Question

Assertion- The thymus gland is quite large in size at the time of birth but shrinks in size with age.
Reason- Immune system produces most of its T cells during childhood and requires very few new T cells after puberty.
(A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
(B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
(C) Assertion is correct but Reason is incorrect
(D) Both Assertion and Reason are incorrect

Answer 1

Hint:-Glands are organs that help in normal functioning of the body by producing and releasing substances with specific functions. Glands may have ducts (Exocrine glands) or may be ductless and pour their secretions directly into the bloodstream (Endocrine Glands). The secretion of endocrine glands are known as Hormones.

Complete solution:
Thymus is a specialised lymphoid organ which is an important part of our immune system as T lymphocytes mature here. It lies in the upper front of the chest. Thymus consists of immature T cells called the thymocytes and epithelial lining cells which help in development of thymocytes.
Thymus is the largest and a highly active gland during neonatal and pre adolescent periods. It then starts to decrease in size and activity and thymus tissue gets replaced by fatty tissue. Hence, the assertion is correct.
As of now, there is no universally accepted explanation as to why thymus shrinks in size with advancement of age. The most accepted hypothesis says that thymus shrinkage is an effect of antagonistic pleiotropy which selects genes that benefits early in life and outweighs cost later in life. The thymus ensures that T cells won't attack the body itself. That's why thymus produces T cells and protects the growing baby from infection. Now to avoid autoimmunity, thymus starts shrinking as there are enough T cells produced during childhood and now very few T cells are required after puberty.So, the reason is correct and correctly explains thymic shrinkage with age.
So, the correct answer is Option (A) - Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.

Note:- Congenital problems due to improper development of thymus can lead to immunodeficiency and make the individual highly susceptible to infection by bacteria, virus or fungi. The most common congenital cause of thymic immunodeficiency is chromosomal abnormality i.e deletion of 22nd chromosome, called the DiGeorge Syndrome, resulting in failure of development of thymus with other systemic abnormalities.