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Anatomy, physiology and pathology of the respiratory system (“but mainly the lungs”). Dr Andrew Potter Registrar Department of Radiation Oncology Royal Adelaide Hospital. Anatomy. Overview. Consists of nose, pharynx, larynx, trachea, bronchi, lungs - PowerPoint PPT Presentation
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Anatomy, physiology and pathology of the respiratory system (“but mainly the lungs”)
Dr Andrew Potter
Registrar
Department of Radiation Oncology
Royal Adelaide Hospital
Anatomy
Overview
Consists of nose, pharynx, larynx, trachea, bronchi, lungs
Conducting portion and respiratory portionObtains O2 and eliminates CO2 to external
environmentHelps regulate pH by adjusting rate of
removal of acid-forming CO2
Nose
External portion– Bone and cartilage, covered by skin– Mucous membrane lining– Nostrils, midline septum
Internal portion– Skull cavity inferior to cranium, superior to mouth
• Bounded by ethmoids, maxillae, palatine bone, inferior nasal conchae
– Communicates with pharynx through the choanae– Communicates with paranasal sinuses
• frontal, sphenoid, maxillary, ethmoid
– Openings of naso-lacrimal ducts, Eustachian tubes
Pharynx (throat)
Funnel-shaped tube, ~13cm longStarts at choanae (internal nares) extending
to level of cricoid cartilagePosterior to nasal cavity, oral cavity,
larynxAnterior to cervical vertebral bodiesMuscular wall lined by mucous membrane
Nasopharynx
Uppermost part of pharynxPosterior to nasal cavityExtends to plane of soft palateEustachian tube openings
– Allows air exchange to equalise ear/nose/throat pressures
Pharyngeal tonsils (adenoids) on post wall
Oropharynx
Posterior to oral cavityExtends from soft palate to level of hyoidCommon passage way for air, food, fluid -
communicates with oral cavityPalatine and lingual tonsils
Hypopharynx (laryngopharynx)
Extends downwards from hyoidContinuous with oesophagus (posteriorly)
and larynx (anteriorly)Common passage way for air and food
Larynx (voice box)
Connects pharynx with tracheaEpiglottis
– cartilage valve to separate food and airMidline in neck, anterior to C4-C6Wall consists of 9 pieces of cartilage
– 3 single• Thyroid, epiglottis and cricoid
– 3 paired• Arytenoid, corniculate, cuneiform
Vocal cords - false (ventricular) and true– Vibration of vocal cords results in phonation– Barrier against foreign bodies entering lower respiratory tract
Upper respiratory tract - summary
System of interconnected spacesTransports, filters, humidifies and warms
inspired airReceptors for smell in the nasal cavityParanasal sinuses act as resonating
chambers for speech– Also reduce weight of facial skeleton
Trachea
Tubular air passage way ~12cm long, 2.5cm diameter
Anterior to oesophagusExtends from larynx (cricoid cartilage) to
~T5Bifurcation at T5 (carina) into left and
right main bronchi
Trachea
16-20 incomplete ‘C’-shaped hyaline cartilage rings provide rigidity– Open part of each ring faces posteriorly to
oesophagus– Allows for oesophageal expansion during
swallowingTransverse smooth muscle (trachealis) and
elastic connective tissue attach open ends of cartilage rings
Trachea
Important relations– Anteriorly: thyroid isthmus, inferior thyroid
veins, sternohyoid and sternothyroid muscles, manubrium, thymus remnants
– Laterally: lobe of thyroid, carotid sheath, SVC (right), aortic arch and branches (left),
– Posteriorly: oesophagus, recurrent laryngeal nerves
Trachea
Ciliated pseudo-stratified columnar epithelium
Seromucous glands and ducts– humidify air
Cilia (‘brush border’)– Transport excess mucus,
foreign bodies upwards like an escalator
Primary (main) bronchi
Incomplete cartilage ringsStratified columnar epithelium as in tracheaRight main bronchus
– To right lung
– Shorter, wider and more vertical than left• More prone to foreign bodies lodging
Left main bronchus– To left lung
Secondary (lobar) bronchi
One for each lobe of each lung– 2 on the left
