Regulation of pH

Question 1

What are three ways of regulating body PH?

Answer 1

Buffer systems
Respiratory control
Renal control

Question 2

What are the three buffer systems?

Answer 2

Bicarbonate buffer
Phosphate buffer
Protein buffer

Question 3

What is the compound formed in the bicarbonate buffer system in acidic conditions?

Answer 3

H2 CO3

Question 4

What happens to extra CO2 created by bicarbonate buffer?

Answer 4

Excreted in lungs

Question 5

What is the compound of the phosphate buffer?

Answer 5

H2 PO4-

Question 6

What is the difference between the bicarbonate and phosphate buffer systems?

Answer 6

Phosphate has a higher pKa, so operates more closely to physiological pH
Phosphate buffer is important intracellularly, particularly in kidneys where there is high phosphate and acidic urine

Question 7

How to protein buffers work?

Answer 7

Carboxyl or amino groups of amino acids can bind H+

Question 8

What is the principle of respiratory pH control?

Answer 8

If CO2 conc. in body increases, pH falls

If CO2 falls, pH rises

Question 9

If bicarbonate ion conc, rises, what happens to pH?

Answer 9

Rises

Question 10

How does pH affect ventilation?

Answer 10

H+ ions have direct effect on respiratory centre in medulla oblongata
If H+ conc. rises, ventilation increases
Works by feedback control

Question 11

What does carbonic anhydrase do?

Answer 11

Forms carbonic acid from carbon dioxide and water

Question 12

What areas of the kidney secrete hydrogen ions into the tubular liquid?

Answer 12

Proximal and distal tubules
Collecting tubules
Thick loop of Henle

Question 13

What is the maximum achievable pH of the tubular fluid by the secretion of H+ ions from the collecting tubules?

Answer 13

4.5

Conc. gradient so high that ions leak into extracellular fluid as fast as the are pumped in

Question 14

Where does most ion secretion take place?

Answer 14

Proximal tubule

Question 15

What is the maximum achievable concentration gradient around the tubule? What is the consequence of this?

Answer 15

6.9

Buffers must keep pH high enough to let H+ ion secretion continue

Question 16

Bicarbonate ions are too large to passs through the tubular membrane. So how does it pass?

Answer 16

Combines with hydrogen to form carbonic acid, then dissociates into CO2 and water
The CO2 diffuses into the blood where it forms new bicarbonate ions

Question 17

What is acidosis?

Answer 17

Hydrogen ion secretion greater than rate at which bicarbonate ions are filtered into the fluid

Question 18

Which additional buffer systems are utilised in acidosis?

Answer 18

Phosphate and ammonia

Na+ also absorbed to form sodium bicarbonate

Question 19

What is the net effect of the phosphate buffer system in the kidney?

Answer 19

Movement of sodium bicarbonate into the extracellular fluid

Question 20

What causes acidosis?

Answer 20

Diarrhoea
Vomiting
Severe renal disease
Diabetes