Pineal and Thymus gland

Thymus and Pineal Gland

Thymus Gland

It is soft bilobed structure where the two lobes lie side by side and joined in the middle by connective tissue.

It is pyramidal in children with maximum size reaching at about 15 years of age.

Its size is reduced somewhat later due to decrease of its lymphoid content.

The weight at birth is 15-20 g in children remaining at that level thereafter.

It is deep red in young age becoming thinner and greyer with age and later yellowing due to infiltration of adipose tissue.

Thymus is covered on the outside by a capsule of loose connective tissue which also penetrates the interior of gland forming septa and irregular lobules.

There is an outer cortex of densely packed thymocytes (or T-lymphocyte lineage) and inner medulla having connective tissue with fewer lymphoid cells.

Balls of flattened epithelial cell called Hassal's corpuscles occur here and there in the medulla.

Thymocytes also occur alongwith some B-lymphocytes.

Hormones produced by the thymus gland is called thymosin.

Thymosin released in the bloodstream has a stimulating effect on the entire immune system.

It promotes proliferation and maturation of T-lymphocytes. It is also called "the throne of immunity", or training school of T-lymphocytes.

Concept Builder

Thymosin play major role in differentiation of T-lymphocytes .which provide cell-mediated immunity. These also promote production of antibodies to provide humoral immunity.

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.