Nutrient Absorption Flashcards
How can water obstruct nutrient absorption?
It forms a layer at the mucosal wall with H-bonds when undisturbed
Impediment to nutrient absorption presented by lack of flow in gut
Water forms layer around intestinal wall with H-bonds.
Brush-border membrane
Microviliated apical tip of enterocytes in small intestine
Which cells secrete mucus in stomach?
Goblet cells
Which cells secrete acid in stomach?
Parietal cells
Which cells secrete pepsinogen in stomach?
Chief cells
Average lifespan of an enterocyte
3-8 days
Migration of entreocytes:
1)
2)
3)
1) Stem cells located in crypts
2) Migrate upwards towards vili
3) Differentiate as migrate
What do crypt cells secrete?
Water, electrolytes
Celiac disease
Gluten causes autoimmune disease
Results in epithelium on villi dying
Enzyme that breaks down polysaccharides
Amylase
Macromolecule broken down by amylase
Polysaccharides
Environment in which amylase works the best
Neutral pH
Efficiency of amylase in mouth
Poor
Food not broken down enough for amylase to access much surface area
Method of digestion in stomach
Peristalsis grinds food against pylorus to break it down
Where does amylase become effective?
In the duodenum
Bicarbonate neutralises acid
Hormones released when food enters duodenum
Secretin
Cholecystokinin
Role of secretin
Activates water secretion
Activates bicarbonate secretion
Inhibits stomach emptying
Action of secretion
Enters blood, stimulates pancreas
Cholecystokinin role
Stimulates pancreatic amylase release into duodenum
Types of absorbable sugars
Glucrose, galactose, fructose
Maltose
2xGlucose
Sucrose
Glucose+Fructose
Lactose
Glucose+Galactose
How do glucose and galactose cross apical membrane?
Sodium-glucose linked transporter (SGLT)
What powers the sodium-glucose linked transporter?
Sodium gradient across endothelial wall
What converts pepsinogen to pepsin?
Low pH
Endopeptidase
Breaks bonds within a polypeptide chain
Limit of endopeptidases
Can’t produce individual amino acids
Where does fat sit in the stomach?
On top of carbs and proteins
Which pancreatic proteases are released upon cholecystokinin signalling?
Trypsin, chymotrypsin
Factors released upon cholecystokinin signalling
Pancreatic proteases
Exopeptidases
Remove amino acids from the ends of proteins
Types of exopeptidases
Carboxypeptidases
Aminopeptidases
How are pancreatic proteases secreted?
As proenzymes
How is protrypsin converted to trypsin?
Enteropeptidase in the brush-border membrane
Enzyme activated by enteropeptidase in the brush-border membrane
Protrypsin –> trypsin
Which enzymes are activated by trypsin?
Chymotrypsinogen –> Chymotrypsin
Procarboxypeptidase –> Carboxypeptidase
What converts chymotrypsinogen to chymotrypsin?
Trypsin
What converts procarboxypeptidase to carboxypeptidase?
Trypsin
Which factor stimulates trypsin release?
Cholecystokinin
What is the pathway for secreted chymotrypsin?
Cholecystokinin –> Protrypsin –> Trypsin –> Chymotrypsinogen –> Chymotrypsin
Types of exopeptidases in the brush-border membrane
Aminopeptidases
Where are fats mostly broken down?
Duodenum
Which fat can stimulate CCK release?
Free fatty acids
An effect of CCK release
Feel sated, release bile (for fat digestion)
Effect of bile on fats
Emulsification
