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The Cardiovascular System Study Guide (page 2)

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Updated on Sep 22, 2011

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.

In Short

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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