Physiology 7 Flashcards
Define pH
It is a measure of the H+ concentration
What does a small change in pH reflect in terms of [H+]?
It reflect s a large change in H+ conc
What are the 3 main things that fluctuations in [H+] influence ?
1.Acidosis can lead to depression of the CNS.
Alkalosis can lead to overexcitability of the peripheral NS and later the CNS.
- [H+] exerts a marked influence of enzyme activity.
- Changes in [H+] influence K+ levels in the body.
What 3 sources is H+ added from ?
- Carbonic acid formation
- Inorganic acids produced during breakdown of nutrients
- Organic acids resulting from metabolism
What is a buffer solution ?
A solution which resists changes in pH when acid or alkali is added to it.
What happens to a strong acid when placed in solution ?
They completely dissociate
What happens to weak acids when placed in a solution ?
The partially dissociate
What is the normal range for the pH of blood?
7.35-7.45
What do buffer systems consist of ?
- 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-
Thinking about buffer systems what would happen if there is an increase in the H+ conc due to addition of acid ?
- 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-
If base is added to a buffer system what would happen to the equilibrium ?
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-
What does K represent when talking about equations relating to acids and pH ?
K = the dissociation constant of an acid or alkali
K = [product][product]/ [substrate]
When does the pK = pH ?
When 50% of the acid is dissociated
What is the henderson hasselbalch equation and what is it used for ?
Used for calculating the pH of solutions
pH = pK + log [A-]/[HA]
What is the most important physiological buffer system in the body ?
C02 + H20 <===> H2CO3 <===> H+ + HCO3-
What are the 2 main ways in which the kidneys control the concentration of HCO3- in the body ?
- Through variable reabsorption of HCO3-
- The kidneys can add new HCO3- to the blood to regernate buffer stored depleted by excess H+
What is the reabsorption and formation of new HCO3- dependent on ?
Secretion of H+ into the tubule
Describe how HCO3- is reabsorbed in the kindeys
- HCO3- in the filtrate combines with H+ forming H2CO3
- H2CO3 is converted into C02 and H20
- H20 is the reabsorbed and combines with C02 in the cell to form H2CO3
- H2C03 then dissociates into HCO3- catalysed by carbonic anhydrase
- HCO3- then transported from the cell into the interstitial fluid
This is known as ‘unorthodox reabsorption’
How is new HCO3- formed ?
- 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
How is the number of new HCO3- calculated ?
- 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
What is the simultaneous effect of excretion of TA and NH4+?
Rids the body of excess acid and regernated buffer stores (HCO3-)
