L38 - Acid Base Balance (resp) Flashcards
(34 cards)
What does arterial blood ph range from intracellular?
- 7.36-7.44
- ~7.2
What is the most important buffer?
HCO3-/CO2 system (bicarbonate system)
What does carbonic anhydrase do in the body? (3)
- catalyse conversion of CO2 + H2O to H2CO3
- H2CO3 (v unstable) -> HCO3- + H+
- (in equilibirum)
What controls regulation of CO2? (2)
- chemoreceptors and lungs
- regulation by ventilation
What controls regulation of HCO3- and H+? (2)
- kidneys
- HCO3- filtering or generation of H+ secretion
What is carbonic anhydrase (CA)? (4)
- zinc metalloenzymes
- expressed in tissues (lungs, kidney, eyes, intestines and RBC
- cytosolic and membrane located isoforms of CA
- plants and corals can also express
What is the eqn to calculate pH (with CO2 and HCO3-)?
pH = 6.1 + log(HCO3-/00.3 x PCO2)
What are the steps of transport of CO2 from tissues? (5)
- CO2 generated by tissues
- 10% CO2 dissolves in plasma and RBC
- 25-30% reacts with Hb to form HbCO2 (carbaminohemoglobin)
- 60-65% converted by CA to HCO3- and H+
- chloride shift - electroneutral exchange of HCO3- for Cl- ions
What are the steps of CO2 to lungs? (3)
- loss of CO2 leads to HCO3- to combine with H+ to generate CO2
- loss of CO2 leads to dissociation of Hb to release CO2
- expired CO2
Why is net diffusion of CO2 into alveolus?
Blood CO2 > alveolar CO2
= net diffusion of CO2 into alveolus
What is the transport of hydrogen ions between tissues and lungs when blood flows through tissues? (4)
- oxyhemoglobin loses oxygen
- CO2 enters blood = HCO3- and H+
- deoxyhemoglobin generated
- greater affinity for H+ than HbO2 = most H+ by CA reaction binds
What is the transport of hydrogen ions between tissues and lungs when blood flows through lungs? (4)
- reaction reversed
- deoxyhemoglobin + O2 = HbO2 oxyhemoglobin
- H+ + HCO3 = CO2 and H2O
- CO2 expired
What is respiratory control of CO2 like? (3)
- arterial PCO2 ~ 40mmHg
- alveolar ventilation inc/dec = maintain arterial PCO2
- chemoreceptors control alveolar ventilation
Where are peripheral and central chemoreceptors found? (2)
- peripheral - neck in bifurcation of common carotid artery (carotid bodies) and thorax at arch of aorta = aortic
- central - medulla
What are the changes in pCO2 and how do chemoreceptors respond? (3)
- peripheral - inc in arterial H+ due to inc pCO2
- inc brain pCO2 - inc brain extracellular H+ - activates central
- both stimulate medullary inspiratory neurons = inc ventilation
What are other pH changes? (2)
- H doesnt pass quickly across BBB - only activate peripheral
- reverse if dec in [H+] and depression of peripheral firing
What role do the kidneys have in regulation of bicarbonate levels? (2)
- reabsorption of filtered bicarbonate
- production of new bicarbonate
What is bicarbonate regulation like in the kidneys? (3)
- filtered at renal corpuscles
- reabsorbed in PCD, loop of henle, cortical CD
- CD also secretes HCO3-
What is the eqn for renal HCO3- excretion?
renal HCO3- excretion = HCO3- filtered + HCO3- secreted - HCO3- reabsorbed
What is bicarbonate reabsorption like in the different parts of the nephron? (3)
- PCT - 80%
- loop of henle - 15%
- CD - 5%
Where is renal CA seen? (2)
- intracellular enzymes - kidney epithelial cells lining tubules
- extracellular - brush boarder surface of epithelial cells
How are filtered bicarbonate ions reabsorbed? (3)
- HCO3- filtered
- binds with H+ = H2O and CO2
- in cells H2CO3 forms HCO3- back to blood
What happens when all filtered bicarbonate has been reabsorbed? (2)
- HPO42- binds with H+ = H2PO4-
- in cell, H2CO3 forms HCO3- back to blood
How are new bicarbonate ions synthesised from a/a catalysis? (3)
- glutamine = NH4+ and HCO3-
- NH4+ excreted
- HCO3- into blood
