Lect 16 - Acid-base homeostasis Flashcards
what buffering systems does the body have?
Haemoglobin Bicarbonate Phosphate Proteins Ammonia Misc organic acids
what is pH
-log [H+]
describe the Henderson-Hasselbalch Equation
pH = acid dissociation + log (base/acid).
shows what pH a weak acid will be.
what needs to be balanced if the body is to maintain [H+] homeostasis
H+ production and regeneration of HCO3-
what are the sites of Sites of Acid-base metabolism
Lungs
Kidneys
GI tract
Liver
how is Hb dependant on acid/base chemistry to dissociate oxygen?
(the same process works in reverse to allow loading of oxygen)
Co2 is broken down by enzymes within the cell to produce bicarbonate and a free H ion. this proton can acidify Hb, causing it to change its shape and release any loaded Oxygen.
what shifts a O2-Haemoglobin dissociation curve to the right?
with Increased:
2,3 diPG
Acidosis H+
Temperature
how does the kidney reclaim bicarb?
it uses a sodium hydrogen pump to take protons from the product of water and carbon dioxide: H2C03, and generate bicarb. (HCO3-)
why does the use of the hydrogen sodium pump in reclamation of bicarb not GENERATE new bicarb?
because the CO2 and water used to produce the H2CO3 came from the breakdown of bicarb in the first place - it is a cycle which is driven by the sodium pump.
How does the kidney generate new bicarb?
it unloads hydrogen from H2CO3 using sodium hydrogen pumps onto other molecules such as (HPO4)2- and NH3. The products of these reactions can be excreted, and essentially allows the conversion of CO2 and water into bicarb at the cost of energy and these proton accepting molecules.
what does Mineralocorticoid Action in the Kidney do?
K+ shares a common point of excretion with H+ in the nephron. Mineralocorticoids control the amount of acid in the body by controlling how much K+ or H+ is secreted.
these two tend to both run into problems together - too much H+ means it will be secreted and you can end up with too much K+ too.
how is the GI tract pH maintained?
Acid from the stomach is neutralised by alkali from the pancreas.
where is the dominant site of lactate metabolism?
the Liver. not it is also the only site of urea synthesis
does urea synthesis increase or reduce concentration of H+ in the body?
increase.
therefore urea synthesis is inhibited by acidosis.
if urea synthesis stops, what can you suffer from?
too much NH3
ammonia poisoning
in severe liver failure, what will the lack of urea synthesis do in addition to causing ammonia poisoning?
cause metabolic alkalosis
what happens to NH4+ in the liver?
it binds with oxo-glutarate to form glutamine.
in liver failure, you therefore end up with NH4+ toxicity as no more glutamine can be made.
what are the different types of acid base pathology?
metabolic acidosis/alkalosis
respiratory acidosis/alkalosis
what causes Respiratory Acidosis
1: inadequate ventilation
2: parenchymal lung disease
3: inadequate perfusion
what causes Respiratory Alkalosis
Increased CO2 excretion due to excessive ventilation producing alkalosis
what can cause Metabolic Alkalosis?
Generation of bicarbonate by gastric mucosa
Renal generation of HCO3- in Hypokalaemia
Administration of bicarbonate
what can cause Metabolic alkalosis?
vomiting a lot (loss of acid)
Lactic acidosis - this is a type of shock. (There is not enough oxygen to pay back oxygen debt)
in lack of glucose, what gets metabolised instead?
fats - leads to keto-acidosis.
what conditions are at risk of keto-acidosis?
Diabetes (no glucose)
cancer (cancer uses glucose)
alcoholism (thiamine deficiency stops krebs cycle, leads to lack of glucose)
what are the implications of renal failure on acid base balance?
Increased bicarbonate loss
Reduced NH4+ excretion
NH4+ to liver for urea + H+ synthesis
only fraction of NH4+ derived from glutamine (normal approx 100%)
OVERALL CASUES ACIDOSIS
What are the signs of respiratory acidosis?
high H+
high pCO2
low pO2
What are the signs of respiratory alkalosis?
low H+
low pCO2
high pO2
What are the signs of metabolic acidosis?
high H+
low pCO2
high pO2
What are the signs of metabolic alkalosis?
low H+
high pCO2
low pO2
