16. Renal Control of Acid-Base Balance

Question 1

what change in pH will double or half [H]

Answer 1

change 0.3 pH

Question 2

what are the body buffer systems

Answer 2

bicarb

Hb

Phosphate

plasma protein

Question 3

what is pKa

Answer 3

pH at wich buffer is half saturated

Question 4

How is H+ buffered by Hb & plasma proteins

Answer 4

CO2 dissolved, bound to Hb

-bind H20 –> make H2CO3 and dissociate into HCO3- and H+ –> HCO3- out of RBC & H+ binds Hb

HbO2 dissociate when O2 out to tissues & Hb binds CO2 & H+

plasma -CO2+protein + NH2 –> protein-NHCOO+H

Question 5

How does buffering of H+ occur in acidemia when exchanging K+

Answer 5

if acidemia - low ECF pH

–>K/H exchange -> increase K+ ECF & increase H+ in ICF

Question 6

how does buffering with H-K exchange happen during alkalemia

Answer 6

if alkalemia - high ECF pH

–>K/H exchange -> increase H+ ECF & increase K+ in ICF

Question 7

henderson-hasselbalch equation to detect pH in body

Answer 7

[HCO3-] controlled by kidneys - slowly (large capacity)

P_CO2 controlled by lungs - fast (limited capacity)

Question 8

how does ventilation rate affect pH

Answer 8

breathe faster - less CO2 –> less H+ –> higher pH

hold breath - more CO2 –> more H+ –> lower pH

Question 9

what is the clearance of glucose & HCO3-

Answer 9

glucose - should be 0 bc reabs all

HCO3- almost 0 bc reabs almost all

clearange = flow rate - how much plasma needed to take solute out

Question 10

what happens at the tip of the countercurrent exchange capillary loop

Answer 10

as flow downward -h2o reabs –> become more concentrate

flow becomes sluggish at tip to keep salty

Question 11

what is the countercurrent multiplier

Answer 11

operates in the TAL

provide solute hypertonic renal medullary interstium while simulataneously diluting tubular fluid

Question 12

what type of reabs happens at PT

Answer 12

2/3 of filtered solutes selectively reabsed

2/3 of filtered h2o reabsed

==> iso-osmotic tubular fluid reabs

Question 13

what occurs at the thin descending limb and thin ascending loop

Answer 13

thin descending - h2o reabs & diffuse Na, Cl in bc gradient

==> passage of tubular fluid down into hypertonic renal medulla

generation of hypertonic tubular fluid

thin ascending- no h2o movement & Na,Cl diffuse out bc gradient

Question 14

what happens at the TAL

Answer 14

urea is trapped

Na, Cl out and flow down into medullary interstitum

no h2o movement

Question 15

what is the tubular fluid like after TAL

Answer 15

hypotonic tubular fluid

Question 16

how does tubular fluid become dilute again in DCT

Answer 16

selective reabs of Na, Cl by Na-Cl cotransporter

Question 17

what/where does the final finetuning of Na reabs happen

Answer 17

aldosterone regulated Na/K exchange in CCT

Question 18

what does dilute urine contain

Answer 18

16% filtered h2o load

1% filtered NaCl load

& rest of solute = waste

Question 19

how/where does urine become concentrated

Answer 19

ADH make late DT and CCT more permeable to h2o

increase reabs

end up w/ <0.2% h2o filtered load, less than 1% NaCl filtered load & rest = waste

Question 20

How is bicarb reabsed in the PT

Answer 20

1. Na/H antiporter on luminal side - Na in & H out
2. H out & react with bicarb –> h2co3
3. use carbonic anhydrase to make CO2
4. CO2 freely cross apical mem
5. combine w/ h2o in cell & use CA to make HCO3 & H
6. HCO3 out of basolat side via Na/HCO3- symporter & recycle H+ w/ Na/H antiporter

Question 21

what increases H+ secretion

Answer 21

primary - decrease plasma HCO3-, increase PaCO2

secondary - increase filtered load of HCO2-, angiotensin II &/or aldosterone, decrease ECF vol &/or plasma [K}

Question 22

what decreases H+ secretion

Answer 22

primary - increase plasma HCO3, decrease PaCO2

secondary - decrease filtered load of HCO3- &/or aldosterone, increase ECF & plasma [K]

Question 23

how is H+ buffered by phosphate

Answer 23

secrete H+ distal nephron

bind NaHPO4- –> NaH2PO4

help regenerate plasma HCO3- that was consumed else where

*PO4^3- limited - so need ammonia for additional buffering*

Question 24

how is ammonia produced & used as a buffer

Answer 24

PT takes glutamine –> cleave into NH4+

metabolize –> NH3 - diffuse into PCT

–> convert back to NH4+

travel thru nephron –> NH3 into CCT

combine w/ H

Question 25

Where is HCO3- reabs in the CCT

Answer 25

alpha-intercalating cell

H+ out cell via K/H ATPase

–> combine w/ HCO3 - in lumen –> convert to CO2 using CA

CO2 back into cell –> convert to HCO3- & H+

HCO3- reabs via HCO3-/Cl- antiporter

Question 26

how is HCO3- secreted in the CCT

Answer 26

if too much HCO3-

secrete out at beta-intercalated cell

Question 27

how do you calculated Net Acid Excretion

Answer 27

= nonvolatile acid production each day to maintain acid-base balance

TA = salts of primarily phosphate, creatinine

Question 28

what is Renal Tubular Acidosis (RTK) type 1

Answer 28

impaired distal H secretion

<10-15 plasma HCO3-

urine pH > 5.5

low plasma K - correct w/ alkali therapy

b/c autoimmune disorder, hypercalciuria, sickle cell anemia, cirrhosis

Question 29

what is RTA type 2

Answer 29

impaired proximal HCO3- reabs

12-20 plasma HCO3-

<5.5 urine pH

low K - worsened by alkali therapy

-fanconi, multiple myeloma, drugs

Question 30

what is RTA type 4

Answer 30

lack of aldo or failure of kidney to respond

> 17 HCO3-

urine pH <5.5

high K+

= diabetic nephropathy, spironolactone, NSAIDS, chronic interstitial nephritis