Control of Breathing

Question 1

What respiratory control centres of the brainstem control breathing?

Answer 1

• Inspiratory centre (medulla)
• Expiratory centre (medulla)
• Pneumotaxic centre (pons)
• Apneuristic centre (pons)

Question 2

What (3) factors control breathing?

Answer 2

• Cerebral cortex: can exert voluntary control over breathing as well as centres involved in emotion and pain
• Peripheral chemoreceptors (in vascular system) & central chemoreceptors (in brain): detect changes to O2 and CO2
• Stretch receptors (in lungs) & activity receptors (in muscles and joints)

Question 3

What are (4) airway characteristics?

Answer 3

• Rich blood supply
• Large surface area
• Tissues have intrinsic elastic properties
• Fluid lubrication (ensure rapid diffusion + counteract physical forces like surface tension)

Question 3

Pontine Centres.

Answer 3

influence output from the medullary respiratory centres

Question 3

Medullary Respiration Centres.

Answer 3

provide output to respiratory muscles

Question 4

How does high levels of CO2 affect the body?

Answer 4

changes the body’s pH = toxic

Question 4

What is partial pressure measured in?

Answer 4

kilopascals (kPa) or millimetres of mercury (mmHg)

E.g.: (0.133kPa = 1mmHg)

Question 5

What is PaPO2?

Answer 5

Partial pressure of oxygen dissolved in plasma of arterial blood

Question 6

What is PO2/PCO2?

Answer 6

Partial pressure of oxygen / carbon dioxide in the air

Question 7

What is PvCO2?

Answer 7

Partial pressure of carbon dioxide dissolved in plasma of venous blood

Question 8

What is partial pressure?

Answer 8

the concentration of each gas in the body

Question 9

What are (3) factors affecting gas solubility?

Answer 9

• Partial pressure of gas
• Partial pressure of gas in liquid phase
• Solubility of a gas

Question 10

How does partial pressure of gas affect gas solubility?

Answer 10

The greater the partial pressure the faster it will dissolve into the liquid phase

Question 11

How does partial pressure of gas in liquid phase affect gas solubility?

Answer 11

If the partial pressure of a gas in the liquid phase becomes higher than its partial pressure in the gas phase, some of the dissolved gas will re-enter the gas phase

Question 12

What (3) key factors will influence gaseous exchange?

Answer 12

• Gas partial pressure and gas solubility
• Matching of alveolar ventilation with pulmonary blood perfusion
• Structural characteristics of the respiratory membrane

Question 13

What is ventilation (V)?

Answer 13

volume of air entering the alveoli

Question 14

What is perfusion (Q)?

Answer 14

volume of blood flowing through the lungs

Question 15

What is the ventilation/perfusion mismatch?

Answer 15

inadequacy of V or Q will significantly impact the oxygenation of the blood and the removal of CO₂

Question 16

When side lying should the patient’s ‘bad’ lung be faced up or down (in terms of VQ)?

Answer 16

Up (so not lying on the bad side)

Question 17

Where (in a healthy adult) is self-ventilating lung ventilation optimal?

Answer 17

lower 1/3 of lung (dependent region)

Question 18

Which regions of the lung have a greater initial volume?

Answer 18

non-dependent (upper) lung

Question 19

Which regions of the lung are partially expanded?

Answer 19

dependent (lower) lung

Question 20

Why are the dependent (lower) lung regions partially expanded?

Answer 20

so they still have the capacity of further expansion + volume change

Question 21

What is perfusion influenced & affected by?

Answer 21

• Gravity
• The interaction of alveolar, arterial + tissue pressure

Question 22

What is perfusion?

Answer 22

the passage of blood, a blood substitute, or other fluid through the blood vessels or other natural channels in an organ or tissue

Question 23

Does the distribution of perfusion increase up/down the lung?

Answer 23

Down

Question 24

What (2) ways can Oxygen be carried in?

Answer 24

• Bound to haemoglobin (Hb) in red blood cells (RBCs) (98.5%)
• Dissolved in plasma (1.5% … this is how we measure PaO₂)

Question 25

What does oxygen bind to in the blood?

Answer 25

Haem molecules in haemoglobin

Question 26

How much O2 is reversible bound or released is determined by what?

Answer 26

• Partial pressure of oxygen in blood (PO2)
• Temperature
• Blood pH
• The partial pressure of carbon dioxide (PCO2) + therefore concentration of H+ ions
• Blood concentration of BPG (2,3-Biophosglycerate) produced by RBC

Question 27

How much CO2 do respiring cells produce per minute?

Answer 27

200ml

Question 28

What (3) ways does blood carry CO2 in the lungs?

Answer 28

• Dissolved as CO2 in blood plasma (7-10%)
• Chemically bound to Hb in RBC’s as carbaminohaemoglobin (20%)
• Bicarbonate ions in plasma (~70%)

Question 29

What is carbaminohaemoglobin?

Answer 29

CO2 binds to globin portion of molecule

Question 30

What happens when CO2 diffuses into red blood cells?

Answer 30

It combines with water to form carbonic acid.

Question 31

Which enzyme speeds up the reaction between CO2 and water in RBCs?

Answer 31

carbonic anhydrase

Question 32

Why is carbonic acid in red blood cells considered unstable?

Answer 32

It quickly dissociates into hydrogen ions and bicarbonate ions

Question 33

What role do hydrogen ions play after being released from carbonic acid in RBCs?

Answer 33

They bind to haemoglobin and facilitate the release of oxygen

Question 34

What is the normal pH of arterial blood?

Answer 34

7.35-7.45 pH

Question 35

What is the normal pH of venous blood?

Answer 35

7.31-7.41 pH

Question 36

How does blood become more acidic?

Answer 36

increased CO2 = increased H+ = decreased pH

Question 37

How does blood become more alkali?

Answer 37

decreased CO2 = decreased H+ = increased pH