The document summarizes renal physiology concepts related to kidney tubular transport. It discusses the processes of glomerular filtration, tubular reabsorption, and secretion that produce urine. Key transport mechanisms and proteins involved in reabsorption and secretion in different segments of the nephron are described, including the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct. Specific transporters, channels, and proteins involved in electrolyte transport and their roles in related kidney conditions are also outlined.
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Renal Physiology Guide: Glomerular Filtration, Tubular Transport Processes
1. Back to Basics: Renal Physiology
Kidney Tubular Transport
Mohammed Abdel Gawad
Nephrology Consultant - Alexandria
MD Nephrology - Mansoura University
drgawad@gmail.com
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37. 37
ADH - Action – H2O
V2
Vasopressin binds V 2 receptors located on the basolateral
membrane of principal cells in the collecting duct
38. 38
ADH - Action – H2O
V2
Vasopressin binds V 2 receptors located on the basolateral
membrane of principal cells in the collecting duct
Defects in aquaporin-2
structure and function
underlie X-linked
nephrogenic diabetes
insipidus
Hypercalcaemia → ↑ intraluminal Ca 2+
→ interferes with aquaporin-2
membrane insertion → defective urinary
concentrating ability, polyuria, and
dehydration
• In addition, K + re-enters the lumen through a luminal K + channel (ROMK channel):
- a recycling process that is necessary to prevent K + availability from becoming a limiting factor for the operation of NKCC.
- This movement of K + back to the lumen also keeps it electrically net positive, which facilitates the passive paracellular reabsorption of Na + (as well as K + , Ca 2+ , NH 4 + , and Mg 2+ ).
The energy for the action of the NCCT co-transporter is again derived from Na + K + -ATPase, as the resulting electrochemical gradient permits Na + reabsorption into the cell.
Thiazide diuretics enhance Ca 2+ absorption (exact mechanisms unknown)
Hypokalaemia occurs, as there will be an increase in Na + delivery to the collecting ducts and additional uptake via ENaCs. This will increase activity of the basolateral Na + K + -ATPase, and the resulting intracellular K + will then move into the lumen and be lost in the urine.
Thiazide diuretics enhance Ca 2+ absorption (exact mechanisms unknown)
Hypokalaemia occurs, as there will be an increase in Na + delivery to the collecting ducts and additional uptake via ENaCs. This will increase activity of the basolateral Na + K + -ATPase, and the resulting intracellular K + will then move into the lumen and be lost in the urine.
Thiazide diuretics enhance Ca 2+ absorption (exact mechanisms unknown)
Hypokalaemia occurs, as there will be an increase in Na + delivery to the collecting ducts and additional uptake via ENaCs. This will increase activity of the basolateral Na + K + -ATPase, and the resulting intracellular K + will then move into the lumen and be lost in the urine.
Thiazide diuretics enhance Ca 2+ absorption (exact mechanisms unknown)
Hypokalaemia occurs, as there will be an increase in Na + delivery to the collecting ducts and additional uptake via ENaCs. This will increase activity of the basolateral Na + K + -ATPase, and the resulting intracellular K + will then move into the lumen and be lost in the urine.
Amiloride and triamterene block ENaC, thus reducing both Na + reabsorption and K + excretion.
Spironolactone inhibits the effect of aldosterone on its receptor, with similar effects on Na + and K + .
Principal cells ( approximately 65% of cells) are responsible for Na + (and water) reabsorption and K + excretion. Intercalated cells secrete H + ( A -intercalated cells) or HCO 3 – ( B -intercalated cells).
Metabolic acidosis converts the collecting tubule from a state of HCO 3 secretion to HCO 3 absorption (and then H + secretion) that involves a phenotypic shift of B -intercalated cells to A -intercalated cells.
In circumstances of severe acidosis or d K + , intercalated cells also express an H + /K + ATPase, similar to that responsible for gastric acid secretion. This allows additional H + secretion in exchange for K + .
Principal cells ( approximately 65% of cells) are responsible for Na + (and water) reabsorption and K + excretion. Intercalated cells secrete H + ( A -intercalated cells) or HCO 3 – ( B -intercalated cells).
Metabolic acidosis converts the collecting tubule from a state of HCO 3 secretion to HCO 3 absorption (and then H + secretion) that involves a phenotypic shift of B -intercalated cells to A -intercalated cells.
In circumstances of severe acidosis or d K + , intercalated cells also express an H + /K + ATPase, similar to that responsible for gastric acid secretion. This allows additional H + secretion in exchange for K + .
Aquaporin-2 is stored in intracellular vesicles ready for membrane insertion (the basolateral membrane is already water-permeable by virtue of aquaporin-3 and -4).