Antiperistalsis is the peristaltic wave occurs in the reverse direction. It occurs in alimentary canal and results in vomiting. The phenomenon is called as “Regurgitation”.
(4) Digestion : The process by which complex food is converted into simple food with the help of digestive enzymes. The process of digestion in mammals starts in buccopharyngeal cavity.
(i) Digestion in buccopharyngeal cavity : In buccopharyngeal cavity of mammals only starch is digested which is 5% of total food or \[20-30%\] of carbohydrates.
(ii) Digestion in stomach : Chiefly proteins is digested in stomach.
(iii) Digestion in small intestine : All three component carbohydrates, proteins and fats digested in small intestine with the help of enzymes secreted by pancreas and intestinal glands.
(5) Absorption : Ingestion and digestion are the first two phases of the physiological processes occuring in the alimentary tract. The third phase is that of absorption by which the digested nutrients are absorb through the wall of gut into blood.
(i) Absorption from the mouth : Normally, there is no absorption from the mouth, but a few drugs may be absorbed into the blood through the mucous membrane, if allowed to dissolve under the tongue, e.g., isoprenaline, glyceryl trinitrate.
(ii) Absorption from the stomach : In the stomach, absorption takes place to a limited degree. The only substances normally absorbed from the stomach are some water, glucose and considerable amounts of alcohol. These substances are absorbed through the walls of the stomach into the venous circulation. Although iron absorption takes place in the small intestine, it is dissolved out of foods most effectively in the stomach in the presence of \[HCl.\]
(iii) Absorption from the small intestine : The small intestine is the main absorptive organ. About 90% of the ingested foodstuffs is absorbed in the course of passage through the small intestine.
There are two general pathways more... | Types of carbohydrate | Examples |
| Monosaccharides | Glucose (the main blood sugar) Fructose (found in fruits) Galactose (in milk sugar) Deoxyribose (in DNA) Ribose (in RNA) |
| Disaccharides | Sucrose (table sugar) = glucose + fructose Lactose (milk sugar) = glucose + galactose Maltose = glucose + glucose |
| Polysaccharides | Glycogen, the stored form of carbohydrate in animals Starch, the stored form of carbohydrate in food Cellulose, part of cell walls in plants; not digested by humans but aids movement of food through intestines |
| Name of food | Recommended amounts (gms. per day) | ||
| Adult man | Adult woman | ||
| (1) Cereals (Wheat/Rice) | 520 | 440 | |
| (2) Pulses | 50 | 45 | |
| (3) Milk | 200 | 150 | |
| (4) Meat/Fish or Egg | 30 | 30 | |
| more...
The substance used for nutrition are called nutrients. Nutreology is the study of food and their use in diet and therapy.
Types of nutrition
(1) Autotrophic / Holophytic : The individuals, which synthesizes their own food. It can be grouped into two following categories –
(i) Photoautotrophs : The individual, which synthesizes their own food from \[C{{O}_{2}}\] and \[{{H}_{2}}O\] in presence of sunlight. Examples – Green plants, euglena, green sulphur bacteria, chlorobium.
(ii) Chemoautotrophs : The individuals which synthesizes their food with the help of chemical. Examples – Sulphur bacteria, nitrite bacteria, nitrate bacteria, nitrosomonas, nitrifying bacteria– nitrosomonas, nitrobacter etc.
(2) Heterotrophic : The animals derive organic food materials by consuming bodies or products of other living or dead plants or animals. Heterotrophs are of following three types on the basis of their mode of feeding.
(i) Holotrophic or Holozoic : These individuals ingest mostly solid food. Example – Animals.
(ii) Saprotrophic or Saprobiotic : They feed on dead organic matter. They absorb food through their body surface, organic fluids formed due to putrefaction of dead organism. Example – Bacteria, fungi, some protozoans etc.
(iii) Parasitic : These individuals derive their food from the body of their host. These may live inside or upon the bodies of their hosts, or may only periodically visit them for feeding. e.g., Ectoparasites (Lice) and endoparasites (Ascaris, Taenia solium).
(3) Myxotrophic nutrition : They carry out autotrophic as well as heterotrophic nutrition. Example – Euglena.
Modes of animal nutrition
On the basis of food, holozoic or holotrophic or ingestive nutritionally animals are classified into following –
(1) Herbivorous : The animal which exclusively feeds on plants. Their length of alimentary canal is more as compared to others. Examples – Tadpole larva of frog, rabbit, cow, horse, sheep etc.
