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.
No comments:
Post a Comment