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Your cardiovascular system transports important substances such as oxygen and nutrients between tissues and organs. It also helps transport and eliminate waste products. Your heart, blood, and blood vessels are all components of the cardiovascular system

The Heart
heart3.gif (1363 bytes)  The heart is the transport system pump, and the blood vessels are the delivery routes. Using blood as the transport medium, it propels oxygen, nutrients, wastes, and other substances to and past the body cells. The heart is a hollow, muscular pump that is divided into 4 chambers. The two top chambers are called atria, and the two lower chambers are called ventricles. The two types of chambers in the heart perform different functions: the atria collect the blood that enters the heart and push it to the ventricles, which push blood out of the heart and into the arteries. In order to move blood through your heart, your heart chambers undergo alternating periods of relaxation and contraction. This allows the chambers to fill up with and pump blood. The right atrium of the heart receives deoxygenated blood from two major veins, the superior vena cava and the inferior vena cava. When this chamber contracts, blood moves out of the right atrium and into the right ventricle through the tricuspid valve. Once the right ventricle has sufficiently filled with blood, this chamber contracts, pumping blood via the pulmonary arteries into the pulmonary circuit of the cardiovascular system. Newly oxygenated blood enters the left atrium of your heart through your pulmonary veins. Once this chamber is filled with blood, the left atrial wall contracts, pushing blood into the left ventricle through the bicuspid valve. After the left ventricle has filled with blood, this chamber contracts, forcing blood out of the ventricle and into the aorta. From the aorta, blood travels through the systemic circuit of the blood vessels, bringing oxygen to tissue cells throughout the body.

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The heart wall is composed of cardiac muscle which contains nuclei, intercalated disks, and cardiac myofibrils. The intercalated disks contain two types of junctions, the desmosomes which, hold adjacent muscle cells together, and the gap junctions that allow stimulating impulses to move across the heart from cell to cell.

heart3.gif (1363 bytes)  The electrical activity of the heart is represented in an EKG tracing.

Normal EKG Tracing

P wave - atrial depolarization
QRS complex - ventricle depolarization
T wave - ventricular repolarization

Blood Vessels
Blood vessels are intricate networks of tubes that transport blood throughout the entire body. Blood vessel walls are composed of three layers: the tanica intima (endothelium or inner most layer), tanica media (the middle layer), and the tunica advetitia . The space in the center of blood vessels in called the lumen.

The tunica adventitia - is the strong outer covering of arteries and veins. It is composed of connective tissue as well as collagen and elastic fibers.

The tunica media - is the middle layer of the walls of arteries and veins. It is composed of smooth muscle and elastic fibers

The tunica intima - is the inner layer of arteries and veins. In arteries this layer is composed of an elastic membrane lining and smooth endothelium that is covered by elastic tissues.

The three main types of blood vessels are the arteries, capillaries, and veins. The arteries can then be broken down into three groups: elastic, muscular, and arteriole. The elastic arteries are the closest to the heart and have a great amount of elastin enabling them to expand. When the heart relaxes, they recoil to propel blood onward. These arteries experience the widest variation in pressure. The second kind of arteries, muscular arteries, contain more smooth muscle than elastic and experience some decline in blood pressure. Lastly, the arterioles are the smallest arteries are composed mainly of all smooth muscle. They also experience the steepest drop in blood presser and offer the greatest resistance to blood flow.

Blood pressure is the force that blood exerts against blood vessel walls. The pumping action of the heart generates blood flow. Blood pressure results when that flow is met by resistance from vessel walls. The pulse which you fell is actually a pressure wave which travels from the heart throughout the arteries. Systolic pressure is the maximum pressure exerted by the blood against the artery wall and is the result of ventricular contraction. Systolic pressure is normally about 120 mm/Hg. Diastolic pressure, is the lowest pressure in the artery. It is the result of ventricular diastole and is usually around 80 mm/Hg. Pulse pressure is the difference between systolic and diastolic pressure. This pressure is the throb felt when taking your pulse. The mean arterial pressure is a calculated average pressure in arteries (diastolic + 1/3 pulse pressure).