Flashcards in Physiology processes (use in conjunction with other physiology) Deck (30):
Why can't you just absorb bicarbonate as you would Na+?
There is no transport mechanism on the apical membrane that can carry it.
Process of absorbing bicarbonate from the tubular filtrate?
Water and carbon dioxide inside the cell bind to from carbonic acid (H2CO3).
This then dissociates to form bicarbonate and a H+. The bicarbonate then exits the cell via the basolateral membrane into the blood via the Na, HCO3 symporter,.
The H+ that is left in the cell is transported into the tubular fluid via secondary active transport with sodium (that is coming into the cell).
The H+ is now in the tubular fluid and it can combine with bicarbonate to form carbonic acid. This then dissociates to form water and carbon dioxide in the tubular fluid which can be readily taken up by the cell.
How does the body go about forming new bicarbonate?
When the bicarbonate in the tubules is low- the H+ that is secreted into the tubules from the creation of bicarbonate inside the cell binds to phosphate and is excreted. (this allows for bicarbonate to still be made when bicarbonate in the tubular fluid is low)
Where is bicarbonate absorbed?
What is the significance of phosphate being used when bicarbonate stores are low?
The phosphoric acid excreted (formed once H+ has combine with phosphate) can be measured as titratable acid. There is a one to one ratio for the amount of phosphoric acid produced as the amount of bicarbonate created.
In a severely acidotic individual (so much H+ they need a lot of bicarbonate to buffer it), what does the body use?
The body can also create new bicarbonate by combining the H+ with ammonia.
Process of using ammonia as a way to produce HCO3?
water and carbon dioxide in the cell combine to form carbonic acid. The carbonic acid then breaks down to form bicarbonate and H+. The bicarbonate gets put back into the blood via the Na, HCO3 symporter on the basolateral membrane.
However now there is the hydrogen to deal with. It gets into the tubular fluid by anti port with sodium. It then combines with ammonia to form ammonium ion. Which is then excreted.
A person is of normal acid base balance when they are:
Concentration of plasma bicarb is 22-27
Arterial PcO2 is 35-45.
What is compensation?
The 1st priority is to restore the pH no matter the consequences.
What is correction?
Restoring the bicarbonate and pCO2 after pH has been restored.
Describe respiratory acidosis?
For some reason you are not getting rid of enough carbon dioxide and it is building up in the fluids.
What could cause respiratory acidosis?
Asthma, tumour blocking, respiratory depression, chest injuries, chronic bronchitis, chronic emphysema.
Which way does the water and carbon dioxide - bicarb and H+ move?
Due to an increase in carbon dioxide- you get formation of more bicarbonate and H+.
(equation driven to the right).
What does respiratory acidosis (non compensated) look like?
A high Co2 and a low pH.
How does the body go about compensating`for respiratory acidosis?
Since the respiratory system is the cause- the renal system has to buffer.
The increased CO2 drives H+ secretion in the kidneys forming titratable acid and ammonia and creating new bicarb to act as a buffer. This returns the pH back to normal (however the Pco2 is still high.
How would you correct a respiratory acidosis?
correction requires lowering the pCO2.
What is respiratory alkalosis?
Excessive removal of CO2 by the body.
When do you get respiratory alkalosis?
When breathing unaided at altitude. Hypoxia stimulates peripheral chemoreceptors causing hyperventilation, however this lowers pCO2.
How would respiratory alkalosis affect the equation?
The equation would move to the left- a decrease in co2 drives the reaction to make CO2. This causes both H+ and bicarbonate to go down.
How would uncompensated respiratory alkalosis present?
A low Co2 and a high pH.
Describe how the body would compensate in respiratory alkalosis?
Since the respiratory system is the issue- the kidneys have to compensate. Due to high Co2 causing hydrogen secretion and bicarb absorption, low co2 means no hydrogen combines with the bicarbonate. This means bicarbonate (an alkaline) is excreted and the urine is alkaline.
What is metabolic acidosis?
H+ from any source other than carbon dioxide.
When would you get metabolic acidosis?
Could be due to ingestion of acids or acid producing food.
Excessive metabolic production of H+ (e.g. lactic acid during exercise)
Excess loss of base from the body (e.g. diarrhoea)
What happens to the equation in metabolic acidosis? What does uncompensated metabolic acidosis look like biochemically?
There is too much H+ therefore the bicarbonate becomes depleted trying to compensate for this.
pH is low, bicarb is low.
How does the body compensate in metabolic acidosis?
Respiratory system can help compensate. A decrease in plasma pH stimulates peripheral chemoreceptors which increases ventilation and more co2 is blown off.
Concentration of H+ is lowered therefore raising pH towards the normal.
Bicarbonate in the plasma is low. It is readily absorbed. H+ secretion produces titratable acid and ammonium ions to generate new bicarbonate.
Describe metabolic alkalosis?
Excessive loss of H+ from the body. Could be due to excessive vomiting, ingestion of alkali producing foods, too much aldosterone (causing H+ secretion in exchange for sodium reabsorption)
How does metabolic alkalosis effect the equation?
Causes it to shift to the left because adding more base combines with H+.
Biochemistry of uncompensated metabolic alkalosis?
As a result of H+ loss or addition of base- ph>7.45 and the bicarb is high.
How does the body compensate for metabolic alkalosis?
Increased pH slows ventilation and carbon dioxide is retained and pCo2 rises. Therefore the H+ rises lowering the pH.