Carbohydrates 2 Flashcards
What are the 2 main undigestible carbohydrates in our diet?
Cellulose and oligosaccharides (with alpha1->6 linked galactose)
What are the 4 main diestible types of carbohydrates in our diet?
- Starch
- Glycogen (meat)
- Monosaccharides (glucose/fructose)
- disaccharides (lactose, sucrose, maltose)
What carb digestion occurs in the mouth?
Salivary amylase hydrolyses (alpha1->4) bonds in starch
What carb digestion occurs in the duodenum and where is it?
Duodenum is the first section of the small intestine
Pancreatic amylase hydrolyses (alpha1->4) bonds in starch
Where is the Jejunum and what carb digestion occurs there?
The jejunum is the 2nd part of the small intestine
- Isomaltase hydrolses (alpha1->6) bonds
- Glucoamylase removes Glc from non-reducing ends of glycogen
- Sucrase hydrolyses sucrose
- Lactase hydrolyses Lactose
What are the 3 main products of carbohydrate digestion in the small intestine?
Glucose, Galactose and Fructose (monosaccharides)
Describe the first of 3 steps through which glucose passes form the gut lumen to the blood:
(1) Glucose passes from gut lumen to epithelial cell through the apical lamina using a Na+/glucose symporter (2 Na+ and 1 glucose pass through together). Na+ conc. gradient provides the energy for this meaning it can occur even when glucose is moving against its conc. gradient
Describe the 2nd of 3 steps by which Glc passes from gut lumen to blood:
Na+K+ATPase pumps 3 Na+ from epithial tissue through basal lamina into the blood and 2K+ the opposite way. Driving the conc. gradient that moves glucose. This requires ATP therefore glucose moves by a Indirect ATP Powered Process.
Describe the 3rd and last step by which Glc moves from the gut lumen to the bloodstream:
Glucose in the epitheial tissue move into the blood through the basal lamina via a glucose uniporter GLUT2 which facilliates downhill efflux.
How do galactose and fructose absorbtion in the gut compare to Glc?
Galactose is very similar.
Fructose needs no sodium gradient and simply binds alone to channel protein GLUT5 moving down its conc. gradient to the blood.
What happens to Indigestible Cellulose?
It increases faecal bulk and decreases transit time. Without it constipation can occur.
What are the 5 possible reasons for dissacharidase deficiencies?
- Surgical removal of the intestine
- Genetics
- Inflammation of the gut wall
- Severe intestinal infection
- Drugs injuring the gut wall
What are the symptoms of dissacharidase deficiencies?
Abdominal distention
Cramps from a build up of gasses released when gut bacteria break down dissacharides.
Others (see lactase deficiency)
How are dissacharidase deficiencies diagnosed?
Testing for enzyme activity of common ones such as lactase, maltase and sucrase
Explain lactose intolerance
In most humans (almost all non-whites) Lactase stops functioning after weaning.
Consumption of lactose after this results in gaseous build up from breakdown by gut bacteria
Lactose is osmotically active so it also drags water out of the blood into the lumen causing dehydration and diarrhoea