Acid Base Balance Flashcards
(40 cards)
What is the target pH of the blood?
7.4
Why are metabolic reactions so sensitive to the pH of the fluid in which they occur?
Due to the high reactivity of hydrogen ions with negatively charged proteins/segments of protein resulting in changes in configuration and function, especially in enzymes
What are the sources of hydrogen ions in the body?
Respiratory acid (Co2 + water results in production of carbonic acid) Metabolic acid- via metabolism of dietary constituents that result in production of inorganic acids or organic acids
When does respiratory acid contribute to acid/base balance?
In some cases where lung function is impaired. In health, the body ensures that respiratory acids do not have an effect
What is the function of a buffer?
To minimise the changes in pH when hydrogen ions are added or removed
What does the Henderson-Hasselbalch equation define?
Defines pH in terms of a ratio of acid:base
What is the most important extracellular buffer?
The bicarbonate buffer
What is the normal range of blood pH?
7.37-7.43
What is the normal range of blood pCO2?
4.8-5.9kPa OR 36-44mmg
What is the normal range of concentration of carbonic acid in the blood?
22-26mmoles/L
How does the bicarbonate buffer system act as a buffer?
An increased concentration of H+ in the ECF drives the reaction to the right to remove some additional H+ from the solution and therefore a change in pH is reduced
How are hydrogen ions eliminated from the body?
Through the kidneys through an excretion that is coupled with the regulation of carbonic acid concentration in the plasma
What are the possible intracellular buffers?
Proteins
Organic and inorganic phosphates
Haemoglobin (in erythrocytes only)
How does buffering of hydrogen ions by ICF buffers cause a change in plasma electrolytes?
To maintain electrochemical neutrality, movement of hydrogen ions must be accompanied by chlorine ions in red cells or exchanged for a cation- K+
What organs is regulation of blood pH reliant on?
Lungs and kidneys
How does the kidney regulate [HCO3-]?
Reabsorbing filtered HCO3-
Generating new HCO3-
Describe the mechanism of reabsorption of HCO3- in the kidneys
H+ is actively secreted from the tubule cells in a process that is coupled to passive sodium reabsorption. Filtered HCO3- reacts with the secreted H+ to form H2CO3, which is converted to carbon dioxide and water in the presence of carbonic anhydrase. CO2 is freely permeable and enters the cell, where it is converted to H2CO3 in the presence of carbonic anhydrase which then dissociates to form H+ and HCO3-. The H+ ions are the source of secreted H+ and HCO3- ions pass into peritubular capillaries with sodium.
Where does most (>90%) of the carbonic acid reabsorption take place?
In the proximal tubule
Why is HCO3- reabsorption vital to life?
Failure to reabsorb results in addition of hydrogen ions to the ECF
What is the buffer for most of the buffering of urine?
Dibasic phosphate
What is the process of buffering urine known as and why is it called this?
Titratable acidity- extent is measured by the amount of NaOH needed to titrate urine pH back to 7.4 for a 24hr urine sample
Why is the formation of titratable acidity important?
It generates new HCO3- and excretes H+
How does Na2HPO4 remove H+ from the body?
One Na+ is reabsorbed in the lumen in exchange for secreted H+
What is the source of new HCO3- in titratable acidity?
CO2 enters the tubule cells and combines with H20 to form carbonic acid (in presence of carbonic anyhdrase), dissociating to yield H+ (used for secretion) and new HCO3-, which passes with sodium ions into the peritubular capillaries
