DIGESTION AND METABOLISM OF CARBOHYDRATE

DIGESTION

ABSORPTION

DISACCHARIDE

FINAL HYDOLYSIS - LUMINAL SURFACE OF SMALL INTESTINE EPITHELIAL CELLS

IN SMALL INTESTINE

IN STOMACH

OTHER UNHYDROLYSED CANNOT BE ABSORBED

IN MOUTH

Action of Ptylin (Salivary amylase)

Incomplete process

Location: mouth

Shorter duration

Action

Require Cl- ion for activation of optimum pH of 6.7 (range 6.6 to 6.8)

Alpha-amylase hydrolyse alpha-1,4 glycosidic linkage in polysaccharide molecule

Type of amylase: alpha- amylase

Ptylin action stop at stomach (pH falls to 3.0)

Action

No enzyme for glucosidic bond linkage

Hydrochloride (HCl) can hydrolyse sucrose form glucose and fructose

Main digestion take place in small intestine by pancreatic amylase

Digestion completed by pancreatic amylase (food stay longer in intestine)

In duodenum

Food bolus meets pancreatic juice

Pancreatic juice contain pancreatic amylase @ amylopsin (carbohydrate splitting enzyme- similar to salivary amylase)

food bolus reach duodenum fom stomach

Action of pancreatic amylase

click to edit

Reaction catalyzed

Pancreatic amylase product

Optimum pH: 7.1

An isoenzyme of salivary amylase but differ in optimum pH of action

Type of amylase: alpha- amylase

Require Cl- ion for its activity

Hydrolyse alpha-1,4 glycosidic linkage of polysaccharide molecule

Starch âž¡ Maltose/ Isomaltose + Dextrin and oligosaccharides

Trisaccharide maltotriose

Alpha-limit dextrin (~glucose unit with 1 or more 1,6-glycosidic bond)

Disaccharide maltose

Types

Reaction catalyzed

Present in the bush border epithelium of intestinal mucosal cells

Maltase

Lactase

Sucrase-isomaltase (bifunctional enzyme catalyzing hydrolysis of sucrose and isomaltose)

Sucrose Isomaltose âž¡ 3 Glucose + Fructose

Lactose âž¡ Glucose + Galactose

Maltose âž¡ Glucose + Glucose

Exoenzyme

Cleave one unit glu at a time

Alpha- glucosidase


Beta- glucosidase

Enter lower tract of intestine

Used by bacteria resulting in producing of

Hydrogen gas

Methane

CO2

monosaccharides

glucose and galactose

fructose

sugars absorbed by enterocytes

mechanisms

absorption of monosaccharides

  1. enzymes on the luminal surface of the small intestine epithelial cells digest disaccharides into monosaccharides
  1. monosaccharides are absorbed into the cells by facilitated diffusion by secondary active transport with Na+
  1. the absorbed monosaccharides enter the blood. the bloodstream distributes the nutrients throughout the body

factors affecting rate of absorption

he absorption is faster through intact mucosa and slower if there is some injury to the mucosa

the rate of absorption of glucose increase by thyroid hormone

mineralorcoticoid increase the rate of absorption

absorbed via secondary active transport by a symporter

glucose transporters

Na+ dependent (SGLT)

Na+ independent (GLUT)

type of co-transporter

2 binding sites : for Na+ and for glucose

after Na+ binding, conformational occurs to make sure glucose can bind

Na+ is transported across membrane where down concentration gradient and glucose against the concentration gradient

used for facilitated transport

numbered from 1 to 14 GLUT

facilitated transport

the absorption is slower than glucose and galactose abosrtion

passive diffusion

facilitated diffusion

active transport

uptake of glucose in peripheral cells

facilitated diffusion

numbered from 1 to 7 (GLUT 1 to GLUT 7)

clinical significance (absorption)

in deficency of SGLT - 1, glucose unabsorbed and excreted in feces

in deficiency of SGLT - 2, the filtered glucose is not absorbed back then lost in urine which cause glycosuria

METABOLISM

Catabolic proses

clinical significance (digestion)

congenital lactose intolerance

deficiency of lactase enzyme

develops immediately after birth

milk feed precipitates symptoms

primary lactase deficiency

develops over time

intolerance to milk and dairy products

secondary lactase defiency

develop in a healthy person during episodes of acute illness

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anabolic proses

Glycolysis

Citric acid cycle

Glycogenolysis

Hexose monophosphate pathway

Uronic acid pathway

Glycogenesis

Gluconeogenesis

breakdown of glucose to pyruvic acid

occurs in the cytoplasm

net gain 2 ATP, 2 NADH and 2 molecules of pyruvic acid

occurs in the mitochondria

gly

produces CO2, GTP, 3 NADH and 1 FADH2

TCA9

Breakdown of glycogen to glucose

glycogenolysis

alternative pathway for glucose oxidation which neither utilizes nor produces ATP

hmp

synthetic pathway for the various uronic acids

uronic acid

Synthesis of glycogen from glucose

glycogenesis

formation of glucose from non-carbohydrate sources

gluconeo glyconeo

Carbohydrate-digestion-2-300x225

by:

  1. Nuhilhadiah Binti Suatman (70832)
  2. Nur Anesa Binti Mohd Sedek (70870)