Lungs Flashcards
What is pressure?
P = F / A Pressure Force Area Unit is Pa
What is Boyles law? And how does it influence gas exchange?
Absolute pressure exerted by gas is inversely proportional to volume it occupies if temp and amount of gas remain unchanged in closed system
P1V1 = P2V2
Creates the pump and vacuum activity in lungs that allows us to breathe
What is Charles’ law?
At constant pressure, the volume of gas changes in direct proportion to its temperature on the absolute temperature scale
V = KT (K is a constant)
V1/T1=V2/T2
What is the universal gas law?
PV = nRT P is pressure V is volume n is number of moles of gas R is gas constant T is temperature Allows calculation of volume changes with pressure and temperature changes
What is a partial pressure?
When two gases in a mixture do not interact, they behave independently and each exerts its own pressure
What is Dalton’s law?
In a mixture of non reacting gases, total pressure exerted is equal to sum of partial pressures
What is the partial pressure of O2 in air?
21.1 kPa
What factor is saturated vapour pressure dependent on?
Temperature
Increased kinetic energy allows more vapour to escape the surface of the liquid
What is Henry’s law?
Number of molecules of gas dissolving in solvent is directly
proportional to the pressure of the gas at the surface of the
liquid
What happens to tension of a gas dissolving in water at equilibrium?
Tension proportional to partial pressure of that gas in adjacent gas mixture
What does gas tension indicate?
How readily a gas will leave a liquid
What is gas tension measured as?
Partial pressure of solute in solvent in kPa
What is the content of a gas in a liquid?
Proportional to its solubility in that liquid and the gas tension at
equilibrium
What is saturated vapour pressure at 37 degrees?
6.28 kPa
What is a difference between convection and diffusion?
No net transport of matter in diffusion
How much oxygen is picked up by the blood in health?
12 mmol O2 per minute
What is an alveolus?
Thin spherical structure where gas exchange occurs
Surrounded by capillary plexus
Fed through tiny bronchiole called alveolar duct
What constitutes total content of gas in a liquid?
Total reacted gas and gas dissolved in liquid
In blood, final gas content is determined by…
Gas tension
Solubility of gas in liquid
Avidity of haemoglobin for oxygen
Where does gas exchange occur?
At alveolar membrane
How does the composition of alveolar gas differ from atmospheric?
Lower pO2 - 13.3 in alveolar, 21.1 kPa in atmosphere
Higher pCO2 - 5.3 in alveolar, minimal in atmosphere
How does mixed venous blood gas composition vary from alveolar?
pO2 - 6 kPa venous, 13.3 alveolar
pCO2 - 6.5 kPa venous, 5.3 alveolar
What factors affect diffusion rate?
Surface area of alveoli
Concentration gradient caused by differences in partial pressures
Resistance of alveolar capillary membrane - thickness
Solubility of gas
Molecular weight of gas
Diffusion rate = D x A x (difference in PP/thickness)
D is proportional to solubility / root of MW
What constitutes the diffusion barrier of the alveolar membrane?
Diffusion through gas to alveolar wall Epithelium of alveolus Tissue fluid and connective tissue Endothelium of capillary Plasma Red cell membrane Cytoplasm
What is solubility?
Amount of solvent that can dissolve in unit volume of solute
Which diffuses faster, O2 or CO2?
CO2
Is oxygen transfer perfusion or diffusion limited?
Perfusion
What may cause a change from perfusion limited oxygen delivery to diffusion limited?
Thickening of diffusion barrier - alveolar membrane
Other than gas exchange, what functions does the respiratory system have?
Reservoir for blood and oxygen
Metabolism of circulating compounds eg ACE
Filter blood
Which part of the airways form the anatomical dead space?
Conducting airways - bronchi and bronchioles
Which parts of the airways form the respiratory airway?
Respiratory bronchioles
Alveolar ducts
Alveolar sacs
What name is given to each level of branching of the bronchial tree?
Generation
What is hypoxic vasoconstriction?
In alveoli with low pO2 due to lower ventilation levels, pulmonary arterioles can be constricted to reduce blood flow to this area where it is not needed
Give an example of a disease which increases the thickness of the diffusion barrier
Pulmonary fibrosis
Give an example of a disease which reduces the surface area available for diffusion
COPD - chronic obstructive pulmonary disease
What non disease state can cause a switch from perfusion to diffusion limited oxygen delivery?
High levels of exercise as the perfusion rate is so fast that the diffusion rate cannot keep up
What can be used as lung function test to determine the thickness of the alveolar membrane?
