Small intestine physiology Flashcards
What are the three carbohydrate products which are absorbed in the small intestine
Glucose
Galactose
Fructose
Where is starch digestion initiated
Mouth - facilitated by salivary amylase
Where does the majority of carbohydrate digestion occur
Small intestine
What is the main enzyme of carbohydrate digestion
Pancreatic amylase
What are the disaccharides produced from carbohydrate digestion
Maltose
Maltotriose
a-dextrins
All converted to glucose by brush border enzymes
Name the brush border enzymes
Lactase
Sucrase
Trehalase
How are glucose and galactose absorbed across the apical membrane
Secondary active transport (along with Na+)
Sodium-glucose cotransporters (SGLT1)
How do glucose, fructose and galactose exit the cell
GLUT2 receptors across the basolateral membrane into the blood
How does fructose enter the cell
Facilitated diffusion via GLUT5
Where does protein digestion begin
Stomach with action of pepsin
Breaks down protein into amino acids and oligopeptides
Where is the process of digestion completed
Small intestine with brush border and pancreatic enzymes
What does the brush border and pancreatic enzymes do to oligopeptides
Split into amino acids, dipeptides and tripeptides
How are amino acids transported into the cell
Sodium transporter
How are amino acids transported into the blood
Facilitated diffusion
What is lipid digestion started by
Lingual and gastric lipase
What % of lipid digestion is done by lingual and gastric lipase
10%
Where are the remainder of lipids digested
Small intestine
How are lipids digested in the small intestine
Bile acid digestion emulsifies the fat goblets into small chunks (micelles) which have a much larger surface area
What happens to micelles
Pancreatic lipase, phospholipase A2 and cholesterol ester hydrolase - hydrolyse the micelles by breaking them down into fatty acids, monoglycerides, cholesterol and lysolecithin
How are lipids absorbed
Inside the cell products are re-esterified to form the original lipids, triglycerides, cholesterol and phospholipids
These lipids are packaged into apoproteins to form chylomicron
Chylomicrons are too large to enter circulation so they enter lymphatic system via lacteals
Where does most water and electrolyte absorption occur
Small intestine
Some is absorbed in the colon
How much fluid does the small intestine absorb a day
7.5L/day
How much fluid does the colon absorb a day
<1.5L
How much intestinal secretions are there per day
1.5L/day
What factors affect absorption
Number and structure of enterocytes
Blood and lymph flows
Nutrient intake
GI motility
What factors affect secretion
Irritants
Bile
Bacterial
Toxins
What do carbohydrates breakdown into
Monosaccharides
What do proteins breakdown into
Amino acids
What do fats breakdown into
Fatty acids/glycerol
What is the small intestine the primary site for
Digestion and absorption of food
What breakdown glucose into disaccharides
Amylase
What is the role of enterocytes
Absorb glucose and galactose through Na-dependent secondary active transport process
Fructose is absorbed by facilitated transport
What breaks down proteins to polypeptides in the stomach
Pepsin
What breaks down polypeptides to short peptides and amino acids in the small intestine
Trypsin
Chymotrypsin
Carboxypeptidase
What breaks short peptides and amino acids to amino acids in the intestinal mucosa
Peptidases
From protein digestion what enters the blood
Amino acids
Why is bile needed to breakdown fats
Fat and water tend to separate
Enzymes are in the water and cannot get at the fat
Bile has affinity for both fat and water
What happens to bile after they perform there function
Recycled back to the liver
What enzymes are found in the salivary glands
Amylase
Lipase
What does amylase target
Starch
What does lipase target
Triglycerides
What enzymes are found in the stomach
Pepsin
Lipase
What does lipase target
Triglycerides
What enzymes are found in the pancreas
Amylase
Lipase and colipase
Phospholipase
Trypsin
Chymotrypsin
What does colipase target
Triglycerides
What does phospholipase target
Phospholipids
What does trypsin target
Peptides
What does chymotrypsin target
Peptides
What enzymes are found in the intestines
Enterokinase
Disaccharidases
Peptidases
What does enterokinase target
Activates trypsin
What does disaccharidase target
Complex sugars
What does peptidases target
Peptides
