Lecture 1: Microanatomy of the respiratory system
• Structure of the respiratory tree:
- Upper respiratory tract: external nose nasal cavity nasopharynx oropharynx laryngealpharynx larynx
- Lower respiratory tract: trachea main bronchus lobar bronchus segmental bronchus smaller bronchus bronchiole terminal bronchiole respiratory bronchiole alveolar duct alveolus
• Features of respiratory tree:
- Conducting passage: extends from external nose to terminal bronchiole in which air flows
- Respiratory passage: starts from respiratory bronchioles to alveoli where exchange of gas occurs
• Nasal Conchae: 3 bony projections in the nasal cavity which provide increased surface area to moisten and warm the inhaled air that passes through
- Middle and inferior conchae is lined by respiratory epithelium
- Superior concha is lined by olfactory epithelium used to detected smell and has connection with nerves and receptors.
• Function of structures:
- Cartilage: hyaline cartilages provide strength to support upper airway and prevent collapsing during exhalation.
- Elastic fibres: span the entire length of the airway and provide elasticity to the walls
- Smooth muscles: located in the walls of airways and surround in a spiral arrangement
- Blood vessels: vessels in the nasal cavity are extensive and allows warming of air while capillaries in the alveoli runs with the airways for gas exchange
- Respiratory epithelium: found only in airways, named tracheobronchial epithelium, which include ciliated pseudostratified columnar cells with goblet cells.
- Glands: found in the connective tissue below epithelium, ducts extended from the glands is continuous with epithelium and can be serous or mucus (innervated by the autonomic nerve system)
• Histological features of the respiratory tree:
- Ciliated: trachea and non-alveolar channels are ciliated
- Epithelial lining: pseudostratified columnar lines trachea to segmental bronchus; columnar lines medium sized bronchi to respiratory bronchioles; alveolar ducts is lined by cuboidal and finally alveolar sacs and alveoli is lined by type II cuboidal and type I squamous epithelium
- Glandular: trachea to small bronchi contains tubuloacinous mucous glands
- Goblet cells: conductive zone beginning at trachea
- Elastic fibres: extends the entire length of respiratory tree
- Smooth muscles: all of respiratory tree except alveoli and trachea (muscle called trachealis)
- Cartilage: C shaped cartilage surround extrapulmonary zone of trachea and main bronchus while plates of cartilage cover intrapulmonary zone from lobar bronchus to small bronchi
• Function of the upper airways:
- Conduit: the upper airways have the role of conducting air from outside to the alveoli hence epithelial cells are of great importance. Stratified squamous epithelium lines the inside of the entrance to the nasal cavity and is keratinized to protect against abrasion. Oropharynx, vocal cords and epiglottis are all lined by stratified squamous as they are subjected to abrasion.
- Conditioner of inhaled air: increased temperature in the respiratory tract as connective tissue has a rich vascular supply (including the nasal cavity). Blood flows in the opposite direction to the flow of air so countercurrent maintain temperature gradient. Furthermore, relative humidity increases to near saturation through water secreted by serous glands around the conchae. Finally filtering hairs at the vestibules remove particles and beating of cilia clears them.
• Swell bodies: structures that block off the nose when engorged with blood and allows to re-humidification of the nose cavity after getting dried up. Hence breathing occurs only through 1 nose at a time
Lecture 19: Microanatomy – Lung 1
• Tracheobronchial lining: pseudostratified ciliated epithelium at the beginning mixed with goblet cells. Pseudostratfied are a type of epithelial in which all the cells are touching the basement membrane but their nucleus are arranged at different levels giving a fake “layered” appearance.
• Ciliated cells: cells that contains micro-cillia on the apical surface, making up majority of the lung epithelium.
- The cilia beat in synchrony in one direction to move the mucus (that contains dirt particles) up the airway. Beats around 4- 10 mm per min
- Kartagener’s disease: genetic condition in which loss of motor units cause cilia to lose their function along with flagella, hence immotile sperm. Situs Inversus also occurs in which organs location are reversed
- Embryonic node cilia: cilia not working
• Goblet cell: the second most frequent cells that secrete mucus from the vesicle in its cytoplasm in response to irritants.
- Along with cilia, forms a mucocillary escalator
- Irritants such as smoking cause hyperplasia of goblet cells to produce more mucus to trap particles while replacing ciliated cells. The result of buildup of mucus can clog up the airway
• Brush cells: cells with microvilli on the surface that act as sensory receptors, e.g. receive impulse about change in physiology of the epithelium. They have nerve endings attached to their base
• Small cells: generative cells at the bottom of the epithelium that is able to divide and differentiate into other type of cells
• Endocrine cells: cells containing granule within it which are hormone that regulate the epithelium.
- Function and type of hormone are still unclear
• Trachea: conducting airway that extends from the larynx to the bronchi division.
