Tubular Reabsorption Flashcards
What is the single most critical function of the kidneys?
sodium reabsorption and maintenance of an effective circulating volume
Where is the majority of sodium reabsorbed?
proximal tubules
What is the driving force for solute transport?
Na-K ATPase
The ECF volume is dependent on what?
sodium concentration
Plasma sodium concentration vs. total body sodium
plasma [sodium] = Na+/H2O total body sodium = grams of Na+
Add 0.9% saline - where does it go?
A. intravascular fluid space (IV)
B. extracellular fluid space (IV + ECF)
C. intracellular fluid space (ICF)
D. total body water (IV + ECF + ICF)
B. extracellular fluid space (IV + ECF)
Sites of sodium reabsorption
PCT - isosmotic TAL - impermeable to water Early DCT - also impermeable to water Late DCT and CD - site of regulation (aldosterone)
What percentage of H2O has been reabsorbed by the end of the proximal tubule?
A. 25%
B. 50%
C. 67%
D. 75%
C. 67%
Name 2 differences between early and late proximal tubule
- early: sodium reabsorption with HCO3 and organic solutes 2. late: sodium reabsorption with Cl and no organic solutes
Apical transport in early proximal tubule
- sodium absorbed down gradient - anions move against their concentration gradient
Most early proximal tubule sodium reabsorption is by what antiporter?
Na-H antiporter
What is occurring by midpoint of the proximal tubule?
- 100% of filter glucose reabsorbed - 85% of filter HCO3 reabsorbed - most of filtered phosphate, lactate, and citrate reabsorbed - large portion of Na+ reabsorbed
What is occurring in late proximal tubule?
- most organic solutes gone - high in Cl- - primarily reabsorbed NaCl
The principal factor promoting glomerular-tubular balance is:
A. Tubular flow rates (in proximal tubule)
B. Peritubular capillary hydraulic pressure
C. Peritubular capillary oncotic pressure
D. Activity of the proximal tubular ATP-ase
C. peritubular capillary oncotic pressure
Glomerulotubular balance depends on the relationship between what 2 things?
- filtration fraction - peritubular starling forces
What is occurring in thin descending limb?
- permeable to water and small solutes - NaCl and urea
What is occurring in thin ascending limb?
- permeable to NaCl - impermeable to water
What is occurring in thick ascending limb?
- active reabsorption of Na+ - load-dependent - impermeable to water
How does sodium leave the loop of Henle?
- passive exit from thin loops - active reabsorption from thick ascending limb
What is occurring in late distal tubule and collecting duct?
- only about 3% of filtered Na+ is reabsorbed - fine adjustments of Na+ excretion occur
What are the two major cell types in the collecting duct?
- principal cells - intercalated cells
What happens in principal cells?
- Na+ channels - accompanying anion is Cl- - K+ secreted
What happens in intercalated cells?
- K+ reabsorbed while H+ secreted
Sodium reabsorption is an active process in all tubular segments except:
A. Thin ascending loop of Henle
B. Thick ascending loop of Henle
C. Distal tubule
D. Diluting segment
E. It is active in all segments
A. thin ascending loop of Henle
Blocking chloride reabsorption in the thick ascending loop of Henle will cause:
A. Hyponatremia
B. Increased urine volume
C. Alkaline urine
D. Increased urine osmolality
B. increased urine volume
In which tubular segment(s) is Na+ reabsorption isosmotic with the ECF?
A. Proximal tubules
B. Distal tubules
C. Collecting tubules
D. All of the above
A. proximal tubules
How does aldosterone regulate sodium reabsorption in the late distal tubule and collecting duct?
insertion of sodium channels
Where are the receptors to regulate sodium balance? (3)
- baroreceptors in carotid sinus and aortic arch 2. volume receptors in atria 3. juxtaglomerular apparatus
What are the signals and targets for regulating sodium balance?
- sympathetic nerve output - atrial natriuretic peptide (ANP) - renin-angiotensin-aldosterone system
know this
know this also
What is the internal potassium balance?
98% in cells, ~2% in ECF
(movement of as little as 1.5-2% of potassium from cells into ECF potentially fatal)
Name some factors influencing ICF-ECF distribution of potassium ions
- physiologic (Na/K ATPase, catecholamines, insulin)
- pathologic (chronic diseases, extracellular pH, hyperosmolality)
What happens to potassium in the distal tubule?
potassium is freely filtered until it reaches the distal tubule where almost all of it is reabsorbed
Enhanced distal reabsorption of K+ by intercalated cells results in:
A. Increased sodium secretion
B. Increased chloride reabsorption
C. Increased bicarbonate reabsorption
D. Increased H+ secretion
D. increased H+ secretion
Where is phosphorus reabsorbed?
proximal tubules
What happens when there is retention of phosphorus in the body?
- release of FGF-23 inhibits renal reabsorption of phosphorus and causes increased phosphorus excretion
- increased PTH levels, which suppress phosphorus reabsorption
- decreased calcitriol levels, which would normally inhibit PTH production
Serum calcium occurs in what 3 forms?
- ionized
- protein-bound (albumin)
- complexed to organic anions
What is ionized calcium?
- biologically active form
- regulated form
- form that is freely filtered
Where is calcium reabsorbed?
- proximal tubule
- thin ascending limb
- distal tubule
A dog is presented with primary hyperparathyroidism. Which one of the following would you expect?
A. Hypercalcemia and hyperphosphatemia
B. Hypercalcemia and normal serum phosphorus
C. Hypercalcemia and hypophosphatemia
D. High levels fo FGF-23
C. Hypercalcemia and hypophosphatemia
