8.1.2 The Main Blood Vessels

• The pulmonary and systemic circulations are features of a double circulatory system, where blood passes through the heart twice in one full circuit around the body
  • The pulmonary circulatory system transports deoxygenated blood to the lungs for gas exchange
  • The systemic circulatory system transports oxygenated blood to the rest of the body

• The diffusion of oxygen is reliant on:
  • The concentration gradients that exists between oxygen in the air in the alveoli of the lungs and oxygen in the blood (net diffusion into red blood cells)
  • The concentration gradient that exists between oxygen in red blood cells and the respiring tissues of the body (net diffusion into the mitochondria of cells)

Main blood vessels table

Worked example

An endothelial layer of squamous cells line every blood vessel.

Which of the following is not an advantage provided by this layer of cells?

1. 1. Reduction in friction
   2. Resisting increases in blood pressure
   3. Increased elasticity of the vessel
   4. Reduced damage the blood vessel

The correct option is C, as the squamous epithelial cells do not increase elasticity.