The circulatory system:
The human body has a well-defined network of blood vessels that connect the heart and the organs. It works as a system for deliver oxygen, nutrients, and hormones to the organs, and remove the waste products. It also provides a route for the immune cells to fight infections anywhere the body. And, finally, it also functions to maintain the temperature and the constancy of the internal body environment (homeostasis).
There are two main parts of the blood circulation system; the systemic circulation and the pulmonary circulation.
The systemic circulation is responsible for connecting the heart and the organs of the body except for lungs, while the pulmonary circulation connects the heart only to the lungs.
Components of the circulatory system:
The circulatory network comprises of 4 main components;
- the heart-pumps the blood through the network with each beat,
- arteries-convey blood from the heart to the organs,
- capillaries-the smallest blood vessel network, found at the cellular level,
- and veins-bring blood back from the organs to the heart.
Arteries are the blood vessels that carry blood from the heart to the organs. They carry oxygen-rich blood, except for the pulmonary artery, which carries oxygen-poor blood (from the heart to the lungs for oxygenation).
The heart pumps the blood into the arteries where it flows under high pressure but in low volumes. The arterial walls usually have a thick, elastic and muscular structure to endure the high pressure, and incollapsible, narrow lumens.
Arteries are located deeper in the body and follow a distinct pathway. The blood flow in arteries is detectable in certain specific locations in the form of pulse, such as the radial pulse is detectable on the wrist.
Arteries are of three types; elastic or conducting ones that have stretchy walls for responding to each heartbeat, muscular or medium sized arteries that connect elastic to arterioles, and lastly, arterioles are the smallest division that passes blood into the capillaries.
Arteries appear red because they contain clean, oxygen-rich blood.
Any injury to these vessels would lead to squirting of blood from the injured artery.
And arteries are also susceptible to diseases such as atherosclerosis, coarctation and aneurysms.
In contrast to the arteries, veins carry blood from the organs to the heart. They all carry oxygen-poor blood except for the pulmonary vein, which carries oxygen-rich blood from the lungs to the heart (for distribution elsewhere). The blood in these vessels usually has a high carbon dioxide content.
The venous walls are also made up of three layers but they are usually thinner and less flexible. The lumen is wider and can expand to hold more blood, which is at lower pressure here.
Veins are of three types; (1) deep veins located deeper in the tissues nearby a corresponding artery, (2) superficial veins located closer to the surface, just beneath the skin, and easily accessible for blood sampling and medicine administration, and (3) connecting veins that allow blood to flow from deep to superficial veins.
Veins usually do not follow a distinct pathway. The larger veins contain valves to keep blood flowing forward to the heart and prevent backflow to the organs, especially against the gravity.
Veins appear bluish because of light penetration of skin.
Any injury to these vessels would lead to oozing and pooling of blood from the injured vein due to the sluggish blood flow.
Veins are susceptible to diseases such as deep vein thrombosis and varicose veins. These are also used in grafting procedures like the bypass heart surgery.
The circulatory system with all its components is essential to support the body and life of the human. Disruptions in vessels can lead to severe and even fatal consequences.