The enlarged portion of the thoracic duct is called the:

A. Macrophages are present in mucosal lymphoid tissue and play a role in immune surveillance, phagocytosis, and antigen presentation.
B. Red blood cells are not associated with mucosal lymphoid tissue. They are primarily involved in oxygen transport and do not play a direct role in the immune functions of mucosal lymphoid tissue.
C. Monocytes are a type of white blood cell that can differentiate into macrophages in tissues, including mucosal lymphoid tissue.
D. Dust cells are a type of macrophage found in the lungs, often associated with inhaled particles, and can also be present in mucosal lymphoid tissue.

A. The spleen does not shrink after puberty. It remains an active part of the immune and blood filtration systems throughout life.
B. The thymus (note: it appears misspelled as "Thygus" in the question) is the correct answer. It plays a crucial role in the development of T lymphocytes (T cells) during childhood but begins to shrink and become replaced by fatty tissue after puberty—a process known as involution.
C. The liver does not shrink after puberty. In fact, it continues to grow and function in metabolism, detoxification, and digestion throughout a person’s life.
D. The cisterna chyli is a dilated sac at the lower end of the thoracic duct involved in lymphatic drainage. It does not shrink after puberty and remains functional throughout life.