Respiratory system

The right and left bronchioles, terminal bronchioles, respiratory bronchioles, alveolar ducts, and alveoli form the right and left lungs respectively.

The trachea, bronchi, bronchiles, and terminal bronchioles make up the conducting zone. The respiratory bronchioles, alveolar ducts, and alveoli make up the respiratory zone.

The pulmonary blood vessels generally accompany the airways and also undergo numerous branchings. The pulmonary circulation has a very low resistance compared to the systemic circulation, and for this reason, all the pressures within the pulmonary blood vessels are low.

Air is moved in and out of the lungs by the movements of the rib cage and diaphragm, which expand the lungs to draw in air and compress the lungs to drive out air. Generally, air moves out of the lungs as a result of the elastic recoil of lung tissue. A simple model of how the lungs are inflated can be built from a bell jar.

Functions

The movement of gas through the larynx, pharynx and mouth allows us to speak, or phonate.

The respiratory tract is constantly exposed to microbes due to the extensive surface area, which is why the respiratory system includes many mechanisms to defend itself and prevent pathogens from entering the body.

Virtually all the body's blood travels through the lungs every minute. The lungs add and remove many chemical messengers from the blood as it flows through pulmonary capillary bed . The fine capillaries also trap blood clots that have formed in systemic viens.

Diseases

• Upper respiratory tract infection
• Severe Acute Respiratory Syndrome
• Tuberculosis

  Respiratory system in plants

  
  Plant respiration is limited by the process of diffusion. Even a baobab tree is mostly dead because air can penetrate only skin deep. However, most plants are not involved in highly metabolic activities like hunting, i.e. they do not need the energy necessary for predators, and thus their breathing is limited.
  

  Respiratory system in insects

  
  Insects have no concentrated respiratory organs. (Perkins, 2003) Instead insects use a system of tracheae, thin channels, that run through their body, to improve on simple diffusion and let air flow more freely throughout the organism. Spiracles are small holes that open to the outside of the body and allow air in. Spiracles can be found along the abdomen and thorax of the insect body but never on the head. (Perkins, 2003) The spiracles can control the amount of air that is let into the insect. The spiracles lead to the trachea which act like "large distribution tubes" for the air being carried. (Perkins, 2003) The trachea lead to smaller tubes called tracheoles. The insects' cells can't be too far from these tracheoles because this is where oxygen and carbon dioxide diffuse in and out of the hemolymph. This simple system limits their size because insects are purely diffusive. No modern insect exists that is larger than a foot or so (in metric units, about half a metre). Many people fear big bugs, and they should be comforted by this fact.
  

  Tissue engineering

  
  In tissue engineering, respiration is an essential problem. The small depth of diffusion respiration sufficient to support the metabolism of an average human cell is less than a millimetre (0.04 in). Various substances can be used to enhance this depth, essentially having a haemoglobising role.
  

  Sources

• Perkins, M. 2003. Respiration Power Point Presentation. Biology 182 Course Handout. Orange Coast College, Costa Mesa, CA.