Blood Vessels 2 Flashcards
What is the purpose of arterioles?
- Carry blood under lower pressure than arteries
- From arteries to capillaries
- Control the flow of blood between the two
How is the structure of arterioles related to function?
• Muscle layer is relatively thicker than in arteries
- Contraction of this muscle layer allows constriction of the lumen of the arteriole, restricts flow of blood and so controls its movement into the capillaries that supply the tissues with blood
• Elastic layer is relatively thinner than in arteries
- Because blood pressure is lower
What is the purpose of veins?
Transport blood slowly under low pressure from the capillaries in tissues to the heart
How is the structure of veins related to their function?
- Muscle layer is relatively thin
- Elastic layer is relatively thin
- Overall thickness of the wall is small
- There are no valves at intervals throughout
Why do arteries have a thin muscle layer?
Compared to arteries, they have a thin muscle layer because:
• Veins carry blood away from tissues, and therefore their constriction and dilation cannot control the flow of blood of tissues
Why is the elastic layer thin in arteries?
Thin compared to arteries because:
• Low pressure of blood within the veins will not cause them to burst
• Pressure is too low to create a recoil action
Why is the overall thickness of the wall small in arteries?
This is because:
• There is no need for a thick wall as pressure within the veins is too low to create any risk of bursting
• Allows them to be flattened easily, aiding the flow of blood within them
Why are there valves in the veins?
- To ensure that blood does not flow backwards
- Blood may flow backwards because the pressure is very low
- When body muscles contract veins are compressed, pressurising the blood within them
- Valves ensure that this pressure directs blood in one direction only: the heart
What is the purpose of the capillaries?
To exchange metabolic materials such as oxygen, carbon dioxide and glucose between the blood and cells of the body.
Why is the flow of blood in capillaries much slower?
To allow more time for exchange of materials
How does the structure of capillaries relate to its function?
- Walls consist mostly of the lining layer
- Numerous and highly branched
- Narrow diameter
- Lumen is so narrow
- Spaces between the lining cells
How does a wall consisting of mostly of the lining layer relate to its function?
- Makes capillaries extremely thin
- The distance over which diffusion takes place is short, allowing for rapid diffusion of materials between the blood and cells
How does having a narrow diameter relate to the function of the capillaries?
narrow diameter can permeate tissues which means that no cell is far from a capillary and there is a short diffusion pathway
How does being numerous and highly branched relate to the function of capillaries?
Provides a large surface area for exchange
How do spaces between the lining relate to the function of capillaries?
Allow white blood cells to escape in order to deal with infections within tissues
