Lect 9 Flashcards
What are the three main components of the homeostatic mechanisms that regulate [H+] in the body
- buffers: bicarb, phosphates, etc
- respiratory compensation: alters CO2 levels
- renal compensation: alters HCO3- levels
what is the plasma concentration of H+
40 nEq/L
equation for pH
pH = -log[H+]
- 10 fold increase in [H+] = 1 unit change in pH
normal blood pH level
- 7.4
- normal range: 7.37-7.42
what is volatile acid
- source of H+ that is produced from respiratory CO2 and handled by the lungs
what are some examples of non-volatile or fixed acid (50 mEq/day)
- degradation of certain amino acids
- sulfuric acid from methionin and cysteine
- phosphoric acid from phospholipid
- exercise (lactate)
- diabetic ketosis
- ingestion of acids
**acid load that kidney must eliminate
differentiate between acid and base in terms of donor and acceptor
- acid: H+ donor
- base: H+ acceptor
in HA <-> H+ + A-, which is the conjugate base
- A-
- The conjugate base of an acid is formed when the acid donates a proton
with this equation in mind HA <-> H+ + A-, how can it be rearranged to make a constant
K = [A-][H+] / [HA]
what is the henderson-hasselbalch equation
pH = pK + log ([A-] / [HA])
with this equation in mind pH = pK + log ([A-] / [HA]), when does pH = pK?
when [A-] = [HA]
describe strong acids. do they have a lower or higher pK?
- lower affinities for hydrogen ions -> will dissociate easily from conjugate base
- lower pKs
describe weak acids. do they have a lower or higher pK?
- have higher affinities for hydrogen ions -> will not dissociate easily from conjugate base
- higher pKs
buffers are the first line of defense against pH changes. effectiveness of a buffer is proportional to?
- its concentration
- its pK
what is the most important buffer system in the ECF?
- bicarbonate buffer system
- due to high concetration and both CO2 and HCO3- are tightly regulated
- CO2 + H2O <-> H2CO3 <-> H+ + HCO3-
what do buffers consist of
acid and conjugate base pairs
- ex: HA/A-
what are the most effective buffers in terms of pH
- most effective buffering is +/- one pH unit from pK
what are the acid/conjugate base pairs form bicarb and phosphate buffer systems
- HCO3-/H2CO3
- HPO42-/H2PO4-
Bicarbonate accounts for 53% of total buffering capacity. Why is it effective
- pK is low (6.1) but effective due to its concentration and because both the acid (H2CO3) and base (HCO3-) are regulated
Hemoglobin accounts for 35% of total buffering capacity. What is the buffer?
- Hb - + H+ <-> HHb
- Imidazole groups on histidine and alpha amino groups are the primary buffer sites on all proteins
What are the four buffers in blood
- bicarbonate
- hemoglobin
- proteins (7%): low conc.
- phosphate (5%): very important in urine
what are the primary intracellular buffers?
- proteins (pK close to 7.4)
- phosphate
how can bone act as a buffer
- takes up H+ in exchange for Na+ and K+
- helps during acute acid load
what are the normal ranges for pH, PCO2, and HCO3-
- pH = 7.4
- PCO2 = 40 mmHg
- HCO3- = 24 mEq/L
what is the equation that determines pH (values inserted for HH equation)
pH = 6.1 + log [HCO3-] / (0.03 x PCO2)
pH = 6.1 + log [HCO3-] / (0.03 x PCO2); decreased bicarbonate or increased PCO2 will give what state
acidosis
pH = 6.1 + log [HCO3-] / (0.03 x PCO2); increased bicarbonate or decreased PCO2 will give what state
alkalosis
buffers can’t return pH to normal, lungs and kidneys regulate CO2 and HCO3- respectively such that the ration of [HCO3-] to dissolved CO2 = X
20
changes in [HCO3-] are considered metabolic or respiratory disturbances? What organs can compensate?
- loss or gain of HCO3- = metabolic disturbance
- compensated for by both kidneys and lungs
which is quicker, metabolic or respiratory compensation?
respiratory
changes in [CO2] are considered metabolic or respiratory disturbances? What organs can compensate?
- respiratory disturbances
- must be compensated for by the kidney
what happens in metabolic acidosis
- plasma HCO3- decreases
- respiratory system responds by increasing ventilation to expel CO2; kidneys synthesize new HCO3-
what happens in metabolic alkalosis
- plasma HCO3- increases
- respiratory system responds by reducing ventilation to retain CO2; kidneys excretes excess HCO3-
what happens in respiratory acidosis
- plasma PCO2 increases
- caused by decreased ventilation (drug overdose, airway obstruction)
- kidneys will synthesize new HCO3- and excrete H+ in the urine to raise blood pH
what happens in respiratory alkalosis
- plasma PCO2 decreases
- caused by hyperventilation (stress, high altitude)
- kidneys will excrete HCO3- causing urine to become alkaline; blood HCO3- and pH will decrease
