In histology, the circulatory system refers to the microscopic structures of the tissues and organs involved in transporting blood, lymph, and other fluids throughout the body. This includes the study of blood vessels (arteries, veins, capillaries) with their distinct layers, the cellular components of blood (red blood cells, white blood cells, platelets), the tissues of the heart (muscle, connective tissue, valves), and the structures of the lymphatic system (lymph vessels, lymph nodes). Histological examination reveals how these components are organized to facilitate efficient transport, exchange, and immune function at the tissue level.