Lec 26 - Lungs

• Respiratory epithelium function is best described as lubrication and motility
• The function of the respiratory portion of the respiratory system is gas exchange
• Terminal bronchioles are part of the conducting system and consist of simple cuboidal epithelium which some cilia. They contain smooth muscle to allow them to contract and dilate
• This is an image of a contracted terminal bronchiole

  A) alveolus

  B) smooth muscle

  
• This is an image of a relaxed bronchiole

  
• Terminal bronchioles contain club cells that produce a surfactant-like substance. They replace goblet cells and help lubricate and decrease surface tension.
• The transition between terminal bronchiole and respiratory bronchiole is if there is alveoli branching off the bronchiole it is respiratory
• This is an example of a respiratory bronchiole

  (contains budding alveoli - can see sharp transition where cuboidal epithelium turns into squamous)

  
• Pressure in the alveoli are equalized by pores between all the alveoli called pores of Kohn. This is how you get diffusion of gases across multiple alveoli at the end terminal.
• Alveolar septum separates the alveoli in a sac. They consists of epithelial cells and endothelial cells (and both their basement membranes) forming air-blood barrier
• Type II pneumocytes secrete surfactant - reduces surface tension to keep alveoli open and produces a surface for particles to get stuck on
• Type I pneumocytes are found in alveoli and make up the alveolar wall
• The following image is a TEM image showing lamellar bodies within granules of a type II pneumocyte

  
• Alveolar macrophages roll around on the surfactant and phagocytose inhaled particles and antigens trapped in mucus or surfactant. They then go up the ciliary escalator and move up the respiratory tract and are disposed of by swallowing
• Type II pneumocytes are filled with granules of fat which are released into the lumen of alveoli. They have a round and prominent nucleus and have lamellar bodies within their granules which can be seen using TEM