FACTS ABOUT HUMAN DIGESTIVE SYSTEM FOR COMPETITIVE EXAMS

• Digestion, essentially a hydrolytic process, is carried out by various enzymes using water molecules for cleavage.The enzymes which bring about digestion are called hydrolases.
• Digestion may be intracellular (within the cell) or extracellular (in digestive cavity).
• The unicellular animals like Amoeba and porifers (Sponges) digest the food within the cells and show intracellular digestion.
• The cnidarians (e.g. Hydra, Aurelia etc.) have sac like coelenteron or gastrovascular cavity, which is lined by various type of endoderm cells. The food is partially reduced to small fragments by extracellular digestion by the enzymes secreted by the gland cells of endoderm. The small fragments of the food are ingested by nutritive cells and complete the digestion intracellularly.
• The free living Platyhelminthes (e. g. Planarian) also employ both types of digestion i.e. intracellular and extracellular.
• Nutritional requirements are basically supplied in the form of nutrients which may be organic and inorganic.
• Food is any substance (especially solid) that can be taken into the body of an animal and plant to maintain its life by providing one or more nutrients for supply of energy and materials.
• The major constituents of food are carbohydrates,proteins, fats, vitamins, minerals and water.
• If all these components are present in optimum proportion and quantity for maintaining the body in perfect state of health, activity and development then the food is called balanced diet.
• According to their utility in the body, these
• nutrients are divided into four categories – energy producers (carbohydrates, fat); body builders (proteins), metabolic regulators (vitamins and minerals and H2O) and hereditary substances [nucleic acids
• (DNA, RNA)].
•  Main component of food and their  sources.
• Carbohydrate:Flour, rice, potatoes, corn. vegetables, bread etc.
• Protein: Milk, eggs, meat, fish, beans, peas,nuts, pulses and cereals etc.
• Fats and Oils: Groundnut oil, coconut oil, sunflower oil, ghee, butter, milk, cheese, meat,egg, fishes like cod and herring.
• Water :Liquids (water, juices, milk) and some fruits like lettuce, orange, melons.
• Vitamins :Balanced diet provide all essential vitamins for body health.
• Minerals: Dairy products, vegetables, fruits meat, chicken etc.
• Balanced diet should have protein 1/5, fat 1/5 and carbohydrate 3/5. Carbohydrates provide energy and heat.
• 1 gm of carbohydrate yield 4 kcal of energy onoxidation in the body. It is called its physiological fuel value.
• Carbohydrates are more suitable for the production of energy in the body than proteins and fats, because carbohydrates contain relatively more oxygen and require less molecular oxygen for their oxidation.
• Athletes, labourers doing heavy work and
• mountaineers should live on high carbohydrate diets.
• Protein are essential for body growth and repair. Basic unit or smallest structural unit of proteins are amino acids.
• Amino acids absorbed from the food are used to synthesise structural proteins (collagen, elastin keratins), enzymes and hormones, (pepsin, trypsin, insulin), haemoglobin, skin pigment, purines, pyrimidines and blood proteins.
• The physiological fuel value of protein is 4 kcal.
• The dietary requirement of proteins rises during pregnancy and lactation, growth and tissue repair.
• Nutritionally amino acids are of two types- essential (not synthesized in body and must be included in diet) and non-essential (can be synthesized in body from carbohydrate metabolites).
• Essential amino acids are 8 in number (methionine, threonine, tryptophan, valine, leucine, isoleucine, lysine and phenylalanine) and non essential amino acids are 12 in number (alanine, proline, glycine, aspartic acid, tyrosine, serine, cysteine, asparagine, glumatic acid, glutamine, arginine and histidine).
• Semi-indispensible amino acids are formed slowly and are required only during periods of rapid tissue growth. Eg. arginine and histidine.
• Twenty amino acids, linked together by peptide bonds, make all different proteins required by the body.
• lf amino acids are used for energy liberation (as during starvation), ketones are formed. The phenomenon is called ketosis or acidosis.
• Fats are used as stored food to be used in the
• production of energy.
