The Lungs & Respiration (Lec 4)

Question 1

Ventilation and Acid-Base Balance

Answer 1

Ventilation removes H+ from blood by the HCO3– reaction

Question 2

Blood Buffering

Answer 2

O2 release from Hb and diffusion into tissues facilitates buffering of H+ ions (Root Effect)

Question 3

Oxygen-Hemoglobin Dissociation Curve

Answer 3

Flat portion provides protection against low atmospheric pO2
• A large decrease in pO2 only results in a small desaturation of the Hb

Steep portion provides protection at tissue level for unloading of O2
• Small decrease in tissue O2 results in large unloading of O2 from Hb

Question 4

Exercise and Oxyhemoglobin Dissociation Curve

Answer 4

Increased temperature and pH result in a downward and rightward shift, referred to as the Bohr Effect

Question 5

Ventilation and Exercise

Answer 5

Increased ventilation results in CO2 exhalation
• Reduces pCO2 and H+ concentration (pH increase)

Decreased ventilation results in buildup of CO2
• Increases pCO2 and H+ concentration (pH decrease)

Question 6

Ventilatory Control During Exercise

Answer 6

Submaximal exercise
• Primary drive Higher brain centres (central command)
• “Fine tuned” by: Humoral chemoreceptors and Neural feedback from muscle

Heavy exercise
• A non-linear rise in VE
• Increasing blood H+ stimulates carotid bodies

Question 7

Rest to Work Transitions

Answer 7

At the onset of constant-load submaximal exercise:
• Ventilation increases rapidly, then a slower rise toward steady state
• Slight decrease in pO2 and increase in pCO2 then plateau

Question 8

Incremental Exercise in Untrained Subject

Answer 8

Ventilation:
−	Linear increase up to ~50–75% VO2 max
−	Exponential increase beyond this point
−	Ventilatory threshold (Tvent)
−	Inflection point where VE increases exponentially

pO2:
− Maintained within 10–12 mmHg of resting value

Question 9

Incremental Exercise in Elite Subject

Answer 9

Ventilation:
• Tvent (ventilator threshold) occurs at higher % VO2 max

pO2:
• Decrease of 30–40 mmHg at near-maximal work (Hypoxemia) due to Ventilation/perfusion mismatch and short RBC transit time in pulmonary capillary due to high cardiac output

Question 10

Respiratory Centre

Answer 10

Respiratory control centres are located in the brain stem (Medulla Oblongata and Pons) and control rhythm and ventilation

Question 11

Input to Respiratory Control Centre: Neural

Answer 11

Higher brain centres
• Voluntary regulation of breathing and emotional response via hypothalamus and limbic system

Sensory information
• Skeletal muscle and right ventricle mechanoreceptors
• Chemoreceptors in muscle

Question 12

Input to Respiratory Control Centre: Humoral

Answer 12

Central chemoreceptors
• Located in the medulla
• Respond to changes in pCO2 and H+

Peripheral chemoreceptors
• Aortic and carotid bodies
• Respond to ↑pCO2, ↑H+, ↓pO2 and ↑K+