Energy production and oxygen consumption

Question 1

What is the equation for partial pressure?

Answer 1

Partial pressure = fractional concentration x pressure

Question 2

What are the steps 1 and 2 of the oxygen cascade?

Answer 2

Step 1 – humidification- Dry air becoming humid (water vapour added, dilutes oxygen)

Step 2 – alveolar gas- CO2 added to reduce the partial pressure of O2 so less CO2 can enter blood

Question 3

What are the steps 3 and 4 of the oxygen cascade?

Answer 3

Step 3 – alveolar-capillary diffusion

Step 4 – ventilation-perfusion mismatch and shunt

Question 4

What are the steps 5 and 6 of the oxygen cascade?

Answer 4

Step 5 – tissue diffusion- We have an excess supply of oxygen (mitochondria only need 0.15kPa for aerobic respiration – mean tissue is PO2 = 5kPa

Step 6 - diffusion within cell

Mitochondria can be far away from the capillary but they have a good reserve.
Big drop as depends where cells live- could be arterial/ venous end where PO2 is lower in venous end

Question 5

Oxygen delivery definition

Answer 5

Amount of oxygen leaving the heart in one minute (D O2) (should be dot on top of D)

Question 6

Oxygen delivery worked out?

Answer 6

1. Amount of oxygen in blood (Oxygen content) = oxygen carried by haemoglobin + dissolved oxygen.
2. Multiplied by amount of blood leaving heart (cardiac output)

Question 7

Oxygen consumption definition

Answer 7

Definition: amount of oxygen used by the body in one minute (V O2)

Question 8

What is the basal metabolic rate?

Answer 8

Basal metabolic rate = VO2 at rest

Question 9

How to measure oxygen consumption

Answer 9

1. Direct calorimetry
2. Indirect calorimetry: measure VO2:
   • Arterio-venous CO2 difference
   • Inspired-expired O2 volume difference

Question 10

Factors affecting VO2

Answer 10

1. Age – peak at age 0-2yrs, then falls for rest of life
2. Temperature – metabolic rate doubles with every 10°C
3. Exercise

Question 11

Anaemia – 4 physiological responses

Answer 11

1. Increased 2,3,-DPG shifts O2-Hb curve to right- gives up more oxygen easily
2. Reduced blood flow to non-essential organs (eg skin, bowel)
3. Increased oxygen extraction from blood
4. Increase in cardiac output

Question 12

Respiratory exchange ratio definition

Answer 12

Definition: the ratio of carbon dioxide production (VCO2) to oxygen consumption (VO2)

Question 13

What is the normal value of respiratory exchange ratio and what is it affected by?

Answer 13

Normal value = 1. Affected by:
• acid base balance
• hyperventilation
• metabolic fuel

Question 14

What is the cardio-pulmonary exercise test?

Answer 14

VCO2 plotted against VO2 while the subject exercises

Common in clinical situation, used to work out the risk of certain surgeries on a patient (change of survival).

Question 15

What are the functions of oxygen?

Answer 15

Glycolysis, tricarboxylic acid cycle and OP

Question 16

What is glycolysis?

Answer 16

• Occurs in cytoplasm
• Glucose to pyruvate or lactate
• No oxygen required
• 2 ATP molecules per glucose

Question 17

What is the TCA cycle?

Answer 17

• Occurs mostly in mitochondria
• Acetyl CoA (from glycolyis) to CO2
• 38 ATP molecules per glucose

Question 18

What is OP?

Answer 18

• Occurs in mitochondria
• NADH provides H+
• H+ combines with O2 to produce water
• ATP produced

Question 19

What is cellular hypoxia?

Answer 19

• Anoxic – lack of oxygen in blood
• Stagnant – lack of blood supply
• Anaemic – lack of haemoglobin