Blood vessel structure and function
Laura Armstrong & Joe Wolfensohn
Teachers
Contents
Recall Questions
This topic requires prior knowledge of the heart and double circulatory system as well as a basic understanding of how blood is transported around the body.
What is the function of the heart?
To pump blood around the body in a double circulatory system - to the lungs and to the rest of the body.
What is meant by a double circulatory system?
It is a system where blood passes through the heart twice for each complete circuit of the body. The right side of the heart pumps blood to the lungs and the left side of the heart pumps blood around the body.
Which side of the heart deals with deoxygenated blood?
The right side.
Topic Explainer Video
Check out this @JoeDoesBiology video that explains blood vessel structure and function, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
Overview
There are three main types of blood vessels in the body. Each is adapted for a different function and has a distinct structure.
|
Feature |
Arteries |
Veins |
Capillaries |
|
Function |
Carry blood away from the heart |
Carry blood towards the heart |
Exchange substances between blood and tissues |
|
Blood pressure |
Higher |
Lower |
Very low |
|
Wall thickness |
Thicker muscular and elastic walls |
Thinner walls with little muscle and little elastic |
One cell thick |
|
Lumen size |
Narrower lumen |
Wider lumen |
Extremely narrow (just wide enough for one red blood cell at a time) |
|
Valves present? |
No |
Yes (to prevent backflow of blood) |
No |
|
Oxygen content |
Usually oxygenated (except pulmonary artery) |
Usually deoxygenated (except pulmonary vein) |
Mixed - gas exchange occurs here |
| Diagram |
|
|
|
Summary of Adaptations
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Arteries: Thick, muscular walls to withstand high pressure; elastic fibres to stretch and recoil.
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Veins: Wide lumen to reduce resistance; valves to stop blood flowing backwards.
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Capillaries: Very thin walls (one cell thick) to allow rapid diffusion of oxygen, glucose and CO₂.
Calculating Blood Flow
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Blood flow refers to the volume of blood passing through a blood vessel per unit of time.
-
It's influenced by pressure and the resistance in blood vessels.
Formula:
Blood Flow (cm³/min) = Volume of blood ÷ Time taken
Example:
A student investigates the flow of blood through a capillary and records that 90 cm³ of blood flows through in 3 minutes.
Blood Flow = 90 cm³ ÷ 3 min= 30 cm³/min
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Key Terms
- Lumen – the hollow central part of a vessel through which blood flows.
- Valves – structures that ensure blood flows in one direction only.
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Exam Tip:
Use comparative language when comparing the structure of blood vessels. For example, the artery wall has a thicker layer of muscle tissue whereas the vein wall has a thinner layer of muscle tissue. Veins have valves whereas arteries do not have valves.
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Practice Question
Compare the structure and function of arteries and veins. (4 marks)
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Arteries have thicker walls than veins to withstand higher blood pressure.
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Arteries have more muscle and elastic fibres compared to veins to maintain higher pressure.
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Veins have a wider lumen than arteries to reduce resistance.
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Veins have valves to prevent backflow of blood whereas arteries do not.
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!