1. TRANSPORT OF OXYGEN AND CARBON-DIOXIDE: Blood transports oxygen from the lungs and skin, etc. to the tissues. It then transports carbon-dioxide from the tissues back to the respiratory surfaces. Thus blood helps in respiration.
2. TRANSPORT OF FOOD: Blood carries soluble food from the intestines, first to the liver and then to the tissues for their cellular activities. As already described under the head—Digestion, in this chapter, the nutritive elements transported by the blood are—glucose, amino acids, fats, vitamins, minerals and water.
3. TRANSPORT OF WASTE PRODUCTS: Waste products are being constantly produced by the body cells, which are harmful to the body. They are eliminated from the body by the blood, which transports these wastes to the kidneys, lungs, skin and the intestines to be finally eliminated.
4. DEFENCE AGAINST INFECTION: Blood contains special products called ANTI-BODIES, etc. which combat viruses and play a protective role by neutralising the toxins.
5. CLOTTING OF BLOOD: Blood prevents loss of blood in injury, as it has the power of conglobation.
6. EXCRETION: This is also one of the fundamental elements of Digestion. By excretion we mean the removal of toxic waste products being eliminated in the body during the process of METABOLISM. These waste products may be in the form of gases, liquids or solids. The gaseous waste, that is, carbon-dioxide is exhaled out in breath from the lungs.
The solid wastes are fibres (the roughage) of vegetables, etc. and fat droplets. These are eliminated as undigested food by the small intestines, the walls of which (the ileum) absorb the digested food and leave out the undigested food.
This solid waste, or undigested food, is pushed out by the small intestine into the large intestine, from which it is finally discharged, or defecated through the anus.
The liquid wastes are ammonia and urea (the nitrogenous wastes). These are separated from blood by the two kidneys. The kidneys collect the excretory products and eliminate them in the form of urine, which passes on to the bladder and from there it is released through the urethra.
IN SUMMARY:
To sum up, this chapter would have given the reader a clear idea of the importance of food, in its components— proteins, carbohydrates and fats; how they are utilized in the cells of our body tissues, with the help of the body’s juices secreted from different organs.
Along with their knowledge, the reader would have learnt how liver provides bile juices, the pancreas, the pancreatic juice and the intestines, the ileum (enzymes):
· further he would have come to know how these three chemical compounds digest the three components of food (proteins, carbohydrates and fats) in the Duodenum and how the digested material is passed on to the cells through the small intestines by the blood for nourishment of the body;
· how the blood reacts in the cells producing energy by chemical oxidation with the help of oxygen, eliminating gaseous, solid and liquid wastes;
· how the gaseous wastes, like carbon-dioxide are exhaled out in respiration process;
· how the solid undigested wastes, like fibres or roughage are eliminated in the excretion process by the small intestine to the large intestine for defecation through the anus;
· how the liquid wastes of nitrogen-ammonia and urea are separated from the blood by two kidneys which eliminate them as urine into the bladder to be passed out of the urethra.