NORMAL CARDIOVASCULAR FUNCTION

The cardiovascular or circulatory system uses a muscular pump to send a complex fluid on a continuous trip through a closed system of tubes.  The pump is the heart, the fluid is blood, and the closed system of tubes is the network of blood vessels.

The Vascular System

The term vascular system refers to the body’s blood vessels.  Although we might be familiar with the arteries (vessels that carry blood away from the heart) and the veins (vessels that carry blood toward the heart), arterioles, capillaries, and venules are also include in the vascular system.

Arterioles are the farther, small-diameter extensions of arteries.  These arterioles lead eventually to capillaries, the smallest extensions of the vascular system.  At the capillary level, exchanges of oxygen, food, and waste occur between cells and the blood.

Once the blood leaves the capillaries and begins its return to the heart, it drains into small veins, or venules.  The blood in the venules flows into increasingly larger vessels called veins.  Blood pressure is highest in arteries and lowest in veins, especially the largest veins, which empty into the right atrium of the heart.

The Heart

The heart is four-chambered pump designed to create the pressure required to circulate blood throughout the body.  Usually considered to be about the size of a person’s clenched fist, this organ lies slightly tilted between the lungs in the central portion of the thorax.  The heart does lie completely in the center of the chest.  Approximately two-third of the heart is to the left of the body midline, and one third is to the right.

Two upper chambers, called atria, and two lower chambers, called ventricles, from the heart.  Te thin-walled atrial chambers are considered collecting chambers, and the thick-walled muscular ventricles are considered the pumping chambers.  The right and left sides of the heart are divided by a partition called the septum.

For the heart muscle to function well, it must be supplied with adequate amounts of oxygen.  The two main coronary arteries (and their numerous branches) accomplish this.  These arteries are located outside the heart.  If the coronary arteries are diseased, a heart attack (myocardial infarction) is possible.

Heart Stimulation

The heart contracts and relaxes through the delicate interplay of cardiac muscle tissue and cardiac electrical centers called nodes.  Nodal tissue generates the electrical impulses necessary to contract heart muscle.  The heart’s electrical activity is measured by an instrument called an electrocardiograph (ECG or EKG), which provides a printout called an electrocardiogram, which can be evaluated to determine cardiac electrical functioning.

Blood

The average-sized adult has approximately 5 quarts of blood in his or her circulatory system.  The functions of blood, which are performed continuously, are similar to the overall functions of the circulatory system and include the following:

·         Transportation of nutrients, oxygen, wastes, hormones, and enzymes

·         Regulation of water content of body cells and fluids

·         Buffering to help maintain appropriate pH balance of body fluids

·         Regulation of body temperature; the water component in the blood absorbs heat and transfers it

·         Prevention of blood loss; by coagulating or clotting, the blood can alter its form to prevent blood loss through injured vessels

Protection against toxins and microorganisms, accomplished by chemical substances called antibodies and specialized cellular elements circulating in the bloodstream.