Phys 4 Flashcards
changes in pH are tightly regulated by what?
- buffer systems
- respiratory function
- renal processing of filtrate
What are the 3 chemical buffer systems?
- phosphate buffer system
- protein buffer system
- carbonic acid - bicarb buffer system
bicarb buffer system
- important in ECF
- bicarb converts a strong acid to a weak one
- carbonate converts a strong base to a weak base
phosphate buffer system
- monohydrogen phosphate ion converts a strong acid to a weak one
- dihydrogen phosphate ion converts a strong base to a weak one
- (think phosporylation)
protein buffer system
- carboxyl group of aa can release H
- amine group of aa can accept H
What happens when our physiologic buffer systems aren’t working adequately?
organ systems have to step in
normal process going on in the respiratory system
- CO2 produced by cells, transported in blood, eliminated by lungs
- exhalation = production
What happens in the respiratory system when CO2 exceeds elimination (i.e hypercapnia)
- central medullary detection of elevated H stimulates increase rate and depth of ventilation to unload CO2
- slower than chemical buffering but is more powerful
since the lungs only deal with carbonic acid via CO2 elimination, what deals with everything else?
- kidneys
- they deal w/ all other metabolic acids:
- phosphoric acids
- uric acid
- ketone bodies
metabolic acidosis
accumulation of the metabolic acids
what is a function that only the kidneys have?
regulation of alkaline substances and renewal of buffer systems
the most important renal mechanism for regulating acid-base balance of the blood involves what?
- excreting H
- conserving or generating HCO3-
(intercalating cells of collecting tubules can do opposite if needed)
secretion of H is a function of what?
tubular cells (PCT, DCT, collecting ducts)
what is responsible for renal secretion of H ions at the PCT?
- Na-H exchanger
- Na/bicarb symporter
Na-H exchanger
- where
- what it does
- at apical surface
- secretes H in exchange for Na
N/bicarb symporter
- bicarb and Na are cotransported from the cell
- Na enters the interstitial space then peritubular capillary
what is the end result of exchanges at the PCT?
for each H secreted, 1 Na and 1 bicarb ion enters the blood
renal secretion of H ions at the DCT and collecting duct is done by what?
-active secretion of protons by proton pump
how does the proton pump work?
- ATPase proton translocation
- no dependence on Na
what effect does acidosis have on proton pump?
it increases its activity
where does the phosphate buffer system primary work at?
DCT and collecting tubules
what is the ammonia buffer system?
- H binds ammonia to form ammonia ion
- source is from aa metabolism from tubular cells
- the ammonia ion is secreted into the lumen
- combines w/ Cl and is excreted
pH of normal urine
- 4.5-8
- depends on the interrelated processes of acid secretion, ammonium ion production and bicarb excretion
possible causes of acidosis
- retention of CO2 via respiratory cause
- excess acids
- strenuous exercise
- starvation
- ketosis
- acid ingestion
- diseased kidneys
- bicarb loss via diarrhea
what is the most important regulator and indicator of respiratory function?
pCO2:
- > 45: acidosis
- <35: alkalosis
metabolic causes of acid-base imbalance
all imbalances not related to CO2, bicarb is the indicator
bicarb
- nl
- alkalosis
- acidosis
- nl: 22-28 mEg/l
- metabolic alkalosis: >28
- metabolic acidosis: >22
how do the lungs compensate for acid-base imbalance
alter CO2 levels for metabolic causes
how to the kidneys compensate for acid-base imbalance?
alter hydrogen and bicarb ion levels for respiratory causes
pH panic levels and their results
- pH <7: CNS depression, coma, death
- pH >7.8: CNS stimulation, tetany, seizure, respiratory arrest
charts
the end of her ppt is many charts repeating respiratory and metabolic compensation
