Buffer symptoms

Question 1

Write equation for bicarbonate buffering? BB

Answer 1

Question 2

Where is HCO3- reabsorbed? BB

Answer 2

Proximal tubule
Ascending loop of Henle
Collecting duct

Question 3

Where is HCO3- excreted? BB

Answer 3

Collecting duct

Question 4

Where is HCO3- filtered? BB

Answer 4

Renal corpuscles

Question 5

How is HCO3- reabsorbed? BB

Answer 5

Combination Na/K ATPase, Na/H counter-transporter, H/K ATPase, and H+ ATPase

Question 6

What happens to secreted luminal H+? BB

Answer 6

Becomes H2O and CO2
Diffuse through cell membrane/ taken up via aquaporins
CO2 and H2O are intracellular
Dissociate again with carbonic anhydrase to form HCO3
HCO3- transported across basolateral membrane
H+ recycled into lumen

Question 7

What happens if most HCO3- reabsorbed? BB

Answer 7

H+ bind with filtered non-bicarbonate buffer e.g. HPO4 2-
If H+ binding with another buffer, intracellular HCO3– transported into blood- alkalinises it

Question 8

Bicarbonate buffering- draw

Answer 8

Question 9

What are three buffering systems?

Answer 9

Bicarbonate
Ammonium
Phosphate

Question 10

Where does ammonium buffering occur? AB

Answer 10

Proximal tube

Question 11

Explain process ammonium buffering?

Answer 11

Uptake glutamine from glomerular filtrate & peritubular plasma
Metabolise glutamine form NH3 (ammonia) & HCO3- (bicarbonate)
NH3 reacts with H+ in cell (derived from dissociation H2CO3 or absorbed due to Na+ reabsorption)
Reaction forms NH4+ (ammonium ion)
NH4+ actively secreted via Na+/NH4+ counter-transport into lumen and excreted
HCO3- moves into peritubular capillaries- increases HCO3- levels (net gain of HCO3-) ALKANISES blood plasma

Question 12

Draw ammonium buffering

Answer 12

Question 13

Ammonium buffering

Answer 13

Question 14

Where does phosphate buffering occurs?

Answer 14

Proximal tubule

Question 15

Most common non-bicarbonate urinary buffer? PB

Answer 15

Alkaline phosphate (HPO4 2-)

Question 16

Explain process phosphate buffering?

Answer 16

When all filtered HCO3- has combined with secreted H+, additional H+ secreted (as a result of Na+ absorption, 1 Na+ is exchanged for 1 H+)
H+ starts combining filtered non bicarbonate buffers- HPO4 2-
H+, generated from dissociation H2CO3 from within tubular epithelial cells, combines with HPO4 2- to form H2PO4-
Excreted in urine

HCO3- produced from the dissociation of H2CO3 enters the interstitial fluid,
Unlike in bicarbonate absorption- no net gain in HCO3- since reabsorption HCO3- replaced HCO3- lost when it was filtered, with the phosphate buffer, t
This case NO absorption HCO3- from tubular lumen
Resulting in a net gain of HCO3- in the interstitium and blood plasma
Results in increase in HCO3- concentration of the plasma and ALKALINIZES it

Only occurs after filtered HCO3- has virtually ALL BEEN REABSORBED