Lungs Flashcards
How many zones can the trachea > alveoli be divided into?
24 (0-23)
Which are the conducting zones?
First 17
Which zones are highly cartilaginous and have their own blood supply?
First 4
Which are the respiratory zones?
Last 6
Why do particulates settle before the alveoli?
Velocity falls as flow is distributed
What is the expiratory/inspiratory reserve volume?
Everything you can breathe out/in after normal breathing
Which values can’t be measured by spirometry?
Residual volume and functional residual capacity
What is functional residual capacity?
Residual volume + expiratory reserve volume
What is distending pressure?
Positive transpulmonary pressure to keep lungs inflated
Volume of one mole of dry ideal gas?
22.4 litres
How is the conducting zone kept open?
Kept open by elastic connections between airways and lung parenchyma
What is the most important variable determining alveolar ventilation?
Frequency
Why is water vapour not an ideal gas?
pV =/= nRT because n changes with temperature
WHat is anatomic dead space?
Conducting portion
What is alveolar dead space?
Little or no blood flow
What is expired minute volume?
Air in and out of lungs per unit time
Why is expired minute volume not quite right?
V in =/= V out because more O2 in than CO2 out
What % of expired CO2 has come from alveoli?
All of it
What happens to alveolar PCO2 as alveolar ventilation increases?
Decreases
Why does alveolar PN2 increase?
Because RER
Why is total pressure in venous blood below atmospheric?
Because PO2 decreases more than PCO2 increases
What happens to arterial PCO2 if you double VA?
Halves
What will rectify a doubling of PACO2?
Doubling ventilation
Why must alveolar PO2 decrease if arterial PCO2 rises?
Pressure can’t exceed atmospheric
Why must alveolar ventilation increase after exercise?
Alters CO2 production and therefore VECO2
WHat is static compliance?
Measured when no air flow
What is normalised static compliance called?
Specific
What is FRC?
Equal and opposite compliance recoil forces of chest wall and lung
What happens to FRC is a less compliant lung?
Lung pulls in more so lower FRC
What can causes a less compliant lung?
Elevated diaphragm, muscle rigidity
What does DPPC stand for?
Dipalmitoyl phosphadityl choline
Which parts of DPPC are in gas and which are in air?
Palmitate in gas, glycerol, choline and phosphate in liquid
Three roles of surfactant?
Reduce surface tension, allow different-sized alveoli to coexist, keep alveoli dry
How does surfactant allow different-sized alveoli to coexist?
Pressure = 2T/r so smaller alveoli have more pressure so gas would flow small>big. Surfactant lowers T in small alveoli.
How does surfactant keep alveoli dry?
Force collapsing alveoli would also pull water from capillaries, surfactant reduces ability to do this
What is the flow in between laminar and turbulent called?
Transitional
When do you get peak flow rate? Why?
Large lung volume because elastic recoil pressure highest
Where is airway resistance highest?
Very high because there are lots of branches in parallel at lower areas
Where is equal pressure point at high and low lung volume?
Further down at low lung volume (less elastic recoil), low compliance tissues at high lung volumes
Factors affecting airway resistance?
Lung volume, bronchial smooth muscle, gas viscosity and density
What happens to forced expiratory flow in obstructive diseases?
Lower - same lung capacity but can’t expire at high rate
What happens to forced expiratory flow in restrictive diseases?
The same - same expiration rate but lower lung capacity
Why can PO2 sometimes not be reached fast enough if diffusion reserve increases?
CO2 solubility is greater so it diffuses faster
Which chains does haemoglobin have?
2 alpha, 2 beta
Which chain is wrong in HbS?
AA substitution in beta chain
Whihc type of Hb is less sensitive to DPG?
HbF
What does DPG do to curve?
Keeps it right-shifted
What shifts Hb saturation curve to the right?
Decreased pH, increased PCO2, increased DPG
What is PO2 of maternal blood to fetus? Why is this significant?
