Nutrition is a process by which organisms obtain those substance which are utilized for their growth and maintenance and for meeting their energy needs. These substance are called Nutrients.
5.1 - FOOD AND NUTRIENTS OF ANIMALS:
Nutrients provide the metabolic energy and raw materials for growth , repair of tissues, production of gametes and protection from diseases.
TYPES OF NUTRIENTS:
1 - Macronutrients :Also called as ‘Proximate Principles of Food’. These are the main energy source for different body functions. e.g. carbohydrates, Lipids, Proteins.
2 - Micronutrients : Also called ‘Protective Principles of Food”. These do not provide energy but their deficiency causes diseases and abnormalities e.g. Minerals, Water, Vitamins
3 - Macroelements: Also known as’ Essential Elements’. These are 21 in number e.g. Na, K, S, Ca, P, Mg. These are essential for human body.
4- Microelements :Also known as ‘Trace elements’. These are required in very less amount e.g. Fe, I, Zn, Mn, Co, Cu, Mo etc.
5.2- MODES OF NUTRITION IN ANIMALS:
Animals have heterotrophic nutrition (i.e. they depend on others for food). Heterotrophic nutrition is of 4 major types:
(I) Holozoic: The mode of taking solid or liquid food through mouth is called holozoic nutrition e.g. in most of the animals, Man.
(II) Saprozoic: In this mode of nutrition , animals secrete digestive enzymes to dissolve decaying organic matter and then absorb it through their body surface e.g. in Fungi, Bacteria
(III) Parasitic: In this , one organism ( parasite) derives food from other organism ( Host) e.g.Plasmodium, Ascaris etc.
(IV) Symbiotic(Mutualism) : In this , two animals live in association with each other and derive nutrition from each other. e.g.E. coli lives in intestine of man and synthesize vit B12 , which is beneficial to man. In returnE. coli receives simpler food from intestine.
TYPE OF HOLOZOIC NUTRITION
There are three main categories of holozoic animals:
* Herbivores: These are plant eating e.g. Cow, Horse.
* Carnivores: These are flesh eaters e.g. Lion, Dog.
* Omnivores: These eat plant and flesh both e.g. Man, Crow.
Other categories of holozoic animals are:
* Insectivores: Insect eaters e.g. Lizards.
* Frugivores: Fruit eaters e.g. Birds, Monkeys.
* Sanguinivores : feed on vertebrate blood e.g. Leech
* Fluid Feeders: Feed on plant fluid e.g. Butterflies.
* Predators: Larger animals feed upon smaller animals e.g. Eagle
* Grainivorous : Feed on grains e.g. Pigeon
STEPS OF HOLOZOIC NUTRITION
It involves following steps:
(i) Ingestion: Intake of food. Intake of microscopic organism is called Microphagy . Intake of larger organisms is called Macrophagy.
(ii)Digestion: Breaking of complex food components into simpler, soluble form by hydrolysis is digestion. It can be Intracellular i.e. occurring inside food vacuole in the cytoplasm of cell e.g. in Protozoans
OR
It can be Extracellular i.e. occurring outside the cell in a digestive cavity .e.g. in all vertebrates. In most animals, there is gastrovascular cavity lined by gland cells which secret enzymes to digest food.
(iii)Absorption: Digested food is absorbed in cell cytoplasm or in the cells lining the alimentary canal. This food is then absorbed in the blood.
(iv) Assimilation : Use of the simple food components to synthesize complex food components is assimilation.
(v) Egestion : Elimination of undigested food as faeces is egestion.
5.3 - DIGESTIVE SYSTEM OF COCKROACH:
It consists of alimentary canal & salivary glands. Cockroach are omnivores. Mandibles cut the food and then it is passed to buccal cavity, where it mixes with saliva. Then it enters into crop where teeth mince the food, then it reaches to gizzard. Lining of midgut and hepaticcaeca secretes various enzymes which digest the food. Food is absorbed in midgut . undigested food passes to hindgut & gets egested through anus.
DIGESTIVE SYSTEM OF HUMANS :
It is formed of two parts:-
(i) Alimentary Canal
(ii) Digestive Glands
1 - ALIMENTARY CANAL: It is coiled muscular tube about 6-9 metres in length. It comprises of
* Mouth: It is an opening bound by2 movable lips. It is meant for ingestion.
* Buccal Cavity ( Oral Cavity): Mouth leads into buccal cavity. Its roof is calledPalate. Posterior palate is hard and called ‘ Hard palate: Anterior part of palate is soft and is called soft palate . Oral cavity has tongue and teeth. Teeth are embedded in the two jaws ( lower jaw and upper jaw). Each half of the jaw holds 4 type of teeth ( Incisors, Canines, Premolars, molars)
Incisors( cutting teeth) are chisel shaped, sharp, pointed and meant for cutting. These are 8 incisors in all.
