Diffusion and Carriage of Gases pt2

Question 1

What is the Hb concentration in normal blood?

in g.l¯¹

Answer 1

150g.l¯¹

Question 2

How much O₂ can 1 gram of Hb combine with?

in ml

Answer 2

1.34ml O₂

Question 3

What is the oxygen capacity of normal blood?

Answer 3

200 ml.l¯¹

Question 4

What is the O₂ content of pulmonary venous blood?

In ml.l¯¹ and %saturation

Answer 4

200 ml.l¯¹

= nearly 100% saturation

Question 5

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)

Answer 5

150ml.l¯¹

or 75% saturation

Question 6

What is the effect of Anaemia on:

• Inspired alveolar & arterial PO₂
• O₂ Capacity of arterial blood
• Arterial O₂ saturation of Hb

Answer 6

• O₂ capacity is reduced
• O₂ content is reduced
• O₂ saturation is normal

Also Anaemia is having a lower than normal Hb concentration.

Question 7

small reminder

Answer 7

During revision review the LC at 36-40mins. Covers more detail on O₂ dissociation curve that might be handy.

Question 8

When is left shift of the dissociation curve useful and where in the body does it occur?

Also what causes this left shift?

Answer 8

In the alveoli, useful because increases the affinity to Hb.
(Caused by increase in PH and decrease in PCO₂, temperature, 2,3 DPG)

Question 9

There are many different reasons for a defect in Hb production leading to anaemia, name 1.

Answer 9

Mutations in the gene or in the production or loss of RBC.

Question 10

What are the effects of CO poisoning?

Answer 10

• 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.

Question 11

What’s the differences between fetal and adult Hb?

And what are the advantages of them?

Answer 11

• 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

Question 12

What is DPG in the blood

Answer 12

An organic phosphate in red blood cells that alters the affinity of haemoglobin for oxygen

Question 13

What is cyanosis?

How does it occur?

Answer 13

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.

Question 14

What are the 2 types of cyanosis that can occur?

Answer 14

Peripheral cyanosis

Central cyanosis

Question 15

What occurs in peripheral cyanosis?

Answer 15

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.

Question 16

What can cause the reduced blood flow that leads to peripheral cyanosis?

Answer 16

• Cardiovascular shock
• Low temperature
• Reduced cardiac output
• Poor arterial supply

(ALSO: under these conditions respiration and arterial O₂ content is usually normal)

Question 17

What occurs in central cyanosis?

Answer 17

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).

Question 18

When does central cyanosis occur?

Answer 18

If arterial blood contains > 1.5-2 g.dl¯¹ of de-oxyHb. Occurs when O₂ saturation is <85% if Hb is normal

Question 19

How is CO₂ carried?

3ways

Answer 19

• 60% of the time its carried as HCO₃ (bicarbonate) = (in plasma and RBC)
• 30% Bound to proteins such as Hb = CarbaminoHb
• 10% dissolved.

-

Question 20

What is the proportion of CO₂ that is dissolved in plasma?

Answer 20

10%?

Question 21

What is the amount of CO₂ carried per dl blood?

Answer 21

2.74ml.dl¯¹

Question 22

How is CO₂ unloaded in the lungs?

1 - CO₂ dissolved in blood plasma

2 - CO₂ reversibly bound as carbamino compounds

3 - HCO₃ from plasma

Answer 22

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.

Question 23

What is the Haldane effect?

And what causes this?

Answer 23

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.

2. Hb binds to H+ better when deoxygenated this favours formation of HCO₃, increasing CO₂ carriage.

Question 24

What is the difference between the O₂ and CO₂ dissociation curve?

Answer 24

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)

Question 25

At rest how many ml of CO₂ is produced by the tissues? (per 100ml of blood passing through)

Answer 25

4ml

Question 26

What happens to PH when the amount of HCO₃ increases?

Answer 26

PH increases

due to the Henderson-Hasselbach equation

Question 27

What happens to PH when CO₂ increases?

Answer 27

PH decreases

due to the Henderson-Hasselbach equation

Question 28

What is the main determinate of PH?

Answer 28

the following ratio CO₂:HCO₃

Question 29

What happens if metabolic rate is normal, but ventilation increases?
( just breathing faster at rest )

Answer 29

CO₂ will be blown off quicker than it can be produced, PCO₂ in alveoli and arterial blood will decrease, PH will increase
= Respiratory Alkalosis.

Question 30

What happens if metabolic rate is normal, but ventilation decreases?

Answer 30

Decreasing ventilation will increase PCO₂ levels, PH fall = Respiratory Acidosis

Question 31

What is normal O₂ consumption at rest?

Answer 31

250 ml.min¯¹

Question 32

Reminder.

Answer 32

Watch LC at 1:11:10 onwards to learn how to calculate O₂ and CO₂ consumption.

Question 33

Define Hyperventilation.

Answer 33

Over-Ventilation in proportion to metabolism leads to a lowering of arterial PCO₂ below normal values

Question 34

Define Hypoventilation.

Answer 34

Under-ventilation in proportion to metabolism results in higher arterial PCO₂ levels.

Question 35

What does Hyperventilation lead to?

Answer 35

Hypocapnia, low arterial PCO₂ (below 5.3kPa), low PCO₂, reduce (H+) and causes Respiratory alkalosis

Question 36

What are the possible causes of Hyperventilation?

Answer 36

Anxiety, pain, excessive mechanical ventilation.

Diseases contributing yo metabolic acidosis (renal failure, diabetes)

Question 37

What are the consequences of Hyperventilation?

• Low PaCO₂
• Alkalosis

Answer 37

Low PaCO₂: Cerebral vasoconstriction leading to, cerebral hypoxia resulting in dizziness and visual disturbances.

Alkalosis: Reduces plasma free (Ca²+) (more binds to proteins) which, increases excitability of cells (VGCC open at lower threshold potentials) resulting in, Disturbed sensation e.g. pins and needles and unwanted tetanic muscle contractions (spasms, typically in fingers)

Question 38

What does hypoventilation lead to?

Answer 38

Hypercapnia = high arterial PCO₂ (higher than 6kPa) (as well as to low arterial PCO₂)
High PCO₂ increases (H+) and causes a respiratory acidosis.

Question 39

What are the possible causes of Hypoventilation?

Answer 39

• Head injury impairing respiration.
• Anaesthetics.
• Drugs.
• Chronic lung disease.

Question 40

What are the consequences of increases PCO₂ due to hypoventilation?

Answer 40

• Increasing arterial PCO₂ causes peripheral vasodilation, flushed skin, full pulse, extra systoles
• Very high PCO₂ (above 10kPa) depresses CNS function causing confusion, drowsiness, coma and death.

Question 41

reminder

Answer 41

look at final slides for all the normal values for gas kPa in airways and blood.
Must know them!!!