Lung Anatomy
Occupy all of the thoracic cavity except mediastinum |
Root |
site of vascular, bronchial attachments |
Costal surface |
anterior, lateral, posterior surfaces |
Upper Respiratory Tract
conduction, filtration, humidification and warming of inhaled air |
Nasal Cavity |
Nasal conchae, nasal vestibule, nostril |
Paranasal Sinuses |
Maxillary, frontal, sphenoidal and ethmoidal sinuses |
Pharynx |
Nasopharynx, oropharynx, laryngopharynx |
Larynx (superior) |
Vocal cords, epiglottis, vestibular fold, thyroid cartilage, vocal fold, cricoid cartilage, thyroid gland |
Lower Respiratory Tract
conduction, gas exchange |
Trachea |
cervical, thoracic |
Bronchi |
left primary bronchus, right primary bronchus |
Bronchioles |
respiratory bronchiole, terminally bronchiole, alveoli |
Lungs |
left lung, right lung (larger) |
Functional Anatomy
Respiratory zone: site of gas exchange |
Microscopic structures: respiratory bronchioles, alveolar, ducts, alveoli |
Alveoli |
~300 million alveoli account for most of the lungs' volume, main site for gas exchange |
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Surrounded by fine elastic fibres |
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Contain open pores that connect adjacent alveoli, allow air pressure throughout lung to be equalised |
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House alveolar macrophages that keep alveolar surfaces sterile |
Conducting zone |
Conduits to gas exchange sites |
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Includes all other respiratory structures |
Trachea |
Windpipe: from larynx into mediastinum |
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Wall composed of 3 layers: mucosa, submucosa, adventitia |
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Carina: Last tracheal cartilage, point where trachea branches into two bronchi |
Conducting zone structures |
Trachearight and left primary bronchi |
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Primary bronchussecondary bronchi3rd, 4th etc. |
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Bronchioles: < 1mm diameter |
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Terminal bronchioles: < 0.5mm diameter |
Respiratory muscles |
Diaphragm and other muscles that promote ventilation |
Respiratory Volumes
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Adult Male average |
Adult Female average |
Tidal volume (TV) |
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500mL |
500mL |
amount of air inhaled/exhaled each breath at rest |
Inspiratory reserve volume (IRV) |
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3100mL |
1900mL |
amount of air during forceful inhalation after normal TV |
Expiratory reserve volume (ERV) |
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1200mL |
700mL |
amount of air during forceful exhalation after normal TV exhalation |
Residual volume (RV) |
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1200mL |
1100mL |
amount of air remaining in lungs after forced exhalation |
Respiratory Capacities
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Adult Male average |
Adult Female average |
Total lung capacity (TLC) |
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6000mL |
4200mL |
max amount of air contained in lungs after max inspiratory effort: TLC = TV+IRV+ERV+RV |
Vital capacity (VC) |
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4800mL |
3100mL |
max amount of air that can be expired after max inspiratory effort: VC = TV+IRV+ERV |
Inspiratory capacity (IC) |
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3600mL |
2400mL |
max amount of air that can be inspired after normal expiration: IC = TV+IRV |
Functional residual capacity (FRC) |
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2400mL |
1800mL |
volume of air remaining in lungs after normal TV expiration: FRC = ERV+RV |
Pulmonary Function Tests
Spirometer |
instrument used to measure respiratory volumes/capacities |
Can distinguish between |
Obstructive pulmonary disease: increased airway resistance e.g. bronchitis, asthma |
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Restrictive disorders: reduction in TLC due to structural/functional lung changes e.g. fibrosis, tuberculosis (TB) |
Minute ventilation |
Total amount of gas flow into/out of respiratory tract in 1 minute |
Forced vital capacity (FVC) |
Gas forcibly expelled after taking a deep breath |
Forced expiratory volume (FEV) |
Amount of gas expelled during specific time intervals of FVC |
Partial Pressure Gradient
Dalton's Law of Partial Pressures |
Total pressure exerted by mixture of gases is the sum of pressures exerted by each |
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Partial pressure of each gas is directly proportional to its percentage in the mixture |
Example: |
Atmospheric pressure is 760mmHg at sea level |
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Oxygen constitutes ~21% of the atmosphere |
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21% x 760 = 159mmHg |
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Mechanisms of Breathing: Pulmonary Ventilation
Inspiration and expiration |
Inspiration: gases flow into lungs |
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Expiration: gases exit the lungs |
Mechanical processes dependant on volume changes in thoracic cavity |
Volume changespressure changes |
