Big Picture Cards

Question 1

How do diuretics (ie furosemide) cause K⁺ wasting?

Answer 1

decrease Na⁺ reabsorption

⇒ increases Na⁺ in collecting tubule

⇒ Na⁺ enters principle cell of collecting tubule via ENaC

⇒ K⁺ leaves principle cell via ROMK to balance charge from Na⁺ loss

Question 2

How and where do we acidify urine first?

Answer 2

proximal tubule

Na⁺/H⁺ ATPase on lumenal surface

reabsorb Na⁺ and secrete H⁺ into lumen

HCO₃^- is reabsorbed via Na⁺/HCO₃^- symporter

Question 3

Where is glucose reabsorbed?

Answer 3

proximal tubule

SGLTs

sodium-glucose linked transporters

Question 4

Probenicid

Sulfinpyrazone

where do they work?

Answer 4

proximal tubule

inhibit OATs that transport uric acid

Question 5

Body’s first attempt to mitigate acidosis

Answer 5

K⁺/H⁺ buffer

H⁺ absorbed by cells to buffer acid

K⁺ ejected by cells to maintain charge balance

Question 6

Why is [K⁺]_serum misleading in DKA?

Answer 6

total body K⁺ is depleted due to osmotic diuresis

[K⁺]_serum is high because K⁺ is charge buffer for H⁺ and because Na⁺/K⁺ ATPase not as active without insulin

Question 7

Which cells secrete K⁺?

Answer 7

principle cells

in collecting duct

Question 8

Which cells reabsorb K⁺ and how?

Answer 8

α-intercalated cells

in collecting duct

K⁺/H⁺ antiporter ATPase

HCO₃^- moved into interstitium via Na⁺/HCO₃^- symporter

Question 9

Where is Ca²⁺ reabsorbed?

Answer 9

distal tubule

Ca²⁺ channel allows calcium to enter

Ca²⁺ binds calbindin

Ca²⁺ pumped into interstitium via Ca²⁺ ATPase

Question 10

What affects Ca²⁺ concentration most dramatically?

Answer 10

PTH concentration

Question 11

Presence of PTHrp (PTH-related peptide) could be an indicator of what?

Answer 11

cancer!

Question 12

Why do you get low pCO₂ in DKA

Answer 12

H⁺ stimulates increased activity in respiratory centers

essentially hyperventilating

breathing off excess CO₂

Question 13

How do ionized drugs, keto acids, and other small ionic substances get into the urine?

Answer 13

OATs and OCTs

organic anion transporters and organic cation transporters

move then into lumen

occurs in proximal tubule

Question 14

How do we reabsorb small organic substances from the urine back into the interstitium?

Answer 14

MCTs

monocarboxylic acid transporters

ie drugs can have a carboxylic acid added onto them in the liver, or so

in proximal tubule

works against OATs and OCTs