gas exchange in mammals

• • As you breathe in, air enters the trachea
  • The trachea splits into two bronchi - one bronchus leading to each lung
  • Each bronchus then branches off into smaller tubes called bronchioles
  • The bronchioles end in small 'air sacs' called alveoli which is where gases are exchanged
  • There are lots of alveoli in the lungs to provide a large surface area for diffusion
  • The ribcage, intercostal muscles and diaphragm all work together to move air in and out
• diagram

  A) trachea

  B) ribcage

  C) intercostal muscles

  D) bronchus

  E) bronchiole

  F) lung

  G) diaphragm

  H) alveoli

  I) bronchiole

  J) alveolus

  
• goblet cells 


  They line the airways and secrete mucus. The mucus traps microorganisms and dust particles in the inhaled air, stopping them from reaching the alveoli.
• Cilia

  The cilia are hair-like structures on the surface of epithelial cells lining the airways. They beat the mucus secreted by the goblet cells. This moves the mucus (plus the trapped microorganisms and dust) upward away from the alveoli towards the throat, where it's swallowed. This helps prevent lung infections.
• elastic fibres

  Elastic fibres in the walls of the trachea, bronchi, bronchioles and alveoli help the process of breathing out. On breathing in, the lungs inflate and the elastic fibres are stretched. Then, the fibres recoil to help push the air out when exhaling.
• smooth muscle

  Smooth muscle in the walls of the trachea, bronchi and bronchioles (except the smallest bronchioles) allows their diameter to be controlled. During exercise the smooth muscle relaxes, making the tubes wider. This means there's less resistance to airflow and air can move in and out of the lungs more easily.
• cartilage

  Rings of cartilage in the walls of the trachea and bronchi provide support. It's strong but flexible - it stops the trachea and bronchi collapsing when you breathe in and the pressure drops.
• diagram

  A) Trachea

  B) elastic fibres

  C) smooth muscle

  D) c-shaped cartilage

  E) ciliated epithelium containing goblet cells

  F) bronchiole

  G) smooth muscle and elastic fibres

  H) ciliated epithelium with some goblet cells

  I) bronchus

  J) smooth muscle

  K) small cartilage piece

  L) elastic fibres

  M) ciliated epithelium containing goblet cells

  N) alveolus

  O) elastic fibres

  P) alveolar epithelium

  Q) capillary

  
• distribution of features

  A) large C-shaped pieces

  B) smaller pieces

  C) none

  D) none

  E) none

  F) none

  G) yes

  H) yes

  I) yes

  J) yes

  K) no

  L) no

  M) yes

  N) yes

  O) yes

  P) yes

  Q) yes

  R) yes

  S) yes

  T) yes

  U) yes

  V) no

  W) no

  X) ciliated

  Y) ciliated

  Z) ciliated

  [) ciliated

  \) no cilia

  ]) no cilia

  
• there is elastic fibres in all of the airways to stretch (inhale) and recoil (exhale)
• there is ciliated epithelium in the trachea, bronchus and bronchiole because they contain goblet and ciliated cells. which traps pathogens and first and moves it up and out
• there is smooth muscle in the trachea, bronchus and bronchiole to control the diameter of the airway
• there is cartilage in the trachea for support