Loop and Distal Tubule - Rao Flashcards
Relationship between TDLH to plasma
Hyperosmotic
What is the TDLH permeable to
Water only
What is the driving force in the TDLH?
Osmotic gradient - so water flows out into interstitium
Why is the TDLH thin?
no active transport/few mitochondria
What is the ThinALH permeable to?
NaCl only
strong NaCl reabsorption here via osmotic gradient (thin ALH is hyperosmotic to interstitium)
What is the thick ALH permeable to?
NaCl only
What kinds of transporters are in the thick ascending limb?
Na/K/2Cl symporter transports down electrochemical gradient and is electroneutral
Na/K ATPase on basolateral side
How do furosemide and bumetanide increase water loss by inhibiting NK2C?
Block transporter so blocked NaCl reabsorption. Increased Na delivered to distal nephron interferes with urine concentration due to water retention in the distal tubule
What happens in the DCT and CD?
Na+ active reabsorption; K+ secretion; Na+ more than K secretion so Cl- is reabsorbed
Is the DCT/CD water permeable?
Depends on needs (ADH)
What kind of sodium transporter is in the DCT?
Two unique ones
- Na+ channels similar to PT let Na+ enter cell going down electro-chem gradient created by Na/K ATPase
- Na+/Cl- co-transporter on luminal surface of DCT only; it is also electroneutral as is NK2C in TALH
Explain lumen-negative voltage in the DCT/CD
Lumen is relatively negative due to Na/K ATPase and Na+ channels (not from NaCl co-transporter!); allows K+ secretion into lumen
More in CD than DCT
Thiazides vs amilorides
Thiazides do not affect membrane potential because they block electroneural Na/Cl symporter, while amilorides prevent depolarization
Which part of the nephron does aldosterone act on?
DCT and CD
What are the end-result effects of aldosterone?
increased Na reabsorption and K secretion
What cellular changes does aldosterone cause?
Inc ENaC synthesis
Increased Krebs enzymes for more ATP
Increase activity of apical K+ channel Increase production of Na/K ATPase
What is Addison’s disease?
Complete absence of aldosterone that causes increased excretion of NaCl
What is Conn’s syndrome and its signs?
Aldosterone secreting tumor that increases Na+ reabsorption and K+ secretion
Hypokalemia
Hypernatremia
Hypertension
What is Liddle’s syndrome?
Hypokalemia, hypernatremia, and hypertension (Symptom’s of Conn’s) with no increase in aldosterone
What kind of changes in the following variables would lead to increased aldosterone secretion?
ECF volume, cardiac output, plasma Na, K, ATII
Reduced ECF volume Reduced cardiac output Decreased plasma Na+ High plasma ATII Trauma and stress
All promote secretion of aldosterone
What kind of changes in the following variables would lead to decreased aldosterone secretion?
ECF, plasma Na, plasma K, plasma ATII, plasma ACTH
Increased ECF volume Increased plasma sodium Decreased plasma K+ Low plasma angiotensin II Low plasma ACTH levels
Describe proton secretion in the DCT and CD
Done by intercalated cells; secreted against gradient, requiring active transport
The H+ comes from H2CO3; HCO3- goes its separate way into the interstitium and is balanced by Cl- influx into cell
What transporter do alpha intercalated cells have and what do they do?
Proton channel in luminal membrane
What transporter do beta intercalated cells have and what do they do?
Bicarbonate channel in luminal membrane
What happens during alkalosis?
H+ and HCO3- switch directions; H+ starts going to interstitum and HCO3- is secreted into tubule; thanks to alpha and beta cells
How does PTH effect calcium reabsorption in the distal tubule?
PTH increases calcium reabsorption
