Syllabus Edition

First teaching 2023

First exams 2025

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The Main Blood Vessels (CIE AS Biology)

Revision Note

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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?

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

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Emma

Author: Emma

Expertise: Biology

Prior to working at SME, Emma was a Biology teacher for 5 years. During those years she taught three different GCSE exam boards and two A-Level exam boards, gaining a wide range of teaching expertise in the subject. Emma particularly enjoys learning about ecology and conservation. Emma is passionate about making her students achieve the highest possible grades in their exams by creating amazing revision resources!