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DIGESTIVE SYSTEM

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Information about DIGESTIVE SYSTEM
Education

Published on March 7, 2014

Author: raniashok

Source: authorstream.com

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Digestive system : Digestive system Mrs. Rani Ashok Associate Professor of Zoology, Lady Doak College, Madurai – 2 Email: eaarani@rediffmail.com DIGESTION & DIGESTIVE SYSTEM: DIGESTION & DIGESTIVE SYSTEM Stepwise degradation of macromolecules into their smaller components which is suitable for absorption and assimilation by body – DIGESTION Done by parts of digestive system DIGESTION: DIGESTION INTRACELLULAR EXTRACELLULAR Primitive Seen in primitive heterotrophs Digestion of food materials occur within the cells Particulate matter enters in by phagocytosis or pinocytosis Eg . Protozoa, porifera , coelenterates Seen in animals which feed on relatively big food Digestion occurs outside the cells in the lumen of digestive tract Characteristic of higher forms Evolved as an adaptation to break large pieces of food for cellular use Eg . Vertebrates Digestive system: Digestive system Consists of openings, organs and glands Openings : anterior – mouth; posterior – anus Organs : alimentary canal Glands : digestive glands ORGANIZATION OF ALIMENTARY CANAL: ORGANIZATION OF ALIMENTARY CANAL INGRESSIVE ZONE: INGRESSIVE ZONE Mouth, vestibule, Oral cavity, Oral glands, Tongue, Teeth Mouth : Mouth Reception part of gut Shape and extent of mouth opeening depend on kind of food utilization Terminal/ sub-terminal/ ventral in position Upper and lower boundaries – LIPS (movable in mammals only except whale and platypus) Mouth : Mouth Used as prehensile organs in grasping, picking up food/ objects Aid in sucking, drinking, modifying voice Extent of opening of oral slit in mammals is set by cheeks Animals without cheeks open to surprising extent Vestibule: Vestibule Space between lips and jaws Seen as cheek pouches Used for temporary storage of food when its collection occurs Oral Cavity: Oral Cavity Cavity enclosed by jaws Responsible for initial breakdown of material by mechanical action Roof – palate In humans, palate show faint ridge – raphe Cats, dogs – prominent ridges Oral glands: Oral glands Absent in fishes, aquatic amphibians Cyclostomes – secretes anti-coagulant Lamphredin ; snakes – secrete venom/ poison Mucous glands on palate and tongue Lingual, labial and serous glands seen Secretions enable tasting and washing after tasting Along with these three sets of salivary glands seen in oral cavity of man Parotid gland Submaxillary gland Sublingual gland Composition and function of saliva: Composition and function of saliva Volume/ day: 100 – 150 mL pH: 6.2 – 7.4 Specific gravity: 1.002 – 1.008 Osmolarity : hypotonic to plasma Water: 99.5% Moistens food; facilitate swallowing; keeps mouth and teeth clean; help in speech; regulates water balance of body; disposes heat in dogs; ptyalin converts starch into sugar Tongue : Tongue Muscular structure which help in tasting the food taken Lined by stratified squamous epithelium Bears papillae of various kinds Filiform – transverse arrangement in apex of tongue; large numbers, narrow conical structures; not associate with taste buds, absent in rabbit Fungiform – sides and apex of tongue; mushroom like, 300 – 400 in number; beset with taste buds Foliate – broad leaf-like, less in number; near base of tongue, bear taste buds; mammals – 2-3; rodents – large numbers Vallate – large size; arranged in V shape; associated with taste buds Teeth : Teeth Absent in birds Enable manipulation of food within mouth cavity – grasping, cutting, grinding Organ of defence In vertebrates – 2 types Epidermal teeth – no pulp; replaced several times – ACRODONT teeth True teeth – fixed in definitive sockets 2 types of roots: open - tusk of elephants; incisors of rodents; closed - human Teeth : Teeth Types of teeth in mammals Incisors (I); canine (C); premolars (PM); molars (M) Dental formula: I; C; PM; M = total Man: 2123 – 32 Mouse: 1003 - 16 PROGRESSIVE ZONE: PROGRESSIVE ZONE Pharynx, Oesophagus , Stomach Pharynx: Pharynx Common part of digestive and respiratory system Entry of food into glottis is prevented by presence of epiglottis Has seven openings: Posterior nares - 2 Eustachian tubes - 2 Oral - 1 Laryngeal - 1 Oesophageal - 1 Oesophagus: Oesophagus Tubular structure 9 – 10 inches long Mammals - Largest in giraffe Birds – form crop sac Provided with cilia to push food into stomach Secrete propepsin which is activated in stomach in presence of HCl Stomach: Stomach Highly dilated part of gut Used for temporary storage of food True stomach has epithelial lining with gastric glands Shape related to shape of body Two types: simple and compound Different parts: cardiac and pyloric DEGRESSIVE ZONE: DEGRESSIVE ZONE Small Intestine Small intestine: Small intestine Short in carnivores and long in herbivores In cyclostomes no separate small and large intestine – seen as typhosole Amphibians – duodenum and ileum Reptiles – colic caecum seen (Exception – crocodiles; turtles) Birds – 2 colic caecae developed (absent in wood pecker) Mammals – 2 intestinal caeca ; 3 parts – duodenum, jejunum and ileum Transfer food into blood stream Small intestine: Small intestine Duodenum – Brunner’s gland Ileum – Crypts of Lieberkuhn Ileum – nodules of lymphoid tissues called Peyer’s patch Caecum present between small and large intestine terminates into vermiform appendix EGRESSIVE ZONE: EGRESSIVE ZONE Large Intestine Large intestine: Large intestine Internal modifications increases the surface area; provided with villi Brings about expulsion of unstable residue Shark – rectum – salt eliminating function Birds – Bursa fabrici is developed from cloaca Mammals – colon and rectum; contain numerous commensal bacteria which enable absorption of vitamins through walls of large intestine LIVER: LIVER Structure, Bile, Bile pigments, Bile salts, function Liver : Liver Largest gland; reddish brown 2 surfaces (parietal, visceral); 4 borders and 2-7 lobes Pours content through common bile duct (bile and pancreatic) into duodenum Kupffer cells are phagocytic and destroy germ cells Bile : Bile Produced by parenchymal cells of liver and stored in gall bladder Alkaline liquid Bitter taste Colour depends on relative concentrations of bile pigments Bile pigments: Bile pigments Obtained as result of haemoglobin breakdown in liver Bilirubin (reddish yellow) and biliverdin (green) On oxidation it forms stercobilin which gives brown colour to faeces Bile salts: Bile salts Sodium salts of glycocholic acid and taurocholic acid Synthesized from cholesterol in liver Stimulate pancreatic solution; activate pancreatic lipase; form micelles; release enterokinase ; absorb substances like fatty acids PANCREAS: PANCREAS Structure, function, Stimulants Pancreas : Pancreas Second largest digestive gland Two kinds of functional cells seen – exocrine or acinar cells and endocrine cells or Islets of Langerhans stimulant of exocrine cells – secretin ; acetyl choline Stimulant of endocrine cells – blood sugar; gastrin PowerPoint Presentation: THANK YOU

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