he cardiovascular system is composed of the heart, blood vessels and blood. The heart is shaped like a blunt cone and is about the size of a clenched fist. In males it weighs about 300 grams, in females about 250 grams. Because of its importance, the heart is one of the first organs to begin functioning in a developing embryo, about four weeks after conception. The heart is divided into four chambers – two entering chambers called the atria and two pumping chambers called the ventricles. Because of this unique arrangement, the heart can be considered a double pump. The oxygen-depleted blood from the body’s tissues returns to the right atrium and is then pumped by the right ventricle into the lungs where oxygen and carbon dioxide are exchanged. The newly oxygenated blood returns to the heart at the left atrium. From there it is pumped by the powerful left ventricle to the rest of the body.
Although the heart is the center of the cardiovascular system, it’s the affiliated blood vessels that carry the blood throughout the body. There are three types of blood vessels – arteries, veins and capillaries. While all three carry blood, each has a different task. Arteries carry blood away from the heart. Because of this function, arterial walls are very elastic and can expand in relation to the blood being pushed by the contracting ventricles. You can feel this sensation the next time you perform a heavy set of squats. Place your fingers on your wrist and notice the pulsations just below the skin surface. Each pulse corresponds to one beat of the heart. We commonly refer to this rate as the pulse, though in fact we are measuring heart rate.
Veins return blood to the heart. They are more flexible than arteries because they have thinner walls, and will collapse if blood pressure is not maintained. The speed of blood traveling through veins is much slower than through arteries. Capillaries are microscopic blood vessels which serve as exchange points among arteries, veins, and the body’s tissues. Their small size and large numbers mean an enormous amount of surface area for the exchange of gases, nutrients and waste products. To give an idea of the amount of surface area involved, if the capillaries of the body were connected end to end, the resulting chain would stretch 60,000 miles. Perhaps more revealing is the fact that for every pound of fat lost, the heart has 1000 fewer miles to pump blood through.
The main purpose of all this plumbing is to provide a highway for the body’s blood supply.Blood makes up about 8 percent of the bodyweight of an average male, translating into a volume of about five to six liters. It consists of a liquid part, called plasma, and a solid part, called formed elements. The formed elements include red blood cells, white blood cells and platelets. As blood circulates throughout the body, tissues are continuously adding their waste products, secretions and metabolites. Simultaneously, the body’s tissues remove vital nutrients, oxygen, hormones and other important substances from the blood.
In summary, blood serves the following functions:
It transports oxygen from the lungs to the body tissues, and transports the resulting waste products of cellular metabolism from the body’s tissues to the various filtration organs. These include the liver, kidneys and sweat glands.
BLOOD REGULATES THE FOLLOWING:
- Blood-clotting to stop bleeding.
- Body temperature, by increasing or decreasing blood flow to the skin.
- Acid-base balance (pH) through the distribution of buffers.
- The amount of water and electrolytes in body fluids.
- Blood protects against harmful microorganisms and other dangerous substances by transporting white blood cells, proteins and antibodies to the site or sites of infection.
THE COMPONENTS OF BLOOD
Plasma — This is the liquid part of blood, which is comprised of 90 percent water, 7 percent proteins, and 3 percent dissolved substances such as amino acids, glucose, enzymes, hormones, electrolytes, wastes and nutrients.
Red blood cells (RBCs) — These make up half the volume of the blood. They are shaped like a flat donut with an indentation rather than a hole in the middle. There are about 25 trillion RBCs in the human body at a density of six million for every cubic millimeter of blood. Virtually the entire weight of the RBC is composed of an oxygen-attracting globular protein called haemoglobin. Since part of the haemoglobin molecule contains iron, the RBC has a reddish color – hence the name red blood cell. The main function of RBCs is to transport oxygen from the lungs to the body’s tissues. At the same time waste gases such as carbon dioxide are transported to the lungs where they are exhaled.
White blood cells (WBCs) — These serve as scavengers. They destroy microorganisms at infection sites, help remove foreign molecules, and remove debris that results from dead or injured tissue cells. In adults there are between 4,000 and 11,000 WBCs per cubic millimeter of blood. This number may increase to 25,000 or more in times of infection.
Platelets — These are dynamically shaped blood cells whose main function is to start the intricate process of blood-clotting. Roughly 200 billion platelets are produced by the body every day, each with a life span of only seven to eight days. When a blood vessel is injured, platelets immediately move to the injured area and begin to clump together. They release a chemical called serotonin, a blood-vessel constrictor. If the cut is small, the platelet plug will prevent blood loss. If the cut is considerable, platelets begin the process of blood-clotting. We will not look at this mechanism here. Suffice it to say there are numerous steps, resulting in a fibrous net which entangles escaping blood cells, forming a clot. After a few hours the clot begins to dry out, and a solid barrier is left. After a few days the dried-out clot (a scab) falls off, exposing the repaired underlying tissue.
In addition to the blood circulatory system, we have a subsystem called the lymphatic system.
Its three main functions are:
- Collection and return of interstitial fluid to the blood.
- Contribution to the immune system’s fight against invading organisms.
- Absorption of lipids from the digestive tract.
The lymphatic system is similar to the cardiovascular system in that it has a network of transport vessels and associated fluid. The fluid, called lymph, is a clear liquid that serves as the system’s transport medium. At regular intervals lymph vessels are organized into small masses of tissue called lymph nodules (nodes). The tonsils and adenoids are two such examples. The thymus gland and spleen are also part of the lymph system. You’re probably aware that it’s possible to survive without parts of the lymph system (spleen and tonsils). If these become infected and have to be removed, other parts of the body take over and perform the same functions.
HOW IT WORKS
As with the cardiovascular system, the lymph vessels terminate at the body’s tissues with a network of capillaries. Interstitial fluid enters the capillaries and is passed on to larger vessels called lymphatics. This fluid is then carried by way of the lymphatics to the various lymph nodes. Here it is filtered to remove bacteria and other harmful matter. Afterward the fluid reenters the circulatory system by way of the subclavian veins found in the shoulder region. Unlike the cardiovascular system, the lymph system does not have a pumping muscle like the heart. Instead, the walls of the lymph vessels pulsate, pushing the fluid along. Valves within the vessels prevent the lymph from flowing backward. The rate of flow is increased when anything compresses body tissue. When muscles contract or arteries pulsate, the increased pressure on the lymph vessels enhances the flow of lymph fluid.
Bodybuilders and other hard-training athletes may periodically notice a swelling of thelymph nodes, particularly in the neck, groin and armpit regions. This can be a sign of overtraining. The increased stress placed on the body taxes the lymph system to the limit. The swelling is the result of a buildup of fluid containing the byproducts of exercise. The lymph system will cleanse itself of such metabolic debris after a few days, and the swelling will go down. Of course, if you keep overstressing the body with a twice-a-day, six-day-a-week program, this process will be impeded.