30 - large Hb saturation difference here
What is hypercapnia?
Excess CO2 from hypoventilation
What is hypocapnia?
Below normal PCO2 from hyperventilation
What is hypoxic hypoxia?
Low arterial PO2 and inadequate Hb
What is anaemic hypoxia?
Reduced ability to carry O2, low RBC count
What is circulatory hypoxia?
Too little blood
What is histotoxic hypoxia?
Normal O2 delivery but can’t use it eg) cyanide
What happens in capillary blood takes too long to reach equilibrium?
Out of breath
WHy is Hb not affected by barometric pressure variations?
Virtually saturated above 60mmHg
Three ways to transport CO2?
Dissolved, carbamino compunds, bicarbonate
How does CO2 bind to protein?
Reversibly binds to amine group
How does the Haldane effect graph work?
Plot a line for PO2 = 40 (veins) and then see how much CO2 is lost between different PCO2s BUT PO2 also changes so must compare between different curves
What must happen if one HCO3- is moved?
Must be replaced with Cl- to prevent electrochemical gradient forming
What ratio must stay the same for pH to stay at 7.4?
[CO2] : [HCO3-]
What should be the pKa of a good buffer?
7.4, so kidney can release or withold HCO3- into urine
What do Davenport diagrams show?
Relationship between pH, pCO2 and HCO3-
What happens to pulmonary resistance as arterial pressure increases? Why?
Decreases - more pulmonary vessels are recruited and then they distend
What are the two circulatory systems in the lungs?
Bronchial (to serve conducting airways) and pulmonary for gas exchange
How does pulmonary circulation protect organs against emboli?
Endothelial cells release fibrinolytic enzymes and absorb air emboli
Why is pulmonary circulation a passive system?
Autonomic nerves don’t control diameter
What happens to blood vessel diameter at high lung volumes?
Reduced because alveoli stretch vessels, the others increase their diameter because of -ve pleural pressure
Where is pulmonary vascular resistance lowest?
Very close to FRC (optimum balance)
What is regional hypoxia?
Reduced blood to hypoxic areas, localised vasoconstriction and compensatory dialtion somewhere else
What is general hypoxia?
Reduced blood flow to all areas, eg) CF or oedema from high blood pressure
What can cause pulmonary oedema?
Left heart failure causing increased capillary pressure, oxidant damage and endotoxins cause increase in capillary permeability, loss of plasma proteins decreases colloid osmotic pressure, lymphatic blockage
How does lack of surfactant increase intersitial pressure?
Increases surface tension
Why does drowning in fresh water cause cardiac arrest?
RBCs burst, K+ released from inside and Na+ is diluted
What is usual value of Va/Q ratio?
0.8
What are units of Va/Q ratio?
No units
Which area of the lungs is Va/Q ratio lower in?
The bottom
Does ventilation or perfusion have a larger difference top to bottom?
Perfusion
How do high Va/Q ratios affect blood O2 content?
Minimal effect because ventilation wasted, PCO2 falls so pH increases so localised increases in airway resistance so ventilation shifted to other alveoli.
How do low Va/Q ratios afect blood O2 content?
Large effect - Increase in overall ventilation to compensate, acute response, regional vasoconstriction from localised hypoxia shunts blood from poorly ventilated alveoli
Two causes of venous admixtures?
Shunting or low Va/Q ratio
What are the types of shunting?
R>L anatomic or alveolar (passes alveolus but doesn’t contact air from pneumonia/collapsed alveoli)
What does the apneustic centre do?
Prolongs inspiration
What does the pneumotaxic centre do?
Inhibits inspiration
What does vagal afferent input do?
Terminates inspirations
What does cutting below medulla do?
Stops breathing
What does cutting above central medulla do?
Rhythmic but irregular breathing
What does cutting at upper pons do?
Slows respiration but increases tidal volume
What happens if saline and CO2 is added to chemosensitive areas?
