Salt & water transport & its control

Question 1

What structures and pathways regulate salt and water transport?

Answer 1

the gut lumen, hormones and enteric NS

Question 2

Outline the importance of water indigestion

Answer 2

provides a medium for digestion & waste elimination

replaces the daily loss of body fluids in sweat, urine and faeces.

Question 3

What are the 3 types of membrane proteins

Answer 3

Protein pump, Protein carrier, protein channel

Question 4

Give examples of protein pumps

Answer 4

Na+/k+ pump, atpase pump

Question 5

give examples of protein carrier channels

Answer 5

Na+/ glucose symport, glucose transporter

Question 6

give examples of protein channels

Answer 6

Ion channels k+, cl- and aquaporin

Question 7

Outline the 3 types of enterocyte transport:

Answer 7

passive: down the electrochemical gradient via ion channels, carriers or tight junctions.

solvent drag: water moves to reach osmotic equilibrium and takes ions

active: requires ATP

Question 8

Enterocytes in crypts and villi have diff combinations of transport proteins outline the differences

Answer 8

in villi, they are absorptive and dominate nutrient transport and in crypts, they are secretory with less nutrient transport

Question 9

Outline water and electrolyte transport from the SI to the colon

Answer 9

In the duodenum osmotic equilibration occurs to form isotonic chyme via permeable tight junctions

in the jejunum, Na+/k+/cl- and water is reabsorbed and in the ileum HCO3- is secreted.

the colon reabsorbs Na+, Cl- and water and secreted K+ & HCO3-

Question 10

Why is Na+ absorption in the SI important

Answer 10

It drives the absorption of other ions and organics driven by basolateral active transport of Na via Na+/K+ ATPase pump into the interstitial fluid which creates an electrochemical gradient which aids cl- absorption in the jejunum.

Question 11

the absorptions of water is dependant on solutes how is the gradient created?

Answer 11

Na+/K+ ATPase increases NaCl which creates an osmotic gradient that draws water into enterocytes.

Question 12

Describe the action of the cholera toxin

Answer 12

the toxin binds irreversibly to increase adenylyl cyclase, generating excess cAMP which increases cl- secretion via CFTR channels which increases cl- and as a results Na+ and water into the crypts. Profuse watery diarrhoea is made and can lead to circulatory shock.

Question 13

how can cholera be treated

Answer 13

antibiotics along with oral rehydration therapy which consists of fluids that contain Na+ and glucose to promote fluid absorption.