(2) Carnivorous : The animal which kills and feeds on other animals. The length of their alimentary canal is minimum. Examples – Tiger, lion etc.
(3) Omnivorous : The animal which can take both plant and animal product as food. They have maximum type of digestive enzymes. Example - Human, Dog, Prawn.
(4) Insectivorous : The animal which feeds on insects. Example - Frog, Common bats, wall lizards.
(5) Sanguivorous : The animal which feeds on blood of other animal. Examples - Leech, body louse, mosquito, vampire bat etc.
(6) Carrion Eaters (scavengers) : They feeds on dead animals also termed as scavengers. Examples - Hyaena, neltura, kites etc.
(7) Cannibalus : Organisms which feeds on its own species. Examples - Cockroaches, some fishes, frog, snakes etc.
(8) Detritus : Animals feed chiefly upon organic matters present in the humus. Examples - Earthworm.
(9) Coprophagus or pseudorumination or refection : Animals which feeds on their own faeces. Example - Rabbit, Guinea pig
(10) Larvivorous : Feeds on larva. Example - Gambusia (mosquito fish) and Dragon fly.
(11) Frugivorous : Feeding on fruits. Example - Parrot, Bat, Squirrel.
(12) Food robbers : Feed upon food formed in alimentary canal. Example - Ascaris, Taenia solium.
(13) Filter feeder more...
Digestion in vertebrates occurs in the digestive tract or alimentary canal. The various parts involved in digestion can be broadly grouped in two groups –
(1) Digestive tract or alimentary canal
(2) Digestive glands
(3) Digestive tract or alimentary canal
On the basis of the embryonic origin, the alimentary canal of vertebrates can be divided into three parts –
(1) Fore gut / Stomodaeum : Ectodermal. It includes buccal cavity / oral cavity, pharynx, oesophagus, stomach and small part of duodenum.
(2) Mid gut / Mesodaeum : Endodermal. It includes small intestine, and large intestine.
(3) Hind gut / Proctodaeum : Ectodermal. It includes anal canal and anus.
Parts of alimentary canal and its histology
Mouth
The mouth is a transverse slit bounded by two movable lips or labia, upper lip and lower lip. Upper lip has small ridges on the sides, a tubercle in the middle and a vertical groove (philtrum) above.
Vestibule
It is a narrow space between lips and gums in front and gums and cheeks on the sides. Its lining contains mucous glands. In the vestibule, a small median fold of mucous membrane, the superior labial frenulum, connects the middle of the upper lip to the gum and usually a similar but sma0ller inferior labial frenulum connects the middle of the lower lip to the gum.
Buccopharyngeal cavity
It includes anterior buccal cavity lined by stratified squamous epithelial cell and posterior pharyngeal cavity lined by columnar epithelial cell. It is distinguished into three region. Pharynx is a vertical canal beyond the soft palate. The food and air passages cross here. Pharynx may be divided into three parts; Nasopharynx, Oropharynx and Laryngopharynx.
Main structures of Buccopharyngeal cavity are –
(1) Fauces : A triangular area present between buccal cavity and pharynx in human.
(2) Palate : The roof of buccal cavity is called Palate. In crocodiles and mammals horizontal shelf like processes of premaxilla and maxilla and the palatine bones of upper jaw fused and form a secondary palate. Which separates the buccal cavity from nasal cavity. Palate is distinguished into three regions –
(i) Hard palate : Anterior, bony portion formed of maxilla and palatine bones in human and premaxilla, maxilla and palatine bones in rabbit. Hard palate have transverse ridges called palatine rugae. Such rugae or ridges are more develop in carnivorous mammals because their function is to firmly grip the food and prevent it from slipping out the cavity.
(ii) Soft palate : Posterior soft part, made up of connective tissue and muscles.
(iii) Vellum palati/uvula : Posterior most part of soft palate, which hangs in the region of pharynx. It closes the internal nostrils during degglutition.
(3) Palatine glands : Numerous mucous glands. Chiefly present in soft palate, secretes mucous for lubrication.
(4) Naso-palatine duct : One pair, present in rabbit, extends from nasal passage to the buccal passage, contains Jacobson’s organ concerned with olfaction.
(5) more...
The process by which complex food is converted into simplest food with the help of digestive enzymes (Hydrolytic enzymes) is called digestion. Hence process of digestion is a hydrolytic process.
