Acid-Base Balance Flashcards
What is an acid?
A molecule capable of releasing a hydrogen ion
What are sources of acid?
Carbonic acid - altered by breathing
Non-carbonic - buffered in body and excreted by kidneys
Metabolism
In complete fat and carbohydrate metabolism
Mixed diet of meat and veg
What is a base?
Molecule capable of combining a hydrogen ion
Why maintain acid-base balance?
Maintenance is essential for normal metabolic reactions - affect enzymes and chemical reactions
What pH does the body keep blood close to?
7.4
ECF - 7.35-7.45
ICF - 7.0 - 7.2
What are the 3 mechanisms controlling blood pH?
Buffers
Respiratory
Renal
What are pH buffer systems?
Combinations of a weak acid and a weak base that exist in balance under normal pH conditions
How do pH buffer systems maintain acid-base balance?
Chemically minimize changes in pH by adjusting proportion of acid and base
1st to act
What are the 2 most important pH buffers?
Bicarbonate/carbonic acid
Haemoglobin
How does bicarbonate maintain the acid-base balance?
Acidic: HCO3- is reduced to neutralize pH
Alkaline: H+ is consumed to neutralize pH = more HCO3- produced from H2CO3 dissociation
What is the HCO3-/CO2 buffer system most important for?
Blood and ECF
What is most carbon dioxide converted to?
Carbonic acid -> dissociates into H+ and a bicarbonate ion
What does the carbonic acid-bicarbonate buffer system prevent?
Changes in pH caused by organic acids and fixed acids in ECF
What 3 things is the carbonic acid-bicarbonate buffer limited by?
Availability of bicarbonate ions
Functions only when respiratory system is working normally
Cannot protect pH against elevated or depressed levels of CO2
What is haemoglobin important in?
In the role of carbonic acid buffering
35% of H+ buffering
What is the MoA of the Hemoglobin buffer system?
CO2 diffuses across RBC membrane
Bicarbonate ions diffuse into plasma in exchange for chloride ions
What compartment does the hemoglobin buffer system maintain?
Intracellular buffer system with a direct effect on ECF pH
Prevents pH changes when plasma PCO2 is rising or falling
What are 2 other buffers?
Plasma proteins (10%)
Phosphate (5%)
What are 4 characteristics of the respiratory acid-base control mechanisms?
Eliminate or retain CO2
Change in pH are rapid
Occurs within in minutes
PCO2 proportional to VCO2/VA
What happens to the alveolar minute ventilation?
Altered to remove or retain CO2 from the lungs
What part of the brain reacts to low pH?
Medullary respiratory centre
What does the brain do to breathing when pH falls?
Increases speed and depth of breathing - more CO2 excreted
What happens to breathing when pH increases?
Rate and depth of ventilation declines - less CO2 excreted
What are 3 characteristics of the renal acid-base control?
Movement of bicarbonate
Retention/excretion of acids
Generating additional buffers
What is the MoA of kidneys in acid-base balance?
Directly secrete H+ into urine - directly regulate body pH
preservation of body’s bicarbonate stores
What is the preservation of body’s bicarbonate stores accomplished by?
Reabsorption of 99.9% of filtered bicarbonate
Regeneration of titrated bicarbonate by excretion
What does H+ ions in the nephron lumen react with?
Bicarbonate ions, phosphate ions and ammonia
