Lecture 10 - pH Flashcards
Body ….. is tightly regulated
H+
What is the normal pH in the body ?
the normal pH in the body is 7.35-7.45
What is the extreme range that is compatible with life in regards to pH?
6.8-8.0
What are some of the acid inputs?
- CO2 production
- metabolic intermediates
- lactic acid
what is a basic input?
-some natural sources
What is the most important kind of pH for the body?
the msot important kind of pH for the body is ICF pH/
In the assessment for pH what do we use ?
we use the ECF pH to make inferences about the ICF conditions.
what is the intracellular pH maintained at and why?
6.8 at 37 degrees celcius because this is the point at which metabolites are all charged and trapped inside the cell.
what is extracellular pH usually at and why?
it is usually higher than ICF pH by 0.5 or 0.6 which is about a 4 fold increase which favours a gradient that reults in the exit of H+ from cells.
What are the lines of defence when it comes to a stable intracellular pH?
- ) buffering
- ) pCO2
- ) acids removal
What is the benefit of buffer systems?
- they are instantaneous
what are buffers?
they are solutions which can resist the changes in pH when acid or alkali is added.
How much of the buffering capacity is in cells?
52%
how much of buffering capacuty is in `RBC?
5 %
how much of buffering capacity is in the extracellular space?
43 %
What are some kinds of buffers?
- ) phosphate
- ) ammonia
- ) proteins
Where is phosphate important as a buffer?
they are important as renal tubular buffers
Where is ammonia important as a buffer?
they are important as renal tubular buffers
Where are proteins important as a buffer?
they are important intracellular and plasma buffers
what is the most important buffer system in the body under normal circumstances?
the most importnat buffer system in the body udner normal circumstances is the bicarbonate buffer system
what is the bicarboante buffer system physiollogically regulated by?
- the lungs (PCO2)
- the kidneys (HCO3-)
What is the bicarboante buffer system catalysed by?
It is catalysed by carbonic anhydrase
Equation for the bicarbonate buffer system?
Changes in ……. or …… alter ECF pH
HCO3- or PCO2
In relation to acid base regulation what are the two functions of the kidneys?
- ) reabsorption of HCO3-
- ) excretion of H+
Why is HCO3- reabsorption vital?
it is vital due to large filtered load
How is acid excretion and bicarbonate reabsorption achieved?
it is achieved by tubular H+ secretion
What are some of the urinary buffers?
phospahte and ammonium
How much HCO3 is reabsorbed in the proximal tubule?
80 %
How much HCO3 is reabsorbed in the thick ascending limb of the loop of henle?
5 %
How much HCO3 is reabsorbed in the distal tubule?
5 %
Reabsorption is ……
transcellular
Reabsorption involves … secretion
H+
What are the steps for reabsorption of HCO3 in the proximal tubule?
- powered by the Na+ gradient
- Apical H+ secretion by the Na-H-antiporter
- secreted H+ binds to filtered HCO3-
- Complex dissociates to CO2 and H2O
- CO2 and H2O reassociate inside of cell
- Reformed HCO3- transported into interstitium
What are the steps for reabnsorption of HCO3 in the distal tubule?
- not powered by the Na+ gradient
- powered by apical H+ pumps - K-H-ATPase and H-ATPase
- Secreted H+ binds to filtered HCO3
- Complex dissociates to CO2 and H2O
- CO2 and H2O re associate inside cell
- Reformed HCO3 transported into interstitium
What are the steps for H+ secretion and phosphate in the distal tubule?
- Secreted H+ binds to the phosphate and is not filtered as HCO3
- Bound H+ is excreted in the urine
- H+ secretion results in HCO3 formation inside the tubular cell
- the new HCO3 is transported into the interstitium
Explain the steps of H+ secretion with ammonium?
- ammonium NH4 is produced by H binding to ammonia NH3
- The proximal tubule creates ammonia only if it is needed, when we need to get rid of acid
- NH3 and HCO3 are produced from the amino acid glutamine
- the new HCO3 is transported into the interstitium
- NH3 diffused into tubular lumen and binds to a secreted H+
acidosis, metabolic vs respiratory ?
- metabolic - decreased HCO3
- respiratory - increased pCO2
alkalosis, metabolic vs respiratory ?
- metabolic - increased HCO3
- respiratory - decreased PCO2
How does the kidney comopensate for acidosis?
intercalated cells will secrete more acid into the tubular lumen and make new bicarbonate and raise the pH back to its set point
How does the kidney compensate for alkalosis?
proximal convoluted cells will not reabsorb filtered bicarbonate and will elimante it formt he body to lower the pH back to the normal.