Types of digestion
(1) Intracellular : When the process of digestion occurs within the cell in the food vacuole. Examples : Protozoa, Porifera, Coelenterata and free living platyhelminthes.
(2) Extracellular : When the process of digestion occurs outside the cell. Examples : Coelenterates and phylum platyhelminthes to phylum chordata.
Organism can be grouped into following four classes on the basis of their respiratory habit.
(1) Obligate aerobes : These organisms can respire only in the presence of oxygen. Thus oxygen is essential for their survival.
(2) Facultative anaerobes : Such organisms usually respire aerobically (i.e., in the presence of oxygen) but under certain condition may also respire anaerobically (e.g., Yeast, parasites of the alimentary canal).
(3) Obligate anaerobes : These organisms normally respire anaerobically which is their major ATP- yielding process. Such organisms are in fact killed in the presence of substantial amounts of oxygen (e.g., Clostridium botulinum and C. tetani).
(4) Facultative aerobes : These are primarily anaerobic organisms but under certain condition may also respire aerobically.
On the basis of the availability of oxygen and the complete or incomplete oxidation of respiratory substrate. The respiration may be either of the following two types : Aerobic respiration and Anaerobic respiration
Aerobic respiration
It uses oxygen and completely oxidises the organic food mainly carbohydrate (Sugars) to carbon dioxide and water. It therefore, releases the entire energy available in glucose.
\[{{C}_{6}}{{H}_{12}}{{O}_{6}}+6{{O}_{2}}\xrightarrow{enzymes}6C{{O}_{2}}+6{{H}_{2}}O+energy\,\,(686Kcal)\]
It is divided into two phases : Glycolysis, Aerobic oxidation of pyruvic acid.
Glycolysis / EMP pathway
(1) Discovery : It was given by Embden, Meyerhof and Parnas in 1930. It is the first stage of breakdown of glucose in the cell.
(2) Definition : Glycolysis ( Gr. glykys= sweet, sugar; lysis= breaking) is a stepped process by which one molecule of glucose (6c) breaks into two molecules of pyruvic acid (3c).
(3) Site of occurrence : Glycolysis takes place in the cytoplasm and does not use oxygen. Thus, it is an anaerobic pathway. In fact, it occurs in both aerobic and anaerobic respiration.
(4) Inter conversions of sugars : Different forms of carbohydrate before entering in glycolysis get converted into simplest form like glucose, glucose 6-phosphate or fructose 6-phosphate. Then these sugars are metabolized into the glycolysis.
(5) Special features of glycolysis : The special features of glycolysis can be summarised as follows :
(i) Each molecule of glucose produces 2 molecules of pyruvic acid at the end of the glycolysis.
(ii) The net gain of ATP in this process is two ATP molecules (four ATPs are formed in glycolysis but two of them are used up in the reaction).
(iii) During the conversion of 1, 3-diphosphoglyceraldehyde into 1, 3-diphosphoglyceric acid one molecule of \[NAD{{H}_{2}}\]is formed. As each molecule of glucose yields two molecules of 1,3-diphosphoglyceric acid, hence each molecule of glucose forms 2 molecules of \[NAD{{H}_{2}}.\]
(iv) During aerobic respiration (when oxygen is available) each \[NAD{{H}_{2}}\] forms 3 ATP and \[{{H}_{2}}O\] through electron transport system of mitochondria. In this process \[{\scriptscriptstyle 1\!/\!{ }_2}\,\,{{O}_{2}}\] molecule is utilized for the synthesis of each water molecule.
In this way during aerobic respiration there is additional gain of 6 ATP in glycolysis
\[\underset{(\text{net}\,\text{gain})}{\mathop{2ATP}}\,+\underset{\text{(addition}\,\text{gain)}}{\mathop{6ATP}}\,\to \underset{\text{(total}\,\text{net}\,\text{gain)}}{\mathop{8ATP}}\,\]
(v) Reaction of glycolysis do not require oxygen and there is no output of \[C{{O}_{2}}.\]
(vi) Formation of 1, 3- diphosphoglyceraldehyde called non enzymatic phosphorylation.
(vii) Overall reaction of glycolysis represented by following reaction :
\[{{C}_{6}}{{H}_{12}}{{O}_{6}}\to \underset{\text{Pyruvate}}{\mathop{2{{C}_{3}}{{H}_{4}}{{O}_{3}}}}\,+4H\]
Total input and output materials in glycolysis
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