Diffusion and Carriage of Gases pt2 Flashcards
What is the Hb concentration in normal blood?
in g.l¯¹
150g.l¯¹
How much O₂ can 1 gram of Hb combine with?
in ml
1.34ml O₂
What is the oxygen capacity of normal blood?
200 ml.l¯¹
What is the O₂ content of pulmonary venous blood?
In ml.l¯¹ and %saturation
200 ml.l¯¹
= nearly 100% saturation
At rest wheat is the average O₂ content of the blood returning from the tissues to the right heart aka mixed venous blood?
(in ml.l¯¹ or % saturation)
150ml.l¯¹
or 75% saturation
What is the effect of Anaemia on:
- Inspired alveolar & arterial PO₂
- O₂ Capacity of arterial blood
- Arterial O₂ saturation of Hb
- O₂ capacity is reduced
- O₂ content is reduced
- O₂ saturation is normal
Also Anaemia is having a lower than normal Hb concentration.
small reminder
During revision review the LC at 36-40mins. Covers more detail on O₂ dissociation curve that might be handy.
When is left shift of the dissociation curve useful and where in the body does it occur?
Also what causes this left shift?
In the alveoli, useful because increases the affinity to Hb.
(Caused by increase in PH and decrease in PCO₂, temperature, 2,3 DPG)
There are many different reasons for a defect in Hb production leading to anaemia, name 1.
Mutations in the gene or in the production or loss of RBC.
What are the effects of CO poisoning?
- Reduces the amount of O₂ bound to Hb.
- Shifts O₂ to the left (which increases the affinity of O₂ for the remaining binding sites) this is bad because it reduces the unloading of O₂ in the tissues.
- Can lead to death.
What’s the differences between fetal and adult Hb?
And what are the advantages of them?
- Has 2 α and 2 γ globin subunits
- The different globin increases the affinity of haem group for O₂
- Also binds to less DPG
- This is good because it favours O₂ moving from the mothers blood to the fetal blood across the placenta
What is DPG in the blood
An organic phosphate in red blood cells that alters the affinity of haemoglobin for oxygen
What is cyanosis?
How does it occur?
When O₂ supply to the tissues is deficient, content of de-oxyHb in tissue capillaries increases due to hypoxia.
De-oxyHb has a blue(ish) tinge this causes discolouration of tissues = CYANOSIS.
What are the 2 types of cyanosis that can occur?
Peripheral cyanosis
Central cyanosis
What occurs in peripheral cyanosis?
Hypoxia but also;
- Reduced blood flow to a region(s) resulting in hypoxic tissue causing a bluish grey tinge to appear in extremities such as hands and feet.
What can cause the reduced blood flow that leads to peripheral cyanosis?
- Cardiovascular shock
- Low temperature
- Reduced cardiac output
- Poor arterial supply
(ALSO: under these conditions respiration and arterial O₂ content is usually normal)
What occurs in central cyanosis?
There is arterial hypoxemia (reduction in O₂ content) - buccal mucosa and lips are best sites to spot this.
- Can also be seen on ear lobes, and the conjunctiva (lower eyelid).
When does central cyanosis occur?
If arterial blood contains > 1.5-2 g.dl¯¹ of de-oxyHb. Occurs when O₂ saturation is <85% if Hb is normal
How is CO₂ carried?
3ways
- 60% of the time its carried as HCO₃ (bicarbonate) = (in plasma and RBC)
- 30% Bound to proteins such as Hb = CarbaminoHb
- 10% dissolved.
-
What is the proportion of CO₂ that is dissolved in plasma?
10%?
What is the amount of CO₂ carried per dl blood?
2.74ml.dl¯¹
How is CO₂ unloaded in the lungs?
1 - CO₂ dissolved in blood plasma
2 - CO₂ reversibly bound as carbamino compounds
3 - HCO₃ from plasma
CO₂ dissolved in the blood plasma diffuses down the partial pressure gradient into the alveoli very rapidly.
CO₂ reversibly bound as carbamino compounds to Hb comes off, assisted by oxygenation of Hb, and diffuses into the alveoli.
HCO₃ from plasma is taken back into RBC, combines with H+ which comes off as Hb as O₂ binds to Hb, forms carbonic acid.
Carbonic acid then dissociates into CO₂ and H₂O via carbonic anhydrase, with CO₂ diffusing into the alveoli.
What is the Haldane effect?
And what causes this?
At any given PCO₂ the quantity of CO₂ is greater in partially deoxygenated blood (venous) than in oxygenated blood ( arterial).
This is because;
1. Hb forms carbamino compounds more readily when deoxygenated so can carry more CO₂.
- Hb binds to H+ better when deoxygenated this favours formation of HCO₃, increasing CO₂ carriage.
What is the difference between the O₂ and CO₂ dissociation curve?
CO₂:
- not sigmoidal in shape
- no plateau
- Approx. linear over physiological range
(line on graph is like a clock at 2 o’clock but slightly curved)
