B.COM Unit – 4 ( CORPORATE SOCIAL RESPONSIBILITY ( CSR ).pptx
Lect35
1. Digestion and Absorption in the GI Tract The major foods can be classified into carbohydrates, fats and proteins Digestion: The enzymatic breakdown of food to components that can be absorbed Absorption: The movement of nutrients, salts and water across the GI epithelium into blood or lymph
2. Digestion and Absorption in the GI Tract Most digestion and absorption occurs in the small intestine The pancreas supplies the digestive enzymes for most foodstuffs Human lacks of digestive enzymes for plant polysaccharides cellulose The indigestible polysaccharides contain in vegetables and fruits make up dietary fibre
3. Digestion of various foods by hydrolysis Monosaccharides, fatty acids and amino acids are bound to one another by condensation The process of hydrolysis is involved in the digestion of carbohydrates, fats and proteins
4. Digestion and absorption of Carbohydrates The most abundant dietary carbohydrates are starch and the three disaccharides sucrose, lactose and maltose Carbohydrates are built from monosaccharides and must be digested to their component monosaccharides so they can be absorbed Starch are digested to glucose Sucrose is digested to glucose and fructose Lactose is digested to glucose and galactose Maltose is digested to glucose
5. Digestion and absorption of Carbohydrates Plant starch and glycogen are long polymers of glucose Digestion of carbohydrates begins in the mouth with salivary amylase Amylase break starch down to disaccharides maltose; fragments of three glucose molecules (Maltotriose); and to small branched fragments (limit dextrin) Acid in the stomach denatures amylase
6. Digestion and Absorption of Carbohydrate The carbohydrate that enter the small intestine for digestion include Starch Breakdown products from starch from salivary amylase digestion Dietary disaccharides
7. Digestion and Absorption of Carbohydrate Pancreatic amylase continues the breakdown of starch Brush border enzyme called maltase breaks down maltose and Maltotriose Brush border enzyme called dextrinase breaks down small branched segments of starch Brush border enzymes also break down sucrose and lactose through sucrase and lactase enzyme
9. Digestion and Absorption of Carbohydrate Most nutrients are absorbed transepithelial transport moving first to the intestinal epithelial cell at the luminal surface then out at the basal surface Glucose and galactose enter intestinal cells cotransported with sodium by secondary active process Fructose enters intestinal cells by facilitated diffusion All monosaccharides leave epithelial cells on a common transporter by the process of facilitated diffusion
11. Digestion and absorption of Proteins Proteins are digested to amino acids and small peptide chains of two or three amino acids In the stomach, pepsin initiates the process of protein digestion Pepsin convert protein to proteoses, peptones and peptide fragment
12. In the small intestine, pancreatic secretions of proteolytic enzyme: trypsin, chymotrypsin and carboxypeptidase continue proteindigestion Trypsin and chymotrypsin cleave proteins into smaller peptides Carboxypeptidase cleave one amino acids at a time from the carboxyl end of a protein Most proteins remain as dipeptides and tripeptides Digestion and absorption of Proteins
13. Enterocyte line the villi of the small intestine continue protein digestion In the membrane of the microvilli are enzymes peptidase Two types of peptidase enzymes, aminopeptidase and dipeptidase They split the remaining larger polypeptides into tripeptides, dipeptides and amino acids Inside the cytosol of the enterocyte are peptidases Dipeptides and tripeptides are digested to form single amino acid Digestion and absorption of Proteins
15. Many single amino acids enter intestinal cells cotransported with Na by secondary active transport Most proteins absorbed as dipeptides and tripeptides use secondary active transport, some driven by Na, others by H Some amino acids leave epithelial cells by diffusion Other amino acids leave cells by facilitated diffusion or cotransport with Na Digestion and absorption of Proteins
17. Digestion and Absorption of Fats Triglyceride are made from glycerol molecule to which three fatty acids are attached Fatty acids may be short, medium or long chain Almost all fat digestion occurs in the small intestine Pancreatic lipase break down triglyceride
18. Agitation in the stomach breaks the large drops of fats into small drops and disperses them throughout the chyme, this process called emulsification Most of the emulsification occurs in the duodenum under influence of bile Bile salts and lecithin are important for emulsification of fat The structure of bile salt and lecithin consist of hydrophobic in one side and hydrophilic on the other side Digestion and Absorption of Fats
