Physio 7 Flashcards
Which blood is more acidic : arterial or venous blood?
Venous blood as it contains more the CO2 and forms carbonic acid
What is the normal pH levels in the body?
7.35-7.45
hence average 7.4
What is the ECF H+ concentration for a plasma pH of 7.4
40 nmol
What is the ECF H+ concentration for a plasma pH of 7.0
100 mnol/l
How does a small change in the pH affect the H+ concentration?
very large chnages in the H+ concentration
What does acidosis do?
Depression of the CNS
What does alkalosis do?
Alkalosis can lead to overexcitability of the peripheral NS and later the CNS.
muscle twitching and spams –> if extreme can affect the respirtatory system
How does H+ changes affect the K+ levels in your body?
If we are acidotic –> increases H+ secretion –> decrease in K+ secretion –> K+ retention increased
How if H+ added to the body?
continuously as a result of metabolic activity
- Carbonic acid formation
- Inorganic acids produced during breakdown of nutrients (meat on breaking)
- Organic acids resulting from metabolism (keto acids, lactic acids)
- Diabetes mellitus(Cells metabolise fat –> increased production of keto-acids –> yield H+ –> disrupt ppH balance)
How does DM cause acidosis?
Cells metabolise fat –> increased production of keto-acids –> yield H+ –> disrupt ppH balance
What do strong acids dissociate to?
dissociate completely
What do weak acids dissociate to?
dossciate partially
What is the first line of defense against any change in pH levels?
Buffer system
What happens if increased H+ added?
Protons are “mopped-up” by A- leading to formation of more HA
[HA] rises, [A-] falls
In other words, the rise in [H+] (fall in pH) has been limited (buffered) by the formation of HA
what happens if more A- added?
Base is “tied-up” by combining with H+, allowing more HA to dissociate
[HA] falls, [A-] rises
In other words, the rise in pH (fall in [H+]) has been limited (buffered) by further dissociation of HA
What is the important buffer system in the body?
Carbon dioxide - bicarbonate system
What regulstes the plasma concentration of bicarbonate
Kidney
What regulates the partial pressure of co2 levels in the body?
Lungs
What is the role of the kidney in the control of bicarbonate?
1.Variable reabsorption of filtered HCO3-
- Kidneys can add “new” HCO3- to the blood
i. e. [HCO3-]renal vein > [HCO3-]renal artery
Higher concentration of bicarbonate as it is secreted by the tubule and can then be added to the blood
What drives the reabsorption of the generation and reabsorption of bicarbonate ions in the kidney?
H+ ions
What is the importance of reabsorbing HCO3- ions?
if not it would be equivalent to adding about 4 litres of 1M HCl to the body
What is t
40 nmol/L of H+
Concentration of H+ or HCO3-(24 mmol/L) is more in the plasma?
HCO3- is more
Why is the rate of filtration of H+ less?
hydrogen ions in the plasma low hence the filtration of H+ is also low
no apical transpot mechanism to move HCO3- from the tubular fluid to the cells - hence indirect methoud of reabsorption
How does the reabsorpotion of HCO3 - occur?
Indirect method depending on the H+ concentration
How is HCO3- reabsprtbed?
H+ (from the dissociation of carbonic acid) secreted across the apical membrane into the fluid in exchange for sodium for the na/ H+ exchanger
the bicarbonate ions makes its way into the interstitial fluid via the exchanger at the basolateral membrane
bicarbonate disappears from the tubular fluid and is seen in the interstitial fluid (not the same though as what it was in the beginning)
What drives the H+ ion secretion in the proximal tubule?
CO2
increased CO2 retention –> increased H+ secretion
Is H+ secreted more or HCO3- filtered more?
renal tubular cells secrete more H+ ions than HCO3- that are filtered
normally reabsorb all the filtered HCO3 -
Formation of new HCO3-
if you reduce the plasma concentrattion of HCO3- ions, then the concentration of the tubular fluid of HCO3- also increases (as rate of F = plasma conc x GFR)
instead of combining with HCO3-, H+ combines with the PO4
Where is the phosphate present from?
Breakdwon of protein
Ways to secrete H+ in the collecting duct cells
H+/K= ATPase
or
H+ ATPase
What happens if HCO3- levels are low?
in bicarbonate levels are low –> H+ combines with pO4 and formed H2PO4
once bicarbonate ion formed for each H+ added to the tubular fluid
Bicarbonate helps to replenish the buffer stores
What is titratable acid?
The amount of hydrogen phosphate excreted
what is the maximin titratable acid that can be exctreted from the kidney?
40 mmol/.day
What is the amount of bicarbonate that is added to the blood?
40 mmol/.day (as the amount of HCO3- ions added is the same as the H+ ions secreted)
What happens if acidosis persists even after all the phosphate levels are depleted?
breaks down ammonium via glutamine and add H+ to it to form Ammonium and one HCO3- added for each ammonium ion added
What is the normal level of ammonium that is excreted from the blood per day?
20 mmol/L
What are the 3 functions done by H+ secretion in the tubule?
- HCO3- ion reabsorption
- Drives the formation of acid phosphate which adds one HCO3- back to the blood
- During acidosis, it can form NH4 and adds one HCO3- ions back to the blood
What is the level of NH4 in someone with acidosis?
5-600 mmol/day
What is the amount of HCO3- generated?
it it
if acidotic
increase ammonium and hydrogen phsophate secretion
What is the amount of HCO3- newlygenerated?
the amount of H+ excretion (TA excretion + NH4 excretion)
