Pulmonary Flood Flow, Gas Exchange and Transport 2 Flashcards
What volume of oxygen is transported in solution in the plasma?
3ml
The presence of haemoglobin increases the carrying capacity of oxygen to what value?
200ml/L
How is the bulk of CO2 carried in the blood?
Various forms of solution in plasma and RBC
What is the O2 demand of resting tissues?
250ml/min
What percentage of arterial O2 is extracted by peripheral tissues at rest?
25%
What form of Haemoglobin makes up 92% of all types found in an RBC?
HbA
Describe the composition of the 8% of other haemoglobin types
- HbA2 (delta chain replaces beta)
- Glycosylated Hb (HbA1, HbA1b, HbA1c)
What factor is the major determinant of the degree to which Hb is saturated with oxygen?
Partial pressure of oxygen
How long does it take to saturate an Hb molecule with oxygen? How does this compare to its overall exposure time?
0.25s to saturate
Overall exposure is 0.75s
Plenty of time
List three factors which decrease haemoglobin oxygen affinity
- Decrease in pH
- Increase in temp.
- Increase is PCO2
Where to the conditions that lead to a decrease in haemoglobin oxygen affinity exist?
Locally in actively metabolising tissues (e.g. muscles) which helps to unload oxygen
What conditions cause a rise in haemoglobin oxygen affinity?
- Increase in pH
- Fall in PCO2
- Drop in temp.
What molecule can cause haemoglobin oxygen affinity to decrease?
2, 3-diphosphoglycerate (2, 3-DPG)
Where is 2, 3-DPG synthesised?
Erythrocytes
Where does 2, 3-DPG activity increase?
Associated with areas of inadequate oxygen supply e.g heart or lung disease, living at high altitude etc.
What is the overall effect of 2, 3-DPG?
Helps maintain oxygen release in the tissues
What occurs to haemoglobin in the presence of carbon monoxide (CO)?
Binds to haemoglobin forming carboxyhemoglobin with an affinity much higher than oxygen
What partial pressure of CO is required to cause progressive carboxyhemoglobin formation?
0.4mmHg
Why is the respiration rate of a person suffering from CO poisoning normal?
PaCO2 remains normal
What are the five main types of hypoxia?
Hypoxic Anaemic Ischaemic (stagnant) Histotoxic Metabolic
What is the most common type of hypoxia?
Hypoxic hypoxia - reduction in oxygen diffusion either due to decreased atmospheric PO2 or tissue pathology
What is the cause of anaemic hypoxia?
Reduction in O2 carrying capacity due to anaemia
What is ischaemic (stagnant) hypoxia?
Heart disease results in poor pumping of blood
What is histotoxic hypoxia?
Poisoning prevents cells using oxygen
Give an example of a cause of histotoxic hypoxia
CO or cyanide
What is metabolic hypoxia?
Oxygen delivery to the tissues does not reach increased oxygen demand by cells
What proportion of CO2 remains dissolved in plasma and erythrocytes?
7%
23% of CO2 combines with deoxyhaemoglobin to form what compounds?
Carbamino compounds
What is the compound which sequesters most of the CO2 excreted by cells?
70% converted to carbonic acid
Describe the fate of carbonic acid in the blood
Dissociates into H+ and bicarbonate ions - the bicarb. is transported into the plasma during the Hamburger Phenomenon to form a buffer and H+ binds to deoxyhaemoglobin to to avoid fucking the pH
Why is monitoring plasma [CO2] very important?
It is capable of changing the ECF pH
What physiological processes monitor plasma [CO2]?
Hypo/Hyperventilation
How does hypoventilation alter plasma [CO2]?
Causes CO2 retardation - plasma [H+] increases - leads to respiratory acidosis
How does hyperventilation alter plasma [CO2]?
Blows off more CO2, decreases plasma [H+] - leads to respiratory alkalosis
