13.5

 Learning Objectives:
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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).

 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.

 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.

 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
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A mechanism for moving the internal medium within the vessels: a pressure difference between different part of the system. This is achieved by either :
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 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

11
10
9
Vena cava
Pulmonary artery
Semi-lunar valve
7
8 Right atrium
Tricuspid valve
6 Right ventricle
1 Aorta
3
2 Pulmonary vein
Left atrium
5
4
Bicuspid valve
Left ventricle

Mammalian Double Circulatory System Mammalian Double Circulatory System

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What does a ‘double’ circulatory system mean?
Blood passes twice through the heart for each circuit of the body.
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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)

 Complete Summary Questions on page 185.

 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).