A nurse is caring for a client who asks about the functions of the thymus, spleen, and lymph nodes. Which of the following responses should the nurse make?

A. Electrolyte balance is primarily controlled by the kidneys, adrenal glands, and hormonal systems, including aldosterone and parathyroid hormone. The thymus, spleen, and lymph nodes do not influence sodium, potassium, calcium, or other electrolyte levels. B. Vitamins, especially fat-soluble ones (A, D, E, K), are absorbed in the small intestine with the help of bile and pancreatic enzymes. The thymus, spleen, and lymph nodes do not participate in nutrient absorption or digestion. C. Digestive functions involve the gastrointestinal tract and accessory organs, such as the stomach, intestines, liver, pancreas, and gallbladder. The thymus, spleen, and lymph nodes are not part of the GI system and have no role in breaking down or absorbing food. D. The thymus, spleen, and lymph nodes are key components of the immune system. The thymus, located in the anterior mediastinum, is essential for T-lymphocyte maturation and self-tolerance, helping the body distinguish self from non-self. It is most active in childhood and adolescence and gradually involutes with age. The spleen functions as a blood filter, removing aged or damaged red blood cells, and plays a role in immune surveillance by trapping pathogens and presenting them to lymphocytes. It contains white pulp, rich in lymphocytes, and red pulp for filtering blood. Lymph nodes, distributed throughout the body along lymphatic vessels, filter lymph fluid, trap pathogens, and provide a site for B-cell and T-cell activation, enabling the body to mount a targeted immune response. Collectively, these organs are vital for defending the body against infection, producing and maturing immune cells, and coordinating adaptive and innate immune responses. Dysfunction in any of these organs can compromise immunity, increasing susceptibility to infections or autoimmune conditions.