Energy production and oxygen consumption

what does O₂ cascade show

• how PO₂ decreases as air moves through respiratory system and into cells

• partial pressure gradient for O₂ between air and mitochondria

steps in the oxygen cascade

1. humidification

2. alveolar gas

3. alveolar-capillary diffusion

4. ventilation-perfusion mismatch and shunt

5. tissue diffusion

6. diffusion within cell

atmospheric PO₂

21kPa

inspired PO₂

19.9kPa

alveolar PO₂

14.9kPa

pulmonary capillary PO₂

14.9 kPa

arterial PO₂

13.6kPa

mean tissue PO₂

5kPa

mitochondrial PO₂

• >0.15kPa

• pasteur’s point→ PO₂ in mitochondria used in cellular respiration

oxygen delivery (ḊO₂)

amount of oxygen leaving the heart in one minute

calculating oxygen delivery

amount of oxygen in blood x amount of blood leaving the heart

normal amount of O₂ in blood for healthy person at rest

19 ml/dL

normal resting cardiac output

5.25 L/min

normal ḊO₂ in health resting individual

1000ml/min

oxygen consumption (VO₂)

amount of oxygen used by the body in one minute

basal metabolic rate

body’s resting rate of energy expenditure

oxygen consumption for healthy, resting individual

200ml/min

measurement of V̇O₂

• direct calorimetry

• indirect calorimetry:

  • arterio-venous CO₂ difference

  • Inspired-expired O₂ volume difference

factors V̇O₂

• age→ peak at 0-2yrs, falls for rest of life

• temperature→ metabolic rate doubles with every 10C

• exercise

physiological responses to anaemia

• increased 2,3-DPG shifts O₂-Hb curve to right

• reduced blood flow to non-essential organs (e.g. skin, bowel)

• increased oxygen extraction from blood

• increase in cardiac output

respiratory exchange ratio

• ratio of carbon dioxide production (V̇CO₂) to oxygen consumption (V̇O₂)

• respiratory quotient=RER at rest

RER for different molecules

• carbohydrates→ 1.0

• fatty acids→ 0.7

• protein→ 0.8

cardio-pulmonary exercise training

• V̇CO₂ plotted against V̇O₂ while subject exercises

• testing used to assess RER pre-surgery→ assesses whether patient can cope with oxygen stress during surgery

cardio-pulmonary exercise test graphs

• V̇O₂ on x-axis

• V̇CO₂ found on y axis

• anaerobic threshold→ hockey-stick bend

glyocolysis

• occurs in cytoplasm

• glucose→ pyruvate or lactate

• no oxygen required

• 2 STP molecules per glucose

TCA cycle

• occurs in mitochondria

• Acetyl CoA from glycolysis to CO₂

• 38 ATP molecules made per glucose

• O₂ required

oxidative phosphorylation

• occurs in mitochondria

• NADH provides H⁺

• H⁺ combines with O₂ to produce water

• ATP produced

causes of cellular hypoxia

• anoxic→ lack of O_2^:

  • leads to respiratory failure

• stagnant→ lack of blood supply:

  • leads to angina

• anaemic→ lack of haemoglobin