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Digestive System Daw San Dar Tun

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Digestive System Daw San Dar Tun DIGESTIVE SYSTEM DAW SAN DAR TUN ASSISTANT LECTURER DEPARTMENT OF ZOOLOGY UNIVERSITY OF MEDICINE,MAGWAY Ingestion • a process by which food is taken in through the mouth • a reflex action which is involuntary • it occurs when the food is put at the posterior position of the tongue A process by which large food molecules are broken down into smaller pieces Mechanical digestion biting & chewing Digestion Chemical digestion Hydrolysis & enzymes (Simple soluble forms) Ingestion and digestion of food Oral cavity Four kinds of teeth Incisors – chisel-shaped teeth ( for biting ) canines – pointed teeth ( for tearing ) Premolars & molars – flattened , ridged teeth ( for grinding, pounding, crushing ) Saliva (pH 6.8) water mucin amylase(ptyalin) lubricates dissolves starch maltose food soluble food helps swallowing Chemical Digestion break down of starch molecules into maltose molecules by salivary amylase (from salivary glands) salivary glands Starch maltoses Peristalsis Oesophagus - the peristalsis passes the bolus to stomach - no digestive enzyme is secreted Stomach Cardiac sphincter (a valve –like ring of muscle ) - relaxes as the bolus passes through,then quickly closes In the stomach, - food is retained for 4-6 hours in man. Layer of stomach muscle contract &churn the bolus of food with gastric juices to make it a soupy chyme. Gastric juice water HCL mucus salt enzyme 90% 0.2-0.5% mucus cells mucus oxyntic cells HCL (Hydrochloric acid) chief cells pepsinogen (proenzyme) In man 2-3 liters of gastric juice is secreted per day The stomach and gastric glands (Oxyntic cell) Function of hydrochloric acid (1) change the pH of food from 1 - 3.5 (2) activates pepsinogen Hcl active pepsin prorennin Hcl active rennin (3) dissolves salts,bones etc. in food (4) stop salivary enzyme action (5) kill harmful bacteria (6) splits nucleoproteins Hcl nucleic acid + protein (7) regulate pyloric sphincter gastrin activate gastric juce inhibit Enterogasterone under nervous reflex Action of gastric juice pepsin + protein split proteoses, peptones, large polypeptides rennin + milk protein split curd (cal. Paracaseinate) (casein) pepsin + milk curd split peptones , proteoses split Lipase + fats fatty acid , glycerol ToTo protectprotect thethe stomachstomach lininglining fromfrom thethe acidacid &enzyme&enzyme mucousmucous cellscells secretesecrete mucusmucus ((thatthat lineslines thethe stomachstomach cavity)cavity) AnAn overover abundanceabundance ofof acidacid due to mucus failure may lead to an ulcer The semidigested acidic chyme is passed in form of small jets to duodenum due to rhythmic release of pylorus Emptying of stomach is reciprocal - to the rate of processing of chyme into intestine. Regurgitation of food - from stomach to oesophagus by cardiac sphincter - & from duodenum to stomach by pyloric sphincter (which is controlled by hormone gastrin) Intestinal hormone Secretin stimulate liver and pancreatic cells Cholecystokinin-pancreo-zymin stimulate c.c.k.p.z - cells of pancreatic acini - contraction of gallbladder - relaxation of sphincter Oddi bile juice water bile salts bile pigments • Sodium/potassium chloride • bilirubin • biliverdin • -------------------- bicarbonates • -------------------- glycocholates • -------------------- taurocholates Cholesterol, lecithin, fatty acid Functions of bile juice (1) intensification of intestinal contraction (peristalsis) (2) neutralization of acidity of HCL and inactivation of pepsin (3) emulsification of fats for easy action of pancreatic juice (4) easy absorption of fatty acids, cholesterol and other lipid by forming micelles (5) absorption vitamin A,D.E & K (6) excretion of the waste products, toxins etc. Bile - contain bile salts which emulsify lipids into smaller droplets without chemical change ( ∴ NOT digest fats) - provide alkaline medium for enzymes to work oil oil droplets • Fats are emulsified by bile salts. • Micelles are tiny droplets consisting of fatty acids and monoglycerides complexed with bile salts. • Micelles diffuse into epithelial cells. – Resynthesized into triglycerides and pass into the lacteals of the lymphatic system. pancreatic juice Water Digestive enzyme 98% • Amylase • Lipase • Endopeptidases • Carboxypeptidase • Nucleases Actions of pancreatic juice 1. Amylase + carbohydrates splits maltose splits 2. Lipase + fats Fatty acids & glycerol some into diglycerides 3. Endopeptidases + protein splits Peptone, proteose small peptides . trypsin , chymotrypsin 4. Carboxypeptidase + polypeptides splits amino acids 5. Nucleases + D.N.A , R.N.A splits nucleotides nucleosides lipid lipase glycerol + 3 fatty acids lipid lipase fatty acids glycerol pancreatic proteases Dipeptides/ protein polypeptides protease dipeptide protein disaccharides intestinal monosaccharides carbohydrase (eg. maltose) (eg. glucose) disaccharide