Carbon monoxide as its delivery is diffusion limited
How can rate of gas exchange be increased when a gases delivery is diffusion limited?
Increase pO2 in alveoli
Which muscles are involved in ventilation?
Diaphragm
Intercostal muscles
What do you use spirometry for?
Measure lung volumes
What 4 parts make up total lung capacity?
Tidal volume
Residual volume
Inspiration reserve volume
Expiratory reserve volume
Maximum force generated by inspiratory muscles balanced by opposing forces
In spirometry, what is the difference between lung volumes and lung capacities?
Lung volumes change with breathing pattern
Lung capacities do not
What factors determine an individual’s lung capacities?
Properties of lung, chest wall and muscles
Which lung volumes make up inspiratory capacity?
Tidal volume and inspiratory reserve volume
Biggest breath that can be taken from resting expiratory level (lung
volume at end of quiet expiration) Inspiratory capacity typically ~3l
Which lung volumes form the vital capacity?
Tidal volume
Inspiratory reserve volume
Expiratory reserve volume
Biggest breath that can be taken, often changes in disease
Which lung volumes make up the functional residual capacity?
Residual volume
Expiratory reserve volume
Volume of air in the lungs at resting expiratory level
Typically ~2 litres Determined by the balance of elastic resistance
between lung and chest wall
What is a normal value for vital capacity?
5L
What is minute ventilation (MV)?
Amount of air moved into and out of the lungs or minute
Product of tidal volume and respiratory rate
MV=Vt x RR
Typically 6-8 L/min at rest
What must be calculated to work out the alveolar ventilation rate?
Amount of wasted ventilation into dead space
What volume of inspired air is within the serial dead space and therefore doesn’t take part in gas exchange?
150 ml
What is the distributive dead space?
Dead or damaged alveoli
Alveoli with poor perfusion
What is the physiological dead space?
Serial and distributive dead spaces combined
What type of breathing amplifies dead space effect?
Rapid and shallow
What is the ideal V/Q ratio?
1
What is the main reason for defective gas exchange in disease?
V/Q mismatch
What would total lung V/Q mismatch cause?
Arterial hypoxaemia
Give an example of a disease which causes a decrease in ventilation and therefore gives a lower V/Q ratio?
Pneumonia
Give an example of a disease which causes decreased perfusion and therefore increases the V/Q ratio
Pulmonary embolus
Describe the V/Q ratio in the apex of the lung and how this differs to the base
In the apex, the ventilation rate is greater than the perfusion so the V/Q ratio is above 1
In the base, perfusion (gravity dependent) is greater than ventilation rate and so the V/Q ratio is below 1
Why is perfusion of the central part of the lung sporadic?
Systole and diastole of the heart mean that pressure changes
What causes the reduction in pH as you move down from apex to base of lungs?
Increasing CO2 levels in alveoli and capillaries. CO2 transfer is ventilation dependent
Why is apical alveolar pO2 relatively high?
Less perfusion
O2 transfer is perfusion dependent
What happens in the lung during exercise to accommodate increased CO?
Distensible apical blood vessels that are usually collapsed, open. This increases oxygen uptake at the top of the lung
What 5 things can cause hypoxia?
Shunt V/Q mismatch Limited diffusion Hypoventilation Decreased O2 in inspired air
Which pathological cause of hypoxia cannot be corrected with increasing inspired oxygen?
Pulmonary shunt
What factors does oxygen delivery to tissues rely on?
Cardiac output Haemoglobin concentration Oxygen saturation Dissolved oxygen DO2 = CO x (( Sa02 x Hb x k) x ( PaO2 x 0.023 ))
Which ribs end in costal cartilage?
1-10
What is flail chest?
When a segment of thoracic cage is separated from rest of chest wall. At least 2 fractures per rib which produces a free segment. This segment is unable to contribute to lung expansion, paradoxical movement
What can be a consequence of having an additional cervical rib?
Thoracic outlet syndrome
Brachial plexus gets squashed
Muscle wasting in the hand
What 3 parts make up the sternum?
Manubrium
Body
Xiphoid process
At what thoracic level would you find the sternal notch?
T2
What do you find at the sternal angle?
T4
2nd rib
What level do you find the xiphoid process at?
T9/10
Which part of the ribs forms a joint with the vertebrae?
Articular facets of head
Which ribs connect directly to the sternum?
Ribs 1-7
Which ribs connect to the sternum via the costal cartilage of the ribs above?
