respiratory system

• what are the structures in the respiratory zone

  • respiratory bronchioles
  • alveolar ducts and sacs
  • alveoli
  • this is where gas exchange occurs
• what are the structures in the conducting zone

  • nasal cavities
  • pharynx and larynx
  • trachea
  • primary bronchi
  • no gas exchange occurs
• what is the function of the nasal cavities

  to warm, humidify and moisten inhaled air
• what do nasal cavities contain

  • sweat glands
  • sebaceous glands
  • hair follicles
  • olfactory mucosa
  • respiratory mucosa (secretes antibacterial enzymes and mucus)
  • cilia
• what are the 3 sections of the pharynx

  nasopharynx, oropharynx, and laryngopharynx
• what is the role of the epiglottis

  separates the trachea and oesophagus, stopping food and drink getting into the lungs
• what is the role of the larynx

  speech

  it has 2 vocal folds that vibrate with breathing, and laryngeal muscles alter the tension to create different sounds
• what is the mucociliary escalator

  cilia move the mucus upwards to the pharynx
• what factors affect mucociliary transport

  • cigarette smoke
  • dehydration
  • oxygen concentration
  • atmospheric pollutants
• Patients with cystic fibrosis have sticky mucus that is hard to move upwards so trapped pathogens are stuck in the airway and infect cells
• what are alveolar ducts

  • ducts connecting bronchioles to alveolar sacs
  • they are surrounded by smooth muscle, elastin and collagen
  • it is important to have balance between these components as too much collagen may thicken alveoli
• what are the 3 types of cell present in alveoli

  • macrophage engulfs pathogens
  • type 1 makes up the alveoli
  • type 2 secretes surfactant, produces anti-trypsin, and replenished type 1 cells
• what is the role of surfactant

  regulate surface tension and helps with stretching
• what is pleura

  the space between the lungs and the chest wall

  • parietal pleura line the thoracic cavity
  • visceral pleura cover the lungs
  • pleural space in between
• what is the importance of the pleural space

  it is less than atmospheric pressure which allows lungs to inflate. If there is damage to the pleural cavity, it equalises pleural and atmospheric pressure causing a collapsed lung (pneumothorax)
• what is pleural effusion

  fluid in the pleural cavity which also reduces expansion of the lung
• what are the important muscles involved in breathing

  • diaphragm
  • intercostal muscles
  • sternomastoids
  • scalenes
• how does inspiration work

  • thoracic cage moves upwards and outwards
  • external intercostal muscles contract to pull ribs together
  • sternocleidomastoid muscles and scalenus pull ribs upwards
  • diaphragm contracts to increase volume
  • lungs expand, lowering pressure
  • decreased pressure causes air to flow into lungs
  • pleural pressure also decreases
• how does expiration work

  • external intercostals, neck/ shoulder muscles and diaphragm relax,
  • thoracic cage moves downwards and inwards
  • this increases pressure
• what are the forces involved in inspiration

  if atmospheric pressure is greater than alveolar, air moves in

  intrapleural pressure is about -8cm H2O
• what is transpleural pressure difference (TPD)

  TPD= intrapleural pressure- alveolar pressure

  TPD increases on inspiration
• what is lung compliance

  change in volume divided by change in pressure

  measure of the lungs ability to inflate

  lower compliance = harder to inflate as more pressure change is required to affect volume (e.g in pulmonary fibrosis scarring)

  higher compliance= easier to inflate (e.g in emphysema)
• how are volume changes in the lung measured

  spirometry
• how are pressure changes in the lung measured

  esophageal pressure measured as a substitute for pleural pressure (esophageal balloon)
• why are compliance curves useful

  • plotting volume against pressure
  • emphysema increases compliance- alveoli inflate more but there is less recoil
  • fibrosis reduces compliance- harder to inflate alveoli and there is more elastic recoil
• what is the pathophysiology of emphysema

  alveoli are collapsed and broken so merge into larger groups of alveoli
• what is the pathophysiology of fibrosis

  scarring thickens alveoli walls increasing diffusion distance
• elastance is the inverse of compliance. Stiff lungs have a high elastance, low compliance
• compliance- how easily lungs inflate

  elastance- how easily lungs bounce back to their starting position
• how do alveoli stay open

  • the surfactant helps reduce surface tension and elastic recoil to prevent collapse
  • water has cohesive forces that pull alveolar walls inwards
  • alveolar interdependence means that alveoli hold each other together, reducing the risk of collapse
• which cell produce surfactant

  type II pneumocytes
• what are alveolar secretions made up of

  • mostly lipids and phospholipids
  • 10- 15% proteins
  • 4 surfactant proteins SP-A, SP-B, SP-C, SP-D
  • SPA and SPD - defence (traps foreign objects)
  • SPB necessary for surfactant function
  • SPC not necessary for breathing but mutations can lead to lung disease
• premature babies without functional surfactant have difficulty inflating their lungs as their alveoli are more likely to collapse. Hypoxia (low oxygen) can reduce surfactant production
• what is spirometry

  • a simple way to measure gas volumes
  • inverted canister in a water filled space
  • person breathes into tubing and breathing pattern is traced
• what is tidal volume

  the volume range during normal breathing
• what is residual volume(RV)

  the volume remaining after maximum forced expiration (usually 1.5L, greater in emphysema)
• what is expiratory reserve volume(ERV)

  volume expelled after maximum forced expiration, starting at the end of normal expiration (normally 1.5L)
• what is inspiratory reserve volume(IRV)

  volume inhaled during maximum forced inspiration starting at the end of normal inspiration (normally 2.5L)
• what is functional residual capacity (FRC)

  volume remaining after normal expiration (3L normally)
• what is inspiratory capacity

  maximum volume inhaled after expiration