Wednesday, 09 September 2015 08:37

Capillaries, Veins and Pulse

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Capillaries and Veins and Pulse







Capillaries are the most significant part of the circulatory system. They are responsible for transporting nutrients, waste, gases, chemicals and heat between the blood and the interstitial fluid that fills the spaces between the cells and the tissues (Daniels, 2007).


There are many different types of capillaries that have many different functions in the circulatory system. Two types of capillaries have been identified below:


  • Fenestrated capillaries are specialised pores that allow for rapid entrance and exit of nutrients and hormones.

  • Sinusoidal capillaries are found in some bone marrow tissue and allow for large molecules and blood cells to pass through (Daniels, 2007).


Capillaries are an extensive network that clumps in groups of 10-100 capillary beds. Their are small sphincters that are directly responsible for controlling the blood flow into the capillary beds by contracting and relaxing up to 10 times per minute depending on the needs of the area that capillaries are located in (Roberts, 2010).


It is the process known as diffusion where their is different pressures that pulls oxygen, carbon dioxide, amino acids and hormones through the gaps between the capillary walls. There are however a few substances like insulin that can squeeze through the capillary walls via a process known as transcytosis. Transcytosis occurs when the substance is enclosed within 

little vesicles which allows the substance to squeeze through the walls (Daniels, 2007).







Capillaries merge into small veins known as venules and these venules then merge into larger veins that carry deoxygenated blood back to the heart. As identified above, capillaries primary role is to carry nutrients to the instertitial fluid between cells and tissues. Once this process has occurred however, capillaries also collect the wastes and other cargos from those tissues and transports back to the heart through the network of veins.


Veins are smaller and have thinner walls then arteries and contain proportionately less muscle and more connective and elastic tissue. This is due to the fact that veins have less pressure than arteries (Daniels, 2007). Some veins contain valves that prevent the blood from flowing backwards as it is pumped upwards towards the heart. Muscles in the legs help pump the blood towards the heart by applying pressure around the veins forcing the blood upwards through the valves.


You may no a relative or friend that has a condition known as varicose veins. Varicose veins occur when the valves in the vein leak or are damaged causing the veins to pool and hold back flowing blood.






Pulse and Blood Pressure



Blood pressure is measured in the brachial artery that is located in the upper left arm. A blood pressure cuff is used to take a blood pressure reading. The first reader taken after the blood pressure cuff is pumped with pressure and then relaxed is called the systolic pressure which is the pressure exerted on the arteries as it leaves the contracting ventricles (Daniels, 2007). The second reading measured is the diastolic pressure which is the pressure in the arteries as the ventricles relax. 


As the blood pumps through the arteries it creates a wave which is known as a pulse which can be felt in any artery close to the body's surface (Roberts, 2010). The pulse beats at the same rate as the heart which is about 60-80 times a minute at rest.








Daniels, P et al. (2007) Body: The Complete Human - How it grows, How it works and how to keep it healthy and strong. National Geographic Society USA.




Roberts, DR A. (2010) The Complete Human Body: The definitive visual guide: DK Publishing - New York.



Read 3450 times Last modified on Wednesday, 09 September 2015 10:00

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