– 3 on the right
Further division into tertiary (segmental) bronchi to supply each segment of each lobe
…progressive branching until reaching bronchioles and finally terminal bronchioles and alveolar ducts
Structural features
Gradual transition from one type of airway to the next
Epithelium– Tall, pseudostratified columnar ciliated
epithelium in larynx and trachea– Simple cuboidal non-ciliated in small airways– Goblet cells (mucus secreting) gradually
disappear
Structural features
Lymphoid aggregates (MALT)– Produces IgA antibodies secreted onto mucosal surface
• protection against invading micro-organisms
Smooth muscle– Lies deep to mucosa (except in trachea)– Becomes increasingly important as airway diameter
decreases– Regulates calibre of airway and hence resistance to air
flow• Sympathetic - muscle relaxation• Parasympathetic - constriction
Structural features
Serous and mucous glands– Progressively less numerous in narrower
airwaysCartilage
– Supporting skeleton for larynx, trachea and bronchi
– Maintains patency during respiration– Gradually diminishes; absent beyond tertiary
bronchi
Lungs - gross anatomy
Paired, cone-shaped organs in thoracic cavitySeparated by heart and other mediastinal
structuresCovered by pleura
– Fibrous membrane with overlying flattened epithelium
– Outer layer - parietal pleura, attached to chest wall
– Inner layer - visceral pleural, attached to lung surface
– Potential space between the two layers (pleural cavity)
• Normally contains small amount of pleural fluid - reduces friction between surfaces during movement of respiration
Lungs - gross anatomy
Extend from diaphragm inferiorly to just above clavicles superiorly
Lies against thoracic cage (pleura, muscles, ribs) anteriorly, laterally and posteriorly
Inferior lung base is concave and fits over convexity of each hemi-diaphragm
Narrow superior apexSurface curved to match curvature of rib cage
Lungs - gross anatomy
Hilum– Medial ‘root’ of the lung– Point at which vessels, airways and lymphatics
enter and exit
Cardiac notch– Lies in medial part of left lung to
accommodate the heart
Lobes and fissures
Lungs divided into lobes by fissures– Both have an oblique fissure extending forwards and
downwards• Separates upper and lower lobes on left• Separates upper, middle and lower lobes on right
– Right lung also has horizontal fissure• Separates upper and middle lobes
Each lobe has its own secondary (lobar) bronchus– Named according to the lobe supplied
Further subdivision of each lobe into segments– …similarly supplied by a tertiary (segmental) bronchus
Lobules
Each segment has multiple small compartments - lobules– Each wrapped in connective tissue– Contains lymphatic vessel, arteriole, venule,
branch from terminal bronchiole– Terminal bronchioles subdivide into
microscopic respiratory bronchioles
Alveoli
Cup-shaped outpouchingsClustered in alveolar sacs
– Resemble microscopic bunches of grapesLined by epitheliumThin elastic basement membraneLined by type I alveolar cells with occasional type II
alveolar cells– Type II cells secrete alveolar fluid and surfactant– Surfactant acts to reduce surface tension of alveolar fluid
(like detergent), helping to keep alveoli from snapping shut
Alveoli
Alveolar macrophages (dust cells)– Phagocytes that remove dust and debris from
alveolar spaces– Derived from peripheral blood monocytes
Alveoli surrounded by capillary network to facilitate gas exchange– Single layer of endothelium and basement
membrane
Alveolar-capillary membrane
Diffusion of gas between air and circulation occurs across alveolar and capillary walls– Type I and II alveolar cells– Epithelial basement membrane beneath alveolar wall– Capillary basement membrane– Capillary endothelium
Total thickness ~0.5µmApprox 300 million alveoli in normal lungResults in large surface area (~70m2) for gas
exchange
Alveoli
Alveoli - micro
Lung - blood supply
Dual supply– Bronchial supply
