Loop and Distal Tubule - Rao

Question 1

Relationship between TDLH to plasma

Answer 1

Hyperosmotic

Question 2

What is the TDLH permeable to

Answer 2

Water only

Question 3

What is the driving force in the TDLH?

Answer 3

Osmotic gradient - so water flows out into interstitium

Question 4

Why is the TDLH thin?

Answer 4

no active transport/few mitochondria

Question 5

What is the ThinALH permeable to?

Answer 5

NaCl only

strong NaCl reabsorption here via osmotic gradient (thin ALH is hyperosmotic to interstitium)

Question 6

What is the thick ALH permeable to?

Answer 6

NaCl only

Question 7

What kinds of transporters are in the thick ascending limb?

Answer 7

Na/K/2Cl symporter transports down electrochemical gradient and is electroneutral

Na/K ATPase on basolateral side

Question 8

How do furosemide and bumetanide increase water loss by inhibiting NK2C?

Answer 8

Block transporter so blocked NaCl reabsorption. Increased Na delivered to distal nephron interferes with urine concentration due to water retention in the distal tubule

Question 9

What happens in the DCT and CD?

Answer 9

Na+ active reabsorption; K+ secretion; Na+ more than K secretion so Cl- is reabsorbed

Question 10

Is the DCT/CD water permeable?

Answer 10

Depends on needs (ADH)

Question 11

What kind of sodium transporter is in the DCT?

Answer 11

Two unique ones

1. Na+ channels similar to PT let Na+ enter cell going down electro-chem gradient created by Na/K ATPase
2. Na+/Cl- co-transporter on luminal surface of DCT only; it is also electroneutral as is NK2C in TALH

Question 12

Explain lumen-negative voltage in the DCT/CD

Answer 12

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

Question 13

Thiazides vs amilorides

Answer 13

Thiazides do not affect membrane potential because they block electroneural Na/Cl symporter, while amilorides prevent depolarization

Question 14

Which part of the nephron does aldosterone act on?

Answer 14

DCT and CD

Question 15

What are the end-result effects of aldosterone?

Answer 15

increased Na reabsorption and K secretion

Question 16

What cellular changes does aldosterone cause?

Answer 16

Inc ENaC synthesis
Increased Krebs enzymes for more ATP
Increase activity of apical K+ channel Increase production of Na/K ATPase

Question 17

What is Addison’s disease?

Answer 17

Complete absence of aldosterone that causes increased excretion of NaCl

Question 18

What is Conn’s syndrome and its signs?

Answer 18

Aldosterone secreting tumor that increases Na+ reabsorption and K+ secretion

Hypokalemia
Hypernatremia
Hypertension

Question 19

What is Liddle’s syndrome?

Answer 19

Hypokalemia, hypernatremia, and hypertension (Symptom’s of Conn’s) with no increase in aldosterone

Question 20

What kind of changes in the following variables would lead to increased aldosterone secretion?
ECF volume, cardiac output, plasma Na, K, ATII

Answer 20

Reduced ECF volume
Reduced cardiac output
Decreased plasma Na+
High plasma ATII
Trauma and stress

All promote secretion of aldosterone

Question 21

What kind of changes in the following variables would lead to decreased aldosterone secretion?
ECF, plasma Na, plasma K, plasma ATII, plasma ACTH

Answer 21

Increased ECF volume
Increased plasma sodium
Decreased plasma K+
Low plasma angiotensin II
Low plasma ACTH levels

Question 22

Describe proton secretion in the DCT and CD

Answer 22

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

Question 23

What transporter do alpha intercalated cells have and what do they do?

Answer 23

Proton channel in luminal membrane

Question 24

What transporter do beta intercalated cells have and what do they do?

Answer 24

Bicarbonate channel in luminal membrane

Question 25

What happens during alkalosis?

Answer 25

H+ and HCO3- switch directions; H+ starts going to interstitum and HCO3- is secreted into tubule; thanks to alpha and beta cells

Question 26

How does PTH effect calcium reabsorption in the distal tubule?

Answer 26

PTH increases calcium reabsorption