Unit VII (38-43) - Respiration Flashcards
What factors cause lung elasticity? Which are most significant?
Tissue elastic forces - 1/3
Fluid-air surface tension forces - 2/3
What cells secrete surfactant?
Type II alveolar epithelial cells
What is surfactant’s function?
Reduces surface tension of water
How does alveolar size affect the pressure caused by surface tension?
Smaller size = greater effect
Draw and label a typical spirogram
pg495
Describe the innervation of the bronchial tree
SNS
- very little direct innervation
- exposed to systemic Ep/NEp
- NEp has greatest effect on betam receptors => bronchodilation
PNS
- nerve fibres from vagus
secrete acetylcholine => bronchoconstriction
How does bronchoconstriction occur in allergic reactions?
Histamine and slow reactive substance of anaphylaxis released by mast cells
How is the pulmonary circulation divided?
High pressure low flow - trachea, bronchial tree, supporting tissue of lung
Low pressure high flow - alveolar capillaries
How is left atrial pressure estimated?
Measuring pulmonary wedge pressure
What is the response in the lung vasculature to alveolar oxygen decreasing <70% normal?
Vasoconstriction
What are the 3 zones of pulmonary blood flow?
Zone 1 - no blood flow during all portions of cardiac cycle. Only occurs under abnormal conditions ie breathing against positive pressure or low pulmonary systolic pressure
Zone 2 - intermittent blood flow only during peak pulmonary artery pressure
Zone 3 - continuous blood flow
What is Henry’s law?
Partial pressure = concentration/solubility
How does the solubility of O2 and CO2 compare?
CO2 >20x more soluble than O2
What factors can cause the haemoglobin dissociation curve to shift to the right?
Increased CO2
Increased temperature
Increased BPG
Increased H+ ions
How does shifting the haemoglobin dissociation curve to the right affect dynamics?
Enhances release of O2
How is CO2 carried in the blood?
As dissolved CO2 (7%), carbaminohaemoglobin, plasma proteins and bicarbonate (70%)
What is the chloride shift?
Cl- content of venous blood greater than arterial
After CO2 is converted to H2CO3 and HCO3 in the red blood cell, HCO3 diffuses out in exchange for Cl- via HCO3-Cl exchnager
What is the Haldane effect?
As O2 binds hgb, Co2 displaced from blood
O2+hgb stronger acid than unbound hgb
- Acidic hgb less likely to combine with CO2
- Acidic hgb more likely to donate H+ to bind HCO3- and produce CO2
Where is the respiratory centre located?
Medulla oblongata and pons
How is the respiratory centre organised?
Dorsal respiratory group - inspiration
Ventral respiratory group - expiration
Pneumotaxic centre - rate and depth of breathing
What does the formal respiratory group of neurons control? Where are its neurons located? Where do they receive input from?
Inspiration and respiratory rhythm
Nucleus of the tracts solitarius
Sensory termination of the vagal and glossopharyngeal nerves
Input from peripheral chemoreceptors, baroreceptors, receptors in liver, pancreas and GIT and lungs
What is the function of the pneumotaxic centre?
Transmits signals to inspiratory area to limit inspiration and increase breathing rate
Controls switch off point of inspiratory ‘ramp’
What limits inspiration to prevent lung overinflation?
Hering-breuer inflation reflex
Stretch receptors in lung transmit signals via vagus into dorsal respirator group when overstretched - terminated inspiratory ramp
What is the function of the ventral respiratory group?
Provide extra respiratory drive during periods of need for greater respiration
Activated when signals from DRG spill over
Contribute to inspiration and expiration
Recruit abdominal muscles during heavy respiration
What causes direct chemical control of respiration? Describe how it works
H+ and HCO3
Chemosensitive area - highly sensitive to H/HCO3 changes
How does oxygen impact chemical control of respiration?
No major direct effect
Stimulates peripheral chemoreceptors in carotid and aortic bodies - when oxygen concentration falls, chemoreceptors stimulated
Aortic bodies contain glomus cells - O2-sensitive K channels - inactivated when O2 falls markedly - opens Ca channels - stimulate DRG
What has the most potent effect on the chemo sensitive area?
Most sensitive to H+
However, has little direct effect as doesn’t cross BBB
Instead CO2 crosses and dissociates into H+/HCO3
How does altered CO2 affect respiration chronically and acutely?
Great acute effect
Attenuated chronic effect - renal readjustment
- HCO3- diffuses across BBB more slowly
