Wize University Physiology Textbook > Renal Physiology
Reabsorption and Secretion
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Secretion and Reabsorption
Once in the nephron, the filtrate will be refined by adding and removing things from it. In order to do this, we need to be able to move things between the lumen of the nephron and the blood vessels outside of the nephron. In other words, molecules must be able to move through the tubule cells. We have two main forms of movement:
- Transcellular movement
- Secretion - moving into the lumen through 2 transporters (one into and one out of the cell)
- Reabsorption - moving out of the lumen through 2 transporters (one into and one out of the cell)
- Paracelular movement - between cells
Transcellular movement is done using channels and transporters to move specific substances across the tubule cells and into/out of the lumen of the nephron. Some of 'gateways' include:
- Sodium Channels
- Aquaporin
- Glucose uniporters
- Sodium/glucose symporters
- Sodium/hydorgen antiporters
- Sodium/potassium ATPase pumps
We can change the amount of a substance being secreted or reabsorbed by either adding/removing/inhibiting or activating these channels from the tubule cells.
- We can promote/inhibit production of the channels by altering gene expression
- We can move the cannel into or out of the membrane to increase or decrease secretion/reabsorption
- We can activate/inhibit the channels using other substances.
EXAMPLE: What transporter/channel might be saturated in an individual with diabetes?
- very high glucose levels in blood = high filtration rate into the nephron
- Glucose uniporters and sodium/glucose symporters will be hard at work and will likely become saturated
- RESULT: not all glucose can be reabsorbed before excretion = urine contains glucose
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What transporters or channels are present in the collecting duct of the nephron?
Na+ ion channels
K+ ion channels
ATPase
aquaporins
Mark Yourself Question
- Grab a piece of paper and try this problem yourself.
- When you're done, check the "I have answered this question" box below.
- View the solution and report whether you got it right or wrong.
Which part of the nephron would be most greatly effected under the following conditions? What would the effect be?
i) removal of all symporters
ii) increased water filtration
iii) increased production of Na+ channel inhibition factor