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
| Blood vessel | Systemic / Pulmonary circulation | Carries blood from | Carries blood to | Blood |
| Pulmonary artery | Pulmonary | Heart | Lungs | Deoxygenated |
| Pulmonary vein | Pulmonary | Lungs | Heart | Oxygenated |
| Aorta | Systemic | Heart | Rest of the body | Oxygenated |
| Vena cava | Systemic | Rest of the body | Heart | Deoxygenated |
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?
- Reduction in friction
- Resisting increases in blood pressure
- Increased elasticity of the vessel
- Reduced damage to the blood vessel
The correct option is C, as the squamous epithelial cells do not increase elasticity.
Examiner Tip
Remember that although large blood vessels carry blood at a faster rate, their overall surface area in the body is much smaller in comparison to the surface area of capillaries. This is because there are many millions of capillaries in the body.
