The Cardiovascular System Study Guide (page 2)
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.
The Composition of Blood
The "vital fluid" and the "river of life" are phrases used to describe blood. It earns these important descriptors because it is the blood that helps regulate our internal environment and keep us in a relatively constant state known as homeostasis. Blood transports and mixes elements up, making it possible for all the organs to contribute to maintaining homeostasis. Blood is not strictly a fluid but is better thought of as a suspension. Suspensions are fluids containing particles suspended inside them. Blood has two components: the liquid portion called plasma and the cells suspended throughout. The cells come in three major types: the red blood cells, the white blood cells, and the cellular fragments called platelets.
Plasma is mostly water in which some substances such as proteins, hormones, and nutrients (glucose sugar, vitamins, amino acids, and fats) are dissolved. Gases (carbon dioxide and oxygen), salts (of calcium, chloride, and potassium), and wastes other than carbon dioxide are also dissolved in blood. The red blood cells contain a protein called hemoglobin. The hemoglobin molecule has an atom of iron contained within its structure. The hemoglobin molecule binds to oxygen and carbon dioxide, and thus provides the mechanism by which the red blood cells can carry these gases around the body. The white blood cells come in many specialized forms and are used in the immune system to fight invading organisms and keep us from getting diseases. The platelets release substances at the site of a wound that start the blood-clotting reaction.
Examples of Things the Circulatory System Carries
- Oxygen from the lungs to the body's cells
- Carbon dioxide from the body's cells to the lungs
- Nutrients from the digestive system to the cells
- Waste products other than carbon dioxide to the liver and kidneys
- Hormones and other messenger chemicals from the glands and organs of their production to the body's cells
Arteries and Veins: Exceptions to the Rules
Earlier we said that blood leaving the heart travels in vessels called arteries. For the most part, this means that the blood is fresh and oxygenated because it is to be distributed to the rest of the body. However, if you read closely, you will notice that the vessels leaving the heart and heading toward the lungs are called arteries as well (the pulmonary arteries), but they contain deoxygenated, nonfresh blood. So it is always true that blood leaving the heart travels in arteries, but it is not always true that this is fresh blood. The reverse is true for veins, which usually carry nonfresh blood, except for the pulmonary veins, which enter the heart from the lungs and carry fresh, oxygenated blood.
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. Arteries lead blood away from the heart, and veins return blood toward the heart. Capillary beds are the site of exchange for gases, nutrients, and wastes. Blood is a special fluid with red and white cells and platelets suspended in it.
Practice problems of this concept can be found at: The Cardiovascular System Practice Questions
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