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Occupy all of the thoracic cavity except mediastinum
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Root
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site of vascular, bronchial attachments
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Costal surface
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anterior, lateral, posterior surfaces
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conduction, filtration, humidification and warming of inhaled air
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Nasal Cavity
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Nasal conchae, nasal vestibule, nostril
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Paranasal Sinuses
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Maxillary, frontal, sphenoidal and ethmoidal sinuses
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Pharynx
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Nasopharynx, oropharynx, laryngopharynx
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Larynx (superior)
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Vocal cords, epiglottis, vestibular fold, thyroid cartilage, vocal fold, cricoid cartilage, thyroid gland
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conduction, gas exchange
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Trachea
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cervical, thoracic
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Bronchi
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left primary bronchus, right primary bronchus
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Bronchioles
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respiratory bronchiole, terminally bronchiole, alveoli
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Lungs
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left lung, right lung (larger)
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Respiratory zone: site of gas exchange
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Microscopic structures: respiratory bronchioles, alveolar, ducts, alveoli
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Alveoli
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~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
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Conducting zone
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Conduits to gas exchange sites
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Includes all other respiratory structures
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Trachea
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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
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Conducting zone structures
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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
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Respiratory muscles
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Diaphragm and other muscles that promote ventilation
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Adult Male average
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Adult Female average
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Tidal volume (TV)
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500mL
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500mL
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amount of air inhaled/exhaled each breath at rest
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Inspiratory reserve volume (IRV)
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3100mL
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1900mL
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amount of air during forceful inhalation after normal TV
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Expiratory reserve volume (ERV)
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1200mL
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700mL
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amount of air during forceful exhalation after normal TV exhalation
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Residual volume (RV)
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1200mL
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1100mL
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amount of air remaining in lungs after forced exhalation
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Adult Male average
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Adult Female average
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Total lung capacity (TLC)
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6000mL
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4200mL
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max amount of air contained in lungs after max inspiratory effort: TLC = TV+IRV+ERV+RV
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Vital capacity (VC)
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4800mL
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3100mL
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max amount of air that can be expired after max inspiratory effort: VC = TV+IRV+ERV
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Inspiratory capacity (IC)
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3600mL
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2400mL
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max amount of air that can be inspired after normal expiration: IC = TV+IRV
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Functional residual capacity (FRC)
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2400mL
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1800mL
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volume of air remaining in lungs after normal TV expiration: FRC = ERV+RV
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Spirometer
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instrument used to measure respiratory volumes/capacities
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Can distinguish between
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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)
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Minute ventilation
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Total amount of gas flow into/out of respiratory tract in 1 minute
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Forced vital capacity (FVC)
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Gas forcibly expelled after taking a deep breath
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Forced expiratory volume (FEV)
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Amount of gas expelled during specific time intervals of FVC
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Dalton's Law of Partial Pressures
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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
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Example:
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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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Inspiration and expiration
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Inspiration: gases flow into lungs
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Expiration: gases exit the lungs
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Mechanical processes dependant on volume changes in thoracic cavity
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Volume changespressure changes
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Pressure changesgases flow to equalise pressure
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Boyle's Law
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Relationship between pressure and volume of a gas
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Inspiration
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Expiration
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Sequence of events
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1. Inspiratory muscles contract diaphragm descends, rib cage rises
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1. Inspiratory muscles relaxdiaphragm rises, rib cage descends due to costal cartilage recoil
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2. Thoracic cavity volume increases
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2. Thoracic cavity volume decreases
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3. Lungs are stretchedintrapulmonary volume increases
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3. Elastic lungs recoil passivelyintrapulmonary volume decreases
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4. Intrapulmonary pressure drops -1mmHg
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4. Intrapulmonary pressure rises+1mmHg
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5. Air flows into lungs down its pressure gradient until intrapulmonary volume = 0 (equal to atmospheric pressure)
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5. Air flows out of lungs down its pressure gradient until intrapulmonary pressure is 0
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Capillary gas exchange in body tissues
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Partial pressures and diffusion gradients are reversed compared to external respiration
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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
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Exchange of O2 and CO2 across the respiratory membrane
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Influenced by:
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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
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Medullary Respiratory Centres
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Pontine Respiratory Centres
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Chemical Factors
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Involves neurons in the reticular formation of the medulla and pons
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Influence and modify activity of the VRG
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Influence of pO2
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1. Dorsal respiratory group (DRG)
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Smooth out tradition between inspiration/expiration and vice versa
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Peripheral chemoreceptors in the aortic and carotid bodies are O2 sensors
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Near the root of cranial nerve IX
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(when excited, they cause respiratory centres to increase ventilation)
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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
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2. Ventral respiratory group (VRG)
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Influence of arterial pH
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Rhythm-generating and integrative centre
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Can modify respiratory rate/rhythm even if CO2 and O2 levels are normal
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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
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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
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Expiratory neurone inhibit the inspiratory neurone
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Molecular O2 is carried in the blood
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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
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O2 and Hemoglobin
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Oxyhemoglobin (HBO2): hemoglobin-O2 combination
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Reduced hemoglobin (HSB): haemoglobin that has released O2
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Influence of pO2 on Hemoglobin Saturation
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Oxygen-hemoglobin dissociation curve
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Shows how binding and release of O2 is influenced by the pO2
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Hemoglobin Saturation Influencing Factors
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Increases in temperature, H+, pCO2, and 2,3-biphosphoglycerate (BPG)
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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
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CO2 is transported in the blood in three forms
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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
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CO2 combines with water to form carbonic acid (H2CO3), which quickly dissociates
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CO2 + H2O H2CO3 H+ + HCO3-
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In systemic capillaries
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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
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In pulmonary capillaries
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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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