Lung physiology 3

Question 1

respiration requirements

Answer 1

• Ensure haemoglobin is as close to full saturation with oxygen as possible
• Efficient use of energy resource
• Regulate PaCO2 carefully – variations in CO2 and small variations in pH can alter physiological function quite widely

Question 2

breathing is automatic

Answer 2

• no conscious effort for the basic rhythm
• rate and depth under additional influences
• depends on cyclical excitation and control of many muscles
• upper airway, lower airway, diaphragm, chest wall, near linear activity, increase thoracic volume

Question 3

pons

Answer 3

• Pneumotaxic (promotion)
• Apneustic centres
• (antagonistic, rate and pattern of breathing)

Question 4

medulla Oblongata

Answer 4

• Phasic discharge of action potentials
• Two main groups: Dorsal respiratory group (DRG), Ventral respiratory group (VRG)
• DRG; predominantly active during inspiration
• VRG: active in both inspiration and expiration
• Each are bilateral, and or project into the bulbo-spinal motor neuron pools and interconnect

Question 5

central pattern generator

Answer 5

• Neural network (interneurons)
• Located within DRG/VRG – precise functional locations not known, start stop and resetting of an integrator of background ventilatory drive

Question 6

inspiration

Answer 6

• Progressive increase in inspiratory muscle activation
• Lungs fill at a constant rate until tidal volume achieved
• End of inspiration, rapid decrease in excitation of the respiratory muscles

Question 7

expiration

Answer 7

• Largely passive due to elastic recoil of thoracic wall
• First part of expiration; active slowing with some inspiratory muscle activity
• With increased demands, further muscle activity recruited
• Expiration can become active also; with addition abdominal wall muscle activity

Question 8

chemoreceptors

Answer 8

• Central (60% influence form PaCO2) and peripheral (40% influence from PaCO2)
• Stimulated by [H+] concentration and gas partial pressures in arterial blood
• Brain stem [ primary influence in PaCO2)
• Carotids and aorta [PaCo2, PaO2 and pH]
• Significant interaction

Question 9

central chemoreceptors

Answer 9

• Central is located in brain stem
• Pontomedullary junction
• Not within the DRG/VRG complex
• Sensitive to PaCO2 of blood perfusing brain
• Blood brain barrier relatively impermeable to H+ and HCO3-
• PaCO2 preferentially diffuses into CSF

Question 10

Peripheral chemoreceptors

Answer 10

Located in:
• Carotid bodies (Bifurcation of the common carotid, IX cranial nerve afferents)
• Aortic bodies (ascending aorta, vagal nerve afferents)
• Responsible for all ventilatory response to hypoxia (reduced PaO2)
• Generally not sensitive across normal PaO2 ranges
• When exposed to hypoxia, type I cells release stored neurotransmitters that stimulate the cuplike endings of the carotid sinus nerve
• Linear response to PaCO2
• interactions between responses

Question 11

lung receptors

Answer 11

• stretch, J and irritant
• afferents; vagus (X)
• combination of slow and fast adapting receptors
• assist with lung volumes and responses to noxious inhaled agents

Question 12

stretch lung receptors

Answer 12

• smooth muscle of conducting airways

* sense lung volume, slowly adapting

Question 13

irritant lung receptors

Answer 13

• larger conducting airways

* rapidly adapting [cough, gasp]

Question 14

j; juxtapulmonary capillary

Answer 14

• Pulmonary and bronchial C fibres

Question 15

airway receptors - nose, nasopharynx and larynx

Answer 15

• Chemo and mechano receptors

* Some appear to sense and monitor flow – stimulation of these receptors appears to inhibit the central controller

Question 16

airway receptors - Pharynx

Answer 16

• Receptors that appear to be activated by swallowing – respiratory activity stops during swallowing to protect against the risk of aspiration of food or liquid

Question 17

joint proprioceptors

Answer 17

• Joint, tendon and muscle spindle receptors
• Intercostal muscles»_space; diaphragm
• Important roles in perception of breathing effort