The Circulatory System

General Functions

            The circulatory system is the body’s main transport network and cooling system (De Graff, 1998). The human body needs many external substances to survive. We need air, food, and water. However, these substances are not readily absorbed by the body through initial intake. For example, food that is eaten and digested is not yet used to fuel the body’s billions of cells. The nutrients that have been processed need to be transported to each cell in the body in order for them to be used.

This is one of the jobs of the circulatory system. The circulatory system is tasked with carrying the important substances that the body needs where they are needed (Hillendale Health, 2007). Furthermore, the system is also responsible for carrying some of the wastes from the cells such as carbon dioxide, away from the cells to be expelled by the body (Delos Johnson, 2006). This cycle of carrying nutrients to body cells and carrying wastes from them is a way by which the system contributes to the maintenance of physiological homeostasis.

Another way that it contributes to homeostasis is by helping maintain the temperature of the body. Without oxygen to burn, the cells in the body will become cold and eventually die (Delos Johnson, 2006). Thus, oxygenated blood carries oxygen to the cells and releases it in order to maintain homeostatic temperature. Last but not the least, the circulatory system also maintains homeostasis by fighting off outside threats that have infiltrated the body. White blood cells which also travel through the system fight back diseases and help keep the body healthy and they need the circulatory system for them to be able to reach the places in the body where particular bacteria are doing damage (Delos Johnson, 2007).

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Interactions with other organ systems

            When we eat food or drink water, it enters our body through our digestive system and is processed in the stomach. Afterwards, the processed food is transported through the small intestines where it is further digested. The small intestine’s inner walls are covered with

microscopic finger-like projections called villi which are primarily responsible for taking the nutrients from the digested food and transferring them to the bloodstream where they are carried to the rest of the body (Maton et. al., 1993). Thus, the digestive system and the circulatory system work closely together to nourish the body with food and drink. The circulatory system also works closely with the respiratory system. We take in air through our nose and from there it travels to our lungs. From there, pulmonary arteries which are a part of the circulatory system carries oxygen-depleted blood to absorb more oxygen while releasing the carbon dioxide that it has accumulated from the cells that it delivered nutrients to (Maton et. al., 1993). Of course, the circulatory system takes blood containing nutrients and oxygen to other organ systems of the body in order to enable them to continue functioning. The blood carries nutrients to our muscles, our sensory organs, our brain, and all other parts of our body that need it (Maton, 2003).

Parts and functions

The Heart  – It is a powerful muscle that pumps the blood through the entire circulatory system (Hillendale Health, 2007).

The Blood – It is the main substance that flows throughout the circulatory system. There are red blood cells and white blood cells that both travel through the circulatory system (Hillendale Health, 2007). Plasma which is the liquid part of the blood carries both these blood cells through the system (Hillendale Health, 2007). The red blood cells carry nutrients from the small intestine and oxygen from the lungs to the cells all over the body (Hillendale Health, 2007). They are also the ones that carry carbon dioxide away from body cells and back to the lungs to be released as waste (Hillendale Health, 2007). The white blood cells travel to areas where harmful germs are infecting body cells and fight those foreign elements to keep the body healthy (Hillendale Health, 2007). There are also platelets found in the bloodstream which acts to help stop bleeding whenever the body gets wounded (Hillendale Health, 2007). For example, whenever we cut ourselves on some sharp object and bleed, the platelets stick to where we cut ourselves and attract more platelets to do the same. This plugs out the wound so that the bleeding stops.

The Blood Vessels – The blood vessels are the tubes where the blood passes through. There are three types of blood vessels which are arteries, veins, and capillaries (Hillendale Health, 2007). The arteries are blood vessels that carrying oxygenated blood away from the heart while veins carry blood back to the heart (Hillendale Health, 2007). Capillaries are very tiny blood vessels that serve as connections between arteries and veins (Hillendale Health, 2007).

The Heart: A closer look

            The human heart is found in the middle of the thorax with its largest part slightly situated to the left just beneath the breastbone (Maton et. al., 1993). It is a mesh of muscle cells that are joined together by contiguous cytoplasmic bridges (Maton et. al., 1993). Tissues found on the heart’s walls are unique because they have qualities both of smooth muscle tissues and skeletal muscle tissues. The heart is covered by a protective sac called the pericardium (Maton et. al., 1993). The pericardium itself is composed of two parts. The fibrous pericardium is made of dense fibrous connective tissue that serves as the heart’s outer protection while the serous pericardium contains fluid that eases friction generated by heart contractions thus protecting the heart from friction caused by its own beating (Maton et. al., 1993). The right atrium is situated on the right side of the heart where the veins carrying deoxygenated blood are found. This is so that the right atrium can collect the deoxygenated blood and pass it through the heart which pumps it by the right ventricle to the lungs to be oxygenated once more (Maton et. al., 1993). After the blood is oxygenated by the lungs, it goes back to the heart through the left atrium and is pumped by the heart through the left ventricle to the rest of the body. It should be noted that the muscle wall that surrounds the left ventricle is thicker than the wall surrounding the right ventricle. This is because it is harder to pump blood to the rest of the body than to just pump it to the lungs and back (Maton et. al., 1993). Hence, thicker muscle means that the left ventricle is more powerful in pumping blood than the right ventricle.

Hypertensive heart disease

            This diseases pertains to complications caused by arterial hypertension that affects the heart (eMedicine, 2007). Arterial hypertension which is more commonly known as high blood pressure is a condition wherein the pressure of the blood being pumped through the circulatory system is steadily increasing (eMedicine, 2007). This happens due to a variety of factors. Excessive intake of fat can clog up arteries and thus make it more difficult for blood to pass through. Thus, this makes the pressure of blood passing through the arteries increase. Because of the heightened pressure, the arterial walls are subjected to greater strain (Lip et. al., 2000). This can be imagined by visualizing a hose whose channel has been partially blocked. Fluid passing through that hose exerts more pressure on the hose walls and threatens to rupture the hose. In the same way, too much clogging in the arteries can cause pressure to build so much that it could rupture the arteries. Once this condition is elevated to dangerous levels, the heart gets affected by the imbalance in the pressure and hypertensive heart disease is developed (Lip et. al., 2000). The disease causes the heart to be strained more and more and may eventually cause it to breakdown and fail. The pressure can also burst blood vessels which can also damage the system. People suffering from this disease are easily fatigued due to the excessive work that the heart is coping with from the increased blood pressure (eMedicine, 2007). They would also have an irregular pulse, have difficulty sleeping, and feel a greater need to urinate at night (eMedicine 2007). If not treated with appropriate medicine, proper exercise and a good diet, hypertensive heart disease can lead death and is in fact one of the leading causes of death in the country (eMedicine, 2007).


De Graaff, V. (1998). Human Anatomy, 5th edition. WCB McGraw-Hill.

Delos Johnson, D. (2006). The Circulatory System. Retrieved May 22, 2008 from:

eMedicine. (2007). Hypertensive Heart Disease. Retrieved May 22, 2008 from:

Hillendale Health. (2007). Circulatory System. Retrieved May 22, 2008 from:

Lip, G., Felmeden, D., Li-Saw-Hee, F., and Beevers, D. (2000). “Hypertensive heart disease. A complex syndrome or a hypertensive ‘cardiomyopathy’?” European Heart Journal. no. 21 p. 1653–1665.

Hopkins, J., McLaughlin, C., Johnson, S., Warner, M., LaHart, D., and Wright, J. (1993). Human Biology and Health. New Jersey: Prentice Hall.

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The Circulatory System. (2018, Sep 16). Retrieved from

The Circulatory System
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