Chapter 21: Acid-Base Flashcards
(48 cards)
base excess definition
amount of strong acid (HCL for BE >0) or strong base (NaOH for BE <0) required to return 1L of whole blood exposed in vitro to a PCO2 of 400 mm hg to a pH of 7.4
does base excess refer to respiratory or metabolic component of acid base disturbance
metabolic
at 37 degrees C the normal hydrogen ion concentration in arterial blood and ECF is what
35-45 nmol/L
normal plasma bicarb concentration is what
24 +/-2meQ/L
buffer systems are composed of what
base molecule and its weak conjugate acid
base buffer system and bind excess hydrogen, weak acid protonates excess base
what is the PKA
pH at which an acid is 50% protonated and 50% deprotonated
most important buffer systems in blood in order of importance
1) bicarb buffer system
2) hemoglobin buffer system
3) other protein buffer systems
4) phosphate buffer system
5) ammonia buffer system
CO2 + H20 —>
CO2 + H20 —> H2CO3 –> H+ + HCO3-
Hgb buffering system is important buffering system bc of its multiple _____ residues which is an effective buffer from ___ to ___ pH because it contains multiple what. this buffering depends on what
histidine
5.7-7.7
multiple protonatale sites on the imidazole side chains
depends on bicarb buffer to move CO2 intracellularly
CO2 diffuses freely into erythrocytes then what happens
hamburger shift
carbonic anhydrase resides, H+ and HCO3- formed, H+ are bound by hemoglbin and bicarb exchange back into plasma with extracellular chloride
at the lungs the reverse process of hamburger shift occurs: explain
chloride ions move out of the RBCs as bicarb enters for convresion back into CO2 which is then released back into the plasma and eliminated by the lungs
oxygenated vs deoxygenated hgb. ____ takes up more hydrogen ions which shifts the co2/bicarb equilibrium to produce more ___ which facilitates removal of ___ from peripheral tissues
deoxygenated hgb takes up more H ions which shifts the equation to the right to make more bicarb and facilitates removal of CO2 from peripheral tissues
central chemoreceptors lie on the ____ surface of the ___ and respond to changes in CSF pH
anterolateral medulla
doses CO2 diffuse across the BBB
yes then dissocates into H+
peripheral chemoreceptors are located where
common carotid arteries and aortic arch
carotid body chemoreceptors are sensitive to changes in what and communicate with the central respiratory centers via what
PaO2, PaCO2, pH, arterial perfusion pressure
communicate via glossopharyngeal nerve
peripheral chemoreceptors are most sensitive to what
PaO2
pts with bilateral carotid endarterectomies have almost no what drive
hypoxic vent drive
how many days does it take for renal response to acid base disturbance to be maximal
can be 5 days
renal response of ph changes occurs via what 3 things
1) reabsorptino of filtered HCO3-
2) excretion of titratable acids
3) ammonia
where in the kidney is bicarb absorbed
80-90% in PCT
10-20% in DCT
ammonia buffer system: describe it
its formed from deamination of glutamine to NH3 which passes cell membrane to enter the tubular fluid where it combines with hydrogen to form NH4+ which is trapped within the tubule and excreted in urine
the kidneys are highly effective in protecting the body against alkalosis except in association with what deficiency or what excess
Na deficiency
mineralocortiocoid excess
venous pH is only ____ to ___ less than arterial values
.03 to .04
