Lung physiology 3 Flashcards
respiration requirements
- 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
breathing is automatic
- 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
pons
- Pneumotaxic (promotion)
- Apneustic centres
- (antagonistic, rate and pattern of breathing)
medulla Oblongata
- 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
central pattern generator
- Neural network (interneurons)
- Located within DRG/VRG – precise functional locations not known, start stop and resetting of an integrator of background ventilatory drive
inspiration
- 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
expiration
- 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
chemoreceptors
- 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
central chemoreceptors
- 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
Peripheral chemoreceptors
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
lung receptors
- stretch, J and irritant
- afferents; vagus (X)
- combination of slow and fast adapting receptors
- assist with lung volumes and responses to noxious inhaled agents
stretch lung receptors
- smooth muscle of conducting airways
* sense lung volume, slowly adapting
irritant lung receptors
- larger conducting airways
* rapidly adapting [cough, gasp]
j; juxtapulmonary capillary
• Pulmonary and bronchial C fibres
airway receptors - nose, nasopharynx and larynx
- Chemo and mechano receptors
* Some appear to sense and monitor flow – stimulation of these receptors appears to inhibit the central controller