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Pressure changesgases flow to equalise pressure |
Boyle's Law |
Relationship between pressure and volume of a gas |
Mechanics of Breathing: Inspiration
Inspiration |
Expiration |
Sequence of events |
1. Inspiratory muscles contract diaphragm descends, rib cage rises |
1. Inspiratory muscles relaxdiaphragm rises, rib cage descends due to costal cartilage recoil |
2. Thoracic cavity volume increases |
2. Thoracic cavity volume decreases |
3. Lungs are stretchedintrapulmonary volume increases |
3. Elastic lungs recoil passivelyintrapulmonary volume decreases |
4. Intrapulmonary pressure drops -1mmHg |
4. Intrapulmonary pressure rises+1mmHg |
5. Air flows into lungs down its pressure gradient until intrapulmonary volume = 0 (equal to atmospheric pressure) |
5. Air flows out of lungs down its pressure gradient until intrapulmonary pressure is 0 |
Internal Respiration
Capillary gas exchange in body tissues |
Partial pressures and diffusion gradients are reversed compared to external respiration |
pO2 in tissue is always lower than in systemic arterial blood |
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pO2 of venous blood in 40mmHg |
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pCO2 is 45mmHg |
External Respiration
Exchange of O2 and CO2 across the respiratory membrane |
Influenced by: |
Partial pressure gradients |
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Gas solubilities |
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Ventilation-perfusion (V/Q) coupling |
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Structural characteristics of the respiratory membrane |
Control of Respiration
Medullary Respiratory Centres |
Pontine Respiratory Centres |
Chemical Factors |
Involves neurons in the reticular formation of the medulla and pons |
Influence and modify activity of the VRG |
Influence of pO2 |
1. Dorsal respiratory group (DRG) |
Smooth out tradition between inspiration/expiration and vice versa |
Peripheral chemoreceptors in the aortic and carotid bodies are O2 sensors |
Near the root of cranial nerve IX |
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(when excited, they cause respiratory centres to increase ventilation) |
Integrates input from peripheral stretch and chemoreceptors |
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Substantial drops in arterial pO2 (to 60mmHg) must occur in order to stimulate increased ventilation |
2. Ventral respiratory group (VRG) |
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Influence of arterial pH |
Rhythm-generating and integrative centre |
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Can modify respiratory rate/rhythm even if CO2 and O2 levels are normal |
Sets eupnea (12-15 breaths/min) |
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Decreased pH may reflect CO2 retention, accumulation of lactic acids, excess ketone bodies in diabetic Pts |
Inspiratory neurone excite the inspiratory muscles via the phrenic and intercostal nerves |
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Respiratory system controls will attempt to raise the pH by increasing respiratory rate and depth |
Expiratory neurone inhibit the inspiratory neurone |
Oxygen Transport
Molecular O2 is carried in the blood |
1.5% dissolved in plasma |
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98.5% loosely bound to each Fe of haemoglobin (Hb) in RBCs |
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4x bound O2 per Hb |
O2 and Hemoglobin |
Oxyhemoglobin (HBO2): hemoglobin-O2 combination |
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Reduced hemoglobin (HSB): haemoglobin that has released O2 |
Influence of pO2 on Hemoglobin Saturation |
Oxygen-hemoglobin dissociation curve |
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Shows how binding and release of O2 is influenced by the pO2 |
Hemoglobin Saturation Influencing Factors |
Increases in temperature, H+, pCO2, and 2,3-biphosphoglycerate (BPG) |
Modify Hb structure decreasing affinity for O2 |
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Occur in systemic capillaries |
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Increases O2 unloading |
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Shifts HbO2 dissociation curve to the right |
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Decreases in these factors shift the curve to the left by decreasing O2 unloading |
Carbon Dioxide Transport
CO2 is transported in the blood in three forms |
7-10% dissolved in plasma |
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20% bound to globin of Hb (carbaminohemoglobin) |
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70% transported as bicarbonate ions (HCO3-) in plasma |
CO2 combines with water to form carbonic acid (H2CO3), which quickly dissociates |
CO2 + H2O H2CO3 H+ + HCO3- |
In systemic capillaries |
HCO3- quickly diffuses from RBCs into plasma |
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Chloride shift occurs when outrush of HCO3- from the RBCs is balanced as Cl- moves in from plasma |
In pulmonary capillaries |
HCO3- moves into RBCs, binds with H+ to form H2CO3 |
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H2CO3 is split by carbonic anhydrase into CO2 and H2O |
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CO2 diffuses into the alveoli |
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