Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The thymus is a lobular structure located on the ventral side of the aorta, behind the sternum and between the lungs.
It acts as a primary lymphoid organ where the development and maturation of -lymphocytes occur.
The thymus secretes peptide hormones called thymosins.
Thymosins play a vital role in the differentiation of -lymphocytes, which are responsible for Cell-Mediated Immunity ().
Thymosins also promote the production of antibodies to provide Humoral Immunity.
The thymus is prominent at birth but undergoes gradual atrophy (degeneration) with age. By old age, it is replaced largely by fibrous and adipose tissue.
The degeneration of the thymus leads to a decreased production of thymosins, resulting in the weakened immune responses observed in elderly individuals.
📐Formulae
(Inverse relationship after puberty)
💡Examples
Problem 1:
A 70-year-old individual is found to have a significantly lower count of mature -lymphocytes and a reduced immune response compared to a 15-year-old. Explain the physiological basis behind this.
Solution:
The physiological basis is the age-related atrophy of the thymus gland.
Explanation:
In humans, the thymus gland is large at birth but starts shrinking after puberty. In old age, the gland degenerates, leading to a drastic reduction in the secretion of thymosins. Since thymosins are essential for the differentiation of -lymphocytes, their lack results in weakened cell-mediated and humoral immunity.
Problem 2:
Identify the chemical nature and the specific site of action for the hormone secreted by the thymus.
Solution:
Chemical nature: Peptide; Site of action: -lymphocytes and -cells.
Explanation:
Thymosins are peptide hormones. They primarily act on undifferentiated lymphocytes to transform them into mature -lymphocytes and stimulate the production of antibodies by -cells.