• Calorific value of fat is 9.45 kcal means lgm of
• fat yield 9.45 kcal energy on oxidation in the body.
• An essential fatty acid (EFA) is one which must be included in the diet because it cannot be made in the body,Linoleic acid and alpha linolenic acid are the two most essential fatty acids.
• Saturated fatty acid do not possess double bonds in their carbon chains,
• eg. palmitic acid.
• Unsaturated fatty acid  possess   more double bonds in their carbon chains. Linoleic acid and linolenic acid are both poly unsaturated fatty acids (PUFAs) and help in - forming the structure of membrane, transport,breakdown and excretion of cholesterol, normaldevelopmenf and functioning of retina and brain.Free fatty acid (FFA) circulate in blood in
• combination with albumin.
• Lumin discovered vitamins and the term vitamin was coined by Casimir Funk (1912).
• Vitamins are non-energy producing organic
• substances which are vitally essential in traces for proper use of macronutrients in cell metabolism and hence for proper growth and function.
• On the basis of solubility, vitamins are divided into 2 main categories - water soluble vitamins (vitamin B complex and vitamin C) and fat soluble vitamins (A, D, E and K).
• Fat soluble vitamins are absorbed in the alimentary canal without any breakdown.
• Vitamin D (steroid vitamin) is synthesized in skin cells in sunlight from 7-dehydrocholesterol (i.e. provitamin DS).
• Vitamin often acts as coenzymes.
• During prolonged fasting first carbohydrates are used up, followed by fat and proteins towards end. Apart from organic chemicals, human body needs inorganic chemical elements, called minerals.
• Depending on the necessity, minerals can be
• divided into - macroelements (required in amount more than 1 gm) and microelement (required in trace amountless than lgm).
• Both macroelements and microelements (minerals) are found in milk, cereals, fresh fruits and vegetables, sea food etc.Basal metabolic rate (BMR) is the minimal caloric
• requirement needed to sustain life in a resting individual. For normal adult it is 1600 Kcal/day.Routine metabolic rate (RMR) is the energy requirement of a moderately active person. RMR is 2800 Kcal for adult males and 2200 Kcal for adult females.
• Sprue, caused by deficiency of folacin (folic acid) is characterised by ulceration of mouth,
• inflammation of bowel, inability to absorb(especially fats), diarrhoea, weakness and anaemia.
• Anorexia nervosa is sometimes referred to as ‘slimmers’s disease’ (literally means “loss ofappetite through nervous causes).
• Disorders of nutrition are of two types-malnutrition and overnutrition.
• Malnutrition (PEM  protein malnutrition) is primarily due to an inadequate intake of food (particularly protein) both in quantity and quality and infections etc, which increases requirements for calories, proteins and other nutrients, while decreasing their absorption and utilization. It generally affects infants and children.
• Two very commonly occurring diseases due to protein malnutrition are - kwashiorkar and marasmus.
• Symptoms of kwashiorkar are retarded growth of body and brain, protruding belly, oedema, slender legs, bulging eyes and diarrhoea.
• Symptoms-of marasmus are mental retardation, lean and ‘weak body, dry thin and wrinkled skin. Marasmus is due to deticiency of protein and calories. It occurs in children between 6 monthsand 3 years of age and kwashiorkar is common in infants under l years of age whose diets are deficient of proteins.
• Over nutrition means excessive intake of particular nutrient which produces adverse symptoms.Eg.obesity and hypercholesterolemia.
• Obesity occurs due to greater intake of food calories than the requirement of body. It is more common in persons having higher intake of sweets, carbohydrates richfood, fried articles, fat rich food and absence of roughage of body.Obesity is characterised by large accumulation of fat in tissues, bulky; overweight body which leads to high blood pressure and heart problems and which are prone to diabetes, hypertension and other disorders.
• Hypercholesterolemia occurs due to excessive intake of saturated fats like butten ghee, vegetable oil, red meat and egg and reduced biotin intake.
• Symptoms of hypercholesterolemia are tremendously increased blood cholesterol level, shrinkage of blood vessels due to cholesterol deposition, high blood pressure and various cardiac disorders.