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In this chapter of AS/A-Level Biology, we will learn about the structure and the adaptations of different parts in the circulatory System.
Artery
- Artery walls are thick to withstand high pressure
- The lumen is small to maintain the high pressure
- The inner layer consists of a thin layer of elastic tissue that allows the walls to stretch and recoil
- The middle layer consists of a thick layer of smooth muscle
- The outer layer is a thick layer of collagen and elastic tissue for strength and to support the recoil for maintaining pressure.
Arterioles
- Small blood vessels that distribute the blood from arteries to the capillaries
- They have a layer of smooth muscle which contracts to increase resistance to flow and reduces the rate of blood flow
- Constriction of arteriole walls is used to divert blood to regions of the body that are demanding oxygen
Capillaries
- Very thin walls consisting of a single layer of endothelium
- Narrow lumen to squeeze red blood cells against the wall to aid in the transfer of oxygen and reduce the diffusion distance
- Leaky walls to allow blood plasma and dissolved substances to leave the blood (e.g. in lymph)
Venules
- These collect blood from the capillary bed and lead into the veins
- Consists of thin layers of muscle and elastic tissue as the pressure is relatively low
Veins
- Carry blood back to the heart
- Large lumen in order to ease the flow of blood
- Walls are thin as they do not need to stretch and recoil and are not actively constricted in order to reduce the blood flow
- They contain valves to prevent back flow of blood and help the blood flow into the heart properly
This is the end of the topic
