Question

what is thymus

Answer 1

Thymus:

Thymus is a lymphoid organ situated in anterior and superior mediastinum of thorax extending above into the lower part of neck. It is well developed at birth continues to grow upto puberty and thereafter undergoes atrophy and replaced by fat.

It is a bilobed structure made up of two pyramidal lobes of of unequal size which are connected together by areolar tissue. It weighs 10 to 15 grams at birth and 30 to 40 grams at puberty. Thymus is supplied by internal thoracic and inferior thyroid vessels.

Functions of Thymus:

• Thymus controls lymphopoiesis and maintain an effective pool of of circulating lymphocytes.
• Thymus controls development of peripheral lymphoid tissues of the body during neonatal period.
• Cortical lymphocytes of the thymus arise from bone marrow stem cells and they are destroyed within the thymus bye phagocytes.
• Medullary epithelial cells of thymus secrete lymphopoietin which stimulates lymphocyte production both in cortex of thymus and in peripheral lymphoid organs. They also secrete competence inducing factor and responsible for making new lymphocytes competent to react to antigenic stimuli.
• Germinal centres in the thymic cortex indicates autoimmune diseases. Involution of thymus is enhanced by hypertrophy of adrenal cortex, injection of cortisone or of androgenic hormone. Involution is delayed by castration and adrenalectomy.
• Thymic hyperplasia or tumors are often associated with Myasthenia gravis characterized by excessive fragility of voluntary muscles.
• Thymic tumors may press on the trachea, oesophagus and large veins of neck causing hoarseness dysphagia, cough and cyanosis.