• Bronchial arteries supply bronchi, airway airway walls and pleura
– Pulmonary supply• Pulmonary arteries enter at hila and branch with airways
• Deoxygenated blood from right ventricle pulmonary trunk left and right pulmonary arteries arterioles capillaries oxygenated blood to venules pulmonary veins left atrium
– Venous return is common (ie. both return via pulmonary veins)
Lymphatics
Lymphatic drainage follows vesselsParabronchial (peribronchial) lymphatics
and nodes hilar nodes mediastinal nodes pre- and para-tracheal nodes supraclavicular nodes
Physiology
Mechanics of breathing
Inspiration - an active process– Diaphragm lowers– Ribs pivot upwards
• Intercostal muscles contract• Action similar to a swinging bucket handle
– Intra-thoracic pressure lowers• Intrapleural pressure is normally 4mmHg lower than atmospheric
pressure, ‘sucking’ the lungs outwards
– Lung expands• As volume increases, pressure decreases - Boyle’s law
– Air flows from higher atmospheric pressure (760mmHg) into low pressure of the lungs (758mmHg)
Mechanics of breathing
Expiration - passive– Inspiratory muscles relax
• Ribs move downwards
• Diaphragm relaxes and its domes rise
– Surface tension of alveolar fluid causes an inward pull
– Elastic recoil of alveolar basement membranes
– Reverse pressure gradient• 762mmHg in lungs, 760mmHg atmospheric
– Gas pushed out
Respiration
External (pulmonary) respiration– exchange of O2 and CO2 between respiratory
surfaces and the blood (breathing)
Internal respiration– exchange of O2 and CO2 between the blood and
cells
Cellular respiration– process by which cells use O2 to produce ATP
External respiration
Exchange of O2 and CO2 between alveoli and blood
Partial pressure of O2 higher in alveoli (105mmHg) than blood (40mmHg) so O2 diffuses into blood
Partial pressure of CO2 higher in blood (45mmHg) than alveoli (40mmHg), so CO2 moves into alveoli in opposite direction and gets exhaled out
GasAtmospheric
airAlveolar air Exhaled air
O2
21%
159 mmHg
14%
104 mmHg
16%
120 mmHg
N2
78%
597 mmHg
75%
569 mmHg
75%
566 mmHg
CO2
0.04%
0.3 mmHg
5%
40 mmHg
4%
27 mmHg
H2O0.5%
4 mmHg
6%
47 mmHg
6%
47 mmHg
Gas partial pressures
Internal respiration
Exchange of O2 and CO2 between blood and tissues
Pressure of O2 higher in blood than tissues so O2 gets release into tissues.
Pressure of CO2 higher in tissue than in blood so CO2 diffused in opposite direction into blood.
CO2 is a waste productO2 is used in cellular respiration
Pulmonary respiration
Internal respiration
Gas transport in blood
Carbon dioxide– 70% as bicarbonate ion (HCO3
-) dissolved in plasma
– 23% bound to hemoglobin
– 7% as CO2 dissolved in plasma
Oxygen– 99% bound to hemoglobin
– 1% as O2 dissolved in plasma
Control of breathing
Respiratory centre in reticular formation of the brain stem– Medullary rhythmicity centre
• Controls basic rhythm of respiration• Inspiratory (predominantly active) and expiratory
(usually inactive in quiet respiration) neurones• Drives muscles of respiration
– Pneumotaxic area• Inhibits inspiratory area
– Apneustic area• Stimulates inspiratory area, prolonging inspiration
Regulation of respiratory centre
Chemical regulation– Most important– Central and peripheral chemoreceptors
– Most important factor is CO2 (and pH) in arterial CO2 causes in acidity of
cerebrospinal fluid (CSF) in CSF acidity is detected by pH sensors in
medulla
• medulla rate and depth of breathing
Regulation of respiratory centre
Cerebral cortex– Voluntary regulation of breathing
Inflation reflex– Stretch receptors in walls of
bronchi/bronchioles
Pathology
Benign pathology
Infective– URTI, pneumonia, bronchitis, bronchiectasis– Bacterial, viral, fungal
Vascular– Pulmonary emboli, vasculitis, pulmonary oedema
Traumatic– Pneumothorax, haemothorax
Inflammatory– Idiopathic pulmonary fibrosis, sarcoidosis
Environmental– Silicosis, asbestosis
Genetic/congenital– Cystic fibrosis
Asthma
