Tubular transport

Question 1

What is the functional part of the nephron

Answer 1

The renal tubular epithelial cells

Question 2

Function of renal tubular epithelial cells

Answer 2

1) Reabsorption of solutes and water

2) Respond to and control the overall organismal balance of acid, solutes, fluid hormones, vitamins and xenobiotics

Question 3

How transport functions of renal tubular epithelial cells are accomplished

Answer 3

• by solute specific transporters and channels

- these are aided by specific accessory proteins

Question 4

What properties of the epithelial cell does transepithelial transport rely on

Answer 4

-transepithelial cell polarity

Question 5

Two types of pathways for transtubular movement of substances

Answer 5

1) Transcellular pathway

2) Paracellular pathway

Question 6

Mechanisms of transcellular pathway

Answer 6

1) Passive or active transporters
2) through channels
3) Through receptor mediated endocytosis

Question 7

General factors influencing tubular transport of substances

Answer 7

1) Electrochemical gradients
2) Endocrine or paracrine hormones
3) Tubular flow

Question 8

Type of transport through channel proteins

Answer 8

1. Can be electrogenic (i.e. ions) or electroneural (H2O, NH2)
   - selective or nonselective

-channels may be open or closed (gated)

Question 9

What about channels regulates transport

Answer 9

Transport regulated by :

1) The probability that the closed channel will open
2) The probability that the open channel will close
3) The number of functional channels in the membrane

Question 10

Transporter poperties

Answer 10

1) Must undergo >/= 1 conformational change to mediate each cycle of transmembrane solute translocation
2) Can move 1 type of solute or greater >1 type of solute in the same (cotransporter/symporter) or opposite direction (antiporter or exchanger)
3) Facilitated diffusion (passive) transporters
4) Primary or secondary active transporters

Question 11

Primary active transporter

Answer 11

• ex ATPases
• able to transport ions against their electrochemical gradient
• fueled by ATP hydrolysis

Question 12

Secondary active transporter

Answer 12

-use the favorable chemical or electrochemical gradient of 1 solute to drive transport of another solute against its unfavorable gradient either as cotransport or antiport

Question 13

what about transporters regulates transport

Answer 13

Activity regulated by:

1) amount of polypeptide in membrane (through retrieval, production and stability)
- transport substrate affinity
- and regulation of rate of the conformational change(s) that mediate ion/solute translocation