Efficient nutrient exchange in the digestive and circulatory systems of mammals is facilitated by specialised structural features. In the digestive system, the small intestine is lined with tiny, finger-like projections called villi, which significantly increase the surface area available for absorption. Each villus is covered with microvilli, further increasing the surface area and enhancing the rate of nutrient uptake. The thin epithelial layer of the villi allows for a short diffusion distance, while a dense network of capillaries beneath the surface ensures that absorbed nutrients, such as glucose and amino acids, are rapidly transported into the bloodstream. This arrangement maximises contact with digested food and ensures that nutrients are efficiently absorbed and delivered to body cells.
Capillaries, the smallest blood vessels, play an important role in nutrient exchange within the circulatory system. Their thin walls, composed of a single layer of endothelial cells, enable rapid diffusion of nutrients, gases and waste products between blood and tissues. The extensive branching of capillaries throughout tissues creates a large surface area for exchange, allowing oxygen and nutrients to reach cells while simultaneously removing carbon dioxide and other metabolic wastes. The close proximity of capillaries to body cells ensures efficient transport, supporting cellular function and overall homeostasis.
The closed circulatory system of mammals further facilitates efficient transport of materials to and from all body cells. In a closed system, blood is confined within vessels, allowing it to be pumped under high pressure and directed precisely to tissues. This system ensures that oxygen-rich blood is rapidly delivered to organs and tissues, while deoxygenated blood and metabolic wastes are efficiently returned to the heart and lungs for reoxygenation and excretion. The closed nature of this system allows for controlled distribution of blood, enabling efficient delivery of nutrients, removal of wastes and maintenance of optimal conditions for cellular function across the body.
