The Cardiovascular System Study Guide
The cells in living organisms need to have nutrients transported to them and waste products removed. In single-celled organisms, there isn't much need for the transport of nutrients and wastes because the organism can diffuse these substances to and from the environment directly through the cell membrane. In larger ulticelled organisms, this is not possible, so instead, these substances diffuse into and out of the circulatory system. In animals, this system is based on a liquid suspension of specialized cells. We call the liquid plasma, and the cells are called blood cells. The two make up what we call blood. In plants, this transport system is based on the special properties of water, not blood.
The Parts of the Cardiovascular System
The cardiovascular system, sometimes also called the circulatory system, has three main parts. From the name, we can see two of those parts mentioned. "Cardio" refers to the heart, which is the pump in the system. "Vascular" refers to vessels, specifically the blood vessels that provide a route for fluids in the system. The third component is a very specialized fluid called blood that serves as the means of transport for nutrients and oxygen, as well as wastes.
The Four-Chambered Heart
In vertebrate animals, the heart has evolved to have four chambers that can fill with blood, which is then squeezed out by the muscular walls of the heart. The four chambers are very important for keeping blood that contains wastes from mixing with fresh blood. In the circulatory system, the vessels that take blood to the heart are called veins, and the vessels that take blood away from the heart are called arteries. The superior vena cava is a vein that brings the blood from the body into the top right chamber called the right atrium. This atrium is separated from the chamber below it by a valve and is separated from the chamber next to it by a muscle wall. Blood flows through the valve when the heart relaxes after a beat from the right atrium into the chamber below called the right ventricle. The right ventricle is muscular enough to send the blood through the pulmonary arteries to the lungs.
Blood is refreshed in the lungs and then flows through the pulmonary veins back to the upper part ofthe heart, but this time, it enters on the left side into the left atrium. This atrium is again separated from the ventricle below by a valve. When this valve opens during the relaxed phase of the heart, blood flows into the left ventricle. This chamber is the largest and has the strongest muscular wall so that it can propel blood into the aorta, which is the largest artery, leading away from the heart to the rest of the body.
Arteries branch off from the aorta and travel to all parts of the body. As you trace a vessel through the body, it continues to branch and get smaller until it becomes what we call an arteriole. Arterioles lead to very small beds of tiny blood vessels called capillaries. These capillary beds are where the exchange of nutrients, gases, and wastes occurs.As blood that now contains wastes leaves the capillary beds, it enters small vessels called venules. These course their way through the body back to the heart and, on the way, become larger veins, which eventually empty into the large vena cava vein that empties into the heart.
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