Respiratory Flashcards
How many airway divisions are there?
23
Which are the conducting airway divisions?
1-16
Which airway divisions are the respiratory zone?
17-23
Define partial pressure of a gas
The individual pressure exerted independently by that gas within a mixture. (Each pressure is equal to the pressure it would exert if it were the only gas present)
What determines how much of a gas dissolves in a liquid?
The amount of gas dissolved in a liquid is proportional to the pressure of the gas in contact with the liquid
How is partial pressure in alveolar air different to atmospheric air?
More water vapour Less O2 (constantly leaving) More CO2 (constantly entering)
What is the pO2 in capillary blood?
13.3KPa
What is the pCO2 in capillary blood?
5.3KPa
What is the pO2 in interstitial fluid?
6KPa
What is the pCO2 in interstitial fluid?
6KPa
What lines the conducting portion of the respiratory tract?
Mucous membrane (mucus secreting cells)
Where in the respiratory system are serous membranes found?
Lining the pleural sacs that envelope each lung
What are the smallest branches of the conducting portion of the conducting system called?
Terminal bronchioles
What histiological cells are in the majority of the conducting portion of the respiratory system?
Pseudostratified epithelium with cilia and goblet cells
What hisiological cells are in the terminal bronchioles, and what portion of the respiratory system are they a part of?
Simple columnar epithelium with cilia and Clara cells (but no goblet cells)
Conducting portion
What type of cells are in the respiratory portion of the respiratory system, minus alveoli?
Simple cuboidal epithelium with Clara cells. Few sparse cilia.
(Respiratory bronchioles and alveolar ducts)
What type of cells are in the alveoli?
Simple squamous, types 1 & 2
How do Venus plexuses avoid overdrying?
Swell every 20-30mins, alternating airflow thus preventing over drying. Patence maintained by surrounding cartilage/bone.
What is the olfactory system?
Your sense of smell
What does the olfactory system look like histiologically?
Particularly thick pseudostratified columnar epithelium, without goblet cells.
Where is the olfactory system located?
In the posterior, superior regions of each nasal fossa
Describe olfactory cells
Bipolar neurones. One dendrite extends to surface to form a swelling from which non-motile cilia extend parallel to surface. These increase surface are and respond to odours
What cells line the vocal cords?
Stratified squamous epithelium
What do the vocal cords consist of?
A vocal ligament (elastic fibre bundle front to back)
A vocalis muscle (skeletal muscle)
Other than talking, what other functions do the vocal cords have?
Help prevent foreign objects from reaching the lungs, close to build up pressure when coughing is required.
What dimensions is the trachea?
10cm long
2.5cm wide
Describe the histology of the primary bronchi
Hisiologically similar to the trachea, but their cartilage rings/spiral muscle completely encircles the lumen
Describe the histology of the secondary/tertiary bronchi
Histiologically similar to primary bronchi, but cartilage arranged as irregular crescent plates/islands rather than rings
What is a bronchiole?
Has a diameter of 1mm or less
What do Clara cells secrete, and what does it do?
Lipoprotein, which prevents walls sticking together during expiration.
Also Clara fell Protein CC16 (a measurable marker for disease)
What is a terminal bronchiole?
Has a diameter of less than 0.5mm
The smallest conducting portion, no goblet cells to prevent ‘drowning’ in own mucous
What can an alveolus open up into?
Respiratory bronchiole
Alveolar duct
Alveolar sac
Another alveolus (via an alveolar pour)
Give 4 features of alveolar walls
Have abundant capillaries
Are supported by a basketwork of elastic and reticular fibres
Have a covering composed chiefly of type 1 pneumocytes
Have a scattering of type 11 pneumocytes
Other than pneumocytes, what other cell may be in alveoli?
Macrophages, to phagocytise particles
What are the name of the 4 facial sinuses?
Frontal
Ethmoid
Maxillary
Sphenoid
What are the 3 different types of rib, and which ones are they?
True - connect directly to sternum 1-7
False - connect to sternum via cartilage 8-10
Floating - don’t connect to sternum at all 11-12
What are the 2 connections via which the ribs connect to the vertebrae?