Canines( Tearing Teeth) are dagger shaped and meant for ripping and shredding. There are total 4 canines.
Pre-molars(Grinding/Cheek teeth) are broad teeth meant for crushing and grinding the food. There are total 8 premolars.
Molars( Grinding/ Cheek teeth) are also broad and meantfor crushing and grinding the food . These are 12 in number.
Dental Formula - It is formula representing the arrangement of teeth.2123 / 2123 or I 2/2 , C 1/1, Pm 2/2 , M 3/3
Where I is incisor, C is Canine, Pm is Pre-molar , M is molars.
Human teeth arediphyodont ( 2 sets - milk & permanent)thecodont ( teeth embedded in jaw socket) andheterodont ( have different types of teeth).
Structure of Teeth: Human tooth has 3 parts- Crown( above the gum and is covered by hard enamel), Neck( fleshy and covered by gum) and Root( embedded in jaw socket). Both, crown and Root are covered by bony dentine . Inside, there is Central pulphaving nerve and blood supply.
Oral cavity leads to pharynx, then to oesophagus. Epiglottis guards the opening of trachea Oesophagus leads into stomach via diaphragm. Oesophageal sphincter guards the opening of oesophagus. Stomach has 3 regions - upper part ‘Fundus’, middle part ‘Body’ and lower part ‘ Pylorus’ or ‘Antrum’. Pylorus opens into small intestine. S. Intestine has 3 parts - Duodenum,Jejum and Ileum. S. Intestine leads into large intestine/colon. A vestigial organ- ‘caecum’ is present at the junction of s. intestine and large intestine. Finger like projection ‘Appendix’ emerges from the top of caecum. L. Intestine ascends from caecum as ‘Ascending colon’. Then crosses to left side as ‘transverse colon’ and descends again as ‘Descending colon’ Colon empties into rectum.
HISTOLOGY OF HUMAN GUT (Alimentary Canal)
Alimentary canal has four basic layers. These are ( from outside to inside)
(i)Serosa : Outermost layer, made of sequamous epithelium.
(ii) Muscularis externa: It is composed of outer longitudinal and inner circular muscle fibres.
(iii)Submucosa: It has dense connective tissue, richly supplied with blood vessels Mucosa>: It is innermost layer and has secretive and absorptive cells. It secretes mucus to lubricate the lining of gut.
(iv) Mucosa has numerous finger like projections called ‘villi’. Villi has blood capillaries and lymph vessels. ‘Central lacteal’ is the largest blood vessel. Villi has microvilli ( brush border) which increase surface area for absorption. Mucous glands or Goblet cells are present on surface of mucosa. These lubricate mucosal epithelium by secreting mucus. Sometimes epithelium invaginates into submucosa and forms pits . Pits of intestine are called ‘Crypts of Leiberkuhn’
THE ACCESSORY DIGESTIVE ORGANS:
Tongue is an accessory digestive organ. It is located in buccal cavity by bones- styloid and Hyoid. Gustatory receptors called ‘ Taste buds’ are present on the tongue. The accessory digestive glands are
1 - Salivary Glands: There are 3 pairs of salivary glands-Parotid glands( in the cheek), Sublingual ( beneath the tongue) and submandibular ( at the angles of lower jaw). These secrete saliva.
2 - Liver: It is the largest gland of the body, is located in the upper right side of abdominal cavity just below the diaphragm.
3 - Gall Bladder: Pear like structure located below liver . It stores bile secreted by liver.
4 - Pancreas: It is an elongated gland lying partly behind the stomach in abdomen
MOBILITY OF HUMAN GUT
The ability of alimentary canal to contract is called ‘Mobility’. Food moves along the length of alimentary canal so as to get digested and absorbed. First the food is tasted ( in mouth), then it mixes with saliva. Tongue helps the food to mix with saliva. And the form a round structure- bolus. Bolus is pushed into oesophagus by process of swallowing. During swallowing , openings of nasal passage & trachea are closed by epiglottis. A contraction wave called ‘Peristalsis’ pushes the food down. Then bolus enters stomach. The sphincter at the junction of oesophagus and stomach closes so that the food doesn’t go back.
GASTRO INTESTINAL SECRETION AND DIGESTION:
The secretions from salivary glands, secretary cells in stomach, secretary cells of Pancreas and liver help in digestion. Group of enzymes called ‘ Hydrolases’ break the food and the process in Hydrolysis. The phases are:-
* Salivary Phase: Occurs in buccal cavity. Salivary glands secrete saliva which contains enzymes (Ptyalin and Maltase) and ions.
