Week 3 - G - Physiology 7 - Acid base balance 1 (H2CO3, TA, NH4+) Flashcards
Acid base balance – relates to the regulation of the free (unbound) hydrogen ion concentration What does the pH normal range of blood vary between in a person? (which is the number for venous and which for arterial)
Varies between 7.35-7.45 Venous blood at 7.35 and arterial at 7.45
What is the equation used to calculate the pH? (involving hydrogen ions)
pH = -log [H+] pH = log (1/[H+])
If the pHdrops below 7.35 or rises above 7.45 what is the patient said to be?
If the blood pH drops below 7.35 then the person is said to be acidic, if above 7.45 then alkalotic
pH of ECF tightly controlled close to 7.4 (40 x 10-9M of hyrogen ions (40nmol H+) What does an increase in [H+] do to pH? What do small changes in pH cause to hydrogen?
Increase in hydorgen ion concentration decreases pH Small change in pH causes a large change in hydrogen ion concentration - pH 7.0 = 100 nmol/l pH 7.8 = 16 nmol/l
Why can a severely acidotic person relapse into a coma? (say in diabetic ketoacidosis)
Severe acididotic conditions depress the central nervous system and therefore can drive someone into a coma
Alkalosis can lead to overexcitability of the peripheral NS and later the CNS. What can over-excitability of sensory nerve fibres and motor nerve fibres cause?
over-excitbaility of sensory nerve fibres can cause tingling in the hands and feet (pins and needles) Overexcitability of the motor fibres can cause muscle spasms
What effect can a change in pH have on enzymes?
Change in H+ concentration will affect the pH and therefore can denature enzymes as it affects the folding of enzymes
Hydrogen ions are being conitinually added to the body fluid mainly as a result of metabolism Always trying to match input to output What are the 3 ways in which hydrogen is continually added to the body?
Carbonic acid formation – most major cause (normally respiratory system regulates this) Inorganic acids produced during breakdown of nutrients Organic acids resulting from metabolism
What are inorganic and organic acids?
Organic acids are carboxylic acids mainly Inorganic acids are like phosphoric acid, or sulphuric acid
Strong acids dissociate completely in solution Weak acids dissociate partially in solution Give an example of a weak acid in a major buffering system?
Carbonic acid - buffer systems are usually weak acids
Buffer system consists of a pair of substances – one can yield free H+ as the [H+] decreases the other can bind free H+ when [H+] increases What is the buffering capacity defined as?
The extent to which a buffering solution can counteract the addition of an acid or a base
What would the first line defence in a change in hydrogen concentration in the body be?
This would be the buffer system
HA ⇄ H+ + A- If acid is added, what way does equilibrium shift and why? If base (e.g. B-) is added to this system, equilibrium shifts to the right? Remember the buffering is all to try and maintain the pH levels
Excess hydrogen ions binds to A- to cause equilibrium to shift to the left and fall in pH is buffered If base is added, the ions bind to the H+ causing equailibrium to shift to the right and further dissociation of HA to limit rise in pH (buffered)
What does thee dissociation constant K, at equlibrium equal?
the disocciation constant equals the vocnentration of reactants divided by the concentration of the product K= [H+][A-]/ [HA]
What is the henderson hasselback equation?
pH = pK + log [A-]/[HA]
Write down the equation for the most important physiological buffer system
CO2 + H2O ⇄ H2CO3 ⇄ H+ + HCO3- This is the CO2, HCO3- buffer system
What are the two organs that function for the most important buffer system?
CO2 + H2O ⇄ H2CO3 ⇄ H+ + HCO3- Kidneys and the lungs Lungs for CO2 and kidneys fro HCO3- (carbon dioxide and biacarbonate)
H2CO3 is formed from carbon dioxide and water What enzyme catalyzes this?
Carbonic annyhdrase H2CO3 is known as carbonic acid
Remember henderson hasselbach equation is pH = pK + log base/acid So rewrite this for the buffer system?
ph = pK + log [HCO3-]/[H2CO3]
Concentraion of carbonic acid is related to the partial pressure of carbone dioxide Need to know the partial pressure of carbon dioxide and how much is physically dissolve in the blood (solubility coeefficent) Therefore when calculating the pH of the blood it is equal to: Kidneys divided by lungs Lungs divided by kidneys Neither?
pH = pK + kidneys divded by the lungs
What is the normal bicarbonate range for concentration?
The normal range for bicarbonate is usaly around 23-27 mmol/l
the kidneys are important in regulating the levels of HCO3- in the blood Variable reabsorption of filtered HCO3- Kidneys can add “new” HCO3- to the blood i.e. [HCO3-]renal vein > [HCO3-]renal artery What do both of these depend upon?
Both the variable reabsorption of filtered HCO3- and the kidney adding new HCO3- to the blood depend on the H+ secretion into the tubular lumen
How would the rate of filtration of HCO3- be calculated?
Rate of filtration = GFR x [HCO3-]plasma
Caluclating the rate of filtration of bicarbonate per day GFR = 125ml/min and [HCO3]plasma is 24mmol/l Calculate the rate of filtration
Rate of HCO3- filtration = GFR x [HCO3-]plasma = 125 ml/min x 24 mmol/l = 180 l/day x 24 mmol/l = 4320 mmol/day