Superior costotransverse ligament
Costotransverse joint
Joint with ventral body
What are the 3 movements of the chest wall?
‘Bucket handle’ - up/down of ribs
‘Pump handle’ - anterior/posterior motion
Diaphragm moves down 1 1/2 intercostal spaces
In which way do the Intercostal muscles pull the ribs?
External - pulls ribs up (1st rib is anchored). inhalation
Internal and innermost pull ribs down. Exhalation
In which order is the intercostal neurovascular bundle arranged?
Vein
Artery
Nerve
Top—>Bottom
In which direction do the external intercostal muscle fibres run?
‘Hands in pocket’ down and medially
In which way do the innermost and internal intercostal muscles run?
Perpendicular to the external
Where abouts in the intercostal space does the neurovascular bundle run?
Along the bottom of each rib/top of each space
Between the internal and innermost muscles
At what level does the vena cava go through the diaphragm?
T8
At what level does the oesophagus go through the diaphragm?
T10
At what level does the aortic hiatus go through the diaphragm?
T12
What is the diaphragm comprised of?
Dome shaped peripheral muscle and central tendon
What does the azygous system do?
Collection of veins which collect blood from intercostal spaces taking it to the superior vena cava
Which way do the lungs themselves pull?
In and up
Which way does the thoracic cavity itself pull?
Out
What way does the passive stretch of the diaphragm pull?
Down
When respiratory muscles relax, what happens?
Expiration
When respiratory muscles contract in resting breathing, what happens?
Inspiration
What are the 4 stages of the respiratory cycle?
- Inhalation
- Rest
- Expiration
- Pause
When is forced expiration required?
Exercise, coughing, singing
What brings about forced expiration?
Contraction of internal intercostal muscles/abdominal muscles
How many lobes has the left lung got? What are they called?
2
Upper and lower
How many lobes has the right lung got? What are they called?
3
Upper, middle and lower
How many fissures has the left lung got? What are they called?
1
Oblique fissure
How many fissures has the right lung got? What are they called?
2
Oblique fissure, horizontal fissure
What vessels has each lung got at its hilum?
Principal bronchus Pulmonary artery 2 pulmonary veins Bronchial vessels Pulmonary plexus (nerves) Lymphatics
What is pneumothorax?
The integrity of the pleural seal is broken, lungs tend to collapse
What vasculature supplies the parietal pleura?
Intercostal arteries/veins
What vasculature supplies the visceral pleura?
Bronchial arteries/veins
What are the 3 surfaces of each lung?
Costal, diaphragmatic, mediastinal
What are the sympathetic efferents of the lungs?
Bronchodilator, vasoconstrictor
What are the two lymphatic plexuses to the lungs?
Superficial sub-pleural lymphatic plexus
Deep bronchopulmonary lymphatic plexus
Where is the superficial sub-pleural lymphatic plexus of the lungs found?
Deep in visceral pleura.
What does the superficial sub-pleural lymphatic plexus drain?
Drains hilar lymph nodes and lung parenchyma and visceral pleura
Where does the deep bronchopulmonary lymphatic plexus drain to?
Hilar nodes
What is compliance?
The ‘stretchiness’ of the lungs
Volume rover unit pressure change
(Higher compliance - easier to stretch)
What does the pleural seal do?
Holds outer surface of the lungs to inner surface of the chest wall, ensuring the 2 move together
When are the elastic forces of lung and chest wall balanced?
Functional residual capacity
Lung volume at the end of resting expiration
What is elastic recoil inversely proportional to?
Compliance of lung
What muscles may you additionally use for forced expiration?
Serratus anterior
Pectoralis maj
Sternocleidomastoid
Scalene
What are the elastic properties of the lung due to?
Elastic tissue
Surface tension of alveolar fluid
What does surfactant do?
Reduces surface tension by disrupting interactions between surface molecules (breaking up hydrogen bonds)
What is surfactant comprised of?
90% phospholipids (60% of which is phosophatidylcholine)
7-15% phosphatidyglycerol
10% protein
Surfactant protein A
What produces surfactant?