Ribs 8-10
What are the 3 layers of intercostal muscle?
External intercostal
Internal intercostal
Innermost intercostal
Where would you make an incision in the intercostal space?
Just above the rib to avoid the neurovascular bundle at the top of the space
What does an intercostal nerve supply?
Skin Muscle Bone Cartilage Parietal pleura
Where can pleuritic pain and shingles refer to?
Dermatome of the spinal nerve of origin
Where does the sympathetic chain lie in the thoracic cavity?
Posterior thoracic wall
What can a pancoast tumour cause?
Compression of the sympathetic chain in the apical region of the lung
Can cause Horner syndrome due to compression of the T1 spinal nerve
Which artery can be harvested for coronary artery bypass graft?
Internal thoracic artery
Where does the blood supply to the thoracic wall derive from?
Intercostal arteries which form anastomotic loops
Where do posterior intercostal arteries branch from?
Descending aorta
Where do anterior intercostal arteries branch from?
Internal thoracic artery
Musculophrenic artery
Where does the internal thoracic artery branch from?
Subclavian artery
What is the venous drainage of the thoracic wall?
Azygous venous system
Azygous vein on right
Hemiazygous on left
What does the azygous vein drain into?
Superior vena cava
What can damage of the thoracic duct lead to?
Chylothorax
Which areas of mediastinum does thoracic duct run through?
Posterior
Superior
Where does the thoracic duct start and finish?
Starts at cisterna chyli
Ends at left subclavian vein
Where does the diaphragm attach?
Costal margin
Ribs 10-12
Lumbar vertebrae
Name 2 types of congenital diaphragmatic hernia
Bochdalek hernia - posterior left sided
Morgagni hernia - retro sternal
Which nerve innervates the diaphragm?
Phrenic nerve C3-5
What can unilateral damage to the phrenic nerve cause?
Hemidiaphragmatic palsy
Which 3 structures pierce the diaphragm and at what levels?
Inferior vena cava T8
Oesophagus T10
Descending aorta T12
At what time during development does the respiratory diverticulum form as an outpouching of the gut tube?
4 weeks
What developmental tissue type are the lining of lungs and glands derived from?
Endoderm
What developmental tissue type are the blood vessels, cartilage, smooth muscle and visceral pleura derived from?
Mesoderm
During development, what divides the oesophagus and trachea?
Tracheo-oesophageal septum which forms weeks 4-5
What 2 developmental defects can occur if septation of the trachea and oesophagus fail?
Blind ended oesophagus
Fistula
How many bronchial buds form?
3 on right, 2 on left
At what time during development do segmental bronchi form?
Week 7
What part of respiratory development occurs at week 26? And what consequence can this have for premature babies?
Initial development of respiratory epithelia
Premature babies lungs are not fully developed and so survival rates are lower
What does the horizontal fissure divide?
Right middle and superior lobes
Which structures are closely related to the right lung?
Oesophagus
Azygous vein
Brachiocephalic vein
SVC and IVC
Which structures are closely related to the left lung?
Aortic arch Descending aorta Cardiac impression Subclavian artery Brachiocephalic vein
Where does the phrenic nerve pass in relation to the hilum of the lung?
Anterior
Which structures pass through the hilum of the lung?
Main bronchi
Pulmonary artery
Autonomic nerves
Pulmonary vein
What is the pulmonary ligament?
Fold of parietal pleura at hilum
What occurs if a venous thrombus passes into the lungs via pulmonary artery?
Pulmonary embolism
What does the parietal pleura line?
Thoracic cage (costal)
Mediastinum
Cervical region
Diaphragm
What holds together the pleural layers at rest?
Surface tension
What signs will you see with a tension pneumothorax?
Mediastinal shift away from pneumothorax Tracheal deviation Diaphragmatic depression Unilateral hyperinflation Increased intercostal space size Hyper resonant
At what point does the trachea bifurcate?
T4 - sternal angle
What vertebral level is the horizontal fissure located at?
4th costal cartilage, horizontally to join the oblique fissure
Where does the oblique fissure start and finish?
T3 spinous process posteriorly
6th costal cartilage anteriorly
Which spinous process is the most prominent in the neck?
C7
Biopsy of which structures will require crossing through the costodiaphragmatic recess?
Liver, spleen, kidneys
Where are chest tubes classically inserted?
Triangle of safety
Bordered by posterior, anterior axillary lines and nipple line (4-5th intercostal space)