Pituitary and Pineal Gland

PITUITARY GLAND

It is pink coloured pea-sized gland about 1.3 cm in diameter and weighs only 0.5 g.

It is located in a bony cavity called sella turcica of sphenoid bone and is attached to hypothalamus via infundibulum.

The pituitary gland has two anatomically and functionally separate lobes, the much larger anterior lobe or adenohypophysis and posterior lobe or neurohypophysis.

Adenohypophysis consists of two portions pars distalis and pars intermedia.

The pars distalis produces cluster of hormones whereas pars intermedia secretes only one hormone called melanocyte stimulating hormone (MSH).

However in humans the pars intermedia atrophies and merges with pars distalis during foetal development.

Hormones of Pituitary Gland and their Action on Target Organs

Concept Builder

1. GH is the only adenohyophysis hormone which is linked directly to body whereas other adenohypophysis hormones mostly control other glands.

2. GH stimulates hepatocytes to release glucose into blood. In this respect GH is an insulin antagonist and thus can be related to have diabetogenic effect.

3. Pitocin is synthetic oxytocin which is often given to induce labor.

Pineal Gland

Pineal gland is regarded as vestige of third eye as well as functional endocrine gland.

It is attached to the roof of third ventricle in the rear portion of brain, ectodermal in origin is known as the pineal gland, named for its resemblance to a pine cone.

It has no direct connection with central nervous system.

It is variable in size and weighs about 150 mg, but is richly vascularised and secretes several hormones, including melatonin.

In humans, it has no light-sensitive cells, like lower vertebrates, where pineal is eye-like and responds to light.

Pineal gland functions as a biological clock and a neurosecretory transducer, converting neural information.

More melatonin is produced during darkness.

Its formation is interrupted when light enters the eyes and stimulates the retinal neurons.

They transmit impulses to the hypothalamus, and finally to the pineal gland.

The result is inhibition of melatonin secretion.

In this way, the release of melatonin is governed by the diurnal dark-light cycle.

Melatonin also influences body temperature, metabolism, pigmentation, menstrual cycle and defense capability.