Acid-Base and Blood Gasses Flashcards
with less CO2 partial pressure what happens to ventilation rate?
decreases
what metabolic processes produce significant amounts of hydrogen?
- digestion of foods
- metabolism of drugs
- errors within metabolism
what organ is responsible for excreting hydrogen ions through the urine?
the kidneys
What two energy substrates produce hydrogen ions when oxidised incompletely?
lactic acid and the metabolism of fats (triacylglycerols)
what metabolic reaction uses up hydrogen ions?
oxidative metabolism of ketones
how is carbon dioxide produced?
as a product of oxidative metabolism
how is CO2 excreted?
by ventilation (expired air)
What equation shows how CO2 contributes to H+ production?
CO2+H2O H2CO3
what is normal body extracellular fluid pH maintained between?
7.35-7.46
what is the equation of the body’s buffering system?
H+ + HCO3 H2CO3
how does renal filtration of Na+ and HCO3- work?
- Na+ and HCO3- are filtered in the glomerulus
- renal tubule cells secrete H+ in exchange for Na+.
- CO2 is formed by the reaction of HCO3-with H+ and diffuses into the tubule.
- CO2 coverted back into HCO3 in the renal tubule cell.
- Na+/HCO3- symporter carry Na+ and HCO3- across basal membrane of tubule cell
what two things are secreted and excreted from the kidneys after filtration?
NH4+ and H+
what is metabolized to release NH4+ and HCO3- in the kidneys?
glutamine
how does the phosphate buffer system work in the renal tubule?
- H2O and CO2 combine to form H2CO3.
- H2CO3 breaks down into HCO3- nd H+
- H+ leaves the renal tubule and enters the tubular lumen
- it binds to HPO4(2-) in the lumen to form H2PO4-
- as H+ leaves, Na+ enters the cell
- Na+ leaves via ATPase transporter which pumps K+ in at the same time.
how does the protein buffer system work?
(at the tissues)
1. CO2 and H2O form HCO3- and H+ which binds with Hb from HbO2 dissociating into O2 and Hb.
2. HCO3- leaves the red blood cell and Cl- enters.
3. CO2 and Hb combine to form HbCO2
(then the reverse of all the reactions take place at the lungs-slide 13 for more details)
how does the carbonic acid-bicarbonate buffer system work?
- Na+ - H+ antiport secretes H+
- H+ combines with HCO3- forming CO2 and H2O
- CO2 diffuses into the cell and combines with H2O forming HCO- and H+
- H+ is secreted and excreted
- HCO3- is reabsorbed
- glutamine is metabolised into ammonium ions and HCO3-
- NH4+ is secreted and excreted
- HCO3- is reabsorbed
two buffer systems that occur in the intracellular fluid (ICF)
- phosphate buffer system
2. protein buffer systems
two buffer systems that occur in the ECF?
- carbonic acid-bicarbonate buffer system.
2. protein buffer systems
What are the three types of protein buffer systems?
- haemoglobin buffer systems (RBCs)
- amino acid buffers (all proteins)
- Plasma protein buffers
what equation links [H+], PCO2 and [HCO3-]?
[H+] = k (PCO2/[HCO3-])
how do you calculate anion gap?
(Na+K) - (Cl+HCO3)
what is acidosis and alkadosis?
acidosis - high H+ conc
alkalosis - low H+ conc
four components that influence non-respiratory acidosis?
- H+ generation
- Buffering
- Compensation
- Correction
what causes non-respiratory acidosis?
- increased [H+]
- Decreased excretion
- Decreased [HCO3-]
what causes increased H+ concentration?
- diabetic ketoacidosis due to lack of insulin so fatty acids are metabolised. Excess glucose causes dehydration
- aspirin poisoning causes acidosis as well.
how does decreased excretion of H+ cause acidosis?
- decreased GFR reduces sodium ion filtration, hence less H+ can be excreted as less Na+ to exchange with. So H+ ions accumulate.
- decreased GFR also means reduced phosphates hence mechanism for H+ ion clearance is compromised.
what happens when H+ concentration rises?
- it is buffered by the bicarbonate whose conc falls as it makes carbonic acid (H2CO3).
- carbonic acid dissociates producing carbon dioxide which is lost on expiration.
- non-respiratory acidosis develops
- respiratory centre is stimulated causing hyperventilation to remove more CO2
- producing a compensatory alkalosis
how is non-respiratory acidosis treated?
- removal of the underlying problem.
2. bicarbonates used with care in patients with pH <7
what causes respiratory acidosis?
- airway obstruction
- depression of respiratory centre
- neuromuscular disease
- Pulmonary disease
- Extra pulmonary thoracic disease
what are all respiratory acidosis characterised by?
increase in PCO2
although H+ concentration increases in respiratory acidosis, why does the pH still fall?
because the HCO3- conc increases also which would then neutralise the H+
what is hypoxemia?
low oxygen levels
what is hypercapnia?
high CO2 levels
what is non-respiratory alkalosis?
an increase in bicarbonate levels
what causes non-respiratory alkalosis?
- excess alkali administration
2. loss of free hydrogen
what happens during respiratory alkalosis?
PCO2 increases in order to increase H+ concentration.
how do we manage respiratory alkalosis?
- infusion of normal saline solution
- taking potassium supplements
what is respiratory alkalosis?
a decrease in PCO2 levels
what causes respiratory alkalosis?
- hypoxia - increased CO2 loss
2. increased drive: infections, hyperventilation, cerebral malignancy etc.
how is respiratory alkalosis treated?
- remove underlying cause
2. if hyperventilation in the cause, re-breathe CO2 in
