Have you seen the IBDP Biology Blog about the structure of Arteries and Veins yet? If yes, then this blog will let you know about the third and final main blood vessel we need to know about: Capillaries, let's go!
Structure and Function
The function of capillaries are:
- exchange materials between cells in tissues and blood travelling at low pressure.
- arteries split into arterioles which in turn split into capillaries, decreasing arterial pressure as total vessel volume is increased.
- the branching of arteries into capillaries ensures blood is moving slowly and all cells are located near a blood supply.
- after material exchange - capillaries pool into venules and eventually veins.Arteries split into arterioles which in turn split into capillaries, decreasing arterial pressure as total vessel volume is increased.
- The
- branching of arteries into capillaries ensures blood is moving slowly and all cells are located near a blood supply.
- After material exchange - capillaries pool into venules and eventually veins.
Specialised structure to allow for efficient material exchange:
- Very
- small diameter ( ~5µm wide ) - allows for passage of only one RBC at a time = optimal exchange.
- Capillary wall made up of a single layer of cells -
- minimises diffusion distance for permeable materials.
- Surrounded by a basement membrane - permeable to necessary materials.
- May contain pores - further aid in transport of materials between tissue fluid and blood.
Capillary structure may vary due to location in the body and specific role
- wall may be
- continuous
- with endothelial cells held together by tight junctions to limit permeability of large molecules.
- tissues specialised for
absorption (e.g. kidney, intestines) - capillary wall may contain pores.
- some capillaries are
sinusoidal - have open spaces between cells, can be permeable to large molecules and cells.
Flow of Blood
Blood flows through capillaries very slowly and at low pressure - allow for max. material exchange
- High bp in arteries is dissapated by extensive branching of vessels and narrowing of lumen.
- Higher hydrostatic pressure at arteriole end of capillary forces materials from the bloodstream to the tissue fluid
- Material that exits the capillaries at body tissues include oxygen and nutrients (needed by cells for respiration).
- Lower hydrostatic pressure at venule enf of capillary allows materials to enter the bloodstream from tissues
- materials that enter the bloodstream from tissues include carbon dioxide and urea (waste products).
That's all for the structure + functions of Capillaries, well done!
Drafted by Venetia (Biology)
References:
- https://www.researchgate.net/profile/Alexandre-Dizeux/publication/281299075/figure/fig5/AS:614326264156160@1523478203117/Diagram-of-a-capillary-the-smallest-blood-vessel-in-the-organism-It-is-characterized-by.png
- https://www.google.com/url?sa=i&url=http%3A%2F%2Fwww.vhlab.umn.edu%2Fatlas%2Fphysiology-tutorial%2Fblood-vessels.shtml&psig=AOvVaw2J0rfK1-9zPAGtRKGIYqVs&ust=1625720093601000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCJDZh7iV0PECFQAAAAAdAAAAABAD
- https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.pinterest.com%2Fpin%2F124904589654682473%2F&psig=AOvVaw1AyWAv7-Mp-HHfLJLX-9sE&ust=1625720225463000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCPConfiV0PECFQAAAAAdAAAAABAK