Circulatory System of a Mammal 13.5 13.5 Circulatory System of a Mammal Learning Objectives: Over large distances, efficient supply of materials is provided by mass transport. The general pattern of blood circulation in a mammal. (Names are required only of the coronary arteries and of blood vessels entering and leaving the heart, liver and kidneys). Mass Transport – Why is it needed? Diffusion is adequate for transport over small distances. Efficient supply of materials over larger distances requires a mass transport system. With increasing size, and decreasing surface area to volume ratio, the needs of the organism cannot be met by use of the body surface alone. Specialised exchange surfaces are located in specific regions of the body to allow absorption of nutrients and respiratory gases and the excretion of waste substances. Materials need to then be transported from the exchange sites to other areas of the body, and to the external environment. Factors determining the presence of mass transport The surface area to volume ratio The activity of the organism Obviously, the greater the activity and smaller the ratio, the greater the need for mass transport and a pump. Features of Transport Systems Internal Medium to carry substances (must be able to dissolve some substances) A closed system of tubular vessels with a branched network allowing supply to all areas of organism A mechanism for moving the internal medium within the vessels: a pressure difference between different part of the system. This is achieved by either : a pumping mechanism – muscles or organ such as heart A passive process, eg evaporation of water A mechanism to maintain mass flow in one direction eg ? A means of controlling the flow to suit the needs of the organism The Heart 11 Pulmonary artery 9 Semi-lunar valve 7 Aorta 2 Pulmonary vein Vena cava 10 8 1 3 Right atrium 4 Bicuspid valve Tricuspid valve 5 6 Left atrium Right ventricle Left ventricle Mammalian Double Circulatory System Mammalian Double Circulatory System Questions What does a ‘double’ circulatory system mean? Blood passes twice through the heart for each circuit of the body. Why is it advantageous/necessary? When blood passes through the lungs, the pressure lowers. If it didn’t go back to the heart before going off to the body, then circulation would be very slow. Having a double circulation boosts pressure and helps to deliver substances to the rest of the body quickly (which is needed due to mammals having a high body temperature and a high metabolism) Task Complete Summary Questions on page 185. 13.5 Circulatory System of a Mammal Learning Objectives: Over large distances, efficient supply of materials is provided by mass transport. The general pattern of blood circulation in a mammal. (Names are required only of the coronary arteries and of blood vessels entering and leaving the heart, liver and kidneys).