13. Gut Fluid Balance - secretion, absorption, malabsorption Flashcards
EPITHELIAL CELLS can … or … WATER and ELECTROLYTES
SECRETE or ABSORB
FLUID INPUT per day
9 L
- Ingest 2L
- Saliva 1.5L
- Gastric secretions 2L
- Pancreatic juices 1.5L
- Bile 0.5 L
- Intestinal secretions 1.5L
FLUID OUTPUT per day
9 L
- Small intestine absorbs 8.5L
- Colon absorbs 0.4L
- Excrete 0.1L
ENERGY is SUPPLIED by … and … GRADIENTS
SODIUM (by sodium pump) and PROTON gradients
what is PARACELLULAR ROUTE
between cells, THROUGH LEAKY TIGHT JUNCTIONS
- Nutrients eg Na+ and most H2O by osmosis
TRANSCELLULAR: Through cells using transporters
ABSORPTION at which part of INTESTINAL walls
VILLUS
SECRETION at the … in Intestinal walls
CRYPT
DIFFERENTIATING CELLS of intestine walls move up from
CRYPT
- STEM CELLS
- PROLIFERATING ZONE
Move up and mature
- old cells shed at top of villus
what FACTORS AFFECT ABSORPTION and SECRETION
- NUTRIENT INTAKE
- GASTRIC MOTILITY
- INTESSTINAL MOTILITY (increased = less time for absorption)
- NUMBER and STATE of ENTEROCTES
- BLOOD and LYMPH FLOWS (clearance rate)
Regulated by
- HORMONAL, PARACRINE, NEURAL networks
TRANSPORTERS for GLUCOSE ABSORPTION
- SGLT-1 (SODIUM GLUCOSE LIKE TRANSPORTER 1)
into cell with Na+
(Na+ pumped out basolateral end via Na+-K+ ATPase) - GLUT2 into blood
H2O can also be absorbed by TRANSCELLULAR ROUTE using which AQUAPORINS
- AQP10
- AQP3
Na+ (and cl-) diffuses down TIGHT JUNCTIONS and what follows
H2O
what is SECRETED into INTESTINAL LUMEN from CRYPT cells
Ca2+
-> draws Na+ through tight junctions (NaCl)
-> H2O follows
ION CHANNELS ACTIVATED /opened for INTESTINAL FLUID SECRETIONS (CRYPT cells)
- NA+/K+ ATPase
- NA+/K+/ 2CL- CO-TRANSPORTER
sodium potassium dichloride cotransporter (2cl-, Na+, K+ in) - K+ CHANNEL
- CL- CHANNEL
- CL- INTO LUMEN
(Na+ and H2O through tight junctions)
what cause the ACTIVATION and OPENING of CHANNELS in INTESTINAL CRYPT CELLS
ACH
-> IP3 -> intracellular CA2+ Release
VIP binding to G-PROTEIN COUPLED RECEPTOR
- cAMP
allow Cl- out
what happens in HYPERMOTILITY type of DIARRHOEA
Transport is TOO FAST in intestines for Absorption
Causes of HYPERMOTILITY type of DIARRHOEA
HIGH FIBRE DIET
DIABETES - ADRENERGIC NEUROPATHY
what happens in OSMOTIC type of DIARRHOEA
NON-SOLUTE ABSORPTION
- ENZYME DEFFICIENCY
or - VILLOUS ATROPHY
so particular solute not absorbed or total reduction in nutrient absorption
When do you get OSMOTIC type of DIARRHOEA
LACTASE DEFICIENCY (cant break down LACTOSE)
COELIAC (sprue) DISEASE
(gluten sensitive)
what happens in DEFECTIVE TRANSPORT type of DIARRHOEA
NA+ or CL- TRANSPORTERS are ABSENT
- electrolytes stay in gut lumen so WATER not absorbed
caused by rare congenital defects
what happens in SECRETORY type of DIARRHOEA
NET SECRETION > NET ABSORPTION
due to
INFLAMMATION
blood HORMONES (ie pancreas secrete VIP, Thyroid - calcitonin)
TUMOURS (secrete)
ENTEROTOXINS
VIRUSES/PARASITES
TRAVELLERS DIARRHOEA caused by
BACTERIA ,VIRUSES, PARASITES
FOOD or WATER BORNE
EXAMPLE of BACTERIA that commonly causes DIARRHOEA
VIBRIO CHOLERAE - CHOLERA TOXIN (on chr. 1)
structure of CHOLERA TOXIN
1X ALPHA SUB-UNIT (large, heavy)
5X Light BETA SUB-UNITS
what happens to CHOLERA TOXIN INTRACELLULAR
- taken up into ENDOSOME
- through GOLGI
- into ER
- ALPHA SUB-UNIT CLEAVED by furin enzyme
- ALPHA SUB-UNIT passed out of pore into CYTOSOL
- ACTIVATES ADENYLATE CYCLASE
- converts ATP into cAMP
- OPENS CHANNELS so CL- SECRETION
-> drives Na+ and H2O through Tight Junctions
HYPERSECRETION NACL, NAHCO3, LOTS H2O
what does CHOLERA TOXIN ACTIVATE INTRACELLULAR (second messenger)
cAMP
- by activating ADENYLATE CYCLASE with ALPHA Sub-Unit
what on CELL SURFACE allows for CHOLERA TOXIN ENDOCYTOSIS
GM1
- glycolipid structure that interacts with BETA SUB-UNITS of CHOLERA TOXIN
what does GM1 on cell surface INTERACT with on the CHOLERA TOXIN
BETA SUBUNITS
when CHOLERA TOXIN INTRACELLULAR, what does the ALPHA 1 SUB-UNIT HYDROLYSE for activation of ADENYLATE CYCLASE
HYDROLYSES NAD+
into ADP-RIBOSE
which is transferred by alpha 1 onto G-PROTEINS
(GDP)
with CHOLERA TOXIN how are the ION CHANNELS and why
ALWAYS OPEN
- CONSTITUTIVE ACTIVATION of ADENYLATE CYCLASE
as ADP-RIBOSE on G-PROTEIN is IRREVERSIBLY ACTIVATED
therefore HYPERSECRETION
ORAL REHYDRATION THERAPY contains:
WATER
ELECTROLYTE (ie NaCl, KCl)
GLUCOSE
for transport of nutrients and water absorption
& replacement of lost K+
