In this article we will discuss about:- 1. Introduction to Metabolism 2. Definition of Metabolism 3. Methods.
Introduction to Metabolism:
The different food materials (mostly complex and unsuitable for absorption) are transformed into their simple and soluble form by digestion prior to the entry from the lumen of the intestine into the body through its gateway (absorption).
After their entry into the body, they undergo a series of biochemical reactions in different organs catalyzed by enzymes, coenzymes, catalysts, and governed by hormones and vitamins to serve the following purposes:
i. Synthesis of many specialized substances for the organization of these substances into the types of characteristic protoplasm of different varieties of cells and tissues forming up the organism, resulting development growth and maintenance of a living organism. Those reactions which are included in the process of synthesis of larger protoplasmic molecules from lower ones for building up tissues are collectively known as synthesis or anabolism.
ii. Production of energy required for the protoplasmic synthesis and other process of the body, viz., maintenance of temperature, movement, and generation of electrical potentials, the secretion and excretion of fluid and transport of substances against concentration gradient. Those reactions which are included in the process of breakdown of large protoplasmic molecules to smaller ones for the supply of energy are collectively called analysis or catabolism.
Definition of Metabolism:
Thus the term metabolism of a food substance is meant by a series of specific biochemical reactions occurring within the living organism from the time of its incorporation into the cell or tissue till its excretion, of which some are concerned with tissue synthesis and others with tissue breakdown what are termed as anabolism and catabolism respectively. Although both anabolism and catabolism are reversible biochemical reactions but growth and loss of tissue mass (breakdown of tissue) depends on predominance of one over the other opposite reaction.
Methods of Metabolic Study:
The chemical reaction of the tissue is so numerous and fast that the study of these reactions, either individual or overall pictures of these reactions had been encountered with much difficulty due to lack of suitable equipment and methods in the past.
But recent advancement in researches in the field of development of different techniques and methods at modern times, it has been possible today in unfolding the total picture of metabolism.
The general principles of the different methods employed in the study of metabolism are as follows:
i. Study of the Metabolic Process:
Few steps in the path of metabolism may be known by the biochemical analysis of body fluids of patients suffering from diseases either congenital or acquired whose metabolic reactions checked or inhibited or deviated abnormally without passing to its final end products, e.g., Diabetes mellitus, ketosis, alcaptonuria, give some information of glucose, fat and protein metabolism respectively. These abnormal metabolic conditions may be produced experimentally in animals and the results may be confirmed.
ii. Study of Metabolism by Arresting Few Metabolic Steps with Certain Metabolic Poisons:
This is an important method of studying the breakdown of fatty acids (vide oxidation of fatty acids.)
iii. Study of Metabolism under the Influence of Endocrines:
This may be observed by extirpation of the gland and introduction of the hormone, and the results are compared and confirmed with the picture obtained in diseases suffering from hypo-activity and hyperactivity of the gland.
iv. Study of Different Organs in Determination of Site of Reaction:
(a) Extirpation of liver (by Mann et al), spleen or other viscera and noting the consequent effect on general metabolism or the metabolism of a particular administered substance.
(b) Perfusion of isolated organs with a solution of the test material and to note to changes therein.
(c) Incubation of the test solution with thin slices of the organ or with the minced tissues of the organ.
(d) Fistula preparations with the purpose of bypassing an organ, such as Eck’s fistula in which communication is established between portal vein and inferior vena cava. The portal blood directly drains into inferior vena cava and liver is by-passed. With this preparation, the role of liver on the metabolism of many substances can be studied.
(e) Angiostomy experiments. Insertion of cannulae into suitable blood vessels through which blood can be withdrawn as well as a test solution can be easily injected. Dogs with such cannulae in the hepatic, portal and renal veins have survived normally for many months.
v. Feeding Experiments:
(a) This is done by altering the quality and quantity of foodstuffs, vitamins, minerals etc., and observing the consequent metabolic changes.
(b) Administration of all theoretically possible intermediate compounds of a substance, to animals, and to see whether such compounds are metabolized in the same way as the parent substance itself. In this way the intermediate stages of metabolism of a substance may be found out.
vi. Biochemical Changes:
Study of biochemical changes of blood, urine, faeces, tissues, organs, etc., is also valuable, particularly in accompaniment with other metabolic experiments.
vii. Study of Basal Metabolic Rate (B.M.R.):
Study of basal metabolic rate (B.M.R.), respiratory quotients (R.Q.) nitrogen equilibrium, specific dynamic action, etc.
viii. Application of Isotopes:
The latest advancement in the study of metabolic processes is the application of natural and radioactive isotopes. Compounds to be studied, is labelled or marked by replacing it’s one of the element by isotope and administered. The changes undergone by such ‘labelled’ compounds, their migration from place to place and finally their excretion from the body are observed with the help of suitable instruments and by other physio-chemical methods.
Since isotopes are treated by the tissues in the same way as their normal homologue, this process is extremely valuable for metabolic studies and all disadvantages of metabolic studies can be overcome with isotopes. Natural isotopes remain as mixtures in all natural sources and can be isolated by careful fractionation. Radioactive isotopes can be estimated by the electroscope or the Gieger-Muller counter, that is, those instruments which can detect radiations.
Stable or partial stable compounds have been prepared by replacing the relevant atoms with the corresponding natural or radioactive isotopes respectively (as and when required) and have been extensively applied in the study of a absorption, metabolism and excretion of proteins, fats, carbohydrates, salts, water and hormones, etc.