH.

Each of the other cell types accounts for only 3 to 5 per cent of the total; nevertheless, they secrete powerful hormones for controlling thyroid function, sexual functions.

Regulation Of Anterior Pituitary Secretion

Hypothalamus controls anterior pituitary by secreting the releasing and inhibitory hormones (factors), which are called neuro-hormones.

These hormones from hypothalamus are transported anterior pituitary through hypothalamo-hypophyseal portal vessels.

Some special nerve cells present in various parts hypothalamus send their nerve fibers (axons) to median eminence and tuber cinereum.

These nerve cells synthesize the hormones and release them into median eminence.

From here, the hormones are transported by blood via hypothalamo-hypophyseal portal vessels to anterior pituitary.

Releasing and Inhibitory HormonesSecreted by Hypothalamus Growth hormone-releasing hormone (GHRH)

Stimulates the release of growth hormone Growth hormone-releasing polypeptide (GHRP)

Stimulates the release of GHRH and growth hormone Growth hormone-inhibitory hormone

(GHIH)/Somatostatin Inhibits the growth hormone release

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

Corticotropin-releasing hormone (CRH) Stimulatesthe release of adrenocorticotropin

Gonadotropin-releasing hormone (GnRH) Stimulatesthe release of gonadotropins, FSH and

LH Prolactin-inhibitory hormone (PIH)

Inhibits prolactin secretion

2. Posterior Pituitary/Neurohypophysis

Bodies of the cells that secrete the posterior pituitary hormones are not located in the pituitary gland.

Large neurons, called magnocellular neurons, located in the supraoptic and paraventricular nuclei of the hypothalamus synthesise post pitutary hormones.

Hormones are then transported in the axoplasm of the neurons

Nerve fibers passing from the hypothalamus to the posterior pituitary gland carry the hormones.

ANT PITUTARY HORMONES1. Growth hormone (GH)2. Thyroid-stimulating

hormone (TSH) 3. Adrenocorticotropic

hormone (ACTH)4. Follicle-stimulating

hormone (FSH)5. Luteinizing hormone (LH) 6. Prolactin

POST PITUTARY HORMONES

1. Anti diuretic hormone/ Vasopressin

2. Oxytocin