Type 2 pneumocytes (cuboidal)
What does surfactant do?
Reduces surface tension when lungs are deflated, but less so when fully inflated (little breaths easy)
What is Laplace law? (Pressure)
Pressure = (2xsurface tension) / radius
Give 3 ways surfactant aids lung function
Increases lung compliance by reducing surface tension
Stabilises lungs, preventing small alveoli collapsing into big ones
Prevents surface tension in alveoli creating suction force causing Transudation of fluid from pulmonary capillaries
What is respiratory distress syndrome in premature babies?
Babies are born with too little surfactant and few large alveoli
What is poiseuilles law? (Movement through tubes)
Resistance = pressure / rate of flow
=(8 x viscosity of fluid x length of tube) / (1 x radius)
What is the key point if poiseuilles law of movement through tubes?
Small tubes have high flow resistance
What helps compensate for the increase of resistance in the lungs as the tubes get narrower?
Each branching point increases the number of airways in parallel, this compensates for increase of resistance as air passes down
Where is the highest resistance in the airways?
Upper airways - trachea and larger bronchi
Each branching point increases the number of airways in parallel, this compensates for increase of resistance as air passes down
What happens to pressure throughout the lung?
Remains constant as surfactant equalises surface tension
What is flicks first law of diffusion?
Flux of molecules across a barrier is proportional to the permeability of the molecules times the surface area over which diffusion can occur times the concentration gradient
What is me soluble, CO2 or O2?
CO2 (~20 times more soluble)
What is the limiting factor of the rate of gas exchange in the lungs?
Rate of O2 diffusion
What compensates for slower O2 diffusion?
Larger pressure difference for O2
What is ficks equation for rate of diffusion?
D = (Pressure diff. x Area x Solubility) / distance x (root of molecular weight of gas)
Assume 37 degrees C
What are the barriers O2 must cross to get from in the alveolus to the RBC?
Epithelial cell of alveolus Tissue fluid Endothelial cell of capillary Plasma Red cell membrane
What is the distance between air and alveolar capillary blood?
~0.6um
Decreases during inhalation as lung distends
How is inspired air different in concentrations to atmospheric air?
Saturated with water vapour as it passes along moist airways (PH2O ~6%)
Therefore O2 and N2 are slightly diluted
What is the normal value for partial pressure of CO2 in the alveoli?
5.3kPa
What is the normal value for partial pressure of O2 in the alveoli?
13.3kPa
CO2 reacts with water to form what?
Carbonic acid, which then dissociates to form bicarbonate ions CO3- and H+
Where is the bodies CO2 found?
5% dissolved in plasma
5% carried as carboxy-haemoglobin on proteins
90% carried as bicarbonate ions in plasma
How does fibrotic lung disease impede gas exchange?
Thickened alveolar membrane due to collagen deposition slows gas exchange
How does emphysema impede gas exchange?
Destruction of alveoli reduces surface area for gas exchange
How does pulmonary oedema impede gas exchange?
Fluid in interstitial space increases diffusion distance
What proportion of air inhaled doesn’t actually partake in gas exchange (only goes to ‘dead space’)
1/3
How much air is usually in the anatomical/serial dead space?
150ml
What is the respiratory zone of the respiratory pathway?
The useful portion (over which gas exchange takes place)
What mathematical equation must you do to calculate alveolar ventilation rate?
Subtract dead space volume from tidal volume
What is the approximate usual pulmonary blood pressure?
~20-30mmHg
Low
What does the low pulmonary blood pressure result in?
Lungs are not perfused evenly (more blood in base of lung)
What does V/Q ratio effect?
The concentration of O2 and CO2 in the alveoli and blood during respiration
How would you measure diffusion resistance?
Carbon monoxide transfer test
14% He, 0.1% CO inhaled. Hold breath for 10s. Rate of diffusion estimated due to its high affinity for CO
What is spirometry?
