Acid-Base Balance Flashcards
What is the range in which plasma pH must be kept within?
7.35-7.45
What does the Henderson-Hassalbalch equation relate?
The pH to the ratio between the concentration of bicarbonate and the partial pressure of carbon dioxide
When blood pH deviates from the normal range, there are two body systems which are activated to restore equilibrium. What are these and how do they do it?
Respiratory system - alters respiratory rate to change concentration of CO2
Urinary system - changes reabsorption or production of bicarbonate/hydrogen ions
Where are peripheral chemoreceptors found?
Aortic arch and carotid sinus
When can metabolic acidosis occur?
Ketoacidosis in diabetes (increase in H+ produced)
Disorder of kidneys themselves (CKD - decreased bicarbonate production)
How does the respiratory system try to compensate for metabolic acidosis?
By increasing respiratory rate
When can metabolic alkalosis occur?
Vomiting (loss of H+)
Or by increase in bicarbonate in blood
How does the respiratory system try to compensate for metabolic alkalosis?
By decreasing respiratory rate - increases pCO2 and lowers pH
Where are central chemoreceptors located?
Medulla oblongata of brainstem
How is the pH of the CSF established?
By the ratio of pCO2 : concentration of HCO3– ions.
What happens in pCO2 levels in the CSF stay the same over a long period of time?
Choroid plexus cells within the Blood Brain Barrier allow HCO3– ions to enter the CSF. As such the system can be ‘reset’ to a different pCO2 by manipulating the pH
What does hypoventilation lead to?
A build up of CO2 in the body which causes the blood to become acidic
What are some common causes of hypoventilation?
COPD, chest wall deformities, neurological defects, obesity
What does hyperventilation lead to?
Hypocapnia - results in the blood being too alkaline which decreases free calcium levels, leading to paraesthesia/muscle cramps due to increased excitability of muscles and nerves
What are some common causes of hyperventilation?
Anxiety, heart failure, pulmonary embolism
What 2 methods does the urinary system use to alter blood pH?
1) H+ excretion
2) Reabsorption and production of HCO3-
How does the urinary system excrete H+ in the form of ammonium?
1) Glutamine is converted to glutamate and ammonium in the PCT
2) Glutamate is converted to alpha-ketoglutarate which is then eventually turned to bicarbonate which can be reabsorbed in the blood
3) Ammonium can then dissociate to ammonium and hydrogen ions, which is then reformed to ammonium on the luminal side to be excreted
Where does bicarbonate reabsorption occur?
PCT
How is bicarbonate reabsorbed in the PCT?
1) Hydrogen ions are secreted into the lumen via the Sodium-Hydrogen exchanger to combine with any filtered bicarbonate
2) This then forms carbonic acid (H2CO3), catalysed by carbonic anhydrase on the luminal side. Carbonic acid then dissociates into carbon dioxide and water, which both can diffuse into the cell.
3) Here, the reaction is undone, and carbonic anhydrase inside the cell converts carbon dioxide and water to carbonic acid, which then dissociates into hydrogen ions and bicarbonate.
4) Bicarbonate can then be transported into the blood whilst the hydrogen ions can be transported back into the lumen for the cycle to repeat.
