In this article we will discuss about the Assimilation of Food in Human Beings.
Meaning of Assimilation of Food:
The absorbed food materials are transported by blood and lymph. Lymph is finally transferred to the blood circulation. The blood transports absorbed food materials to different body cells where food materials become integral component of the living protoplasm and are used for energy, growth and repair. This is called assimilation of food.
Assimilation of Proteins, Carbohydrates and Fats:
Amino acids are not stored but are taken up by the cells in connection with the synthesis of proteins. Proteins are used for growth, repair, etc.
Excess amino acids can be converted into glucose and then to fat and are thus stored. This is an irreversible reaction. Amino acids can also be converted to glucose and used as fuel for the cell. During their conversion to glucose the amino acids are deaminated (removal of amino groups NH2).
The liver is chief site for deamination, i.e., a process by which the amino group is removed from the amino acids resulting in the production of ammonia. The ammonia is soon converted into urea, which is filtered from the blood in the kidney.
The excess of the monosaccharide’s; the glucose, fructose and galactose are usually stored in the liver and muscle cells in the form of glycogen (glycogenesis). Whenever, there is a deficiency of glucose in the blood the glycogen is converted into glucose (glycogenolysis).
Muscle glycogen is utilized during muscle contraction. Glucose is utilized in the production of energy for various body activities. A considerable amount of glucose is converted into fat and stored as such.
The fat is stored in the fat deposits of the body, such as subcutaneous layers, mesenteries, etc. The fat stored is a readily available source of fuel for the cells. Fat has important insulating properties in connection with the conservation of heat and maintenance of body temperature.
Fat also plays a protective role as filling or around packing material and between organs. In the liver phospholipids are formed which are returned to the blood to be used by all the cells. In the liver cells the fats are converted into amino acids and carbohydrates. Vitamins, salts and water are also useful for various metabolic processes.
Egestion (= Defecation):
Meaning of Egestion:
The elimination of faeces from the alimentary canal is called egestion or defecation. The faeces is waste matter discharged from the alimentary canal.
Mechanism of Egestion:
Peristalsis gradually pushes the indigestible materials of the small intestine into the large intestine or colon. Normally 1500 ml of chyme passes into the large intestine per day. The colon absorbs most of the water. It also absorbs electrolytes, including sodium and chloride from the chyme.
The epithelial cells of the colon also excrete certain salts such as iron and calcium from the blood. Escherichia coli (bacterium) lives in the colon which feeds on undigested matter. This bacterium, in turn, produces vitamin B12 (cobalamin), vitamin K, vitamin В1 (thiamine) and vitamin B2 (riboflavin) which are absorbed by the wall of colon. Consequently, the chyme converts into semisolid faeces.
As the pellets of faeces enter the rectum, distension of rectal wall induces the feeling of defecation due to a “defecation reflex”. This reflex initiates peristalsis in the last part of the colon (sigmoid colon) and the rectum, forcing the faeces towards anus. As the faeces reaches anus, involuntary relaxation of the internal anal sphincter and voluntary relaxation of external anal sphincter cause defecation.
Voluntary contractions of the diaphragm and abdominal muscles forces the sphincters open, and the faeces is expelled through the anus (contraction of the abdominal muscles and lowering of the diaphragm increases the intra-abdominal pressure which aids in the process of defecation). In infants, the defecation occurs by reflex action without the voluntary control of the external anal sphincter.
Constituents of Faeces:
The faeces consists of about three-fourth water and one- fourth solid matter. Of the solid matter is about 3 per cent bacteria, 10 to 20 per cent fat, 2 to 3 per cent protein, about 15 per cent inorganic matter and 30 per cent undigested roughage and dry constituents of digested juices.
Dead mucosal cells, mucus and cholesterol also occur in the faeces. Its brown colour is due to brown pigments, stercobilinogen and stercobilin, which are derivatives of bilirubin.
A diet is said to be balanced when various nutritional materials i.e., proteins, carbohydrates, fats, minerals, vitamins, roughage and water are present in sufficient amount and proper proportion.
