Week 11 - Blood Gas Transport & Control Of Breathing

Question 1

What factors affect rate of diffusion at the alveoli

Answer 1

• diffusion surface area
• diffusion distance
• concentration gradient
• solubility of gases
• coordinated blood flow and airflow

Question 2

What is Dalton’s law of partial pressure?

Answer 2

“The total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture”

Question 3

What is partial pressure?

Answer 3

The pressure exerted by each individual gas (directly proportional to its % in the total gas mixture)

Question 4

What is Henry’s law?

Answer 4

“ the amount of gas that dissolves in water is determined by its solubility in water + its partial pressure in air”

• this means that, at equilibrium, the amount of dissolved gas in solution is proportional to the partial pressure of the gas

Question 5

Oxygen is not very soluble in blood - much less soluble than CO2 - how does it get around this problem?

Answer 5

By binding to haemoglobin to transport it around the bloodstream - 97% of O2 in blood is transported in combo with Hb

Question 6

What 4 factors control the binding of O2 to Hb in the blood?

Answer 6

• PO2 in the blood
• Blood pH
• temperature
• state of O2 binding of the Hb molecule

Question 7

How does increasing the pO2 affect binding to Hb?

Answer 7

The higher the pO2, the more O2 combines with Hb

Question 8

How does decreasing the pH affect the binding of O2 to Hb?

Answer 8

• decreasing pH shifts oxygen dissociation curve to the right - Bohr shift
• allows for better unloading of oxygen

Question 9

How does temperature affect the binding of O2 to Hb?

Answer 9

• increasing the temperature increases the dissociation of Hb from O2
• allows for more efficient unloading

Question 10

What are some alternative forms of Hb?

Answer 10

• carboxyhaemoglobin - CO binds much tighter to Hb than O2 (200x tighter) - dramatically reduces ability of O2 to bind to Hb
• foetal haemoglobin - higher affinity for O2 - important for transferring O2 across placenta

Question 11

What are the 3 ways in which CO2 is transported in bloodstream?

Answer 11

• convert to carbonic acid, then transport in plasma as HCO3- ion (bicarbonate ion)
• bind to Hb - form carbaminohaemoglobin
• dissolve in plasma

Question 12

How does Hb buffering work?

Answer 12

• Whenever CO2 is converted to HCO3-, it yields an H+ ion
• deoxygenated Hb can consume or release H+ ions to minimise pH changes in blood

Question 13

Demonstrate the Haldane effect in the lungs

Answer 13

• Hb is oxygenated
• this means it has a lower affinity for H+ ions
• decreases its buffering power
• therefore H+ ions are released

Aids the unloading of CO2 in the lungs

Question 14

Demonstrate the Haldane effect in the tissues

Answer 14

• Hb is deoxygenated
• therefore has a higher affinity for H+ ions
• increases buffering power
• more H+ ions are uptaken

Aids CO2 transport from tissues

Question 15

What are the types of sensors that can detect changes in breathing?

Answer 15

Central chemoreceptors - medulla
- detect hypercapnia (too much CO2)
- detect pH changes
Peripheral chemoreceptors - aortic + carotid body
- detect hypercapnia and hypoxia
Mechanoreceptors - lung receptors
- respond to stretch
- has slowly and rapidly adapting receptors

Question 16

What factors influence rate & depth of breathing?

Answer 16

• exercise (changing body demands in general)
• altitude - acute mountain sickness
• disease
• changing levels of CO2, H+, or O2

Question 17

How do central chemoreceptors aid in regulating breathing?

Answer 17

• increase in pCO2 = decrease in pH
• detected by chemoreceptors
• increase ventilation
• decrease pCO2

Question 18

What are some features of peripheral chemoreceptors?

Answer 18

• detect changes in pO2, pCO2 & pH
• Innervated by carotid sinus nerve (CSN) - connects to glossopharyngeal nerve
• vital for response to change in pO2, as this has no effect on central chemoreceptors

Question 19

What is respiratory acidosis?

Answer 19

• blood pH <7.35 (becomes more acidic)
• lots of H2CO3 -> H+ + HCO3- occurring

Happens as a result of CO2 increasing

Question 20

What is respiratory alkalosis?

Answer 20

• decrease in H+ ions
• pH increases

Occurs as a result of pCO2 decreasing

Question 21

What if pO2 changes?

Answer 21

• if pO2 goes up, free radicals are generated which leads to coma and death
• if pO2 goes down, peripheral chemoreceptors increase breathing rate

Question 22

What are the 3 types of mechanoreceptors in lung tissue + airways?

Answer 22

• slowly adapting (hering-Breuer reflex)
• rapidly adapting (cough reflex)
• c-fibre endings (defence mechanism)

Question 23

What are the 3 reflexes of the lung tissue + airways?

Answer 23

• hering-breuer reflex - prevents overinflation of lungs
• cough reflex - prevents inhalation of noxious substances
• defence mechanism - response to anything that irritates the airways (e.g. sneeze)

Question 24

What are some examples of central controller for breathing?

Answer 24

rhythmicity centre (medulla)
- controls automatic breathing

Pneumotaxic and apneustic centres (pons)
- modify firing pattern of medullary centres

Question 25

What are some features of the rhythmicity centre?

Answer 25

• sets pace for respiratory movements
• Dorsal Respiratory Group (DRG) - inspiratory centre
• Ventral Respiratory Group (VRG) - expiratory centre

Question 26

What are some features of the Pneuomotaxic and Apneustic centres?

Answer 26

• to regulate respiratory rate & depth of respiration
• AP centre - promote inspiration
• PN centre - inhibit AP centre, stop inhalation, promote exhalation

Question 27

How is ventilation rate calculated?

Answer 27

Ventilation rate = tidal volume x respiratory rate