Lung function test
Subject breathes from a closed chamber over water, chambers volume changes with ventilation
Define tidal volume
Volume in and out with each resting breath
Define inspiratory reserve volume
Extra volume that can be inhaled at rest
Define expiratory reserve volume
Extra volume that can be exhaled at rest
Define residual volume
Volume remaining after a maximal expiration (contributes to total lung capacity)
What is a lung capacity?
2 or more lung volumes added together
What is inspiratory capacity?
TV + IRV
What is vital capacity?
IRV + TV + ERV
What is a typical value for tidal volume?
0.5l
What is a typical value for expiratory reserve volume?
1.5l
What is a typical value for inspiratory capacity?
3.0l
What is a typical value for vital capacity?
5.0l
What is a typical value for inspiratory reserve volume?
2.5l
What is a typical value for residual volume?
0.8l
What is a typical value for functional residual capacity?
2.3l
What is a typical value for total lung capacity?
5.8l
What factors influence vital capacity?
Inspiration - compliance of lungs, force of inspiratory muscles
Expiration - airway resistance, increases as expiration proceeds
What is single breath spirometry?
Patient fills lungs, then breaths out as far and fully as possible. Volumes measured by detector over time - how much and how fast.
What is FEV 1.0?
Forced expiratory volume for the 1st second - volume expired over the 1st second, effected by how quickly air slows down, decreased if airways are narrowed.
What is FVC?
Forced vital capacity ~5l
What should the ratio between FVC and FEV 1.0 usually be?
More than 70% FVC
If reversible, then suggestive of asthma
What is a vitalograph trace?
A plot of volume expired Vs time
Why is peak expiratory reserve rate often used as a screening test for airway narrowing?
Can be measured simply using a cheap device
What is a helium dilution test used for?
Measuring the volumes of air left in lungs after expiration
How is a helium dilution test carried out?
Patient inhales a known volume of gas containing a known concentration of helium. Helium is not metabolised, so as patient breaths, helium conc. changes as it gets diluted as it is in a larger volume. (Adding to air already in lungs)
What test would you use to measure dead space?
Nitrogen washout
How would you carry out a nitrogen washout test?
The last gas in the airways is the first out. Subject inhalers breath of pure O2, then exhales via a metre measuring the % N2. Initially only O2 expired, then mixture of O2 and air (including N2) from alveoli. Volume expired at transition is serial dead space.
At a pO2 of 13.3 kPa in the alveoli, how much O2 will be dissolved into blood?
0.13mmol/l
Describe the structure of haemoglobin
Tetramer (2 alpha, 2 beta subunits, each consisting of 1 haem and 1 globin), can hold up to 4 O2 molecules
Describe the structure of myoglobin
Monomer, 1 O2 molecule
What is myoglobin used for primarily?
O2 store for when O2 gets very low, e.g. In muscle
Why is %saturation a good measure to use?
Takes into account the amount of pigment present, independent of pigment concentration
What state is haemoglobin in when pO2 is low?
Tense - difficult for O2 to bind
What state is haemoglobin in when pO2 is high?
Relaxed - easy for O2 to bind
When is haemaglobin ‘saturated’?
Above 9-10kPa
When is haemaglobin unsaturated?
Below 1kPa
When in haemaglobin half saturated?
3.5-4kPa
What will the effect of pO2 and O2 content in a patient with anaemia?
pO2 will be normal (saturation will be normal), but O2 content will be lower
What does tissue pO2 depend on?
How metabolically active the tissue is
What is a typical value for tissue pO2?
~5kPa
To what level does Hb saturation usually drop to?
~65% (~35% O2 given up)
What level can the pO2 not fall below in most cells? Why?
3kPa
Must be this high to drive diffusion of O2 to cells
How does capillary density effect how low pO2 can be in tissue?
The higher the capillary density, the lower the pO2 can fall (doesn’t have as far to diffuse)
There will be a high capillary density in very metabolically active tissue
How does decreased pH effect haemaglobin?
Promotes T-state (O2 dissociation)
How does increased pH effect haemaglobin?
Promotes R-state (O2 association)
What is the Bohr effect?
pH is lower in more metabolically active tissues (CO2 production), so extra O2 is given up
In which direction does the Bohr effect cause the curve to shift?