Reversible airways obstructionCommon (10% children, 5% adults)Recurrent wheeze and breathlessnessMultiple triggers
– Allergy, infection, cold, exertion, irritation, drugs, occupational exposure
Complex chronic inflammation of bronchial mucosa
Chronic obstructive airways disease (COAD, COPD)
Combination of chronic bronchitis and emphysema– Chronic inflammation of bronchi
• Chronic cough with sputum
– Destruction of normal alveolar structure• Loss of inhibition of proteases (esp. 1-
antitrypsin)• Reduced surface area for gas exchange - fewer,
large dilated air spaces• Relative hypoxia, worse on exertion
Neoplastic diseases of the lung
Common cancerPeak incidence 40-70 years of ageClosely related to cigarette smoking and
industrial carcinogens4 main histological types
– Squamous cell carcinoma (SCC) - 50%– Small cell carcinoma (SCLCa) - 20%– Adenocarcinoma - 20%– Large cell anaplastic carcinoma (LCLCa) - 10%
Neoplastic diseases of the lung
Commonly grouped as small cell (SCLCa) and non-small cell (NSCLCa) based on natural history and response to treatment
70% arise in relation to main bronchi30% arise from peripheral airways or
alveoli
Lung cancer
Squamous cell carcinoma– Arises in metaplastic squamous epithelium that develops to
line airways against chronic exposure to irritants such as smoke
– More common in men but women catching up– Mostly central/close to carina
Adenocarcinoma– Tend to be peripherally located– Less closely associated with smoking– Equal sex distribution– 4 sub-types
• Acinar, papillary, solid, bronchoalveolar
Lung cancer - gross appearance
Central squamous cell carcinoma arising near right main bronchus
Peripheral adenocarcinoma
Lung cancer
Small cell carcinoma– Highly malignant– Centrally located– Rapidly growing– Neuro-endocrine properties and behaviours
• eg. SIADH
– Commonly present with metastatic disease– Often chemo- and radio-sensitive and
responsive but rarely curable
Lung cancer - presentation
Respiratory features– Cough (80%), haemoptysis (70%), dyspnoea (60%), chest
pain (40%), wheeze (15%)Systemic features
– Anorexia, weight loss, malaise70% present with metastatic disease
– Local spread - bronchus, mediastinum– Lymphatic spread - peribronchial, hilar nodes– Trans-coelomic spread - malignant effusion, chest wall
invasion– Haematogenous spread - brain, bone, liver, adrenal glands
Lung cancer - prognosis
Poor 5-year survival– (5-30% depending on type and stage at
presentation)NSCLCa
– 75% inoperable due to age, poor lung function or advanced stage (CT head/chest/abdo, PET, WBBS, mediastinoscopy)
– If inoperable, consider chemo-radiotherapy (radical or palliative depending on stage)
Lung cancer - prognosis
SCLCa– ~30% are ‘limited stage’ (confined to within
an achievable RT field)• Good local control with chemoRT but usually
progress to systemic disease
• Role of PCI
• Median survival 11 months
• 45% 1-year survival
– Extensive stage• Palliation only
Malignant mesothelioma
Primary neoplasm of pleura Closely related to asbestos
exposure Latent period of up to 50 years Chest pain, breathlessness Forms a thick rind around
lung and pericardium Death usually occurs within
10 months No effective treatment RT to prevent spread along
biopsy/drain tracks as needed
Respiratory system - summary
Upper respiratory tract– Series of cavities to filter, warm, humidify and
conduct air to lower respiratory tract
Lower respiratory tract– Trachea, bronchial tree deliver air to alveoli
– Gas exchange within alveoli• Diffusion down partial pressure gradients
– Dual blood supply• Unique features of pulmonary circulation
– Mechanics of breathing
Respiratory system - summary
Lungs– Paired thoracic organs
– Facilitate gas exchange
– Differences between left and right
Pathology– Huge range of benign conditions
– Neoplastic disease• SCLCa
• NSCLCa - SCC, adenoca, LCLCa
• Mesothelioma
• Poor prognosis
“The real reason dinosaurs became extinct…”
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