Add CO2 and ventilation increases, add saline and it decreases
What produces cerebrospinal fluid?
Choroid plexus
What is the composition of cerebrospinal fluid?
Low protein, HCO3-, K+ and Ca2+. High Na+, Cl-
Are carotid or aortic bodies dominant in breathing control?
Carotid
Which cells in the carotid bodies are responsible?
Glomus
What can carotid bodies sense?
PCO2, pH, PO2
What do the pulmonary stretch receptors in the airway do?
Discharge in response to distension via the vagus nerve
What is the Hering-Breuer inflation reflex?
Discharge of pulmonary stretch receptors slows breathing frequency by inhibiting inspiration and prolonging expiration
What is the deflation reflex?
Lung deflation induces inspiration
What must tidal volume be greater than for CPG?
1 litre
What happens to tidal volume and breathing frequency if vagal afferent input to higher brain is blocked?
Nothing
What does the intrinsic ramp pattern of the pontine respiratory group do?
Stimulation terminates inspiration, still get breathing pattern if afferent input is cut
What does the apneustic centre innervate?
Respiratory muscles
Why is blood flow bad at the top of the lung?
Alveolar pressure is greater than artery and vein pressure, so blood vessels closed
Why is blood flow good a the bottom of the lung?
Artery and vein pressure greater than alveolar pressure so vessels stay open
What are the ventilation/perfusion zones of the lung called?
West Zones
Are the base and apex over-perfused or over-ventilated?
Base is overperfused, apex is over-ventilated
How do the medullary central chemoreceptors monitor PCO2?
Use H+ (CO2 crosses blood-brain barrier into CSF and forms H+)
Why can’t protons in blood just cross the blood brain barrier to the chemoreceptors?
They could have come from lots of places
What does cutting pneumotaxic centre cause?
Goes to full tidal volume because pneumotaxic centre aids inspiration termination
What does cutting apneustic centre do?
Get small variable inhalations because it contains motor nerves which drive inspiration
What do stretch receptors carried by the vagus stimulate?
Pneumotaxic which inhibits apneustic so exhalation
What is rate limiting at altitude?
O2 diffusion
What do hyperventilation at altitude do?
Decreases PCO2 so alveolar PO2 increases again - BUT falling PCO2 opposes low PO2 which triggers ventilation increase
Hyperventilation at altitude causes alkaline CSF - what does this do?
Choroid plexus stops producing HCO3- which removes the “braking effect” - a good thing here.
What is Caisson disease?
The bends
Why is He used instead of N2?
Reduces bends risk because it’s half as soluble
What is the neurogenic response?
Increases Ve at the start of exercise
What does the humeral response do?
Maintains increased Ve during exercise
Why don’t PCO2, PO2 and pH not change during exercise?
NOBODY KNOWS
What do peripheral chemoreceptors control?
Adding/removing CO2
What can blood supply vasoconstriction during low O2 cause?
High pressure so fluid pools in alveoli
What is the vicious circle from chemoreceptors signalling opposite things at altitude?
Normal CO2 and decreased O2 > increased ventilation > increased O2 and decreased CO2 > decreased ventilation > back to where we started
What is “central adaptation”?
To stop decreased ventilation, [HCO3-] is removed from CSF so more H+ produced (so goes back to normal) which is detected by chemoreceptors so ventilation increases again - NOT TO MAKE VENTILATION INCREASE, JUST TO STOP IT GOING DOWN
What is the Haldane effect?
The CO2 content of blood is modulated by PO2/saturation - more CO2 is carried in deoxygenated that oxygenated blood
Why is more CO2 carried in deoxygenated than oxygenated blood?
Deoxy Hb is a weaker acid so will bind more protons at physiological pH which maintains gradient for bicarb production AND deoxy Hb forms more carbamino compounds
Why is the slope of “adding carbonic acid” line steeper on a Davenport diagram than titrating plasma?
Because of Hb buffering properties
