Acid Base Regulation

Question 1

Where is ammonia excreted into?

Answer 1

The collecting duct

Question 2

What are the two main urinary buffers?

Answer 2

Phosphate

Ammonia

Question 3

What encourages secretion of H+ into the late distal and collecting tubules? (2)

Answer 3

Aldosterone

Hypokalaemia (H+/K+ATPase transporter)

Question 4

Which cell type in the late distal and convoluted tubules secrete H+

Answer 4

Type A intercalated cell

Question 5

Where does the majority of the reabsorption of HCO3- take place?

Answer 5

Proximal convoluted tubule

Question 6

Metabolic alkalosis with respiratory compensation

Answer 6

High pH
High HCO3-
High CO2

Question 7

Metabolic acidosis with respiratory compensation

Answer 7

Low pH
Low HCO3-
Low CO2

Question 8

Metabolic alkalosis

Answer 8

High pH
High HCO3-
Normal CO2

Question 9

Metabolic acidosis

Answer 9

Low pH
Low HCO3-
Normal CO2

Question 10

Respiratory alkalosis with metabolic compensation

Answer 10

High/normal pH
Low CO2
Low HCO3-

Question 11

Respiratory acidosis with metabolic compensation

Answer 11

Low/normal pH
High CO2
High HCO3-

Question 12

Respiratory alkalosis

Answer 12

High pH
Low CO2
Normal HCO3

Question 13

Respiratory acidosis

Answer 13

Low pH
High CO2
Normal HCO3-

Question 14

Where does the protein buffer system take place?

Answer 14

Mainly intracellular

Question 15

Where does the phosphate buffer system take place?

Answer 15

Intracellular and urine

Question 16

Where does the bicarbonate buffer system take place?

Answer 16

Extracellular

Question 17

What are the 3 main buffer systems?

Answer 17

Bicarbonate buffer system
HCO3- + H+ H2CO3

Phosphate buffer system
HPO42- + H+ H2 PO4-

Protein buffer system
Pr- + H+ HPr

Question 18

What is a buffer?

Answer 18

Any substance that can reversibly bind H+

Question 19

What 3 mechanisms minimise the changes in pH?

Answer 19

Buffer systems

Lungs - adjusting CO2

Kidneys - adjust the excretion of H+ into the urine

Question 20

How is H+ linked to Ca2+?

Answer 20

Low H+ is linked with increase binding of Ca2+ to albumin

Question 21

How are carbamino compounds formed?

Answer 21

When CO2 reacts with protein amino groups

Question 22

How does HCO3- leave a cell (respiratory physiology)

Answer 22

Cl - HCO3- exchanger

Question 23

What is a base?

Answer 23

Any chemical that can accept H+

Question 24

What two things stimulate secretion of H+ into the tubular lumen?

Answer 24

Increase in pCO2 of ECF

Decrease in pH of ECF

Increased aldosterone and hypokalaemia can also stimulate H+ secretion

Question 25

What is the ratio of HCO3- to CO2 in the HH equation?

Answer 25

20:1

More HCO3-

Question 26

List the 2 main processes by which kidneys regulate pH

Answer 26

Reabsorption of filtered HCO3-

Excretion of H+

Both processes rely on ability of kidneys to secrete H+

Question 27

How is filtered HCO3- reabsorbed in the PCT?

Answer 27

H+ secreted into the tubular lumen via Na/H exchanger

H+ binds with filtered HCO3- to form carbonic acid, catalysed by carbonic anhydrase

H2CO3 dissociates into CO2 and H20, which both are absorbed by the tubular cells

Carbonic anhydrase then dissociates H2CO3 into HCO3- and H+

H+ moves back out of the cell to do it again

HCO3- moves out of the basolateral membrane in symport with Na+

Question 28

How is H+ secreted in the late distal and cortical collecting tubules?

Answer 28

H+ is moved into the tubular lumen via H+/K+ ATPase pumps in type A intercalating cells

Activity can be stimulated by aldosterone (increased activity of H+ATPase) and hypokalaemia

Question 29

How can hypokalaemia cause alkalosis?

Answer 29

Hypokalaemia stimulates the activity of the H+/K+ ATPase in type A intercalated cells in the late distal tubules

More K+ is reabsorbed from the tubular lumen in exchange for H+ being lost into the tubular lumen

Question 30

Describe how the urinary phosphate buffer system is able to excrete H+

Answer 30

Filtered phosphate has 2 forms:

HPO42- and H2PO4-

HPO42- is in excess of the other one. It can pick up excess H+ and excrete it in urine

Excreting H+ leads to HCO3- production which passes into the blood

Question 31

Describe how the urinary ammonia buffer secretes H+

Answer 31

Ammonium NH4+ is synthesised from glutamine as it is broken down into glutamate

Ammonia and ammonium form a buffer pair

NH3 + H+ NH4+

Ammonia NH3 is secreted in the collecting duct and picks up excess H+ and excretes it in the urine as ammonium NH4+

This process leads to production of HCO3-

A decrease in pH stimulates renal glutamine metabolism which eventually increases secretion of H+

Question 32

Why are renal responses to pH slower than respiratory responses?

Answer 32

Because renal responses require protein synthesis/breakdown e.g. breakdown of glutamine to make ammonia

Question 33

In compensated disorders HCO3- and CO2 are…

Answer 33

Outside of their normal ranges, but both in the same direction