Gut Fluid Balance

Question 1

Daily Gut fluid balance

Answer 1

▪️in (9 L/day)
-ingest (2)
-saliva (1.5)
-gastric secretions (2)
-pancreatic juices (1.5)
-bile (0.5)
-intestinal secretions (1.5)
▪️out (9 L/day)
-SI absorption (8.5)
-LI absorption (0.4)
-excreted in faeces (0.1)

Question 2

Diarrhoea

Answer 2

▪️malabsorption of water

-failure of GIT to absorb water

Question 3

Movement of water and solutes in GIT

Answer 3

▪️electrolytes moves down its conc gradient- water follows
▪️paracellular route-between tight junctions
-at start of GIT tight junctions are quite leaky, but as you go further down they become tighter therefore a more active process needed
-water mostly moves by osmosis in between cells
▪️transcellular route-through the cells
-aquaporins allow water to be pumped through the cell

Question 4

Structure of SI gland

Answer 4

▪️crypt
-made from SC which move up and differentiate into villus
-secretory in function 
▪️villus 
-mature absorptive cells 
-absorptive in function

Question 5

Factors affecting absorption and secretion in SI

Answer 5

▪️nutrients
-can alter gastric and intestinal motility and secretion
-fibre creates more mechanical stimuli and speed up peristalsis therefore less absorption
▪️number and state of enterocytes
-damaged
-limited number
▪️blockage in blood and lymph flows
-restrict ability to absorb water and electrolytes

Question 6

Absorption of nutrients in SI

Answer 6

▪️apical
-sodium glucose like transporter 1 (SGLT-1- takes in glucose and Na into cell
-amino acids/Na transporter
-short chain fatty acids/Na in ileum and colon
-aquaporin 10 pumps water into cell
-Na/Cl in exchange for H/HCO3
▪️basal-lateral
-Na/K ATPase - pumps out Na to maintain conc gradient and K pumped in
-GLUT-2- pumps out glucose into blood
-aquaporin 3- pumps water out into blood
▪️NaCl goes through tight junction allowing water to follow by osmosis
▪️leads to solvent drag which drags Na into the blood creating a larger conc gradient

Question 7

Intestinal secretion in SI

Answer 7

▪️crypt cells
▪️dilute food content and enzymes
▪️presence of food creates distension that releases ACh or VIP that activate intercellular mechanism that stimulate realise of fluids and enzymes
▪️the more food the more the stimuli and secretion
▪️ACh-Ca or VIP-cAMP lead to release of Cl into lumen
▪️basal-lateral side - Na/K/2Cl co transported inside the cell
▪️NaCl is release into lumen which causes water to follow
▪️bacterial toxins can cause this process to be irreversibly active

Question 8

Types of diarrhoea

Answer 8

▪️hypermotility 
-transport too fast for absorption 
-high fibre diet
-diabetics 
▪️osmotic 
-water and nutrients stays in lumen
-lactose intolerance 
-villi and enzyme deficiency 
▪️defective transport 
-Na/Cl transporters absent 
-congenital 
▪️secretory 
-inflammatory-cytokines releases 
-tumours- pancreatic 
-E.coli, cholera, rotavirus

Question 9

Cholera toxin mechanism

Answer 9

▪️bacteria relaxes toxin when close to cell surface
▪️toxin bind to cell membrane and enters the cell
▪️goes through the Golgi and ER
▪️a part of the toxin binds to adenylate cyclise which activates cAMP
▪️cAMP activates Cl channel to open the fore Cl- exit into lumen
▪️water follows into lumen
▪️cannot stitch itself off
- irreversible activation

Question 10

Why not antibiotics for cholera infection

Answer 10

▪️only clears cholera bacteria not the toxin that is causing harm
▪️no way of getting rid of toxin except shedding enterocyte which takes days
▪️builds up antibiotic resistance
▪️instead use oral rehydration therapy to get fluid and electrolytes back in body