Absoprtion + Digestion Flashcards
What type of carbs can be absorbed?
Only monosaccharides
What is needed for glucose to be absorbed in SI?
Na+
How do we digest starch?
- amylase breaks down a 1-4 bonds of straight chain > maltose
- maltase breaks down maltose in 2 glucose
- isomaltase breaks down a 1-6 bonds of branches
- glucose is absorbed
How do we digest lactose?
Lactase breaks down lactose into glucose + galactose to be absorbed
How do we digest sucrose?
Sucrase breaks down sucrose into glucose + fructose to be absorbed
How are monosaccharides absorbed?
- Na+ + glucose + galactose enter enterocyte via SGLT1 (Na+ is needed for this to occur)
- fructose enters via GLUT5
- glucose, galactose + fructose exit on basolateral membrane via GLUT2 into venous drainage of small intestine
How are proteins digested?
- stomach
- intestinal lumen
- brush border
Stomach:
- chief cells secrete pepsinogen
- converted to pepsin due to acidic environment
- proteins broken down to oligopeptides + amino acids
Intestinal lumen:
- pancreas releases proteases in inactive form (zymogens)
- enteropeptidase coverts trypsinogen into trypsin
- trypsin activates the other inactive proteases
Brush border:
- short peptides enter enterocytes via PepT1
- amino acids co transported with Na
What are the major proteases secreted by the pancreas in their inactive + active form?
What are the two groups?
Endopeptidases:
- trypsinogen > trypsin
- chymotrypsinogen > chymotrypsin
- proelastase > elastase
Exopeptidases:
- pro-carboxypeptidase A > carboxypeptidase A
- pr-carboxypeptidase B > carboxypeptidase B
Describe protein digestion in the stomach
- chief cells secrete pepsinogen
- converted to pepsin due to acidic environment
- proteins broken down to oligopeptides + amino acids
Describe protein breakdown in the intestinal lumen
- pancreas releases proteases in inactive form (zymogens)
- enteropeptidase converts trypsinogen into trypsin
- trypsin activates the other inactive proteases
What are the different groups of proteases and what’s the difference between them?
- Endopeptidases: break bond in the middle of chain > shorter polypeptides
- Exopeptidases: break bond at end of chain > amino acids + short peptides
How are proteins absorbed in the small intestine?
- short peptides enter enterocytes via PepT1
- amino acids co transported with Na+
- amino acids + short peptides enter venous drainage
- or cytosolic peptidases act on short peptides in enterocytes
What does SGLT1 transport?
Glucose + galactose into enterocyte
Need Na+ to work
What does GLUT5 transport?
Fructose into enterocyte
What does GLUT2 transport?
Glucose
Galactose
Fructose
Into venous drainage
What does PepT1 transport?
Dipeptides
Tripeptides
Into enterocyte
What ion is responsible for water absorption?
Na+
What ion is responsible for water secretion?
Cl-
Outline water secretion
- Cl- enters cells via NKCC contransporters
- increase in cAMP > increased Cl- secretion through CFTR protein
- Na+ drawn through tight junctions into lumen
- water follows
What anaemia can vit B12 deficiency cause?
Megaloblastic anaemia
Causes of vitamin B12 deficiency
- lack of intrinsic factor
- hypochlorhydria
- inflammation of terminal ileum e.g. Crohn’s disease
- inadequate intake in diet (uncommon)
What is hypochlorydria?
Low stomach acid production
Outline lactose intolerance
- deficiency in lactase enzyme
- lactose not broken down so is not digested
- bring water into gut lumen > diarrhoea
- in colon,lactose is fermented in gut > flatulence and bloating
How is irritable bowel syndome diagnosed?
In absense of documented abnormalities
