Which heart sound is caused by the closure of the semilunar valves?

A. By absorbing excess interstitial fluid and returning it to the blood: The lymphatic system collects fluid that leaks from capillaries into tissues, known as interstitial fluid, and transports it back to the circulatory system, preventing edema and maintaining fluid balance.

B. By controlling the osmotic pressure in blood vessels: Osmotic pressure is primarily regulated by plasma proteins and electrolytes, not directly by the lymphatic system.

C. By producing hormones that regulate fluid secretion: Hormonal regulation of fluid balance involves organs like the kidneys and adrenal glands, not the lymphatic system.

D. By filtering toxins from the bloodstream: Lymph nodes filter lymph to remove pathogens and debris, which supports immunity but does not directly regulate fluid balance.

A. To provide immediate defense against all pathogens: Nonspecific, or innate, immunity acts as the first line of defense by responding rapidly to pathogens. It includes barriers like skin, mucous membranes, and phagocytic cells that act regardless of the pathogen type.

B. To enhance the body's inflammatory response: While nonspecific immunity involves inflammation, enhancing the inflammatory response is a mechanism rather than the primary role. Its main function is broad and immediate defense.

C. To target specific pathogens based on antigens: Targeting specific pathogens is a function of specific (adaptive) immunity, which recognizes antigens and produces tailored responses.

D. To produce memory cells for long-term immunity: Memory cell production is part of adaptive immunity. Nonspecific immunity does not have memory and reacts the same way to repeated exposures.