Respiratory system

• Diffusion is a respiratory structure where O2 and CO2 pass through the body surface (skin). The skin must stay moist. Worms and amphibians use this structure.
• Gills are a respiratory structure made of outfoldings of tissue as gas exchange surfaces. They work well in water but not air due to gravity. Fish use them.
• Tracheae are a respiratory structure made of small air tubes that branch internally and carry air to cells. They are rudimentary and common in insects.
• Lungs are a respiratory system that are a complex internal structure.
• Breathing in: Diaphragm contracts, thorax and lungs expand. The larger volume decreases pressure, so air flows in.

  
  

  Breathing out: Diaphragm relaxes, thorax and lungs contract. The pressure goes up, so air flows out.
• The external nares and nasal cavity warms, filters and moistens the air.
• The nasal cavity opens to the pharynx by a pair of internal nares called choanae located above the soft palate.
• The pharynx is the joint respiratory and digestive tract channel where the two systems cross.
• The glottis is the ventral opening into the larynx. The epiglottis covers the glottis during swallowing so food and water don't get into the respiratory tract.
• The larynx (voice box) protects the opening to the trachea. It is made of cartilage.
• The trachea (windpipe) takes air from the larynx into the thoracic cavity. The lining is ciliated. The cilia beat in a wave like action that carry foreign particles and mucous up the trachea. A series of C shaped rings of cartilage prevent the trachea from collapsing upon inhalation.
• Branches from the trachea are called the bronchi which further divide into bronchioles which lead into the lungs.
• The lungs contain the gas exchange surfaces and lie in the pleural cavity of the chest.
• The bronchioles ultimately terminate into tiny air pockets called alveolar sacs which have walls pocketed with alveoli. The walls of the alveoli are one cell thick and are surrounded by blood capillaries. The alveoli are the site of gas exchange. Oxygen diffuses into the surrounding capillaries when there is a higher concentration of oxygen in the air than in the cells.
• Respiratory system steps order :

  1. Nasal chamber

  2. Internal nares

  3. Pharynx

  4. Glottis

  5. Larynx

  6. Trachea

  7. Paired Bronchi

  8. Lungs

  9. Alveoli