13. Gut Fluid Balance - secretion, absorption, malabsorption

Question 1

EPITHELIAL CELLS can … or … WATER and ELECTROLYTES

Answer 1

SECRETE or ABSORB

Question 2

FLUID INPUT per day

Answer 2

9 L

• Ingest 2L
• Saliva 1.5L
• Gastric secretions 2L
• Pancreatic juices 1.5L
• Bile 0.5 L
• Intestinal secretions 1.5L

Question 3

FLUID OUTPUT per day

Answer 3

9 L

• Small intestine absorbs 8.5L
• Colon absorbs 0.4L
• Excrete 0.1L

Question 4

ENERGY is SUPPLIED by … and … GRADIENTS

Answer 4

SODIUM (by sodium pump) and PROTON gradients

Question 5

what is PARACELLULAR ROUTE

Answer 5

between cells, THROUGH LEAKY TIGHT JUNCTIONS

• Nutrients eg Na+ and most H2O by osmosis

TRANSCELLULAR: Through cells using transporters

Question 6

ABSORPTION at which part of INTESTINAL walls

Answer 6

VILLUS

Question 7

SECRETION at the … in Intestinal walls

Answer 7

CRYPT

Question 8

DIFFERENTIATING CELLS of intestine walls move up from

Answer 8

CRYPT
- STEM CELLS
- PROLIFERATING ZONE

Move up and mature

• old cells shed at top of villus

Question 9

what FACTORS AFFECT ABSORPTION and SECRETION

Answer 9

• 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

Question 10

TRANSPORTERS for GLUCOSE ABSORPTION

Answer 10

• SGLT-1 (SODIUM GLUCOSE LIKE TRANSPORTER 1)
  into cell with Na+
  (Na+ pumped out basolateral end via Na+-K+ ATPase)
• GLUT2 into blood

Question 11

H2O can also be absorbed by TRANSCELLULAR ROUTE using which AQUAPORINS

Answer 11

1. AQP10
2. AQP3

Question 12

Na+ (and cl-) diffuses down TIGHT JUNCTIONS and what follows

Answer 12

H2O

Question 13

what is SECRETED into INTESTINAL LUMEN from CRYPT cells

Answer 13

Ca2+

-> draws Na+ through tight junctions (NaCl)
-> H2O follows

Question 14

ION CHANNELS ACTIVATED /opened for INTESTINAL FLUID SECRETIONS (CRYPT cells)

Answer 14

• 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)

Question 15

what cause the ACTIVATION and OPENING of CHANNELS in INTESTINAL CRYPT CELLS

Answer 15

ACH
-> IP3 -> intracellular CA2+ Release

VIP binding to G-PROTEIN COUPLED RECEPTOR
- cAMP

allow Cl- out

Question 16

what happens in HYPERMOTILITY type of DIARRHOEA

Answer 16

Transport is TOO FAST in intestines for Absorption

Question 17

Causes of HYPERMOTILITY type of DIARRHOEA

Answer 17

HIGH FIBRE DIET

DIABETES - ADRENERGIC NEUROPATHY

Question 18

what happens in OSMOTIC type of DIARRHOEA

Answer 18

NON-SOLUTE ABSORPTION

• ENZYME DEFFICIENCY
  or
• VILLOUS ATROPHY

so particular solute not absorbed or total reduction in nutrient absorption

Question 19

When do you get OSMOTIC type of DIARRHOEA

Answer 19

LACTASE DEFICIENCY (cant break down LACTOSE)

COELIAC (sprue) DISEASE
(gluten sensitive)

Question 20

what happens in DEFECTIVE TRANSPORT type of DIARRHOEA

Answer 20

NA+ or CL- TRANSPORTERS are ABSENT

• electrolytes stay in gut lumen so WATER not absorbed

caused by rare congenital defects

Question 21

what happens in SECRETORY type of DIARRHOEA

Answer 21

NET SECRETION > NET ABSORPTION

due to
INFLAMMATION
blood HORMONES (ie pancreas secrete VIP, Thyroid - calcitonin)
TUMOURS (secrete)
ENTEROTOXINS
VIRUSES/PARASITES

Question 22

TRAVELLERS DIARRHOEA caused by

Answer 22

BACTERIA ,VIRUSES, PARASITES

FOOD or WATER BORNE

Question 23

EXAMPLE of BACTERIA that commonly causes DIARRHOEA

Answer 23

VIBRIO CHOLERAE - CHOLERA TOXIN (on chr. 1)

Question 24

structure of CHOLERA TOXIN

Answer 24

1X ALPHA SUB-UNIT (large, heavy)

5X Light BETA SUB-UNITS

Question 25

what happens to CHOLERA TOXIN INTRACELLULAR

Answer 25

1. taken up into ENDOSOME 2. through GOLGI 3. into ER 4. ALPHA SUB-UNIT CLEAVED by furin enzyme 5. ALPHA SUB-UNIT passed out of pore into CYTOSOL 6. ACTIVATES ADENYLATE CYCLASE 7. converts ATP into cAMP 8. OPENS CHANNELS so CL- SECRETION -> drives Na+ and H2O through Tight Junctions HYPERSECRETION NACL, NAHCO3, LOTS H2O

Question 26

what does CHOLERA TOXIN ACTIVATE INTRACELLULAR (second messenger)

Answer 26

cAMP - by activating ADENYLATE CYCLASE with ALPHA Sub-Unit

Question 27

what on CELL SURFACE allows for CHOLERA TOXIN ENDOCYTOSIS

Answer 27

GM1 - glycolipid structure that interacts with BETA SUB-UNITS of CHOLERA TOXIN

Question 28

what does GM1 on cell surface INTERACT with on the CHOLERA TOXIN

Answer 28

BETA SUBUNITS

Question 29

when CHOLERA TOXIN INTRACELLULAR, what does the ALPHA 1 SUB-UNIT HYDROLYSE for activation of ADENYLATE CYCLASE

Answer 29

HYDROLYSES NAD+ into ADP-RIBOSE which is transferred by alpha 1 onto G-PROTEINS (GDP)

Question 30

with CHOLERA TOXIN how are the ION CHANNELS and why

Answer 30

ALWAYS OPEN - CONSTITUTIVE ACTIVATION of ADENYLATE CYCLASE as ADP-RIBOSE on G-PROTEIN is IRREVERSIBLY ACTIVATED therefore HYPERSECRETION

Question 31

ORAL REHYDRATION THERAPY contains:

Answer 31

WATER ELECTROLYTE (ie NaCl, KCl) GLUCOSE for transport of nutrients and water absorption & replacement of lost K+