Mammmlian gas exchange system

• Why do mammals need an exchange system (2)

  -have a small SA: V ratio

  -high metabolic rate since they are active
• What is the site of mammalian gas exchange system

  The lungs
• What are the Alveoli

  They are tiny air sacs which are the main gas exchange surfaces of the body.
• What is the diameter of the alveoli

  200-300 um
• How to the alveoli stretch

  They have elastic fibres
• Name 4 adaptions of the alveoli

  -large SA: about 300 to 500 million per adult lung

  -thin- they have a wall of a single epithelial cell like the capillaries to make the diffusion distance short

  -good blood supply: network of around 280 million capillaries to allow a constant flow to the alveoli

  -good ventilation: breathing moves air in and out of alveoli helping to maintain a steep diffusion gradient.
• What airways carries the air from the nose

  The trachea
• What supports the trachea

  Supported by incomplete rings of strong flexible cartilage stopping the trachea from collapsing
• Why are the cartilage rings in the trachea incomplete

  To food can move easily down the oesphogus behind the trachea
• What is the trachea lined with

  Ciliated epithelium and goblet cells which secrete mucus
• What does the trachea lead to

  it splits into two bronchus (bronchi = plural)
• what does the bronchi lead to

  The bronchioles
• How big are bronchioles

  Less than 1mm
• what do the walls of the bronchioles contain

  Smooth muscle and epithelial tissue which allows them to contract
• What is ventilation

  The movement of air moving in and out of the lungs as a result of pressure changes.
• What is the pleural membrane

  Lines the thorax surrounding the lungs
• What is the pleural cavity

  Space between the lungs and the pleural membrane and contains lubricating fluid so the membranes slide easily
• what is inspiration

  taking air into the lungs and requires ATP
• what is expiration

  Breathing air out and does not require ATP
• What are the steps of inspiration

  1. External intercostal Contact and internal intercostal muscles relax
  2. diaphragm contracts and flattens
  3. the ribs are pushed up and out
  4. volume of the thorax increases
  5. pressure in the thorax decreases
  6. atmospheric pressure is greater that pulmonary pressure
  7. air is drawn into the lungs
• What are the terms of expiration

  1. External intercostal muscles relax and internal intercostal muscles contract (only when expiration is forced)
  2. the diaphragm relaxes and is pushed upwards
  3. the ribs are pulled down and in
  4. The volume of the thorax decreases
  5. the pressure in the thorax increases
  6. Pulmonary pressure is greater than atmospheric pressure
  7. air is forced out of the lungs
• how does the nasal cavity increase the efficiency of gaseous exchange system

  • large SA and good blood supply
  • mucus secreting cells
• Why does the diaphragm increase the efficiency of gas exchange

  • contract to increas volume in lungs and reduce pressure and cause inspiration
• Why can expiration be a passive process

  • it does not involve muscle contraction
  • Rib cage drops due to gravity