Carbohydrate and Protein Digestion and Absorption in the Gastrointestinal Tract
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Course
Integration Of Physiological Systems (BMS2038)
Institution
University Of Surrey (UNIS)
Starts off by introducing the different groups of carbohydrates e.g. simple and complex, which is good if haven't studied biochemistry. Then goes on to explain how carbohydrates are digested in different sections of the GI system, mainly the small intestines. It explains the role of the enzyme call...
• STARCH IS COMPOSED OF 2 KINDS OF POLYSACCHARIDES:
1. AMYLOSE = a compact chain D-glucose molecules linked via α 1-4 glycosidic bond (~>20,000
glucose units; 15-20% starch)
2. AMYLOPECTIN (and glycogen) = is a highly branched D-glucose chains linked via α 1-6
glycosidic bond (~80-85% starch, ~>2 million glucose units
STEPS OF DIGESTION OF STARCH:
1. IN THE MOUTH, SALIVARY α-AMYLASE breaks starch into shorter polysaccharides (~2%)
• In the STOMACH, the SALIVARY α-AMYLASE is INACTIVATED by LOW pH. NO
CARBOHYDRATE DIGESTION OCCURS
2. IN THE SMALL INTESTINE: complete digestion of starch products; disaccharides into monosaccharides by:
i. PANCREATIC α-AMYLASE
ii. ENZYMES released from the BRUSH BORDER of SI LUMEN
• In small intestine: MOST CARBOHYDRATE DIGESTION and ABSORPTION OCCUR
• STEP 1: PANCREATIC α-AMYLASE:
i. ABSORPTION of GLUCOSE (amino acids and fatty acids) from DUODENUM
ii. STIMULATE the RELEASE of HORMONES (CCK, secretin) from the SMALL INTESTINE
iii. STIMULATE the PANCREATIC EXOCRINE SECRETION of α-AMYLASE
iv. α-amylase digestion liberates short-chain glucans, oligosaccharides, tri- and di-saccharides
• STEP 2: SI BRUSH BORDER ENZYMES
i. FURTHER ENZYME DIGESTION by enzymes released from the brush border of SI lumen
ii. Most starch digestion and breakdown of disaccharides occur
α
ACTION OF α-AMYLASE:
• α-AMYLASE = is an ENDOENZYME
Integration of Physiological Systems Page 1
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