eLFH - Renal Physiology Part 2 Flashcards
Percentage of sodium reabsorption at each division of the renal tubule
Proximal convoluted tubule - 65%
Descending and ascending parts of loop of Henle - 25%
Distal convoluted tubule - 8%
Collecting tubules - 2%
Where does primary active transport occur in the renal tubule
Throughout the nephron
Sodium reabsorption in proximal convoluted tubule
Na+ concentration in filtrate is high ~ 140 mmol/L
Na+ concentration in tubular cells is low ~10 to 20 mmol/L due to gradient produced by Na+/K+ ATPase
Gradient favours transport of Na+ from filtrate to tubular cells and contributes to driving force for secondary active transport
Sodium reabsorption in Loop of Henle
Thin descending limb is poorly permeable to Na+
Some Na+ reabsorbed from thin ascending limb
Most Na+ reabsorption in loop of Henle occurs in thick ascending limb
Mechanism for Na+ reabsorption in Thin ascending limb of Loop of Henle
Thin ascending limb is permeable to Na+ but impermeable to water
Na+ diffuses from tubule lumen to medullary interstitium down concentration gradient
Osmolarity of tubular fluid decreases as it ascends
Mechanism for Na+ reabsorption in Thick ascending limb of Loop of Henle
Thick ascending limb is impermeable to both Na+ and water
Na+/K+ ATPase creates concentration gradient for secondary active transport
Therefore reabsorption of Na+, K+ and Cl- occurs (K+ and Cl- co-transported)
H+ ions are counter transported
Carrier proteins in Thick ascending limb of loop of Henle
Na+ / K+ / Cl- co-transporter (from tubule luminal fluid into tubular cell)
Na+ / H+ counter transporter (Na+ from tubule fluid into tubular cell, and H+ from cell to tubular fluid
Sodium reabsorption in Distal convoluted tubule
Na+/K+ ATPase again generates Na+ gradient
Na+ reabsorbed via specific sodium channel
AND
Via co-transport with chloride ions
Sodium reabsorption in the collecting ducts
Na+ reabsorption occurs in cortical collecting duct under influence of aldosterone
Percentage of water reabsorption occurring in Proximal convoluted tubule
70%
Mechanism for water reabsorption in proximal convoluted tubule
Solute movement out of tubular cells generates osmotic gradient from tubular fluid to interstitial fluid
Osmosis occurs via transcellular and paracellular paths
Water reabsorption in Loop of Henle
Descending limb highly water permeable
Ascending limb impermeable to water so tubular fluid delivered to distal convoluted tubule is hypotonic
Percentage of water reabsorption occurring in Descending limb of Loop of Henle
15%
Percentage of water reabsorption occurring in Distal convoluted tubule and collecting ducts
DCT - 0 to 15%
Collecting ducts - 5%
Mechanism of water reabsorption in distal convoluted tubule and collecting ducts
Dependent on ADH
DCT and collecting ducts are impermeable to water except in presence of ADH
ADH results in aquaporin insertion into luminal membrane
Water then diffuses into cortical interstitium and tubular fluid becomes more concentrated
Location of reabsorption of Potassium
Proximal convoluting tubule - 60%
Ascending limb of loop of Henle - 30%
Determinate of urinary potassium concentration
Secretion of K+ in distal convoluted tubule or collecting ducts by principle cells
Mechanism of K+ secretion into urine
Active transport of K+ into tubular cells by basolateral membrane Na+/K+ ATPase
Passive secretion via channels and K+/Cl- co-transport
Factors which increase K+ secretion into urine
Aldosterone increases K+ secretion into distal convoluting tubule by:
- Increased Na+/K+ ATPase activity
- Increased luminal membrane permeability to K+
Why does glucose appear in urine in diabetes
Renal tubular transport of glucose has a maximum threshold
In health this is not reached but in diabetes plasma glucose concentration is raised so renal threshold is reached
Renal threshold of plasma glucose concentration and tubular transport maximum
Renal threshold: 11 mmol/L
Tubular transport maximum: 21 mmol/L/min (aka 380 mg/min)
Mechanism of glucose reabsorption in renal tubule
Co-transport with sodium into the tubular cell
Glucose then diffuses into peritubular interstitium
Graph illustrating glucose filtration, reabsorption and excretion as plasma glucose concentration increases
Location of Glucose reabsorption in renal tubule
Proximal convoluted tubule
Location of bicarbonate reabsorption in the renal tubule
Proximal convoluting tubule - 80%
Thick ascending limb of loop of Henle - 10 to 15%
Mechanism of Bicarbonate reabsorption in the renal tubule
Importance of ammonia reabsorption
Part of ammonia buffer system
Role in acid base balance when H+ ions secreted in excess of the bicarbonate filtered into tubular fluid
Other buffer systems (all of which are much less important than the ammonia buffer system)
Phosphate buffer system
Urate and citrate systems
Mechanism of Ammonia reabsorption
Location of Morphine cation secretion into the renal tubule
Proximal convoluting tubule
