The Circulatory System
Its made up of the heart and blood vessels, the heart pumps blood around the body through the blood vessels. Blood transports gases, products of digestion, metabolic wastes and hormones around the body. There are two circuits, one takes blood from the heart to the lungs then back to the heart and the other takes blood around the whole body. Blood Vessels:
- Pulmonary Vein - lungs to heart
- Pulmonary Artery - Heart to lungs
- Vena cava - body to heart
- Aorta - Heart to body
- Hepatic vein/artery - liver
- Renal vein/artery - kidneys
The heart also has its own blood supply from the left and right coronary arteries.
Arteries - Have thick muscular walls to help cope with high pressures. They have elasstic tissue to expand to help cope with high pressure from the heartbeat and the endotheliumis folded which also expands to cope with high pressures.
Aterioles - Muscles inside the arterioles which contract to restrict blood flow and relax to allow blood flow.
Veins - They have a wider lumen and contain valves to prevent backflow. Blood flow through veins is helped by the contraction of body muscles surrounding them.
Capillaries - Substances like glucose and oxygen are exchanged between cells and capillaries. Theyre adapted for diffusion. Theyre always found near cells, they are only once cell thick which both provide a shor diffusion pathway and there are lots to provide a large surface area (networks of capillaires are called capillary beds).
Tissue fluid is the fluid that surrounds cells, made up substances that leave the blood like: oxygen water and nutrients. Substances move out of capillaries and into the tissue fluid by pressure filtration. At the start of the capillary bed (near the arteries) the pressure in the capillaries is greater than the tissue fluid so fluid is forced out into the spaced around cells forming tissue fluid. At the end (near the veins) the pressure is lower. Large proteins (because theyre too large) stay in the capillary which decreases the water potential. The capillary has a smaller WP than in the tissue fluid so water enters the capillary by osmosis. Any excess fluid is drained into the lymphatic system and put back into the bloodstream.