To the right
High way does increased temperature cause the oxygen disassociation curve to shift?
To the right
What effect does temperature have on haemaglobin affinity for O2?
Decreased
Metabolically active tissues have slightly higher temperature, so more O2 is given up
When might maximum unloading of haemaglobin occur?
In tissues where pO2 can fall to low level and conditions where increased metabolic activity results in more acid environment and higher temperature - up to 70% of bound O2 can be given up
What is the maximum % of bound O2 which can be given up?
70%
Over the whole body, what percentage of bound O2 is generally given up?
~27%
This will increase during exercise (oxygen reserve)
What effect does 2,3-diphosphoglycerate have on oxygen association curve?
Shifts curve to the right
Allows more O2 to be given up at tissues
What happens to 2,3-DPG levels in stored blood?
Levels decrease due to refrigeration
What causes 2,3-DPG levels to increase?
Altitude, anaemia
When CO binds to Hb, what does it form? What is key about this reaction?
COHb
Irreversible reaction
Increases affinity of subunits for O2, so they wont give it up in tissues
At what level does CO poisoning become fatal?
If HbCO > 50%
What is cyanosis?
Bluish colouration due to unsaturated haemoglobin (deoxygenated Hb is less red than oxygenated Hb)
Can be peripheral or central
What causes peripheral cyanosis?
Poor circulation
What causes central cyanosis?
Poorly saturated blood in systemic circulation
What does pulse oximetry detect?
Hb saturation
How does pulse oximetry detect Hb saturation?
Difference in absorption of light between oxy and deoxy Hb
Only detects pulsatile arterial blood, ignores levels in tissues and non-pulsatile venous blood
When may pulse oximetry give an incorrect reading?
If patient is anaemic - doesn’t take into account how much Hb is present
What is a more accurate alternative to pulse oximetry?
Arterial blood gas
However more invasive and time consuming
Does blood contain more CO2 or O2?
2.5 times more CO2 than O2
Approximately how much CO2 is dissolved in blood?
21mmol/l
Approximately how much O2 is dissolved in blood?
8.9mmol/l
What is CO2s major role in the blood?
Controlling blood pH (maintaining pH 7.35-7.45)
At pCO2 5.3kPa, how much CO2 is dissolved in blood?
1.2mmol/l
What is the pH of plasma dependent on normally?
How much CO2 reacts to form H+
What determines how much CO2 reacts to form H+ normally?
Concentration of CO2 dissolved (pushing reaction to the right, increasing H+)
Concentration of HCO3- (pushing reaction to left, decreasing H+)
What determines how much dissolved CO2 is in the blood normally?
Directly dependent on partial pressure of CO2. If pCO2 rises, pH will fall (more H+)
If pCO2 in alveoli is the determining factor, this is controlled by rate of breathing.
What cation is associated with HCO3- in the plasma?
Na+
How much bicarbonate is normally in plasma?
25mmol/l
What can the Henderson-Hasselbalch equation be used for?
Calculating pH from pCO2 and HCO3- conc.
Where is most of the HCO3- found in the blood produced?
In RBCs
Contain enzyme carbonic anyhydrase CA
What is the reaction catalysed by carbonic anhydrase in RBCs?
CO2 + H2O —> H+ + HCO3-
How is HCO3- removed from RBCs once it has been produced?
Via chloride bicarbonate exchanger on their cell surface
What determines how much HCO3- is produced by erythrocytes?
How much H+ is bound to haemoglobin
Do RBC control HCO3- concentration in plasma?
No
What controls amount of HCO3- in blood?
Kidneys via excretion
What determines how much CO2 is in the blood?
Rate of breathing
What buffers extra acids in the blood (e.g. Lactic, keto…)
Hydrogen carbonate
How does bicarbonate act as a buffer for extra acids produced by the body (e.g. Keto, lactic…)
Acids react with HCO3- to produce CO2, therefore decreasing concentration of HCO3-. CO2 produced is removed by breathing and pH changes are minimised.
What determines arterial pCO2?
Alveolar pCO2
What does buffering of H+ by haemoglobin depend on?
