Endocrinology(Pituitary Gland)

By

Mujahid Hussain

Endocrine System

The endocrine system controls body activities by releasing mediator molecules called Hormones. Hormones released into the bloodstream travel throughout the body and their results may take hours, but last longer.

Exocrine Glands– secrete products into ducts which empty into body cavities

or body surface– sweat, oil, mucous, & digestive glands

Endocrine Glands– secrete products (hormones) into bloodstream

• pituitary, thyroid, parathyroid, adrenal, pineal

– other organs secrete hormones as a second function• hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach,

liver, small intestine, skin, heart & placenta

Pituitary Gland

Introduction

The Pituitary Gland is also known as Hypophysis. It is a small gland

about 1 cm in diameter and 0.5-1 g in weight.

LocationIt lies in sella turcica (bony cavity at the base of the brain) of sphenoid

bone

Division Of HypophysisPhysiologically, it is divided into two lobes:

1. Adenohypophysis (anterior pituitary)

2. Neurohypophysis (posterior pituitary)

There is a zone between these divisions which is known as Pars

Intermedia.

Origin

Embryologically, two portions of pituitary gland originate from different

sources:

Posterior pituitary is derived from the neural tissues: During the embryological development , from the hypothalamic

portion of diencephalon there is an evagination which goes

downward and posteriorly.

Anterior pituitary is derived from the epithelial

tissues: It is a derivative of “Rathke’s Pouch”. From the nasopharynx

an epithelial evagination develops in upward direction,

eventually this evagination comes very close to posterior

pituitary.

Relationship b/w Hypothalamus & Pituitary Gland

The connection b/w hypothalamus and posterior pituitary is neural

connection.

The connection b/w hypothalamus and anterior pituitary is vascular

connection.

Hypothalamic Hypophysial Portal System

This system represents the connection between hypothalamus and

anterior pituitary. Hypothalamic arteries enter into hypothalamus and

break up into capillaries and fenestrated capillary network and this

capillary network recollects as long and short hypothalamic hypophysial

portal vessels. These veins come down to anterior pituitary through the

pituitary stalk and again break up into another capillary network which

again recollects into general blood circulation.

Why it is called portal system ??? Because one group of arteries

breakup into capillaries which recollects into veins but these veins don’t

drain into systemic circulation, before going to systemic circulation these

draining veins again breakup into capillary network.

Importance of Hypothalamic Hypophysial Portal System

The cells of anterior pituitary are controlled by certain factors coming

from the hypothalamus.

These hypothalamic factors are released by neurons which are a part

of hypothalamic nuclei. These certain factors are taken up by the

primary capillary network and carried through the vascular system into

anterior pituitary, from here these factors go out and influence the

cells of anterior pituitary cells.

There is a small amount of factors which are released by hypothalamic

system into primary capillary network of hypothalamus and these

substances don’t get diluted into systemic circulation rather through

the portal they reached directly into the anterior pituitary. If the veins drain directly into general circulation before going into the

anterior pituitary then these factors become very much diluted and they cannot influence the anterior pituitary cells properly. By this system, hypothalamus controls the anterior pituitary not through the neural connection but through the vascular portal system.

Hypothalamus Controls Pituitary Secretions

Almost all secretions by the pituitary is controlled by either hormonal or

nervous signals from the hypothalamus.

Secretion from the posterior pituitary is controlled by nerve signals

that originate in the hypothalamus and terminate in the posterior

pituitary.

In contrast, secretion by the anterior pituitary is controlled by

hormones called hypothalamic releasing and hypothalamic inhibitory

hormones (factors) secreted within the hypothalamus and reached to

the anterior pituitary through the hypothalamic hypophysial portal

vessels.

The hypothalamus receives signals from many sources in the nervous

system. The hypothalamus is a collecting center for information

concerning the internal well-being of the body, and much of this

information is used to control secretions of the pituitary hormones.

Posterior Pituitary Hormones

Posterior pituitary hormones are synthesized in some nuclei of

hypothalamus while the posterior pituitary gland only stores and

release the hormones into the systemic circulation.

There are two types of nuclei in the hypothalamus responsible for the

synthesis of posterior pituitary hormone:

A) Supraoptic Nucleus ADH or Vasopressin

B) Paraventricle Nucleus Oxytocin

90% of the supraoptic nucleus cell bodies produce ADH and 10% of the

paraventricle nucleus may produce oxytocin.

90% of the paraventricle nucleus cell bodies produce oxytocin and 10%

of the supraoptic nucleus may produce ADH.

Cont…

Anti-diuretic hormone (ADH) or Vasopressin It acts on smooth muscle cells around blood vessels to cause muscle

contraction.

It acts within the kidneys to decrease water excretion in the urine

that’s why it is also a anti-diuretic hormone because it retains the

water from kidney in the body.

Oxytocin It stimulates contraction of smooth muscle cells in breasts which

results into milk ejaculation.

It stimulates contraction of uterine smooth muscles during labor.

Remember milk synthesis is under control of prolactin but

milk ejection is under control of oxytocin.

Anterior Pituitary Hormones

Anterior hormones are synthesized by the anterior pituitary cells but the

release of these hormones is under the influence of certain factors which

are released by some nuclei that are present in the hypothalamus.

Types Of Nucleus

A. Pre Optic Nucleus Gonadotropin releasing

hormone (GnRH)

B. Ventro medial nucleus Growth hormone (GH) &

Somatostatin

C. Para ventricular nucleus Thyrotropin releasing hormone

(TRH) & corticotropic releasing hormone (CTRH)

D.Arcute nucleus Prolactin (PRL)

Cont…

Types Of CellsThere are five types of cells in the anterior pituitary:

1) Somatotropes release Human Growth Hormone (GH)

2) Corticotropes release Adrenocorticotropic Hormone (ACTH)

3) Thyrotropes release Thyroid Stimulating Hormone (TSH)

4) Gonadotropes release Gonadotropic Hormones which include both

luteinizing hormone (LH) and follicle stimulating hormone (FSH)

5) Lactotropes release Prolactin (PRL)

Anterior Pituitary can be divided into chromophobic cells and

chromophilic cells

Chromophobic cells are usually inactive and chromophilic cells are active

and are divided into acidophilic cells and basophilic cells