In part I of the cardiovascular system we will gain an understanding of the various parts of this system and then put these organs together to gain an understanding of how blood is circulated through the body.
In part II we will learn more about the blood itself.
The cardiovascular system consists of:
- The heart
- Blood vessels including arteries, capillaries, and veins
- Blood
The Heart
The heart is a muscular organ made up of involuntary striated muscle tissue. It is located in the thoracic cavity in between the lungs and just above the diaphragm. It is covered in protective membranes called the pericardium. Besides forming a protective layer, these membranes also secrete a fluid that helps to reduce friction as tissues rub together during heart contractions.
The next layer of the heart is a thick layer of cardiac muscle tissue called the myocardium. It is the contraction of the myocardium that creates the force necessary to pump blood through the body.
Attached to the outer surface of the myocardium is the epicardium. This membrane consists of blood vessels that nourish the heart.
Blood Supply
The heart is supplied blood through the coronary arteries, which come off of the aortic artery. Blockage of the coronary artery is what causes a heart attack.
The Heart Chambers
There are four chambers in the heart. The two upper chambers are called the atria. They receive blood from the veins. The two lower chambers are the ventricles. Blood is pumped from the ventricles to the arteries and to the rest of the body. The heart consists of two pumps. The left atrium and left ventricle is the left pump. The right atrium and the right ventricle is the right pump. There is no opening between the atria or between the ventricles. Instead, there are valves in between the atria and the corresponding ventricles.
The Heart Valves
There are two types of valves located in the heart: the atrioventricular valves and the semilunar valves. The atrioventricular valves are located between each atrium and its corresponding ventricle. These valves allow blood to flow from the atrium to the ventricle without allowing any blood to flow backwards from the ventricle to the atrium. The two atrioventricular valves are the tricuspid valve and the mitral valve.
Semilunar valves are located in the arteries that carry blood from the ventricles to the rest of the body. The two semilunar valves are called the pulmonary semilunar valve and the aortic semilunar valve.
The sound we associate with the heartbeat is actually the closing of the heart valves. “Lub-dub” is the sound often used to describe the sound of the heartbeat. The first sound, “lub”, is the sound of the atrioventricular valves closing. The second sound, “dub”, is the sound of the semilunar valves. If any of the heart valves are not working correctly then another sound might be heard. This is referred to as a heart murmur.
Blood vessels
There are three main types of blood vessels. Arteries, capillaries, and veins form a system of tubes that carry blood to and from the heart. The blood vessels form an incredible network of tubes throughout the body. An adult has as many of 100,000 miles of blood vessels in their body.
Arteries
These large blood vessels are made of a thick muscular layer to withstand higher blood pressure. They carry blood from the heart to the capillaries.
Capillaries
Capillaries form a vast network of very small vessels that enable the exchange of materials between blood and the tissue cells. The term capillary bed refers to a network of capillaries that supply blood to an organ.
Veins
Veins return blood from the capillaries back to the heart. They are made up of a relatively thin muscular layer and contain internal valves to keep the blood from ever flowing backwards. About 60% of the blood volume is located in the veins at any given time.
Blood Flow
Deoxygenated blood from the body flows from the superior and inferior vena cava veins to the right atrium. This blood is pumped to the right ventricle and then proceeds to the pulmonary trunk where it is oxygenated by the act of inhalation. This newly oxygenated blood then flows through pulmonary veins to the left atrium and is pumped to the left ventricle to continue to the aorta and the rest of the body. These are referred to as the pulmonary and systemic circuits.
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Pulmonary Circuit
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Assists deoxygenated blood from the right ventricle to the lungs and then assists newly oxygenated blood from the lungs to the left atrium. (This is the flow of blood between the heart and lungs.)
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Systemic Circuit
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Assists oxygenated blood to all parts of the body (except the lungs) and then returns deoxygenated blood to the right atrium. (This is the flow of blood from the heart to the rest of the body.)
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The following diagram illustrates the flow of blood. Blue indicates deoxygenated blood and red indicates oxygenated blood.
Blood Pressure
The circulation of blood throughout the body happens due to changes in blood pressure. Blood naturally flows from areas of high pressure to areas of lower pressure. When the ventricles contract it creates the pressure necessary to push the blood into the arteries. As the blood travels throughout the body the pressure continually decreases.
Blood pressure is measured in two numbers. The systolic blood pressure is the measurement of the ventricular contraction. The diastolic blood pressure is the pressure measured during a ventricular contraction. Optimal blood pressure is around 120/8
Further Resources:
General Heart Health
Hypertension
Cholesterol
Angina
Congestive Heart Failure
Heart Attack
Varicose Veins
Hemorrhoids
Arteriosclerosis
Anemia
Hypotension
Bruises
Works Consulted
- The anatomy and physiology in this article was extracted mainly from The Principles of Anatomy & Physiology, Tortora, Grabowski. I also used Anatomy and Physiology by Stanley E. Gunstream 4th ed.
- The second half of this article giving us an herbal perspective on the nervous system would not have been possible without jim mcdonald’s Article Index. Thanks a thousand times to jim for putting this together.
