Nutrient digestion Flashcards
What are the membranes of the small intestine?
Apical membrane
basolateral membrane
What are paracellular pathways?
Pathways between the cell to allow water to enter the cell
What are the principle dietary nutrients?
Carbohydrates
Protein
Fats
What are the forms of polysaccharides?
Starch
Cellulose
Glycogen
What is starch?
Plant storage form of glucose
What are the types of starch?
⍺ amylase
amylopectin
What is the difference between ⍺ amylase and amylopectin?
⍺amylase has glucose linked in straight chains while amylopectin has highly branched glucose chains
What is the structural makeup of starch?
Glucose monomers linked by ⍺-1,4 glycosidic bonds
How is starch broken down?
Amylase
What is cellulose?
Constituent of plant cell walls, dietary fibre
What is the structure of cellulose?
Unbranched linear chains of glucose monomers lined by β-1,4 glycosidic bonds
Why is cellulose a dietary fibre?
No enzymatic digestion in vertebrates
What is glycogen?
Animal storage form of glucose
What is the structure of glycogen?
Glucose monomers linked by ⍺-1,4 glycosidic bonds
How is starch and glycogen broken down?
by amylase
How are glucose and galactose absorbed into the cells of the small intestine?
Via SGLT1 accompanied by Na
How are glucose and galactose transported out of the small intestinal cells and into the bloodstream?
Via GLUT2
Why are glucose and galactose accompanied by Na?
Create a gradient to allow for passive absorption of water
How is water absorbed into the bloodstream?
Na/K pump created a gradient that allows water to passively pass through the paracellular pathway
How is fructose absorbed into the cells of the small intestine??
Via GLUT5 accompanied by Na
How is fructose transported out of the cells of the small intestine and into the bloodstream?
Via GLUT2
What are the transporter proteins of glucose and galactose?
Into cell= SGLT1
Out= GLUT2
What are the transporter proteins of fructose?
in= GLUT5 out= GLUT2
What are proteins?
Polymers of amino acids linked together by peptide bonds of varying length
What are peptides?
Small proteins constituting of 3-10 amino acids
What breaks down proteins and peptides?
Proteases and peptides
How are amino acids absorbed into the bloodstream?
Via SAAT1 accompanied by Na then cross over into the bloodstream
How are dipeptides absorbed into the bloodstream?
Taken into the cells via Pep1 accompanied by H
Na is taken into the cell by NHE3 as H is transported out
Dipeptides cross into the bloodstream
Why is NHE3 essential?
maintains the Na gradient to allow water to enter the bloodstream via the paracellular pathway
What is the most common form of ingested fat?
Triacylglycerol
Where does fat digestion take place?
Small intestine
What enzyme is involved in fat digestion?
Pancreatic lipase
What does lipase break triacylglycerol down into?
Monoglyceride and 2 fat acids
What makes lipase inefficient on triacylglycerol?
Triacylglycerol is insoluble in water while lipase is, so lipase can only work on the surface of lipid droplets
What is done to make digestion of fats more efficient?
Emulsification
What are the requirements of emulsification?
Mechanical disruption
Emulsifying agent
What mechanical disruption is used in emulsification of fats?
Smooth muscle contraction of the stomach
Grinds and mixes lumenal contents
What is the purpose of an emulsifying agent?
Prevents small droplets reforming into large droplets
What emulsifying agent is used for fats?
Bile salts and phospholipids
How do emulsifying agents work?
Have a polar and a non polar end
Non polar end associated with lipid droplet, leaving polar ends exposed at the water surface to repel each other
What can emulsifying agents be classified as?
Amphipathic molecules
What are micelles?
Bile salt, monoglyceride, fatty acid and phospholipid
What is the structure of a micelle?
Polar portion at surface, non polar core
How do micelles break down?
As micelles come into contact with the villi in the acid microclimate, they release the fatty acids and monoglyceride for passive diffusion across the intestinal cell membrane
What happens to fatty acids and monoglycerides once they enter the small intestinal cells?
Smooth endoplasmic reticulum
What do fatty acids and monoglycerides form into in the small intestinal cells?
Triacylglycerol
How are fatty acids and monoglycerides formed into triacylglycerol?
Via enzymes in the smooth endoplasmic reticulum
How is triacylglycerol transported in the cell?
In vesicles formed from the smooth endoplasmic reticulum membrane
What happens to triacylglycerol in the small intestinal cells?
Processed through the Golgi apparatus and exorcised to the extracellular fluid at the basolateral membrane
What are chylomicrons?
Coated extracellular fat droplet containing phospholipids, cholesterol and fat soluble vitamins
What happens to chylomicrons in the small intestine?
Pass into lacteals between endothelial cells as they are too large to pass through the capillary basement membrane
What are the fat soluble vitamins?
A, D, E, K
How are fat soluble vitamins absorbed?
Via the same absorptive path as fat
What are the water soluble vitamins?
B group, C, folic acid
How are water soluble vitamins absorbed?
Passive diffusion
Carrier mediated transport
How is B12 absorbed?
Binds to intrinsic factor in stomach to form a complex which is absorbed via a specific transport system in the distal ileum
How much B12 can the body store?
3 years worth stored in liver
What does a B12 deficiency cause?
Prenicious anaemia- failure of RBC maturation
How is iron absorbed?
Transported across brush border membrane via DMT1 into duodenal enterocytes
What are the 2 fates of iron in cells?
Incorporated into ferritin in the cell
Bound to transferrin in the blood for transport
Why does iron bind to transferrin in the blood?
Cannot travel alone in the blood due to the charge and dangers of free radical creation
How is ferritin expression controlled?
Depending on the body’s iron status
