Lung AnatomyOccupy all of the thoracic cavity except mediastinum | Root | site of vascular, bronchial attachments | Costal surface | anterior, lateral, posterior surfaces |
Upper Respiratory Tractconduction, 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 Tractconduction, 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 AnatomyRespiratory 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 | | | Surrounded by fine elastic fibres | | | Contain open pores that connect adjacent alveoli, allow air pressure throughout lung to be equalised | | | House alveolar macrophages that keep alveolar surfaces sterile | Conducting zone | Conduits to gas exchange sites | | | Includes all other respiratory structures | Trachea | Windpipe: from larynx into mediastinum | | | Wall composed of 3 layers: mucosa, submucosa, adventitia | | | Carina: Last tracheal cartilage, point where trachea branches into two bronchi | Conducting zone structures | Trachearight and left primary bronchi | | | Primary bronchussecondary bronchi3rd, 4th etc. | | | Bronchioles: < 1mm diameter | | | Terminal bronchioles: < 0.5mm diameter | Respiratory muscles | Diaphragm and other muscles that promote ventilation |
Respiratory Volumes| | Adult Male average | Adult Female average | Tidal volume (TV) | | | 500mL | 500mL | amount of air inhaled/exhaled each breath at rest | Inspiratory reserve volume (IRV) | | | 3100mL | 1900mL | amount of air during forceful inhalation after normal TV | Expiratory reserve volume (ERV) | | | 1200mL | 700mL | amount of air during forceful exhalation after normal TV exhalation | Residual volume (RV) | | | 1200mL | 1100mL | amount of air remaining in lungs after forced exhalation |
Respiratory Capacities| | Adult Male average | Adult Female average | Total lung capacity (TLC) | | | 6000mL | 4200mL | max amount of air contained in lungs after max inspiratory effort: TLC = TV+IRV+ERV+RV | Vital capacity (VC) | | | 4800mL | 3100mL | max amount of air that can be expired after max inspiratory effort: VC = TV+IRV+ERV | Inspiratory capacity (IC) | | | 3600mL | 2400mL | max amount of air that can be inspired after normal expiration: IC = TV+IRV | Functional residual capacity (FRC) | | | 2400mL | 1800mL | volume of air remaining in lungs after normal TV expiration: FRC = ERV+RV |
Pulmonary Function TestsSpirometer | instrument used to measure respiratory volumes/capacities | Can distinguish between | Obstructive pulmonary disease: increased airway resistance e.g. bronchitis, asthma | | | 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 GradientDalton's Law of Partial Pressures | Total pressure exerted by mixture of gases is the sum of pressures exerted by each | | | Partial pressure of each gas is directly proportional to its percentage in the mixture | Example: | Atmospheric pressure is 760mmHg at sea level | | | Oxygen constitutes ~21% of the atmosphere | | | 21% x 760 = 159mmHg |
| | Mechanisms of Breathing: Pulmonary VentilationInspiration and expiration | Inspiration: gases flow into lungs | | | Expiration: gases exit the lungs | Mechanical processes dependant on volume changes in thoracic cavity | Volume changespressure changes | | | Pressure changesgases flow to equalise pressure | Boyle's Law | Relationship between pressure and volume of a gas |
Mechanics of Breathing: InspirationInspiration | 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 RespirationCapillary 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 | | | pO2 of venous blood in 40mmHg | | | pCO2 is 45mmHg |
External RespirationExchange of O2 and CO2 across the respiratory membrane | Influenced by: | Partial pressure gradients | | | Gas solubilities | | | Ventilation-perfusion (V/Q) coupling | | | Structural characteristics of the respiratory membrane |
Control of RespirationMedullary 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 | | (when excited, they cause respiratory centres to increase ventilation) | Integrates input from peripheral stretch and chemoreceptors | | Substantial drops in arterial pO2 (to 60mmHg) must occur in order to stimulate increased ventilation | 2. Ventral respiratory group (VRG) | | Influence of arterial pH | Rhythm-generating and integrative centre | | Can modify respiratory rate/rhythm even if CO2 and O2 levels are normal | Sets eupnea (12-15 breaths/min) | | 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 | | Respiratory system controls will attempt to raise the pH by increasing respiratory rate and depth | Expiratory neurone inhibit the inspiratory neurone |
Oxygen TransportMolecular O2 is carried in the blood | 1.5% dissolved in plasma | | | 98.5% loosely bound to each Fe of haemoglobin (Hb) in RBCs | | | 4x bound O2 per Hb | O2 and Hemoglobin | Oxyhemoglobin (HBO2): hemoglobin-O2 combination | | | Reduced hemoglobin (HSB): haemoglobin that has released O2 | Influence of pO2 on Hemoglobin Saturation | Oxygen-hemoglobin dissociation curve | | | 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 | | | Occur in systemic capillaries | | | Increases O2 unloading | | | Shifts HbO2 dissociation curve to the right | | | Decreases in these factors shift the curve to the left by decreasing O2 unloading |
Carbon Dioxide TransportCO2 is transported in the blood in three forms | 7-10% dissolved in plasma | | | 20% bound to globin of Hb (carbaminohemoglobin) | | | 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 | | | 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 | | | H2CO3 is split by carbonic anhydrase into CO2 and H2O | | | CO2 diffuses into the alveoli |
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