Page 629 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

Renal ` RENAL—PhysioLogy Renal ` RENAL—PhysioLogy SeCTIOn III 585

Nephron transport physiology
Lumen - urine Interstitium - blood Lumen - urine Interstitium - blood
SGLT-2 inhibitors Proximal convoluted tubule Distal convoluted tubule
Na + Thiazide 3Na +
diuretics
Glucose 3Na + Na + ATP
Angiotensin II ATP + CI – 2K +
Na + 2K
R PTH
HCO₃ – H + H + + HCO₃ –
Ca 2+ Na +
H₂ CO₃ 2+
Acetazolamide H₂ CO₃ Ca
–
CA CA CI – CI channel
+
+
CO₂ H₂O CO₂ H₂O di usion
CI –
Base –
Early DCT—reabsorbs Na , Cl . Impermeable to H O.
+
−
2
Makes urine fully dilute (hypotonic).
PTH— Ca /Na exchange Ca reabsorption.
2+
+
2+
Early PCT—contains brush border. Reabsorbs all glucose 5–10% Na reabsorbed.
+
and amino acids and most HCO , Na , Cl , PO 4 3– , K ,
–
+
–
+
3
H O, and uric acid. Isotonic absorption. Generates and Lumen - urine Collecting tubule Interstitium - blood
2
secretes NH , which enables the kidney to secrete more CI –
3
H . Principal cell
+
PTH—inhibits Na /PO 4 3– cotransport PO 4 3– excretion. H₂O V 2 ADH
+
+
AT II—stimulates Na /H exchange Na , H O, and Aquaporins on
+
+
2
HCO reabsorption (permitting contraction alkalosis). vesicle membrane
−
3
+
65–80% Na and H O reabsorbed. Amiloride K + 3Na +
2
Triamterene ATP 2K +
Thin descending loop of Henle—passively reabsorbs H O Na +
2
+
via medullary hypertonicity (impermeable to Na ). R Aldosterone
Concentrating segment. Makes urine hypertonic. Spironolactone
α-intercalated cell
Lumen - urine Interstitium - blood
Thick ascending limb
ATP R Aldosterone
Loop diuretics H +
Na + 3Na + + –
K + ATP K HCO₃
2CI – 2K + ATP CI –
H +
K +
(+) K + Di usion down β-intercalated cell +
potential the electrochemical CI – H
gradient
CI – ATP
HCO₃ –
2+
Mg , Ca 2+
+
Collecting tubule—reabsorbs Na in exchange for
+
+
secreting K and H (regulated by aldosterone).
+
+
Thick ascending loop of Henle—reabsorbs Na , K , and Aldosterone—acts on mineralocorticoid receptor mRNA
+
−
2+
Cl . Indirectly induces paracellular reabsorption of Mg protein synthesis. In principal cells: apical K
+
+
+
+
2+
and Ca through lumen potential generated by K conductance, Na /K pump, epithelial Na channel
+
backleak. Impermeable to H O. Makes urine less (ENaC) activity lumen negativity K secretion. In
2
+
concentrated as it ascends. α-intercalated cells: lumen negativity H ATPase
−
+
−
+
10–20% Na reabsorbed. activity H secretion HCO /Cl exchanger
3
activity.
ADH—acts at V receptor insertion of aquaporin H O
2
2
channels on apical side.
+
3–5% Na reabsorbed.
FAS1_2019_14-Renal.indd 585 11/7/19 5:42 PM