1) A small object has a large relative to its volume: as volume increases, relative surface area .
2) In large organisms the organs which absorb materials are situated at a distance from many of the cells in need of these essentials. A system is required to deliver materials to cells at a rate faster than .
3) are thick-walled vessels which carry blood away from the heart: veins are thinner-walled vessels with which carry blood back to the .
4) Arteries divide into smaller vessels called arterioles: veins are formed by a convergence of smaller vessels called . Blood passes from arterioles to venules through tiny exchange vessels called .
5) When blood is forced through a capillary bed, some plasma passes out through the vessel walls. This liquid which bathes the cells is called . It differs from plasma in that it contains little or no .
6) Some tissue fluid returns to blood capillaries by : the remainder enters tiny lymphatic vessels and becomes .
7) The heart has two upper chambers called and two lower chambers called . Deoxygenated blood returns to the heart from the body by the : it is pumped by the heart to the lungs via the . Oxygenated blood returns to the heart from the lungs by the : it is pumped by the heart to the body via the .
8) The aorta divides into arteries which supply oxygenated blood to all parts of the body. The artery supplies cardiac muscle, the arteries take blood to the head, the artery supplies the liver, the arteries transport blood to the kidneys. Similarly veins from each of these organs return deoxygenated blood to the vena cava.
9) The hepatic vein is exceptional in that it connects one capillary bed (the gut) to another (the liver).
10) Coronary heart disease involves the restriction or blockage of the coronary blood supply to the heart wall. This may be caused by fatty deposits called or blood clots.
11) The risk of heart disease is increased by cigarette smoking, , a diet rich in fatty foods, and lack of exercise.
12) A cardiac cycle consists of a period of contraction called and a period of relaxation called .
13) During a cardiac cycle two separate heart are heard: each indicates the closing of a set of valves.
14) A cardiac cycle is initiated in the heart itself by the (sino-atrial node). Its messages are picked up by the node and passed via conducting to the ventricular walls which respond by contracting.
15) The electrical activity of the heart can be displayed on a screen as an .
16) Blood pressure can be measured using a .
17) Blood pressure shows a progressive decrease as it travels round the circulatory system: the greatest drop occurs in the and capillaries which offer the greatest to flow.
18) The system transports lymph in lymphatic vessels: lymph is returned to the bloodstream via two which enter veins from the arms.
19) The products of digestion are transported from gut to bloodstream via the lymphatic system.
20) Lymph are the sites of formation and phagocytic removal of microbes.