The circulatory system and transport in animals involves complex mechanisms for moving materials throughout the body efficiently.
Blood vessels play crucial roles in the circulatory system, with each type specially adapted for its function. Arteries have thick, elastic walls and a relatively small lumen to maintain high pressure and transport blood away from the heart. The structure of arteries includes multiple layers: the tunica externa (outer layer), tunica media (middle muscular layer), and tunica intima (inner endothelial layer). Veins have thinner walls, larger lumens, and contain valves to prevent backflow of blood returning to the heart. Capillaries are microscopic vessels with walls just one cell thick, allowing efficient exchange of materials between blood and tissues.
The double circulatory system consists of two main circuits: pulmonary circulation (heart to lungs and back) and systemic circulation (heart to body tissues and back). This system enables efficient oxygen delivery and waste removal. Tissue fluid formation occurs as blood pressure forces plasma components through capillary walls, creating interstitial fluid that bathes body cells. The lymphatic system then collects excess tissue fluid and returns it to the bloodstream. The composition of blood plasma, tissue fluid, and lymph varies slightly, with plasma containing more proteins than tissue fluid or lymph due to selective filtration at capillary walls. Understanding these transport systems is crucial for OCR A Level Biology Module 3, which covers these concepts in detail along with related topics like gas exchange and cardiac cycles. The relationship between blood pressure, vessel structure, and tissue fluid formation demonstrates how physical and biological processes work together to maintain homeostasis in living organisms.
