20.1.11 bronchi and alveoli

features of bronchi

primary bronchi → secondary bronchi → tertiary bronchi → primary bronchioles → terminal bronchioles

bronchi

supported by cartilage; interior contain ciliated mucous cells

bronchioles

lack cartilage but have smooth muscle instead; lack mucous but still have ciliated cells (the lack of things help with efficiency of gas exchange)

• the more branches, the more surface area for passage of gas

respiratory bronchioles

minimal smooth muscle

alveolar ducts

short conduits of mainly connective tissue

alveolar sacs

grape-like clusters of individual alveoli that opened from the alveolar ducts

• surrounded by capillaries

  • the thin layer of the capillary allows for gas to pass from the alveoli to the capillaries

    • structures are very elastic, helps with expanding when breathing

alveoli

• structures across which gas exchange occurs

• thin walled with large lumen

• provide intimate contact between inhaled air and blood in pulmonary capillaries that wrap the alveolar walls

• collectively, the alveoli have a surface area of 70m2 (size of a single tennis court (2 tennis courts if we count both lungs)

Type I

• most common cell type

  • connected to a thin basement membrane with a pulmonary endothelial cell on the other side (“respiratory membrane”)

Type II

• releases surfactant

  • cuboidal cells; make and secrete the surfactant

  • a mixture of lipids and proteins, helps reduce surface tension in the alveoli, preventing them from collapsing, especially during exhalation when the alveoli shrink.

  • Surfactant allows the alveoli to remain open and facilitates more efficient gas exchange

surfactant

reduces surface tension between water molecules lining inner alveoli surfaces

Type III

aka alveolar macrophages; resident alveolar immune cells

• scavenge microorganisms, other particles