Acid-base balance Flashcards
Why is it important to keep the pH in a narrow range?
→ The body has a lot of enzymes which only function at a particular pH
What is the normal pH of body fluids?
→ 7.35-7.45
What are the sources of acid in the body?
→Metabolism of carbohydrates and fats produces CO2
→ CO2 + H2O → H2CO3 → H+ + HCO3-
→ can be removed by the lungs
→ Metabolism of proteins
What does metabolism of proteins generate?
→ Non-volatile (fixed acids)
→ S- containing amino acids → H2SO4
→ Lysine,arginine,histidine → HCl
How do we know that we can control our pH?
→ 156 ml of HCl infused IV into a dog
→ 156 ml of HCl added to 11.4 l of water ( same as body water of dog)
→ Dogs arterial plasma decreased gradually from 7.44 to 7.14 (severe acidosis but survival is possible)
→ pH of water dropped to 1.84 (fatal if in vivo)
What is it about plasma that controls pH?
→ Presence of buffers that are effective in vivo
What is the first line of defense when there is a change in pH?
→ Buffer system in the blood (ICF and ECF)
What is disturbance in H+ compensated for?
→ ICF & ECF buffering systems
→ Respiratory systems
→ Kidney
What is the equation for the bicarbonate system?
→ H+ + HCO3- ⇌ H2CO3 ⇌ CO2 + H2O
What is the equation for the phosphate system?
→ H+ + HPO4 2- ⇌ H2PO4-
What is the equation for protein buffers?
→H+ + Pr - ⇌ HPr
What is pK?
→ The equilibrium point of a buffer
→ Where it most strongly resists changes in pH
→ Near where [acid and base] are equal
What is the range over which a buffer is effective?
→ 1 pH on either side of the PK
If the pK of the phosphate buffer is 6.8 what are the pH ranges over which it is effective?
→ 5.8
→ 7.8
Which buffer is theoretically better and why?
→ Phosphate
→because the PK lies within the body pH ranges
Which buffer is biologically better and why?
→ Bicarbonate
→lungs control PCO2
→ Kidneys control HCO3-
→ Independent controlled regulation of both variables
What is the henderson hasselbach equation used for?
→ Measuring the pH of a buffer system
What is the ratio of [HCO3-]: [CO2]?
→ 24 : 1.2
How do you calculate the concentration of CO2 in the blood if it is a gas?
→ Plasma CO2 is proportional to the partial pressure of CO2
How do kidneys control acid base levels?
→ Excrete acidic or basic urine
What are the primary mechanisms involved in excretion of urine?
→ Reabsorption and secretion of HCO3-
→ Formation of new HCO3-
→ Secretion of [H+] into tubular fluid
→ Buffer systems within the tubule that react with secreted [H+]