Respiratory System - Gas Transport and Breathing Control

Question 1

oxygen transport in blood

Answer 1

1. physically dissolved (2%)
2. chemically bound to hemoglobin (98%)
   - 02 is much less soluble in blood than CO2
   - at PO2 of 100 mmHg: 100 mL blood contains 20.5 mL O2

Question 2

oxygen content

in arterial vs venous blood

Answer 2

• arterial blood: CaO2 = 20 ml O2 / 100 ml of blood
• venous blood: CvO2 = 15 ml O2 / 100 ml blood
  –> 5 ml O2/100 ml blood diffuses into tissues every time blood circulates through systemic circulation

Question 3

pulse oximeter

+ range of SaO2

Answer 3

• non invasive method to estimate oxygen saturation (SaO2)
• shines two beams of light through translucent part of the body with two different wavelengths to be absorbed by oxygenated and non oxygenated Hb
• normal range: 95-100%

Question 4

oxyhemoglobin curve and shifting

Answer 4

• left shift: curve is steeper, hemoglobin holds onto oxygen
• right shift: hemoglobin giving away more oxygen and doesn’t want it as much
  –> exercise, 23BPG, and hypothermia all maximize the giving of oxygen to muscles and reduces O2 affinity of Hb RIGHT SHIFT
  –> fetal Hb is LEFT SHIFTED compared to maternal Hb, because it has lower 23BPG, so oxygen delivery from maternal to fetal blood is favoured

Question 5

anemia and carbon monoxide

Answer 5

anemia: not enough Hb in RBC, so can’t carry as much Oxygen, so increased PO2 does not relate to increased O2 content as it should
CO: Hb affinity for CO is 250 times greater than O2

Question 6

CO2 transport in blood

Answer 6

1. physically dissolved (7%)
2. dissolved as bicarbonate ion HCO3- (70%)
3. bound to Hb (23%)

Question 6

CO2 content in blood

Answer 6

content of arterial blood:
CaCO2 = 48 ml/100ml
CvCO2 = 52 ml/100ml
–> 4ml/100ml blood diffuses out of tissues and is delivered to lungs to be exhaled

Question 7

carbonic anhydrase

Answer 7

• enzyme in transport of CO2 in blood
• resides in RBC
• speeds up formation of carbonic acid from CO2 and H2O to sink CO2 from tissue to RBC

Question 8

Haldane effect

Answer 8

CO2 dissociation curve is influence by the oxygenation state of Hb –> increased PO2 lowers curve

Question 9

where/how is breathing established

Answer 9

• in the CNS, initiated in the medulla
• modified by chemoreceptors mechanoreceptors in lungs and other signals

Question 10

medullary respiratory groups

Answer 10

Dorsal respiratory group (DRG)
- inspiratory neurons driving inspiratory muscles
- receive input from peripheral chemo and mechano- receptors

Ventral respiratory group (VRG)
- expiratory neurons
- active during active expiration

Question 11

sending information from the medulla to respiratory muscles

what nerves signal to what muscles?

Answer 11

• phrenic nerves in neck supply motor output to diaphragms: C3,4,5 keep the diaphragm alive
• intercostal nerves exiting thoracic and lumbar spine supply motor output to intercostal and abdominal muscles
• cranial nerves supply motor output to upper airway dilator muscles

Question 12

feedback and feedforward

Answer 12

movement of chest walls –> mechanoreceptors –> medulla
arterial PCO2, PO2, and pH –> chemoreceptors –> medulla

Question 13

Hering Breuer Reflex

Answer 13

• reflex to prevent over inflation of lungs
• mediated by vagus nerve
• stretch receptors in the smooth muscle of the airways respond to stretching of lung during inflation, allowing for expiration

Question 14

central chemoreceptors

Answer 14

• do not sense oxygen
• sense CO2

Question 15

peripheral chemoreceptors

Answer 15

• sense O2
• sense decrease in P1O2 levels below 60 mmHg
• low PaO2 = hyperventilation which lowers PaCO2 below normal resting levels (hypocapnia) and raises PaO2 above normal resting levels (hyperoxia)
• metabolic alkalosis leads to hypoventilation

Question 16

Ondine’s curse

Answer 16

• aka congenital central hypoventilation syndrome
• you sleep, you die
• low/absent ventilatory response to elevated CO2 and low O2