Resp. Physiology Flashcards
What is Boyle’s Law?
P = 1/V
- Increase volume = decrease pressure
- Decrease volume = increase pressure
What 2 opposing forces must be overcome in the work of breathing?
- stiffness of the lungs (related to compliance)
- resistance of the airways
What is the formula for compliance?
C = ∆V/∆P
What is a clinical example of low lung compliance?
Pulmonary fibrosis
◊ Thickening and scarring of alveolar membranes
◊ From chronic inflammation or exposure to chemicals
What chemical phenomena increases the stiffness/elasticity of the lungs? Explain how this works
Surface tension from the fluid surrounding the lungs
□ The tendency of a fluid surface to occupy the smallest possible SA
-> Walls of the alveoli very thin - enhances this effect
-> H bonds between water molecules collapse to achieve smallest surface area possible
What is used to reduce surface tension in the alveoli?
Surfactant
What cells produce surfactant?
type II pneumocytes
How does surfactant work?
- Reduces attractive forces between fluid molecules lining alveoli, making it easier to expand -> increased compliance
- Surfactant is a detergent/soapy molecule made of mainly phospholipids
◊ Inserting phospholipid molecules stops the water molecules from nearing each other and forming H bonds
What is a clinical example of not having enough surfactant?
Premature babies don’t produced surfactant, results in respiratory distress syndrome (RDS)
What formula relates radii and resistance?
R = 1/r^4
What is the main airway of resistance in the lungs?
BRONCHI - because arranged in series
- The small airways contribute very little to resistance b/c high cross sectional area
What is the volume of air moved in and out during normal breathing called?
Tidal volume (VT)
What is the extra volume that can be inhaled above tidal volume called?
Inspiratory reserve volume (IRV)
What is the extra volume that can be exhaled voluntarily after normal breath out called?
Expiratory reserve volume (ERV)
What is the volume remaining after max exhalation called?
Residual volume
What is the volume remaining in lungs if they collapsed called?
Minimal volume
Define tidal volume
Volume of air moved in and out during normal breathing
Define inspiratory reserve volume
Extra volume that can be inhaled above tidal volume
Define expiratory reserve volume
Extra volume that can be exhaled voluntarily after normal breath out
Define residual volume
Volume remaining after max exhalation
Define minimal volume
Volume remaining in lungs if they collapsed - can’t get this out
What volumes add to give vital capacity?
Inspiratory reserve + Expiratory reserve + Tidal volume
What is vital capacity?
Volume of air that can be moved in and out of your lungs
What volumes add to give total lung capacity?
Vital capacity + Residual volume
What is total lung capacity?
Total volume in lungs when it is filled to max
What volumes add to give inspiratory capacity?
Inspiratory reserve + Tidal volume
What is inspiratory capacity?
Total volume of air that can be inspired from rest
What volumes add to give functional residual capacity?
Expiratory reserve + Residual volume
What is functional residual capacity?
Volume remaining in lungs after normal exhalation
What is indicative of a restrictive lung disease?
low FEV1
What is FEV1?
forced expiratory volume in 1 second
a.k.a. how much of forced vital capacity comes out in 1 second
What are 2 examples of restrictive lung diseases?
fibrosis, insufficient surfactant release (premmie babies)
What is indicative of an obstructive lung disease?
FEV1/FVC ratio < 0.70
What is an example of an obstructive lung disorder?
asthma (=bronchial inflammation), COPD
What is the formula for alveolar ventilation?
VA = (VT - VD) x f
What is VD? (subscript D just fyi)
Dead space = the inhaled air filling the upper airways that doesn’t reach the alveoli for gas exchange
What is alveolar ventialtion?
volume of air that gets to the alveoli
What is Fick’s Law of Diffusion?
- in words and in formula
F = A / T x D (P1 - P2)
Flux (amount flowing) = surface area/thickness x diffusion constant (pressure difference)
What factors influence the rate of diffusion?
- SA of membranes
- Thickness of membranes
- Pressure difference [MAJOR determinant]
- Diffusion constant [MINOR determinant]
What feature increases the SA of the alveoli?
the bulbous structure of the alveoli and high density of capillaries
What happens if alveolar SA is reduced?
less contact between air and capillaries = O2 exchange reduced
What is a clinical example of reduced alveolar SA? What are the effects?
Reduction of SA (e.g. emphysema) by dilation of alveolar spaces/destruction of walls = less contact between air and capillaries = O2 exchange reduced
What feature contributes to the thick/thinness of the blood air barrier?
