Anuj Flashcards
SI
Folds of Kerching Microvilli + Crypts of L Microscopic Microvilli 6m, 200cm2 Absorbs: na, k, cl, h2o, nutrients Secretes: HCO3-
LI
Semilunar folds crypts microvilli 2.4cm, 25cm2 Absorbs: na, cl, h2o Secretes: K+ HCO#-
Glucose and a/acid co-transporters
2 active transport
usually on “active” membrane
1. Apical SGLT (2 Na Glucose/a/acid)
2. Basolateral GLUT2
Na+ channels dependance
- Fasting/post prandial state
2. GI region
Na/K ATPase blockage
Digitalis drug
Paracellular
Tight junctions
Lower resistance
Passive
H2o absorption
Jejunum mainly
Fluid movement
Fluid movement always coupled by active solute movement
coupled to Solvent drag: dissolved solute swept along with bulk H2O movement (solvent)
Na+ movement
- Na+K+ ATPase
- Na+/H+ (counteracts acidosis) (secretes H+ for Na+)
- Parallel Na+/H+ and Cl-/HCO3-
- Epithelial Na+ (aldosterone dependant, for Na+ retention)
- Cl- movement is dependant on Na+
Cl- movement
- Passive or Paracellular
- Cl-/Hco3-
- Parallel Na+/H+ and Cl-Hco3-
K+ movement
BK and IK1
CFTR
cystic Fibrosis Transmembrane Receptor
Activated: increased Ca, cAMP and VIP (vasopeptides)
ECF –> ICF –> Lumen
Na follows (homeostasis) + H2O follows (osmolarity)(losing fluid)
=NaCl in lumen
Control of Absorption and Secretion
- Enteric: Ach, VIP(vasopeptides) and other Secretagoges
- Endocrine: Aldosterone
- Paracrine: 5HT
Diarrohea
> 200ml day/3+ bowel movements
1.5 mil 5 1mil
SI: voluminous (where most reabsorption occurs)
LI: small volume
Osmotic D: mal absorption (increased osmotic load)
Secretory D: increased secretion due to Na and Cl channels
Osmotic Diarrohea
macronutrients malabsorption retaining osmotic pressure in the lumen and therefore water is retained
-pancreatic disease (proteases, lipase and amylase),
-large intakes of sugar
alcohols(sorbitol)
- fructose and lactose intolerance
-coeliac disease
Lactose intolerance
• Lack of the enzyme lactase
• 75% world population show some intolerance
- 5% incidence N Europe to > 90% in Africa and Asia
Coeliac disease Non tropical spruce/ gluten enteropathy Autoimmune reaction: AB against gluten destruction of epithelial cells and severe villi blunting Nutrient malabsorption
Secretory Diarhoea
increase active secretion
congenital absence of Cl-HCO 3 exchanger
E. Coli or cholera toxin
bacterial microorganisms produce enterotoxins which raise intracellular [cAMP], [cGMP] or [Ca+2]
stimulation of anion secretion, especially Cl- (via CFTR).
Na+ too (To maintain lumenal charge balance) , along with water
Does not impact on nutrient coupled Na absorption, ORS (Oral Rehydration Therapy) containing glucose and Na+ is an effective treatment for secretory diarrhea
Case Study
The ambulance was called in and the paramedics who attended to Sandy recorded a low BP and extremely high HR (trying to maintain her BP).
As all her ECF fluid was being lost her skin was dry and indicated dehydration.
Microscopic examination of the patient’s stool reveals the presence of a large number of Vibrio cholera bacteria. Increase Cl- secretion > increase Na+ secretion > Water loss
Losing fluid from ECF. (less ECF > less plasma > less blood flow > less BP > increased HR)
She has Secretory Diarrhoea
Treated with ORT
ORT
Oral Rehydration Therapy
Reduced mortality by 60%. 500 million ORS sachets per year.
• glucose, bicarbonates, ions.
Cholera only impacts the Cl- channels, not the Na+/glucose co-transporters.
Na+ and glucose moved into the cell, Cl- follows into the cell also. Effectively nutrients lost are brought back in.
•Bicarbonates are to counteract the acidotic effect of diarrhea, maintaining pH
o To correct the loss of electrolytes from the body
o To restore fluid loss from the body
o To restore Na+ balance across the brush border to maintain the transport mechanism
o To aid osmotic reabsorption in the lumen
