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Topic 3- Circulation
Over large distances, efficient supply of materials is provided by mass transport.

The Human Circulatory System
The 4 blood vessels of the heart are the pulmonary artery,
pulmonary vein, aorta and the vena cava (superior and
inferior). The superior vena cava returns blood from the head,

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increases, forcing blood up the vein. Valves prevent it flowing back down.
The reduced pressure on the atria during atrial systole means blood flows up into the atrium because blood always
moves from a higher pressure to a lower pressure.

Tissue Fluid
High blood pressure at the arteriole end of…

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The Effect of pH
Carbon dioxide and water produced by respiring cells react to make a hydrogen carbonate ion and a hydrogen ion (CO2 +
H2O HCO2 + H+). The hydrogen ion lowers the pH of the blood.
The more carbon dioxide the more hydrogen ions there are and therefore…


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