Various constituents of the balanced diet provide energy, growth, repair, replacement of cells, and physiological regulation. Our food should contain the various nutrients in such proportions as can satisfy all the needs of m body.
It has been discovered that of our energy requirement, we obtain about 50% from carbohydrates, 35% from fats and 15% from proteins. Thus, we daily require about 400 to 500 grams of carbohydrates, 60 to 70 grams of fats and 65 to 75 grams of proteins. Balanced diet of each individual can be determined according to his or her needs.
Nutritional Requirements of Humans:
(i) Energy yielding nutrients:
Carbohydrates and lipids (fats) are chief energy giving nutrients. Proteins can also give energy.
(ii) Body building nutrients:
Proteins are chief body building nutrients.
(iii) Metabolic regulators:
E.g., vitamins, water and mineral salts.
(iv) Hereditary substances:
E.g., Nucleic acids (DNA and RNA).
Besides carbohydrates, proteins, fats, vitamins, minerals and water, roughage is also essential in diet.
Calorific Value of Carbohydrate, Protein and Fat:
Carbohydrates, proteins and fats serve as the chief sources of energy in humans. These are oxidized and transformed into ATP, the chemical energy form used by cells for their various activities.
Because heat is the ultimate form of all energy, the energy value of food (or any fuel) is expressed in terms of a measure of heat energy it produces on combustion. The heat energy released by combustion of one gram of food is usually known as its gross calorific value.
It is defined as the amount of heat produced in calories (cal) or in joules (J) from complete combustion of 1 gram food in a bomb calorimeter (a closed metal chamber filled with O2). The calorific value is usually expressed in terms of kcal per gram or kilojoules per gram.
(1kcal = 4.184kJ) One kilocalorie is the amount of heat energy needed to raise the temperature of one kilogram of water through 1°C (1.8°F). It is referred to kcal as the Calorie or to kJ as Joules (always capitalized). The calorific values of carbohydrates, proteins and fats are 4.1 kcal/g, 5.65 kcal/g and 9.45 kcal/g, respectively.
Physiologic Value of Carbohydrate, Protein and Fat:
The actual amount of energy liberated in the human body due to combustion of 1g of food is the physiologic value of food. It is always less than gross calorific value calculated by bomb calorimeter. The physiologic values of carbohydrates, proteins and fats are 4.0 kcal/g, 4.0 kcal/g and 9.0 kcal/g respectively.
The Physiologic Value:
The actual amount of energy liberated in the human body due to combustion of 1 g of food is the physiologic value of food. It is always less than gross calorific value calculated by bomb calorimeter. The physiologic values of carbohydrates, proteins and fats are 4.0 Kcal/g, 4.0 Kcal/g and 9.0 Kcal/g respectively.
Calorific Value and Physiologic Value of Carbohydrate, Protein and Fat:
1 Kilocalorie (Kcal) = 1000 calories
N.I. Lunin (1881) discovered vitamins. Hopkins and Funk (1912) pro-founded a ‘Vitamin Theory’. Vitamin was chemically an amine and was vital to life. Hence Funk (1911) named it Vitamine (L. vita – life + amine = vital amine). The term ‘vitamin’ is retained now omitting the terminal ‘e’ in its spelling. The book entitled ‘The vitamins’ was written by Funk and published in 1922.
Vitamins are regarded as organic compounds required in the diet in small amounts to perform specific biological normal maintenance of optimum growth and health of the organisms.
Vitamin С is the most sensitive of all vitamins to heat. Antineuritic vitamins are B1, B6 and B12. Antioxidant vitamins are A, E and C.
Vitamins are divided into two main groups.
Fat soluble vitamins, e.g., vitamins A, D, E and К
Water soluble vitamins, e.g., vitamins В-complex, С and P.
Fat soluble Vitamins:
Minerals are classified as major and trace. This classification is based on how much of the mineral is needed to the body. Major minerals (macro minerals) are important nutrients in our diet. It is suggested that we consume 0.1 gm of each of these minerals per day. Trace minerals (micro minerals), as their name indicates, are needed in only small amounts. It is suggested that we consume 0.01 gm of each trace mineral per day.