Department of physiology Aimst university Department of physiology DR.P.SUNITHA

COMPONENTS OF FOOD CARBOHYDRATES: STARCH ( POLYSACCHARIDE) SUCROSE( DISACCHARIDE) LACTOSE ( A DISACCHARIDE IN MILK) CELLULOSE(DIETARY FIBER) NOT DIGESTED IN HUMAN GIT PROTEINS FATS (TRIGLYCERIDES) Minerals Na, K, Ca, PO4, Fe Vitamins Water

DIGESTION AND ABSORPTION OF FOOD STUFFS

Features of Digestion and Absorption 92% to 97% of the diet is absorbed Small intestine—key role in digestion and absorption Intestines: 7 meters long —Villi and microvilli/brush border

Digestion in the Stomach Different nutrients leave the stomach at different rates: —Carbohydrates first, followed by protein, fat, and fibrous foods

DIGESTION OF STARCH MOUTH SALIVARY α- AMYLASE SPLITS SOME STARCH TO MALTOSE( NOT IMP.) STOMACH-------NIL INTESTINE PANCREATIC- α-AMYLASE SPLITS ALL STARCH TO MALTOSE CELLULOSE CANNOT BE DIGESTED BECAUSE IT REQUIRES β- AMYLASE NOT PRESENT IN HUMAN GIT SECRETIONS

BRUSH BORDER OF SMALL INTESTINE MALTASE MALTOSE-----------------GLUCOSE+GLU LACTASE LACTOSE-------------GLU + GALACTOSE SUCRASE SUCROSE--------------GLU. +FRUCTOSE MONOSACCHARIDES ABSORBED IN UPPER SMALL INTESTINE

The Gradual Breakdown of Large Starch Molecules

Digestion of carbohydrates Area Juice Enzyme Substrata End product Mouth Saliva Salivary amylase Polysaccharides-cooked starch Disaccharides-maltose Stomach Gastric juice Gastric amylase Weak amylase Action is negligible Small intestine Pancreatic juice __________ Succus entericus Pancreatic amylase __________Sucrase Maltase Lactase Polysaccharides -Sucrose Maltose lactose Disaccharides-dextrin, maltose ______________ Glucose and fructose Glucose, glucose Glucose, galactose

Absorption of Monosaccharides Intestinal epithelium absorbs monosaccharides: by facilitated diffusion and co-transport via a carrier protein

FATS DIGESTION MOUTH ------- NIL STOMACH-------NIL SMALL INTESTINE PANCREATIC LIPASE AND BILE SALTS ESSENTIAL FOR DIGESTION AND ABSORPTION OF FATS

Digestion of fats Area Juice Enzyme Substrate End product Mouth Saliva Lingual lipase Triglycerides Fatty acids stomach Gastric juice Gastric lipase Fatty acids and Glycerol Small intestine Pancreatic juice Pancreatic lipase Monoglycerides and Fatty acids

Digestion Fats Fats Bile salts Emulsified fat Pancreatic lipase activation Emulsified fat Pancreatic lipase Fatty acids & 2-monoglycerides

DIGESTION AND ABSORPTION OF FATS 1.FIRST Fats EMULSIFIED BY BILE SALTS 2. Pancreatic lipase splits triglycerides into fatty acids and glycerol lipase triglycerides----------fatty acids +glycerol

Lipid Absorption Intestinal cells synthesize new triglycerides from monoglycerides and fatty acids Triglycerides and other absorbed molecules are coated with proteins: creating chylomicrons Intestinal cells secrete chylomicrons into interstitial fluid by exocytosis

Fatty acids transported by bile salts from intestinal lumen to intestinal wall as mixed micelles 4.FATTY ACIDS ENTER INTESTINAL MUCOSAL CELL BY DIFFUSION

Micelle

PROTEINS VEGETABLE PROTEINS ANIMAL PROTEINS DIGESTION MOUTH--------NIL STOMACH PEPSIN-----SPLITS PROTEINS TO SMALLER FRAGMENTS CALLED PROTEOSES

SMALL INTESTINE PANCREATIC PROTEOLYTIC ENZYMES BREAK DOWN PROTEINS AND PROTEOSES INTO AMINO ACIDS AND DI-PEPTIDES. BRUSH BORDER - DIPEPTIDASES DI-PEPTIDES---------------------------AMIN0 ACIDS AMINO ACIDS ABSORBED

Digestion of proteins Area Juice Enzyme substrate End product Mouth Saliva No proteolytic enzyme - Stomach Gastric juice Pepsin Proteins Proteoses, Peptones,large polypeptides Small intestine Pancreatic juice --------------------- Succus entericus Trypsin ------------chymotrypsin ---------- Carboxy peptidases Peptidases Proteoses and Peptones ------------------- Polypeptides Large polypeptides ____________ Amino acids

Absorption of Amino Acids Dipeptidases: enzymes on epithelial surfaces of small intestine break short peptide chains into individual amino acids After diffusing to basal surface of cell: amino acids are released into interstitial fluid by facilitated diffusion and co-transport

