2 digestion pdf
TRANSCRIPT
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• It is the breakdown &
degradation of polysaccharides &
oligosaccharides into their
simplest units (Monosaccharides)
Digestion of Carbohydrates
1. Digestion
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Digestible
Monosaccharides
Do not need
digestion
Starch
Hexoses
Classification of Carbohydrates
Glycogen
Lactose
Sucrose
Pentoses
Non-Digestible
Cellulose
1
2
3
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The Digestive System
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PH 6.4 – 6.9. Activated
by Cl-, digests starch to
dextrins, maltose &
isomaltose
Acidic PH of stomach (1-2) is
unsuitable for salivary
amylase
3. Brush border (Intestinal juice,
Succus Entericus) containing:
Maltase, Lactase & Sucrase
(Activated by Cl-).
4.
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Carbohydrate Digestion in Small Intestine
• Salivary amylase stops working in acidic
stomach (if pH 4.5)
• 50% of dietary starch digested before it
reaches small intestine
• Brush border enzymes act upon
oligosaccharides, maltose, sucrose & lactose
• lactose indigestible after age 4 in most
humans (due to lack of lactase)
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Carbohydrate Digestion
in Small Intestine
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& Isomaltose
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Monosaccharides Absorption
• Pentoses are absorbed by facilitated diffusion then
excreted through the kidney
• Fructose is absorbed by facilitated diffusion then
converted to glucose inside the cell
• Sodium-glucose transport proteins (SGLT) in
membrane help absorption of glucose & galactose
2. Absorption
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Absorption of Pentoses & Hexoses
Pentoses absorbed
by Passive Diffusion
Hexoses absorbed
by Active Transport
According
concentration
gradient
Against
concentration
gradient
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Types of Transport Carriers
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Monosaccharides Absorption
Liver
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GLUT1 in RBCs membrane is Facilitated Diffusion
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Digestion of Lactose
(Lactase)
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Lactose Intolerance• Some individuals (90% of adult blacks & Orientals)
have a defect in lactase enzyme
• Undigested lactose (osmotically active compound)
passes to the bowel (large intestine), acted upon by
bacteria of large intestine producing short chain fatty
acids & CO2 gas, leading to:
1. Abdominal distention (cramping)
2. Abdominal pain
3. Nausea
4. Bloating
5. Watery diarrhea
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Lactase deficiency
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Fate of Absorbed Glucose
• Glucose enter Liver & Brain by Passive
diffusion
• Glucose enter other tissues (skeletal muscle,
adipose tissue, etc…) by Active transport
• Active transport is enhanced by Insulin
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Utilization of Glucose
Anabolic
Reactions Catabolic
Reactions
1) Storage in the form of
Glycogen (Glycogenesis)
2) Storage in the form of Lipid
(Lipogenesis)
3) Synthesis of sugar alcohols
and amino sugars
4) Interconversion between
monosaccharides
1) Glycolysis
2) Kreb’s Cycle
3) Pentose Shunt
4) Formation of Uronic acids