When food is eaten, the teeth and oral cavity are geared to break large food particles into smaller ones that may be swallowed with ease. The food is mixed with saliva, which contains weak chemicals that put the process of digestion into operation. From the oral cavity, the food slips into the food tube called the esophagus. This tube has a small valve at the far end, called the cardiac valve. This opens at regular intervals, enabling the food mass (called a bolus) to enter the stomach. The stomach is merely a dilated portion of the digestive system. It is lined with specialized cells that actively secrete a powerful acid (hydrochloric acid) and certain digestive juices. Here digestion of the food really gets under way. The food particles are reduced into still smaller particles, until a thick fluid volume is produced. From here, the food passes through another valve, called the pylorus, into the next part of the intestinal (or digestive or bowel) system, called the duodenum. Here there is a prolongation and intensification of the digestive process. Gradually the duodenum empties the food into the next part, the so-called small intestinal system. This is the lengthy bowel system, and here digestion continues. This is also where the final ingredients of the broken-clown food are actively absorbed by the cells lining the bowel wall and pass into the bloodstream. Apart from the gaseous interchange occurring, other vital blood-borne products are also deposited at these points – food, vitamins, enzymes, immunological agents. The great carrying capacity of the blood fluid is fully taken advantage of at this juncture.
Just as carbon dioxide is passed back into the blood, so other waste products of the body’s metabolism are also injected into the blood. These are unwanted chemicals and other contaminants that are totally useless at the cell face.
As these are passed back into the fluid of the blood, the circulation rapidly moves onwards. The capillaries commence to link up with larger vessels, and these in turn join bigger ones called venules. As venules flow into still larger ones, called veins, the total oxygen-reduced blood accumulates. The blood enters larger and still larger veins until it finally flows into a major one that conveys it directly back into the right-hand atrium of the heart once more.
There is a relatively small volume of blood in your body, but it is recycled continuously throughout the system.
If you would like to know how much blood is in your body, you can work it out with this simple sum. Check your body weight on the scales. Now for each kilogram of body weight, the body contains 60 – 80 ml of blood. So if you weigh about 50 kg (approximately 8 stone), and are a nice trim female, and allow an average of 70 ml for each kg, it works out as: 50 kg x 70 ml = 3500 ml, or 3.5 litres of blood.
Considering the tremendous amount of work the blood does, and the remarkable load of material it carries, this is efficiency of the highest order.
If human beings applied this same efficiency to their own physical output of work, in terms of achievement, the net effect would be earth-shattering.
The nation’s highway system would be built in a few weeks; the total work-entailing programs would be finished in record time. Perhaps this would not be a good thing, for very soon there would be nothing left to do. Then humans might turn to warfare and bloodshed again, and totally revoke all the good that had been done. But they are doing this anyway, so what’s the difference? Maybe it is food for contemplation.
For the heart to be able to carry this enormous, incessant workload it must receive a substantial amount of oxygen and food supplies itself. It cannot receive this directly from the fluid it pumps, for this is purely a mechanical procedure, and the blood flows through the cardiac chambers.
However, the heart has an important circulation buried in the deep tissues of the heart muscle. This is termed the coronary blood supply, and it plays a vital part throughout life.
Major vessels gradually branch out through the heart structure, taking valuable supplies to every part. Similarly, a venous system collects this deoxygenated blood to take it back via the general circulation to the lung system.
It is essential that the efficiency of these heart vessels be maintained throughout life. Unless they are, problems loom. If the heart is deprived of its vital elements, then it is no longer capable of operating at peak efficiency.