Lecture 6 - Carriage of O2 and CO2 in the blood Flashcards
In what 2 forms is oxygen carried in the blood
dissolved in the blood
combined with haemoglobin
What is the relationship between temperature and proportion of gas dissolved?
amount of gas dissolved in solution is proportional to the temperature.
more dissolves at a lower temperature and depends on partial pressure also.
Volume of O2 in blood is
solubility (0.0232) x PO2 (Partial pressure)
Oxygen saturation equation
oxy haemoglobin/ (deoxy +oxy haemoglobin)
Volume of oxygen carrying haemoglobin
Saturation x concentration of haemoglobin (14) X hufners constant (1.39)
What are the different structures of haemoglobin
Primary, secondary, tertiary and quartenary
Primary structure of
141-146 AA’s per chain
Secondary
globular structure
tertiary structure
crevice for haem and O2 binding
Quartenary structure
hb A 4 chains - 2 alpha and 2 beta chains
what does one haemoglobin molecule comprise of
4 globin chains
4 haem groups
4 iron atoms
4 oxygen molecules
What is the molecular basis of o2 binding?
o2 binding occurs in a crevice of haem
when in relaxed form (oxygenated) - o2 can access the binding site
when in a tense form (deoxygenated) - O2 is pushed out
Hb- O2 dissociation curve concept
the tense nature of deoxyhaemoglobin makes it difficult for oxygen to bind and so starts off having a low saturation. as oxygen molecules one by one the saturation shoots up, the oxy hb is relaxed and O2 binding sites become available to acces. this eventually happens until there is maximum saturation and curve levels off.
whys is systemic blood only 97% saturated?
because of a mix in the blood that crosses the pulmonary capillaries
What causes a right shift in haemoglobin dissociation curve?
Carbon dioxide Acid (decrease in pH) Diphospho-glycerate increase Exercise Temperature increase
What shifts the dissociation curve to the left?
an increase in pH
A decrease in temperature
a decrease in DPG
What happens in thalassaemia
absent globin chain
Defective blobin chain
sickle cell disease (HbS)
single amino-acid defect
Defective Fe atom (Fe3+)
Methaemoglobin
Drug induced: metHb does not carry oxygen
Wrong ligand
CO Hb
smoking/house fires
CO blocks O2 binding site
What is a buffer?
a solution that can minimise changes in the Free H+ concentration and therefore in pH
Example of a buffer
usually a weak acid and its base in equilibrium
Blood buffer systems in the body
includes proteins - carboxyl and amino groups at each end of the chain and basic?acidic
bicarbonate, plasma proteins, haemoglobin and phosphate
Normal Blood pH
7.35-7.45, H+ concentration 35-45 nmol-1
in what 3 forms is CO2 carried in the blood?
1. dissolved in the blood temperature dependent at 37 degrees = 3ml CO2 per dl of blood 2. Carbamino compounds - bound to R-NH2 groups on proteins. includes terminal amino group and side chains of lysine and arginine - 4ml 3. as carbonic acid/bicarb = 45 ml CO2
how is carbonic acid formed in the blood and broken down?
formed from co2 and water and is broken down by carbonic anhydrase into H+ ions and HCO3-
How are H+ ions and HCO3- handled from breakdown of carbonic acid buffered?
H + buffered by Hb ions.
HCO3- pumped out of RBC’s in exchange for a chloride ion (Hamburger shift)
What happens in the CO2 dissociation curve and the haldane effect
since deoxygenated blood binds more H+ than oxyhaemoglobin, and forms carbamino groups readily, binding of O2 to haemoglobin reduces its affinity for CO2 which is the haldane effect. consequently, venous blood carries more CO2 than arterial blood.
What is Henderson-Hesselbalch equation
Measure of pH in a biological system, assuming all CO2 is converted into H2CO3 and using law of mass action, equation can be rearranged to:
pH= pK (6.1) + log10 [HCO3-]/[CO2]
Compensatory systems of acid base balance?
Respiratory: blood pH regulates ventilation and so controls PCO2 - rapid response
Renal: excretion of H+ in urine controlled by pH - slow response
What is pK in hendersons eqution?
6.1
What is alkalosis
pH greater than 7.45
What does respiratory alkalosis involve
low PC02, normal HCO3-. Hyperventilation (Anxiety, iatrogenic
What is metabolic alkalosis
normal PCO2, high HCO3-
Loss of H+ - eg. vomitting
abuse of antacid remedies
Normal ranges of P02 and PC02
PO2 - 10 - 13.33
pCO2 - 4.67 -6
HCO3- - 22-26 mmol/L
Respiratory acidosis
less than pH 7.35
High PCO2, high HCO3- - renal compensation
Ventilatory failure
Metabolic acidosis
low HCO3- and low PCO2-
Respiratory compensation
Renal failure, diabetic ketoacidosis, shock, poor tissue perfusion
