Physiology - The proximal tubule and loop of Henle Flashcards
In normal physiological conditions what percentage of glucose is reabsorbed?
Same for urea
Same for creatinine
Glucose - 100%
Urea ~50%
Creatine - 0%
What is the name for the original fluid found in Bowman’s capsule?
What is the difference between it and blood?
Glomerular filtrate
Lacks RBCs + large plasma proteins
Where does the vast majority of reabsorption occur in the nephron?
Proximal convoluted tubule
What are the two pathways that a substance can take for reabsorption?
transcellular - across tubular epi cells
paracellular - between tubular epi cells
What is the difference between primary and secondary active transport?
Primary active transport - need a carrier to move the substance against concentration gradient
Secondary
- move with a carrier against concentration gradient but with another ion (normally Na+)
Where is the only part of the nephron where Na+ is not reabsorped?
Descending loop of Henle
How are glucose and AA reabosorbed?
Via secondary active transport into tubular capillary cell
(helps to drive Na+ reabsorption)
Then diffusion into interstitial fluid beside peritubular capillary/vasa recta
In what situation would glucose be excreted?
Use scientific language
When rate of filtered glucose surpasses the transport maximum
(filtered glucose = plasma conc. x GFR - as plasma conc. increases rate of filtration increases)
This occurs in uncontrolled DM
Draw a graph of filtration, reabsorption and excretion of glucose to plasma glucose conc.
Compare to graph in Onenote
Only absorbed substances have a Tm (transport maximum). T/F?
F - same occurs for secreted substances
e.g. some substances can max
What drives Na+ reabsorption?
Basolateral Na+K+ ATPase channels
this bit is important
What part of the nephron is responsible for generating a cortico-medullary solute concentration gradient?
Why is this important?
Loop of Henle
Enables formation of HYPERTONIC urine
(hypertonic = low H2O = concentrated)
Compare ascending and descending limb of loop of Henle in terms of:
- salt reabsorption
- water reabsorption
Descending limb
- no salt reabsorption
- water reabsorption
Ascending limb
- salt reabsorption
- no water reabsorption
Why in the ascending limb of Henle when NaCl- is being reabsorbed does H2O not follow?
Tight junctions between tubular epi cells -> no paracellular diffusion of H2O can take place
What is the difference in osmolality between the beginning and end of the proximal convoluted tubule?
Explain
There isn’t any
Although a lot of solutes are being absorbed e.g. glucose and AA - water is also following so osmolarity remains the same
What part of the loop of Henle do loop diuretics act on?
Why can they cause a side effect on hypokalaemia?
Ascending loop of Henle
- prevent NaCl from being reabsorbed by blocking triple transporter
- lower NaCl in blood -> reduce BP
NaCl reabsorption requires the recycling of K+ ions (they are no longer reabsorbed in the same way)
Where in the loop of Henle is the tubular fluid most concentrated/hypertonic/highest osmolality?
Where in the kidney does the intersitital fluid have the highest osmolarity/most concentrated/hyerptonic?
End of descending loop of Henle
Deepest in the medulla
Explain why osmolality changes in the loop of Henle?
Increases as go down descending loop of Henle as losing water but not salt
Decreases as go up ascending limb of Henle as losing salts but not water
How does the vasa recta work to maintain the medullary gradient within the loop of Henle?
Vasa recta has v leaky vessels
Hairpin pattern
Blood in vasa recta follows same osmolality pattern and means that no osmolality is washed away