- Enzyme Ptyalin ( a-Amylase) acts on starch and breaks it into maltose.
- Enzyme Maltase acts on Maltose and converts it into glucose.
- Bicarbonate ions in saliva neutrilize acids of food.
- Thiocyanate ions of saliva act as antimicrobial agents. Food passes into stomach from buccal
cavity.
* Gastric Phase: Takes place in stomach . Food is acted upon mechanically and chemically. Mechanically, wall of stomach undergoes rhythmic contractions and breaks the food.
Chemically, food is acted upon by gastric juice secreted by gastric glands of the stomach. Gastric juice contains:-
- HCl:- Secreted by oxyntic ( parietal) cells. Acts as disinfectant and activator of proenzymes.
- Propepsin:-It is inactive form . It is converted into active form Pepsin by HCl. It breaks proteins into proteoses and peptones.
- Mucus : Secreted by goblet cells present in epithelium of stomach. Acts a lubricant.
Semidigested food called ‘Chyme’leaves the stomach and enters duodenum.
* Intestinal Phase: It takes place in small intestine . There are three juices: Bile juice ( from liver), Pancreatic juice ( from pancreas) and Intestinal juice ( from intestinal glands).
-Bile Juice : It is stored in gall bladder, reaches to small intestine by bile duct . It contains water, cholesterol, bile salts, bile pigments and phospholipids. Bile salts ( Na2CO3, Sodium taurocholate, Sodium glycocholate) emulsify the fat i.e. break bigger fats into smaller fat droplets. Bile ligments ( Biliverdin & Bilirubin) are the wastes products of breakdown of Hb and are excreted out along with faces. - Pancreatic Juice: It secreted by Acinar cells of Pancreas. It reaches intestine through pancreatic duct. It contains proenzymes.
Trypsinogen - It is inactive form and is converted into active form Trypsin by enzyme Enterokinase of intestinal juice. It converts proteins→ polypeptides.
Chymotrypsinogen- It is inactive form. Active form Chymotrypsin is formed by action of trypsin. Its function is same as Trypsin.
Procarboxypolypeptidase : Inactive form , Active form Carboxy Polypeptidase is formed by trypsin. It breaks polypeptides into amino acids. - Intestinal Juice : ( Succus Entericus). It is secreted by two glands, Crypts of Leiberkuhn and Brunner’s Glands. Cryts of Leberkuhn secrete digestive enzymes and mucus. Brunner’s Glands secrete little enzyme and mucus.
Secretion of intestinal glands is called Intestinal Juice. It contains enzymes like Maltase, Sucrase, Lactase, Aminopeptidase, Enterokinase, nucleotidase, Nuclease, nucleosidase, lipase.
Goblet cells secrete mucus which protects duodenal wall from getting digested.
5.5 - HORMONAL CONTROL OF DIGESTION IN HUMANS:
Hormones control the secretion of juice during digestion.
(i) Salivary Phase : It is under nervous control ( Sympathetic and Parasympathetic nerves). Hormones don’t control this phase.
(ii)Gastric Phase: It is under nervous hormonal , chemical and mechanical control. In hormonal control, Pyloric epithelium secrets hormone Gastrin when food reaches the stomach . It reaches glands ( via blood) which release gastric juice.
(iii)Intestinal Phase: Bile secretion is controlled by hormones Cholecystokinin. Secretin hormone controls pancreatic juice secretion. Gastric Inhibitory Peptide ( GIP) homone inhibits gastric secretion . It is secreted by upper small intestine. Hormones Duocrinin and Enterocrinin control intestinal juice.
5.6 - ABSORPTION AND ASSIMILATION OF DIGESTED PRODUCTS IN HUMANS:
Absorption is the process by which nutrients pass from alimentary canal into blood and lymph.
Assimilation is the process by which absorbed food becomes a part of protoplasm and is used for energy, growth and repair.
No absorption occurs in buccal cavity, very little occurs in stomach and all the absorption occurs in small intestine. Projections villi and microvilli help in absorption. There are two type of absorption process : Passive & Active absorption. Passive Absorption : Nutrients are absorbed along the concentration gradient . It occurs by processes like Diffusion ( Fatty acids, monoglycerides, cholesterol, fat soluble substances are absorbed by this) , Osmosis (e.g. water & water soluble substances) and Facilitated Diffusion ( e.g. Fructose). In facilitated diffusion , carrier proteins carry the nutrients. Active Absorption: It is independent of concentration gradient, is brought by carrier proteins and utilizes energy derived from hydrolysis of ATP. Glucose, Galactose , Amino acids, Na+ are absorbed by this method. For Na+ absorption, a sodium pump operates in cell membrane. Absorption of Fats: It occurs differentially. Products of lipid digestion ( e.g. long chain fatty acids , monoglycerides, diglycerides) are insoluble in water and can’t be directly absorbed. So these combine with bile salts & phospholipids to form small spherical, water soluble molecular aggregate called ‘Micelles’. From micelles, fatty acids, glycerides, sterols and fat soluble vitamins are absorbed into intestinal cells by diffusion.
