Loop of Henle, Distal tubule and Collecting Duct - Rao Flashcards
Describe the cells of the thin descending limb.
Thin epithelial cells with few mitochondria
What is the tonicity of the interstitial environment compared to plasma?
Interstitial environment is hyperosmotic compared to plasma
Describe the permeability to water, NaCl, and urea in the thin descending limb.
Water - highly permeable
NaCl - impermeable
Urea - impermeable
Describe the permeability to water, NaCl, and urea in the thin ascending limb.
Water - highly impermeable
NaCl - permeable (strong reabsorption 20-25%)
Urea - impermeable
Describe the cells of the thick ascending limb.
Thick epithelial cells with many mitochondria
What transporters are present in the thick ascending limb?
Na K 2Cl cotransport - apical Na K ATPase antitransport - basolateral Cl channel - basolateral K Cl cotransport - basolateral K channel - apical (K -> lumen)
What can inhibit NaK2Cl transporter?
Diuretic agents with high affinity for Cl site
Furosemide, bumetanide
What is the net result of fluid passing through the DCT and CT?
Dilution of tubular fluid (if impermeable to water)
How is sodium reabsorbed in the DCT?
Electrically conductive Na channels
Na / Cl cotransporter
What diuretics block electrically conductive Na channels?
Amiloride
Triamterene
What diuretics inhibit Na / Cl cotransporters?
Thiazide diuretics
What is the driving force for potassium secretion in the DCT and CT?
High intracellular concentration of K caused by Na K ATPase
Lumen-negative transepithelial voltage
What are regulatory factors affecting K secretion?
Increased flow by diuretics cause increased K secretion
Increased Na reabsorption increases K secretion
What is the affect of loop diuretics, thiazides, and amilorides on K secretion?
Loop diuretics - increase K secretion
Thiazides - no change
Amilorides - no change
How is Na reabsorbed in the CT?
Electrically conductive Na channels
Where is aldosterone synthesized and where does it act?
Synthesized - adrenal cortex
Act - DCT and CT
What are aldosterone’s actions?
Increase Na reabsorption
Increase K secretion
What is Addison’s disease?
Complete lack of aldosterone
Increased urinary excretion of NaCl
What is Conn’s Syndrome?
Aldosterone secreting tumor
Increased Na reabsorption / K secretion
Hypokalemia, hypernatremia, hypertension
What factors stimulate aldosterone?
Reduced ECF volume Reduced plasma Na Increased plasma K Increased plasma AT II Trauma / stress
What is reabsorbed and secreted in the DCT and CD to maintain acid-base balance?
Bicarbonate - reabsorbed
Protons - secreted
What do principal cells do?
Na - reabsorb
K - secrete
What do intercalated cells do?
Proton - secrete
Bicarbonate - secrete (some cells)
How are protons secreted in the DCT and CD?
Under acidosis conditions
Proton activated ATPase (luminal; proton pumped to lumen)
H K ATPase (luminal; H to lumen; K to cell)
HCO3 / Cl exchanger (basolateral; HCO3 to ISF; Cl to cell)
Under what conditions and how is bicarbonate secreted?
Under alkalosis condition H ATPase (basolateral; proton to ISF) HCO3 / Cl exchanger (luminal; HCO3 to lumen) alpha cell - luminal proton channel beta cell - luminal bicarbonate channel
What sitmulates distal nephron calcium reabsorption?
Parathyroid hormone