Blood air barrier is mostly made up of the alveolar and capillary walls = thin = small distance between air and blood
What is the driving factor for diffusion of gases across the blood air barrier?
Pressure difference
What is the pressure difference between?
The alveolar and arterial pressures
What determines O2 alveolar partial pressure? (3)
- Alveolar ventilation
- O2 consumption - blood O2
- Partial pressure of O2 in air (usually constant, so less important)
What determines CO2 alveolar partial pressure? (3)
- Alveolar ventilation
- CO2 production
- Partial pressure of CO2 in air (negligible)
How is O2 transported? (2)
- Dissolved in blood
- Bound to hemoglobin in RBCs
Why is there very little O2 transported dissolved in the blood?
O2 has low solubility at physiological partial pressure
What reduces O2 binding affinity to hemoglobin? (4)
- Lower pH
- Higher temp
- Increased PCO2
- Increased [BPG]
The upper flat part of the sigmoidal curve indicates…
moderate changes in PO2 around normal have small effects on % saturation = reserve capacity for exercise etc.
The steep part of the sigmoidal binding curve indicates…
Steep at low PO2 -> helps with loading in the lungs and unloading in the tissues, small changes in PO2 = large changes to % O2 bound
How does exercise influence O2 binding?
Increased metabolism = increase CO2 (and .: H+) and temp = shift curve right = reduced affinity for O2
How is CO2 transported in the blood? (3)
- Dissolved in plasma (~7%)
- Combined with proteins as carbamino compounds (23%)
- As bicarbonate (70%)
How is CO2 carried as bicarbonate?
○ Carbonic anhydrase enzyme converts CO2 + H20 <==> H2CO3
○ Then dissociates into H+ and HCO3-
- H+ lowers the pH, binds to Hb
- HCO3- into plasma in exchange for Cl- = chloride shift
What enzyme is involved in CO2 transport (as bicarbonate)?
Carbonic anhydrase enzyme
What is an example of CO2 combined with protein as a carbamino compound?
Carbaminohemoglobin (HbCO2) - competes with O2
What controls respiration? (that we need to know about)
Respiratory Rhythmicity Centres
What are the functions of the Respiratory Rhythmicity Centres? (3)
- generate cycles of contraction and relaxation,
- establish pace,
- modify activity in response to chemical and pressure signals
Where is the respiratory rhythmicity centres located?
In the medulla (brain)
What are the 3 parts that make up the Respiratory Rhythmicity Centres?
- Inspiratory centers of the dorsal respiratory group (DRG)
- Ventral respiratory group (VRG)
- Pre-Bötzinger complex
What are the inspiratory centers of the dorsal respiratory group (DRG), and what do they control?
○ Inspiratory neurons
○ To diaphragm and ext. intercostal muscles
When does the ventral respiratory group (VRG) send signals?
○ No signals at quiet breathing
○ When required: send signals to…
- Inspiratory centers = to accessory inspiratory muscles
- Expiratory centers = to accessory expiratory muscles
What is the role of the Pre-Bötzinger complex?
Similar to SA node = rhymical/cyclical respiration
What sensors control/influence respiration?
- Central chemoreceptors
- Peripheral chemoreceptors
- Inflation/deflation reflexes
- Protective reflexes
Where are the central chemoreceptors located?
medulla
What are the central chemoreceptors sensitive to?
PCO2 of the blood, but not PO2
What is the role of the central chemoreceptors?
Most important sensors for determining resp activity
How do the central chemoreceptors detect changes in pCO2?
- CO2 diffuses across the blood-brain barrier
- Changes pH of cerebrospinal fluid (CSF)
- Central chemoreceptors respond to pH change
Where are the peripheral chemoreceptors located?
carotid and aortic bodies, close to baroreceptors
What do the peripheral chemoreceptors respond to?
mainly to changes in arterial PO2
What is the role of inflation/deflation reflexes? How do they work?
○ Input from lungs to stretch receptors
○ Brain then sends efferent output to prevent them stretching too far either way
What is the role of protective reflexes?
○ Receptors also detect irritation
○ Brain sends efferent signal that triggers sneeze (forceful expiration) or cough (stepwise expiration)
What is the process to restore PCO2 homeostasis when arterial PCO2 increases?
- Change detected by chemoreceptors in the medulla and in arteries, stimulated by increased PCO2 and decreased pH [receptor]
- Respiratory muscles stimulated [effector]
- This results in increased resp rate and elimination of CO2 at alveoli = decreased arterial PCO2
