Circulation & Respiration pt 1

Unifying Concepts of Animal Circulation Organisms must exchange materials and energy with their environment. While simple animals exchange materials with the environment by diffusion, most animals use a circulatory system, which facilitates the exchange of materials. This system typically consists of three main components: a central pump, a vascular system (a set of tubes), and a circulating fluid.

Two main types of circulatory systems have evolved in animals. The open circulatory system involves fluid being pumped through open-ended tubes and flowing out among cells. Many invertebrates, most mollusks, and all arthropods have this type of circulatory system. In contrast, the closed circulatory system involves blood being pumped within a set of closed tubes and is distinct from the interstitial fluid. Nearly all other animals have a closed circulatory system.

The cardiovascular system is the closed circulatory system of humans and other vertebrates, consisting of the heart, blood, and three types of blood vessels: arteries, capillaries, and veins. Arteries carry blood away from the heart, capillaries allow exchange between blood and interstitial fluid, and veins return blood back to the heart, completing the circuit.

Vertebrates have two distinct types of cardiovascular systems. The single circulation system involves blood flowing only once through the heart by way of a single loop or circuit. This system is found in bony fishes, rays, and sharks. In contrast, the double circulation system involves blood flowing twice through the heart: once between the lungs and heart in the pulmonary circuit, and a second time between the heart and the rest of the body in the systemic circuit. This system is found in amphibians, reptiles (including birds), and mammals.

Animal Circulation The pulmonary circuit carries blood between the heart and lungs. In the lungs, carbon dioxide (CO2) diffuses from the blood into the lungs while oxygen (O2) diffuses from the lungs to the blood. The pulmonary circuit then returns this oxygen-rich blood back to the heart. The systemic circuit carries blood between the heart and the rest of the body. The blood supplies oxygen to body tissues while it picks up carbon dioxide. The oxygen-poor blood returns to the heart via the systemic circuit.

Issues in Animal Circulation Obstruction of the cardiovascular system is dangerous and can be deadly. For example, if a blood clot gets lodged in a lung vessel, it can cause shortness of breath and lung tissue damage. A clot may completely obstruct blood flow through the pulmonary circuit and cause sudden death as the heart and brain lose access to oxygen. Clots often originate from clots that form in the veins of the legs, a condition known as deep vein thrombosis (DVT), which can be exacerbated by physical inactivity and dehydration.