8.3 Renal Physiology II - Fluid Balance ACID-BASE

Question 1

In HUMANS, pH of Extracellular fluid must remain between..

Answer 1

7.35 - 7.45

below 7.35: acidosis
above 7.45: alkalosis

fluctuation can result in coma, cardiac failure and circulatory collapse

Question 2

pH is from a Mixture of..

Answer 2

H+ IONS and SODIUM BICARBONATE (BUFFER)

need constant ratio to maintain correct pH

Question 3

how do we get H+ and HCO3- in BLOOD

Answer 3

CO2 and H20 (products of respiration) COMBINE to form CARBONIC ANHYDRASE

• not stable

BREAKS DOWN into H+ and HCO3-

Question 4

in order to MAINTAIN ACID-BASE BALANCE what 2 tasks must the KIDNEY do

Answer 4

• REABSORB FILTERED BICARBONATE (buffer)
• EXCRETE DAILY ACID LOAD (H+)

Question 5

how does the KIDNEY achieve EXCRETION of DAILY ACID LOAD (3)

Answer 5

by:
- HCO3- REABSORPTION
- SECRETING H+
- SECRETING AMMONIUM (NH4+)

Question 6

Where in the nephron is MOST of the HCO3- RECLAIMED and by what synthesis

Answer 6

PCT

by DE NOVO SYNTHESIS (new bicarbonate molecules created)

Question 7

in a healthy nephron, how much of the BICARBONATE HCO3- is RECLAIMED in PCT (DE NOVO SYNTHESIS)

Answer 7

85-90%

Question 8

explain how HCO3- is REABSORBED FROM PCT into blood (high HCO3- after bowman’s capsule)

Answer 8

• in TUBULAR LUMEN (FILTRATE) HCO3- not stable and BROKEN DOWN into carbonic acid (H2CO3) to CO2 and H20
• CO2 DIFFUSES INTO PCT CELLS
• CO2 and H20 in PCT CELLS RECOMBINE (using carbonic anhydrase) to form H2CO3 which dissociates to HCO3- and H+ (BICARBONATE REASSEMBLED)
• HCO3- TRANSPORTED OUT of CELLS with SODIUM NA+ into renal interstitial fluid into blood
• H+ Transported back INTO LUMEN (FILTRATE) by Na-H exchanger (H+ out of blood)

Question 9

what can you find in the PCT cells that keep gradient steady for transport of molecules

Answer 9

NA-K ATPASE

LOTS of SODIUM

Question 10

what happens to the H+ in the PCT CELLS and BLOOD

Answer 10

TRANSPORTED INTO FILTRATE
(using sodium)

Question 11

where is there FURTHER RECLAMATION of BICARBONATE (HCO3-)

Answer 11

DCT and COLLECTING DUCT

Question 12

how much HCO3- is RECLAIMED in the DCT and COLLECTING DUCT

Answer 12

10-15%

Question 13

How is HCO3- RECLAIMED in DCT (and collecting duct)

Answer 13

• CO2- DIFFUSES INTO CELLS (from interstitial fluid)
• HCO3- ASSEMBLED
  from CO2 + H20 using carbonic anhydrase to form H2CO2 - dissociates to HCO3- and H+
• HCO3- TRANSPORTED OUT
  EXCHANGED for Cl- using HCO3- - CL- EXCHANGER
• H+ TRANSPORTED INTO LUMEN (filtrate) WITH Cl- USING ATP

Question 14

in DCT and collecting duct how does the HCO3- MOVE OUT of the DCT CELLS into BLOOD

Answer 14

EXCHANGED FOR CHLORIDE IONS

using bicarbonate-chloride EXCHANGER

Question 15

in DCT and collecting duct how does the H+ MOVE INTO LUMEN (filtrate) from the DCT CELLS

Answer 15

TRANSPORTED WITH CHLORIDE Cl-
- uses ATP

Question 16

what is URINARY BUFFERING

Answer 16

the process where secreted H+ are BUFFERED IN the URINE by COMBINING with weak acids or with NH3 AMMONIA to be excreted

Question 17

what is the major ADAPTATION to an INCREASED ACID LOAD

Answer 17

INCREASED AMMONIUM SECRETION (NH4+)

Question 18

ammonium production also has a role in

Answer 18

further generation of bicarbonate ions

Question 19

how is H+ REMOVED from BLOOD
by a…

Answer 19

SODIUM-HYROGEN EXCHANGER

(sodium into blood and H+ into cell)
(another exchanger for H+ into filtrate)

Question 20

how is NH4+ (Ammonium) REMOVED from DCT CELLS

Answer 20

SODIUM-AMINE EXCHANGER

NH4+ removal means a LOT of H+ REMOVED

Question 21

what is AMINO ACID DEAMINATION in DCT

Answer 21

BREAK DOWN of PROTEINS FROM DIET into AMINO ACIDS

• LIBERATES HCO3- and H+ IONS
• BUFFERED by NH3
  into NH4+

Question 22

Diets rich in MEATS provide … to the bloods when digested

Answer 22

ACIDS

Question 23

Diets rich in FRUITS and VEGETABLES are rich in…

Answer 23

BICARBONATES

Question 24

exercising muscles produce..

Answer 24

lactic acid
(must be eliminated from body or metabolised)

Question 25

Respiration variations in gaseous exchange can affect our blood..

Answer 25

pH

Question 26

what are H+ BUFFERED WITH in urine

Answer 26

NH3 (AMMONIA)
- to form NH4+ (AMMONIUM)