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B.3.2 Transport - Coggle Diagram
B.3.2 Transport
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B.3.2.1 Adaptations of capillaries for exchange of materials between blood and the internal or external environment
Introduction
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Many narrow capillaries have a total surface area greater than blood vessels. Capillary network in any tissue increases the scope for diffusion between the blood and the tissue cells.
Capillary wall
The capillary wall consists of one layer of endothelium cells. This layer of cells has a coating of extracellular fibrous proteins which are crosslinked to form a gel
This gel is called the basement membrane and it acts as a filter that allows small or medium sized particles to pass through.
There are pores between the epithelium cells, so the capillary wall is very permeable - the pores allow part of the blood plasma but not the red blood cells, to leak put through the basement membrane
The fluid that leaks out is very similar but not identical in composition to blood plasma - it is called tissue fluid
The fluid contains oxygen, glucose and all other substances in blood plasma except large protein molecules.The fluid flows between the cells in a tissue fluid then re-enters the capillary network
In some tissues there are greater numbers of large pores in the capillary walls - fenestrated capillaries. Allows larger volumes of tissue fluid to be produced, which speeds up exchange between the tissue cells and the blood. The glomerulus of the kidney has fenestrated capillaries so it can produce large volumes of filtrate in the first stage of urine production.
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