carbohydrase monosaccharide intestinal proteases dipeptides amino acids protease amino acid Succus entericus(Intestinal juice) -is released from Crypts of Lieberkuhn -Is an alkaline fluid – pH 7.5 – 8.0 - (about 2 liters secreted daily in man ) Crypts of Lieberkuhn succus entericus (intestinal juice) 1. Erepsin exopeptidases- (aminopeptidases ,carbooxypeptidases) 2 .Carbohydrases maltase sucrase lactase 3. Enterokinase - Action of succus entericus 1.Peptidase + small peptide , dipeptide Amino acids 2.Carbohydrases Maltase + maltose split Glucose Sucrase +sucrose split Glucose & fructose split Lactase +lactose Glucose & galactose 3.Enterokinase activates trypsinogen convert trypsin chymotrypsinogen chymotrypsin Absorption and assimilation Absorption End products of digestion - monosaccharide sugars ( glucose, fructose ) - amino acids -fatty acids - glycerol - nitrogenous bases - pentose sugars simple soluble substances can easily diffuse through cell membranes About 9 liters of contents (1 1/2 liter of digested nutrients & rest water) are absorbed daily from gastrointestinal tract in man. In stomach of man ,absorption - water, - glucose, - alcohol - some drugs The intestine alone is well adapted - whose wall is produced into villi increasing the area for absorption about 600 times in man. Structure of Villi blood capaillaries lacteal villi Epithelial cell venule arteriole lymph vessel - Sugars Villi have -salt,waterdense network capillaries lacteal are absorbed into blood capillaries -vitaminsa single lymph vessel -nitrogenSugar bases Salt -aminoWater acids Vitamins -digestiveNitrogen bases juice etc amino acid digestive juice Fatty acids absorbed by mucosal cells forming triglycerides Monoglycerides in their smooth endoplasmic reticulum Within the reticulum, cholesterol -the fat molecules are synthesized into phospholipids These fat globules encased in a protein coat chylomicrons make their way out of absorptive cells as chyle & enter lacteals. Lacteals conduct chylomicrons into larger lymphatics --- carry them to thoracic lymphatic ducts --- from they reach venous blood via jugular or subclavian vein In the large intestine only water is absorbed. Assimilation The amino acids First coming into liver through portal circulation monosaccharides after process of absorption & then go to the heart for circulation in the different parts & ofthen the go body to the where heart tissues for circulation pick up their in the requirements. different parts Theof the amino body acids where are tissues building pick up materials their requirements. & constantly needed for formation of The amino acids are buildingprotoplasm. materials & The excess of amino acidsconstantly are subjected needed to the process of deamination in liver forming ammonia for formation of protoplasm. ----which is soon convered into urea ----excreted by the kidneys. The excess of amino acids the process of deamination in liver forming ammonia ----which is soon converted into urea ----excreted by the kidneys. The excessexcess of of monosaccharides monosaccharides stored stored in the form ofglycogen glycogen-----------in the liverin the cells. liver cells. Wheneverglucose level glucose falls down level in falls the blooddown thenin the blood then ----glycogenglycogen is isconverted soon converted into glucose into-------- ( glycogenolysisglucose ) -to maintain its ( glycogenolysis) normal level ----to maintain its normal level in the blood. in the blood. Liver is also concerned with fat metabolism & ---the fatty globules are found filled -------liver cells. Energr is also released from the fats. The fats maino acids carbohydrates Liver is also concerned with fat metabolism & ---the fatty globules are found filled -------in liver cells. Energy is also released from the fats. The fats amino acids by the liver carbohydrates Egestion ( Defaecation) After absorption of the digested food, --remaining contents ,bile pigments ,others pass into large intestine where water is absorbed from them ----whatever left ----------- is called faeces. Vegetable foods form large amount of faeces than animal foods Milk forms relatively large amount of faeces (due to large amount of unabsorbed salt in it.) Animal proteins are absorbed 98%- 99% Vegetable proteins to lesser extent. The faeces are collected in distal end of large intestine the rectum their removal through anus defaecation or egestion Table 1: Enzymes in Digestion Area Secretion/Enzyme Substrate Product Mouth Saliva - amylase Starch Maltose Gastric Juice - Peptides, Stomach Protein, Lipids pepsin, lipase fattyacids/gycerol Pancreatic juice - Maltose, peptides, amylase, trypsin, Starch, protein, peptides, amino Duodenum chymotrypsin, protein, peptides, acids, carboxypeptidase, lipids fattyacids/glycerol lipase None secreted, glucose, remain on villi cells, maltose, sucrose, glucose/fructose, Ileum Maltase, sucrase, lactose, peptides glucose/galactose, lactase, peptidase amino acids. .
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