L2 - mammalian gaseous exchange

• How gas exchange differs between small unicellular organisms compared to large multi cellular organisms:

  -small; gas exchange takes place through the cell surface membrane

  -large; less surface area per unit volume of organism so diffusion through the body surface may not be sufficient enough. therefore specialised gas exchange surfaces exist
• Structures of mammalian gaseous exchange system:

  -nasal cavity

  -trachea

  -bronchi

  -bronchioles

  -alveoli
• Nasal cavity function: air passes through to lungs
• Nasal cavity features:

  -large surface area to increase air movement

  -good blood supply to warm air to body temperature

  -ciliated epithelium lining (cilia hairs) to trap pathogens

  -mucus secreted by goblet cells to increase humidity of incoming air and reduce evaporation from exchange surface
• Nasal cavity:

  -lined with squamous epithelium

  -hairs and sebaceous glands are present

  -deeper in cavity, squamous becomes columnar and epithelium tissue with goblet cells

  -tissues on the superior concha and the nasal septum form the olfactory region

  -cell membrane covering the surface of the cilia contains olfactory receptors which respond to odour producing substances

  -supporting cells and the secretion of the serous glands contain lipofuscin granules, gives a yellow brown colour to the surface of the olfactory region
• Trachea function:

  -main airway to carry clean, moist, warm, air to lungs

  -needs to be strong to prevent collapse
• Trachea features:

  -incomplete (c shaped) rings of cartilage to allow flexibility and prevent collapse

  -lined with ciliated epithelium lining to waft away pathogens

  -goblet cells below epithelial cells to secrete mucus to trap pathogens
• Bronchi function:

  -trachea divides to form two bronchi, similar structure to trachea with smaller c rings of cartilage

  -need to be strong to prevent collapse
• Bronchi feature:

  -incomplete rings of cartilage to allow flexibility and prevent collapse
• Bronchioles function:

  -bronchi divides into many bronchioles, these constrict to force air in and out of the lungs
• Bronchioles function:

  -lined with smooth muscle which contracts to constrict the bronchioles, and relaxes to dilate. this works in conjunction with elastic fibres to recoil and return to original shape and size

  -lined with thin layer of flattened epithelium making some gas exchange possible

  -ciliated epithelium

  -may have some cartilage but reduced in smaller bronchioles
• Alveoli function:

  -site of gaseous exchange
• Alveoli features:

  -the wall of alveoli is formed by a thin sheet of tissue separating two neighbouring alveoli

  -collagen fibres (few and fine)

  -elastin elastic fibres (allow alveoli to stretch and recoil to squeeze air in and out)

  -lined with thin layer of flattened epithelium making some gas exchange possible

  -a wall of pulmonary capillaries are in direct contact with the epithelial lining of the alveoli
• The goblet cells under the epithelium secrete mucus. This mucus traps particles from air reducing the risk of infection
• Epithelium consists of ciliated cells. These have tiny hair-like structures (cilia). These waft mucus back to the throat allowing bacteria to be killed in the stomach acid when swallowed