Human Endocrine System

The thymus gland serves as a crucial primary lymphoid organ within the immune system, situated in the upper thorax just behind the sternum.
Role of the Thymus:
(i) The thymus is vital for the development and maturation of T-lymphocytes (T-cells), which are key to adaptive immunity.
(ii) In childhood, it actively generates immune cells.
(iii) The gland undergoes involution (gradual shrinkage) starting at puberty, with its functions increasingly assumed by other immune structures like lymph nodes and the spleen.
Involution of the thymus is a normal physiological process, leading to its replacement by fatty tissue in adulthood.

The islets of Langerhans are specialized clusters of endocrine cells within the pancreas that play a key role in regulating blood glucose levels.
(i) Beta cells ( -cells) primarily produce and secrete insulin, a hormone essential for reducing blood sugar levels.
(ii) Following a meal, as blood glucose levels increase, beta cells release insulin, which helps cells absorb glucose and stores surplus glucose as glycogen in the liver.
(iii) Insufficient production or malfunctioning of beta cells can lead to diabetes mellitus, marked by elevated blood sugar levels.