Renal - Physiology Flashcards
(53 cards)
What are the three ways the GFR autoregulates?
1) autonomic vasoreactive (myogenic) reflex in afferent arteriole
2) tubuloglomerular feedback:
- reflex vasoconstriction or dilation of AFFERENT arteriole
- mediated by macula densa in thick ascending loop of henle:
Increased GFR –> increased solute delivery to macula densa–> vasoconstriction of afferent arteriole –> decreased GFR
3) angiotensin II mediated vasoconstriction of efferent arteriole
Increased GFR results in increased solutes delivered to what?
(In the tubuloglomerular feedback mechanism)
To the macula densa
In the tubuloglomerular feedback model, when increased solutes are delivered to the MACULA DENSA what happens?
Vasoconstriction of the AFFERENT arteriole
–> decreased GFR
In autoregulation of GFR angiotensin II does what?
Angiotensin II mediated VASOCONSTRICTION of EFFERENT arteriole
When there is decreased GFR how does that increase angiotensin II
Decreased GFR results in Renin produced by granular cells in afferent arteriole at Juxtaglomerular apparatus
Renin then catalyses angiotensinogen to angiotensin I
Angiotensin I is converted to angiotensin II by ACE
Where is renin produced and in response to what?
Renin is produced by granular cells in AFFERENT arteriole in juxtaglomerular apparatus
In response to decreased Renal blood flow
What does renin do?
Catalyses conversion of angiotensinogen to angiotensin I
In the PROXIMAL TUBULE is NaCl reabsorbed?
60% of NaCl resorption is in PROXIMAL TUBULE
In PROXIMAL TUBULE
Where is water resabsorped?
Through tight junctions driven by oncotic pressures and hydrostatic pressure
Also ACTIVE CHANNELS aquaporin-1
In the PROXIMAL TUBULE
How is Na absorbed?
Basolateral 3Na/2K-ATPase keeps a gradient
On APICAL SIDE: Na-H+ exchanger Symporter with phosphate Symporter with glucose Symporter with amino acids
In the PROXIMAL TUBULE
How is Cl absorbed?
Early in the tubule it isn’t absorbed
Because when Cl is left in the lumen it then enables removal of HCO3- from the lumen early on (pushing it to be converted to H20 and CO2)
But later:
APICAL side:
Cl/formate exchanger
BASOLATERAL:
K/Cl symporter
In the PROXIMAL TUBULE what happens to the Formate that gets secreted in exchange for Cl absorption?
Formate binds to H+ and forms formic acid which is reabsorbed by passive diffusion
In the PROXIMAL TUBULE:
How is bicarbonate reabsorbed?
H+ is in the lumen from Secretion by the H+/Na+ exchanger
HCO3- then binds to H+to form carbonic acid H2CO3
Carbonic acid in the lumen is converted by CARBONIC ANHYDRASE to H20 and CO2. The CO2 then diffuses passively into the cell.
Inside the cell CARBONIC ANHYDRASE reforms H2CO3 which dissociates to H+ and HCO3-.
HCO3- then exits via APICAL Na/HCO3- symporter
Once Bicarbonate is absorbed into the cell in the PROXIMAL TUBULE how does it exit the cell?
Via the Na/HCO3- symporter
Where does acetazolamide act?
Inhibits carbonic ANHYDRASE at the proximal tubule
Therefore blocks bicarbonate reabsorption
Therefore acetazolamide alkanylises the urine
In the PROXIMAL TUBULE what happens to ammonia?
Secretion
glutamine breaks down to form NH3 which diffuses out of the cell and in the lumen combines with H+ to become NH4+
In the cell some NH3 combines with H+ to become NH4+ which gets EXCHANGED with Na to be secreted into the lumen
What is the effect of a high K+ on ammonia in the PROXIMAL TUBULE
Because in the cell there is high K+ there is reduced NH+ creations (high intracellular K+ such as in HYPERALDOSTERONISM reduces ammoniogenesis)
That is why hyperaldosteronism creates Renal Tubular Acidosis Type IV
In the PROXIMAL TUBULE what happens to phosphate?
Filtered phosphate ion (PO4-) in the lumen combines with H+ (secreted by Na/H+ exchanger) to form H2PO4
Phosphate also cotransports with with Na (and this cotransporter is regulated by PTH
How is glucose reabsorbed?
In the PROXIMAL TUBULE
Apical side has SGLT2 cotransporter that moves glucose with Na from lumen into the cell
Basal side has GLUT2 transporter to exit glucose from the cell into the blood
How are amino acids reabsorbed?
In the PROXIMAL TUBULE there are Multiple apical transporters specific for different amino groups, usually cotransporters with Na+
What happens if peptide hormones get filtered?
In the PROXIMAL TUBULE
Peptide hormones (ie insulin, growth hormone, beta2 microglobulin and albumin) absorbed by absorptive endocytosis then degraded by acidified endocytic lesions.
What happens to protein bound drugs not filtered but that need to be renally cleared?
In the PROXIMAL TUBULE protein bound drugs not filtered at glomerulus (ie penecillin / cephalosporins / salicylates / oseltamivir) are SECRETED
Probenecid inhibits this secretion so raises drug plasma concentration
How does Probenacid lower urate levels?
In the PROXIMAL TUBULE the organic anion transporter (OAT) reabsorbs uric acid from the lumen
If probenecid (an organic acid) is present, the OAT binds preferentially to it (instead of to uric acid), preventing reabsorption of the uric acid.
Lumen then retains more uric acid, lowering uric acid concentration in the plasma
Why does trimethoprim raise Cr?
In the PROXIMAL TUBULE there is cation secretion of organic cations including Creatinine, and amine neurotransmitters such as ACh, dopamine, adrenaline and noradrenaline
trimethoprim competes with these cation transporters and raise Cr levels but don’t impair GFR