Here they are resynthesized into very small fat droplets ‘Chylomicrons’ which are released in lymphcapillaries called ‘ Lacteals’
.Assimilation : In this absorbed food are utilized e.g. Amino acids are utilized for synthesis of proteins. Glucose provides fuel and energy for metabolism fats from cellular biomembranes , act as fuels etc.
5.7 - EGESTION: The elimination of undigestible remains of food from alimentary canal is called ‘Egestion’. The undigested food along with water and excessive digestive enzymes enters large intestine. Colon absorbs water and concentrates undigested food into faeces. Faeces are temporarily stored in rectum where more water is absorbed. Then faeces are expelled through anus. Muscles of large intestine, abdomen and diahragm contract to expel faeces. Muscles of anal sphincter relex to expel faeces.
Composition of Faeces : 75% water, 25% solid matter. Solid matter is formed of undigested roughage ( 30%), fats ( 20%), inorganic matter( 15%) , Proteins (3%) and bacteria (3%). Bacteria is E. coli
5.8 - NUTRITIONAL REQUIREMENTS OF HUMANS:
Food contains carbohydrates, lipids, proteins minerals, vitamins and water. Carbohydrates, lipids and protein provide energy. Minerals , water and vitamins do not provide energy.
ENERGY YIELDING NUTRIENTS
1 - Carbohydrates: These provide energy and are stored in body cells as Glycogen. Synthesis of Glycogen is called Glycogenesis. Production of new glucose is called Gluconeogenesis e.g. during starvation liver converts aminoacid & glycerol into glucose.
2 - Proteins: Proteins provide energy on their breakdown into amino acid. Essential aminoacids are essential for body but are not synthesized in the body so these must be obtained from outside . An average person needs 70-100 gms of proteins daily. About 15% of human diet should be formed of proteins.
3 - Fats:– These are concentrated energy reserves. Adipose tissues can store upto 95% of their volume of fats. So these are called ‘Fat Depot’ of body. Essential Fatty acids are taken in diet. These are linoleic acid, linolenic acid and arachidonic acid. An adult needs about 100 gms of fat on an average CALORIE VALUE:– Heat is the ultimate form of energy. So energy requirement of animals and energy content of food is expressed as ‘Calorie’ (cal) or ‘Joule’(J). It is the amount of energy required to raise the temp of 1gm of water by 1°C. Commonly it is called ‘Kilocalories’ (1 kcal = 1000 cal) or ‘Kilojoule’ (1 kJ = 1000 J), which is the amount of energy required to raise the temp of 1 kg of water by 1°C.
GROSS CALORIFIC / GROSS ENERGY VALUE:– It is the amount of heat liberated from complete combustion of 1g food in bomb calorimeter in the laboratory
Physiologic Value:– The amount of energy liberated in human body due to combustion of 1g of food is called physiologic value
Nutrient Gross calorific value Physiologic value
Carbohydrate 4.1 kcal/g 4.0 kcal/g
Proteins 5.65 kcal/g 4.0 kcal/g
Fats 9.45 kcal/g 9.0 kcal/g
4 - Minerals:– These are taken in as salts dissolved in water or as part of organic compound. Major Minerals are important to the body 0.1 gm of each of these minerals is required everyday. Trace minerals are required in lesser amount. 0.01 gm of each trace mineral is required everyday
e.g of essential minerals are Ca, Cl, P, K, Na, S, Mg
e.g, of trace minerals are Cu, I, Fe, Zn, F, Mn, Mo, Cr, Co, Zn
5 - Vitamins:– These are the organic substances required for normal growth and metabolism of the body and are taken from outside. These do not provide energy. Some vitamins are fat soluble (eg Vitamin B complex, vit C). Vit. D is synthesized in the skin in the presence of ultraviolet rays of sun.
5.9 - NUTRITIONAL DEFICIENCIES AND DISORDERS:–
Deficiency of vitamins, minerals proteins etc. causes disorders, diseases and abnormalities in humans
MALNUTRITION:– Improper intake of food or nutrients causes impairment of health called-Malnutrition Malnutrition can be undernutrition or overnutrition Excess intake of saturated fats (butter, ghee, vegetable oil, eggs etc) causes Hypercholesterolemia in which blood. Cholesterol level becomes very high causing cardiac disorder Overweight and obesity are also results of overnutrition
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