Physiology 7

Question 1

Define pH

Answer 1

It is a measure of the H+ concentration

Question 2

What does a small change in pH reflect in terms of [H+]?

Answer 2

It reflect s a large change in H+ conc

Question 3

What are the 3 main things that fluctuations in [H+] influence ?

Answer 3

1.Acidosis can lead to depression of the CNS.

Alkalosis can lead to overexcitability of the peripheral NS and later the CNS.

2. [H+] exerts a marked influence of enzyme activity.
3. Changes in [H+] influence K+ levels in the body.

Question 4

What 3 sources is H+ added from ?

Answer 4

1. Carbonic acid formation
2. Inorganic acids produced during breakdown of nutrients
3. Organic acids resulting from metabolism

Question 5

What is a buffer solution ?

Answer 5

A solution which resists changes in pH when acid or alkali is added to it.

Question 6

What happens to a strong acid when placed in solution ?

Answer 6

They completely dissociate

Question 7

What happens to weak acids when placed in a solution ?

Answer 7

The partially dissociate

Question 8

What is the normal range for the pH of blood?

Answer 8

7.35-7.45

Question 9

What do buffer systems consist of ?

Answer 9

• Buffer system consists of a pair of substances – one part of the buffer solution can produce more H+ when there is a decrease in [H+]
• The other part of the system can bind to free [H+] when [H+] increases

The equation to use when thinking about shifts in equilibrium of buffers is HA <===> H^₊ + A^-

Question 10

Thinking about buffer systems what would happen if there is an increase in the H+ conc due to addition of acid ?

Answer 10

• It would shift the equilibrium to the left - where the excess H+ ions would be taken up by the conjugate base A- to form more HA
• HA <===> H+ + A-

Question 11

If base is added to a buffer system what would happen to the equilibrium ?

Answer 11

It would shift to the right - due to H+ ions decreasing when they bind to the excess A- which results in HA dissociating hence shifting equilibrium to the right

HA <===> H+ + A-

Question 12

What does K represent when talking about equations relating to acids and pH ?

Answer 12

K = the dissociation constant of an acid or alkali

K = [product][product]/ [substrate]

Question 13

When does the pK = pH ?

Answer 13

When 50% of the acid is dissociated

Question 14

What is the henderson hasselbalch equation and what is it used for ?

Answer 14

Used for calculating the pH of solutions

pH = pK + log [A-]/[HA]

Question 15

What is the most important physiological buffer system in the body ?

Answer 15

C0₂ + H₂0 <===> H₂CO₃ <===> H⁺ + HCO₃^-

Question 16

What are the 2 main ways in which the kidneys control the concentration of HCO3- in the body ?

Answer 16

1. Through variable reabsorption of HCO3-
2. The kidneys can add new HCO3- to the blood to regernate buffer stored depleted by excess H+

Question 17

What is the reabsorption and formation of new HCO3- dependent on ?

Answer 17

Secretion of H+ into the tubule

Question 18

Describe how HCO3- is reabsorbed in the kindeys

Answer 18

1. HCO3- in the filtrate combines with H+ forming H2CO3
2. H2CO3 is converted into C02 and H20
3. H20 is the reabsorbed and combines with C02 in the cell to form H2CO3
4. H2C03 then dissociates into HCO3- catalysed by carbonic anhydrase
5. HCO3- then transported from the cell into the interstitial fluid

This is known as ‘unorthodox reabsorption’

Question 19

How is new HCO3- formed ?

Answer 19

• This is done when HCO3- in the filtrate is low so H+ secreted will bind to the next most plentiful buffer phosphate or 2nd most abundant ammonia
• Basically H+ binds with the ammonia or phosphate to form phosphoric acid or ammonium
• This will then equate to 1 new HCO3- being formed
• The ammonium or phosphoric acid is then excreted in the urine

Question 20

How is the number of new HCO3- calculated ?

Answer 20

• The phosphoric acid excreted can be titrated to find out the amount excreted and the ammnonium can be measure also
• 1mmol/day or ammonium or phosphoric acid equates to 1 H+ which equates to 1mmol/day or HCO3- formed

Question 21

What is the simultaneous effect of excretion of TA and NH4+?

Answer 21

Rids the body of excess acid and regernated buffer stores (HCO3-)