Physiology 7 Flashcards
pH refers to what
free unbound hydrogen ion concentration
what happens if there is an increase in the hydrogen ion concentration
A decrease in the pH
What is the pH of the blood
between 7.35 and 7.45
venous blood is more or less acidic than arterial blood and why
Venous is more acidic due to the presence of CO2 and therefore carbonic acid (weak acid)
What happens if the pH of blood is less than 7.35
Patient is suffering from an acidosis
What happens if the pH of blood is more than 7.45
Patient is suffereing from an alkalosis
A relatively small change in pH reflects what
A larger change in H+ concentration
What are the units of the H+ ion concentration
nanomoles per liter (x10 ^9)
What can acidosis lead to
Depression of the CNS
disorientated, could die after lapsing into a coma in extreme cases
What can alkalosis lead to
Over-excitability of both the peripheral NS and in more severe cases the CNS
What happens if the Sensory fibres are overstimulated
Pins and needles
What happens if the Motor fibres are overstimulated
Muscle twitches and spasms –> spasms of respiratory muscles in severe cases
What can influence the way in which proteins are folded and what does this result in
H+ concentration and pH
Enzymes activity can be altered because of this
What happens in the kidney when a patient becomes acidotic
Renal tubular cells increase H+ secretion
There is a corresponding decrease of K+ ion secretion which can lead to K+ ion retention
How is H_ continually added to the plasma
Carbonic acid formation
Inorganic addict produced during breakdown of nutrients (lactic acid or free fatty acid)
Organic acids resulting from metabolism
How is carbonic acid formed (HCO3)
Water + CO2
Why is the formation of HCO3 not normally a problem
Respiratory system can remove this and regulate the levels of this
Why can uncontrolled diabetes mellitus cause an increase of H+ ions
the main fuel resource used here is fat metabolism which causes an increase in the production of ketoacids and therefore cause an imbalance of acid-base balance
What is a strong acid
An acid which completely dissociates in solution
What is a weak acid
An acid which partially dissociates in solution
What is a buffer system
Consists of a pari of substances - once can yield free H_ as the H+ decreases and another that can bind free H+ when H+ concentration increases.
If excess H+ ions are added to a weak acid, what does the buffer do
It mops up the excess leading to the formation of more of the strong acid
If excess base is added to a weak acid, what does the buffer do
equilibrium shifts an increase in the dissociation rate occurs
What does pK tell us
The pH at which the reaction will be at equilibrium
What is the formula to calculate the dissociation constant
K= [H+] [A-] / [HA]
What is the most important buffer system in the body
CO2 - HCO3 buffer
How can we calculate the pH using the Henderson-Hasselbalch equation
pH = pK + log [HCO3-] / [H2CO3]
Why is the CO2 - HCO3 buffer so important
The pH of the body = kidneys / lungs
What do the kidneys regulate
The plasma concentration of bicarbonate ions
What doe the lungs regulate
The levels of the CO2 in the blood
How do the kidneys control the concentration of Bicarb
- Variable reabsorption of filtered HCO3 back into the blood
- Kidneys can generate “new” HCO3 to the blood
Why is the HCO3 reabsorption important
If none was reabsorbed then more H+ ions would be in the blood and we would become acidotic
Describe the difference between the H+ conc and the Bicarb ions
H+ ions are nano molar range
Bicarb ions are in the mili molar range
Where does H+ ion concentration occur
Proximal and distal tubules as well as the collecting duct of the nephron
Describe the filtration of the bicarb ions
They are freely filters but cannot cross the apical membrane of the tubular cells - we need an indirect way of getting the bicarb ions from the tubular fluid back towards the blood
How is Bicarb reabsorbed
Water and carbon dioxide combine to form carbonic acid (H20 +CO2 –> H2CO3)
The carbonic acid then dissociates inside the epithelial cell to form H+ + HCO3-
The H+ is then filters across the membrane in exchange of a sodium ion into the tubular fluid
Bicarb is then released back into the interstitial fluid along with the Na+ ion
What happens if we have CO2 retention
we observe an increase in H+ ion secretion by the renal tubular cells
What drives bicarbonate ion reabsorption
H+ secretion
Where is titratable acid broken down
it isn’t - it is excreted in the urine
What is the next most plentiful buffer in the filtrate when the Bicarb ions are low (due to them being reabsorbed)
Phosphate ions
What does H+ combine with when phosphate acts as the tubular buffer
Acid phosphate which is then excreted in the urine
What is titratable acid
The amount of H+ excreted as H2PO4- is measured as titratable acid
What is the maximum amount of titratable acid that can be excreted in a day
40 mmol/day
How is ammonia formed in the tubular cells
glutamine (from the liver) is broken down by glutaminase to form ammonia
How can ammonia diffuse so easily
It is a gas
What 3 things does H+ ion drive
Bicarbonate ion reabsorption
Formation of acid phosphate (titratable acid)
Forms ammonium ion
The excretion of TA and NH3 simultaneously rids the body of what
What does this do
Acid load
Regenerates the buffer stores (alkalinises the body)
