What do lymphatic capillaries primarily drain?

• A. Air from the alveoli
• B. Accumulating fluid and alveolar macrophages
• C. Blood from the pulmonary veins
• D. Carbon dioxide from the blood

Answer: (B)

Lymphatic capillaries primarily drain accumulating fluid and alveolar macrophages. In the context of the lungs, these structures play a crucial role in maintaining fluid balance and immune defense. Lymphatic capillaries are specialized vessels that collect interstitial fluid, which can accumulate in tissues due to various factors such as inflammation or infection. The fluid collected by these capillaries not only contains excess tissue fluid but also can include proteins, waste products, and cellular debris, such as alveolar macrophages that are essential for the immune response within the respiratory system.

By draining this fluid and associated immune cells, lymphatic capillaries help to prevent edema and ensure that the lungs remain clear of pathogens and debris, promoting proper respiratory function. Thus, option B accurately reflects the primary function of lymphatic capillaries in this anatomical context.