Level of oxygenation (amount bound is dependent on state of Hb molecule)
How does having lots of O2 bound to a Hb molecule effect the amount of H+ ions it binds?
More O2 - R state - less H+ bound
How does having not much O2 bound to a Hb molecule effect the amount of H+ ions it binds?
Less O2 bound to Hb - T state - More H+ ions bound
What does more H+ ions being able to bind to Hb (in venous blood) incur?
More HCO3- can be produced, therefore more CO2 (unreacted) is present in plasma
When in lungs, and Hb gives up O2, returning to relaxed state, what happens to the H+ associated to it?
Hb gives up extra H+, which then goes on to react with HCO3- to form CO2, which is then exhaled
What are carbamino compounds?
CO2 bound directly to proteins (onto amino groups on globin of Hb)
Does the binding of CO2 to proteins contribute to blood pH?
No, but does contribute to CO2 transport
Where are most carbamino compounds formed?
At the tissues, because pCO2 is higher and the unloading of O2 facilitates binding of CO2 to Hb (which will then be given up at lungs)
What are the 3 forms by which CO2 are transported? (And what proportion of CO2 transport is via this mechanism)
Dissolved (10%)
As hydrogen carbonate (60%)
As carbamino compounds (30%)
What is the approximate value of CO2 in whole arterial blood?
~21.5mmol/l
What is hypoxia?
O2 deficiency at tissue level. If it persists tissue will undergo ischaemic damage or necrosis
What are the 4 types of hypoxia?
Hypoxaemic, or respiratory hypoxia
Anaemic hypoxia
Stagnant, or circulatory hypoxia
Cytotoxic hypoxia
What is hypoxaemic (or respiratory) hypoxia?
Poor oxygenation at the lungs, low pO2 and low O2 saturation
What is anaemic hypoxia?
Normal pO2, but insufficient Hb to carry the O2, e.g. CO poisoning
What is stagnant, or circulatory hypoxia?
Reduced delivery of O2 due to poor perfusion. Could be global (e.g. Shock), or local (e.g. Peripheral vascular disease)
What is cytotoxic hypoxia?
O2 delivery is adequate, but tissues unable to utilise O2, e.g. Cyanosis poisoning
What is the normal level of O2 saturation?
94-98%
What is the normal pO2?
11.1 - 14.4 kPa
At what level of O2 is tissue at serious risk of being damaged?
Less than 90%
At what O2 saturation level is tissue at serious risk of being damaged?
Less than 8kPa
Describe type 1 respiratory failure (pO2, O2 saturation, pCO2)
pO2 of arterial blood low (less than 8kPa)
O2 saturation less than 90%
pCO2 normal or low
Describe type 2 respiratory failure (pO2, O2 saturation, pCO2)
pO2 in arterial blood less than 8kPa
O2 saturation less than 90%
pCO2 high, above normal range (4.3-6.4 kPa)
What are the 3 mechanisms for respiratory failure?
Ventilators (pump) failure - unable to move sufficient air in/out of the lungs
Poor diffusion across alveolar membrane
Mismatching of ventilation and perfusion
What happens when V/Q ratio is less than 1?
Alveolar pO2 falls, pCO2 rises
Type 1 respiratory failure
What might call V/Q ratio to fall below 1?
Could be due to reduced ventilation of part of lung, or reduced perfusion of part of lung (increases Q as rest of lung receives excess of what’s available)
What is the treatment for type 1 respiratory failure?
Treat cause
Oxygen therapy might help hypoxia
What is the treatment for type 2 respiratory failure?
Treat cause
Problems of hypercapnia might require assisted ventilation (particularly if acute)
What are the clinical features of hypoxia?
Exercise intolerance
Tachypnoea (may be perceived as breathlessness)
Confusion
Central cyanosis (late/when O2 saturation <85%)
When is cyanosis present?
When more than 50gm/l of desaturated Hb is in the blood
What is cyanosis?
Purplish decolorisation of skin and mucous membranes due to the colour of desaturated Hb
What does central cyanosis indicate ?
Arterial hypoxia
O2 Saturation <85%