Digestion and Absorption of Macromolecules PDF

BIOCHEMISTRY Digestion and Absorption of Macromolecules Prepared by: Group 6 & Group 9 Lecturer: Dr. Farr Krizha Tangkusan, RN, MD Date: September 20, 2024 OBJECTIVES: I. Discuss digestion and absorption in the GI...

BIOCHEMISTRY Digestion and Absorption of Macromolecules Prepared by: Group 6 & Group 9 Lecturer: Dr. Farr Krizha Tangkusan, RN, MD Date: September 20, 2024 OBJECTIVES: I. Discuss digestion and absorption in the GIT. A. General principles of digestion and absorption B. Digestion and absorption of carbohydrates C. Digestion and absorption of proteins D. Digestion and absorption of lipids II. Describe how the following are absorbed into the GIT: Water Ions Vitamins Minerals Digestive System Processes: 1. Digestion 2. Absorption 3. Motility 4. Secretion 5. Excretion CARBOHYDRATES DIETARY CARBOHYDRATES Monosaccharides(glucose, fructose, galactose) Disaccharides (sucrose, lactose) Polysaccharides (starch, glycogen, nonstarch polysaccharides) DIGESTION OF CARBOHYDRATES ⑥ Salivary amylase (ptyalin) - hydrolysis of α(1→4) glycoside bonds → Dextrins ○ 20 – 40% activity ○ Inactivated in the stomach – high acidity (pH < 4) Pancreatic amylase - identical to salivary amylase seen ○ 60 - 80 % activity echolecystokingdigestive ○ Optimum pH is 7 – 8(remember: · CCK & secretin) hormones -> DIGESTION & ABSORPTION OF MACROMOLECULES ○ Endproduct: maltose, maltotriose, α-limit 1. Significant mechanical component to digestion dextrins (chewing/mastication) Brush border enzymes - “disaccharidases” 2. Saliva acts as lubrication to facilitate swallowing. 3. Enzymes are secreted that break down macromolecules into a mixture of oligo-, di- and monomers. 4. Specific transporters of digested material into enterocytes and then either to the blood or lymph. BIOCHEMISTRY 1 Prepared by: Iklaman, Monsanto, Alih, Aman, Arah, Godoy, Guzman, Laja, Mansan, Nebab Date: September 20, 2024 BIOCHEMISTRY Digestion and Absorption of Macromolecules Prepared by: Group 6 & Group 9 Lecturer: Dr. Farr Krizha Tangkusan, RN, MD Date: September 20, 2024 2 ABSORPTION Occurs in the small intestine 1. Wall of small intestine covered with 100s of folds 2. Each fold covered with 1000s of villi 3. Each villi contains 100s of microvilli SUMMARY 1. Overview of digestion and absorption. ABSORPTION & TRANSPORT 2. Digestion of carbohydrates -areas in the GIT, enzymes, Absorbed nutrients enter either the: hormones involved 1. Vascular system –water-soluble nutrients (monosaccharides, 3. Absorption of carbohydrates –forms, transport processes amino acids, water-soluble vitamins, minerals, water) enter the and transporters blood via the portal vein for transport to the liver F system –fat-soluble nutrients (*lipids, fat-soluble vitamins) 2. Lymph PROTEINS -> enter here, eventually entering the blood near the heart DIETARY PROTEINS ***Transport of *lipids –since fats are insoluble in water, they must Source of amino acids (essential amino acids) be packaged for transport as lipoproteins (triglyceride, phospholipid, ○ PVT TIM HALL protein, cholesterol) Animal sources: more easily digested ○ Plant sources: less easily digested —> Pro, HydroxyPro and Gly o DIGESTION OF PROTEINS Native proteins are resistant to digestion →need for denaturation (by heat in cooking and by action of gastric acid) Proteases – responsible for degrading proteins Produced by: stomach, pancreas and small intestines ABSORPTION OF CARBOHYDRATES Digestible carbohydrates are absorbed only in the form of monosaccharides: ○ Glucose, fructose and galactose ○ Through transporters Rate: SGLT-1 >>> GLUT 5 BIOCHEMISTRY 2 Prepared by: Iklaman, Monsanto, Alih, Aman, Arah, Godoy, Guzman, Laja, Mansan, Nebab Date: September 20, 2024 BIOCHEMISTRY Digestion and Absorption of Macromolecules Prepared by: Group 6 & Group 9 Lecturer: Dr. Farr Krizha Tangkusan, RN, MD Date: September 20, 2024 Hydrochloric acid (HCl) secreted by the parietal cells; functions by denaturing proteins (more susceptible to subsequent hydrolysis) ○ May also kill some bacteria which may affect digestion and absorption of nutrients Pepsin → secreted by chief cells as pepsinogen (zymogen) ○ Releases peptides and few free amino acids Rennin (Chymosin) - secreted by the chief cells; highest secretion during the first few days after birth then declines after. ABSORPTION OF DI- AND TRIPEPTIDES Enter the brush border of intestinal mucosa ○ Hydrolyzed by intracellular Dipeptidases and tripeptidases to become free amino acids ○ Some dipeptides are absorbed via H+ co-transporter ○ Free amino acids are transported into the portal circulation → Either metabolized by the liver or released in the circulation Upon entering the duodenum, large polypeptides→ acted upon by pancreatic proteases Trypsin, chymotrypsin, elastase, carboxypeptidaseTCEC ABSORPTION OF OLIGOPEPTIDES Mediated by CCK and secretin Large peptides may be absorbed either by: ○ Uptake of mucosal cells (transcellular) ○ Passing between epithelial cells (paracellular) Large peptides may be large enough to stimulate antibody production → basis of allergy to foods IgA And Neonates “Neonates can absorb substantial amounts of intact protein from colostrum through the process of endocytosis” Only active until 6 months of age (passive immunity) ○ … even adults can absorb small amounts of intact protein (