Muscles involved in Inspiration (and also Forced)
- Diaphragm- creates negative pressure in lungs
- (Diaphragm + External intercostal muscles + SCM and Scalenes)
Muscles involved in Expiration (and also Forced)
- passive process
- Relaxtion of the Diaphragm which causes it to flatten out- increases pressure in lungs
- (Abdominal muscles such as Abdominus Rectus)
Boyle’s Law
- Pressure is inversely proportional to volume
- Air moves from higher pressure to lower pressure
Intrapulmonary pressure
Pressure in the lungs
Atmospheric pressure
Pressure outside the lungs
Intrapleural pressure
- Pressure in the space between the visceral and parietal pleura.
- Arrises due to surface tension in pleural fluid in the layers
- This pressure creates a suction
- Inspiration: chest wall recoils outwards and parietal pleura is pulled out
If the intrapleural pressure is less than or equal to atmospheric pressure
Lung will collapse
Physical properties of the lung
- Compliance- can expand up to a certain limit
- Elasticity- Ability of the ling to move back to its original shape
- Surface tension- alveoli are lined by a thin layer of fluid which exerts a force inwards which prevents them from collapsing
Mechanoreceptors/ Stretch receptors
Where? - present on alveolar/bronchial walls and visceral pleura
- Prevents over-expansion of the lungs
- When activation they send signals (vagus) to respiratory centre to inhibit inspiration
Hering-Breuer reflex
Peripheral Chemoreceptors
Where? - Found in aortic arch and carotid bodies
- Sensitive to ph, pCO2, pO2 of arterial blood (mainly O2)
- When stimulated, signals are sent via vagus and glossopharyngeal nerves to respiratory centre in medulla
Central Chemoreceptors
Where? - found in the ventral-lateral medulla
- Detect CO2 increase by CSF and monitoring H+
NOTE on CO2
- Small increase or decrease in CO2 will greatly affect breathing patterns and rhythms
Pneumotaxic center of Pons
- Fine tuning and decreases inhalation (inhibits Apneustic centre and DRG)
Apneustic Centre
- Causes inhalation and signals DRG and inhibits Pnemotaxic Centre
Dorsal respiratory group
- receives signals from receptors
- Has control over diaphragm and active normal inspiration
Ventral respiratory group
- Forced inspiration and forced expiration
Buffering when there’s too much CO2 (Hamburger effect)
- Bicarbonate ions from blood are swapped with Chloride ions from RBC cytosol
- Allows formation of CO2 and take excess protons away
Buffering when there’s too much O2 (Haldane effect)
- Increase in pO2 forces CO2 to be released from Hb at the lungs
- More H+ binds to HCO3- in order to recreate stored Co2
Bohr Effect
- More protons at tissues due to increase in CO2
- Protons decrease Hb’s affinity to oxygen so cause it to be released.
Role of kidneys in O2/pH balance
- Produce erythropoietin whihc increases no. of Rbc
- H+ and HCO3- are selectively excreted in the urine
- Increase in CO2, more bicarbonate is retained.