Brush border di -and tri -peptidases

Absorption of Ions and Vitamins Table 24–4

Small Intestine Absorbs Lipids 80% ingested water Monoglycerides Electrolytes Vitamins Minerals Carbonates Active/facilitated transport Monosaccharides Proteins Di-/tripeptides Amino acids Lipids Monoglycerides Fatty acids Micelles Chylomicrons

Large Intestine Functions Concentrate/eliminate wastes Mechanical digestion Haustral churning Peristalsis Reflexes Gastroileal Gastrocolic Chemical digestion – Bacterial digestion Ferment carbohydrates Protein/amino acid breakdown Absorbs More water Vitamins B K Concentrate/eliminate wastes

Absorption of food stuffs

Absorption The food is then ABSORBED through the wall of the small intestine into the blood stream. To do this effectively, the small intestine needs to have a large surface area. This is achieved in the following ways:

Absorption 1 The tube is over 6 meters long The inner wall of the tube has bends in it The wall is covered in villi (small finger-like structures) Outer wall Pathway for Food Inner wall

The carbohydrates are absorbed from the small intestine mainly as monosaccharides viz. glucose, galactose and fructose. The proteins are absorbed in the form of amino acids from the small intestine. The absorption of amino acids is faster in duodenum and jejunum and slower in ileum. The fats are absorbed from the intestinal mucosa in the form of fatty acids, cholesterol and monoglycerides. Most of the fats are absorbed in upper part of small intestine. Presence of bile is essential for fat absorption.

Sites of Secretion and Absorption into Gastrointestinal Tract

 Absorption of main nutrients * Water 8 L/day, passive & iso-osmotic absorbed Different absorbability in different parts * Inorganic slats Sodium: 95%~99%, jejunum>ileum>colon active transport Ferrum: 1/10, mainly in duodenum & jejunum, transferrin dependent, active transport Calcium: promote by Vit. D, active transport Anions: mainly Cl  & HCO3, passive transport

* Carbohydrate Absorptive form: monosarccharide Mechanism: secondary active transport * Protein Absorptive form: amino acid * Fats Absorptive form: glycerol, monoglyceride, fatty acid, cholesterol Mechanism: passive diffusion Pathway: blood & lymph

FUNCTIONS OF DIETARY FIBER IN DIET 1.Adds bulk to food---slows down gastric emptying------lowers insulin requirement 2. Retains water –makes feces larger and softer----no constipation 3. lowers blood cholesterol by interfering with its intestinal absorption 4. Reduces incidence of diabetes mellitus coronary art. dis cancer colon

  Action of dietary fibers on the intestinal function Reduce absorption of water; Enhance colonic movement; Increase the volume of feces; Low the caloric ratio of the food

Summary of Enzymatic Digestion and Absorption Secretion Enzyme Substrate Action Final Product Saliva Ptyalin Starch Hydrolysis to form dextrins Gastric juice Pepsin Protein Hydrolysis of peptide bonds Gastric lipase Fats Hydrolysis into free fatty acids

Secretion Enzyme Substrate Action Final Product Pancreatic exocrine secretion Lipase Fat Hydrolysis to mono-glycerides Fatty acids Cholesterol esterase Cholesterol Hydrolysis to esters of cholesterol and fatty acids Choles-terol alpha-Amylase Starch, dextrins Hydrolysis Dextrin, maltose

Secretion Enzyme Substrate Action Final Product Pancreatic exocrine secretion Trypsin Protein Hydrolysis Polypeptides Chymotrypsin Carboxy-peptidase Polypep-tides Amino acids Ribonuclease Ribonu-cleic acids Mono- nucleotides Elastase Fibrous protein

Secretion Enzyme Substrate Action Final Product Brush border enzymes Carboxy-peptidase; aminopep-tidase; dipeptidase Polypep-tides Hydrolysis Amino acids Entero-kinase Trypsino-gen Activates to trypsin Polypep-tidases and peptides Sucrase Sucrose Glucose, fructose

Secretion Enzyme Substrate Action Final Product Brush border enzymes Isomaltase Dextrin Hydrolysis Glucose Maltase Maltose Lactase Lactose Glucose, galactose Nucleotidases Nucleic acid Nucleotides Nucleosidases and phosphorylase Nucleosidases Purine and pyrimidine bases

Digestive system -revise

Lactose intolerance: This is due to deficiency of lactase and is common in africans and asians. The treatment involves elimination of lactose (milk and milk products )from the diet. Flatulence: flatulence is characterized by increased intestinal motility, cramps and irritation due to excess production of gases under the influence of bacteria.

1. Steatorrhea: excess fat is excreted into the stools 1.Steatorrhea: excess fat is excreted into the stools. The defect may be either due to deficiency of pancreatic lipase or due to inadequate quantity of bile salts. Crohn’s desease: In this condition mucosal degeneration in the terminal part of ileum results in failure of absorption of bile salts. This in turn causes steatorrhoea.

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