- Structure: airway lumen surrounded by connective tissue of elastin (allows stretching and also contains mucus glands). A C-shaped cartilage disk is embedded within the connective tissue around the airway.
- Trachealis: smooth muscle present only in the trachea that spans the gap between the ends of the incomplete cartilage disk, i.e. the disk does not connect there. fibroelastic connective tissue are also present to join the ends.
• Bronchi: series of airway that branches from the trachea, passing from main bronchi to lobar bronchi to segmental bronchi and to bronchioles.
- Structure: the bronchi are surrounded by discontinuous plates of cartilage (not C-shaped). The lumen at first is lined by pseudostratified epithelium which progress to columnar epithelium in smaller bronchi. Mucus gland and cartilage present in bronchi but not bronchioles.
- Features: with each dichotomous branching of the bronchi, the diameter decreases. The bronchi supply lobules of the lung and is surrounded by connective tissue
• Bronchioles: smaller airways derived from bronchi containing no cartilage and tubuloacinus mucus glands. Goes from terminal bronchioles that supply an acinus to respiratory bronchioles.
- Structure: lined by columnar ciliated epithelial cells with goblet cells. Smooth muscles are present arranged in a spiral fashion around the airway. Running along the walls of the bronchioles are blood vessels.
Lecture 21: Microanatomy – Lung 2
• Acinus: small group/collection of alveoli supplied by one terminal bronchiole.
- Structure: each acini has branching respiratory bronchiole leading alveolar ducts and alveolar sacs. It is lined by cuboidal epithelium lacking cilia. The walls contain smooth muscles.
• Alveolar space: air sacs lined with alveolar cells and are in close relation with blood vessels to allow gas exchange.
• Cells of the alveolar space:
- Type 1 epithelial: 97% made of squamous cells between the alveolar space and capillary lumen. Contributes to the blood-air barrier
- Type II epithelial: 3% made from granular cuboidal looking cells that secrete surfactant to reduce surface tension and so alveolar does not stick together during expiration. This is also a progenitor cells and can differentiate to type I.
- Macrophages: situated on the surface of epithelial in alveolar space. It phagocytoses debris in the sac and mediate inflammatory processes.
• Blood-air barrier: the basement membranes with the sandwiched connective tissue are virtually stuck together.
- Alveolar space
- Type I cells cytoplasms
- Basement membrane of squamous cells
- Connective tissue
- Basement membrane of endothelial cells
- Endothelial cells cytoplasms
- Lumen
• Pulmonary blood supply of the lung:
- Pulmonary arteries runs with the airways in the outer wall to reach the respiratory bronchioles and forms the pulmonary capillaries
- Pulmonary capillaries located in the interalveolar septum is where exchange of gas occurs
- Pulmonary veins first pass within the connective tissues of the interlobar septa and eventually with the structure upon reach the level of bronchi
• System pressure of lung:
- Bronchial arteries supplies for the bronchi and it runs within the connective tissue of airway
- Capillaries eventually formed from the bronchi occupy the connective tissue of the airway
- Deoxygenated bronchial veins formed from the capillaries and drain into the azgos vein.
• Anastomosis:
- bronchopulmonary anastomoses include bronchopulmonary arterial from pulmonary to bronchi artery.
- Bronchopulmonary vein drains to pulmonary vein
- Bronchial
Lecture 32: Respiratory clinical case
• Assess asthma control:
- Exercise tolerance
- Night time waking
- Treatment for exacerbation
- Time off work or school
- Use of bronchodilator
• Lung function test: asthma reduces peak flow. Lung function is worst at 2-3 in the morning causing night time wake-ups (breathlessness)
• Exacerbation: worsening of the condition
- Viral infection is the most common form of exacerbation
• Clinical case: patient with asthma suffers exacerbation
- Develops symptoms of running nose, fever and sore throat. Two days later develop cough of green sputum (dead neutrophils and myeloperoxidase)
- Amoxycillin was prescribed but conditions became worse. Inhaler is used every 3-4 hours and breathless with climbing stairs
- Peak flow rate was 300L/min (reference is 550L/min). Nebulised salbutamol relieved his symptoms
- Asthma attack further worsened and inhaler had minimum effect (does not work due to mucus plugging)
- At hospital there is an audible wheeze and PEF is 150L/min
• Arterial blood examination: decreased pO2 (mucus plugging causing poor ventilation and perfusion ratio) and decreased pCO2 (increase breathlessness cause increase frequency of breathing and CO2 blow off)
• Chest X-ray: hyperinflation with flattened diaphragm as narrowed airway trap gas. No pneumonia or pneumothorax was present
• Initial treatment:
- Fed with oxygen 8L/min
- Nebulised salbutamol and ipratropium (bronchodilators)
- Intravenous hydrocortisone (works faster and infusion to whole lung)
• Supporting treatment:
- Intravenous aminophylline
- Intravenous salbutamol
- Intravenous magnesium
- Intubation and mechanical ventilator
• Advice: steroid is very important
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