RESPIRATORY SYSTEM
Alveoli-Ravioli
Imagine covering the playing surface of a racquetball court with a thin plastic wrap and stuffing it into a 3 liter soft drink bottle. .....................Sounds impossible?
But the size of a racquetball court is about the same size as the gas exchange surface of a 70 kg man and that is then compressed in to a volume lesser than the size of a 3 liter bottle. This tremendous area of gas exchange is what is required to supply the trillions of cells in the body with adequate amount of oxygen.
Animal cells survive on a steady supply of oxygen and nutrients from the environment, coupled with removal of carbon dioxide and other gases. In small, simple aquatic animals, these needs can be met with simple diffusion across the body surface.Diffusion is the phenomenon by which particles diffuse from areas of higher concentration to areas of lower concentration.
The rate of diffusion is limited by distance and as a result most multicellular animals, use specialized respiratory organs associated with the circulatory system. Respiratory organs take a variety of forms, but all possess a large surface area compressed into a small space.
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Frogs have three respiratory surfaces; meaning three areas of its body which can aid in gas exchange. A frog's respiratory surfaces are its skin, lungs, and the thin membranes lining its mouth and pharynx.
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Some terrestrial animals such as the slug, a shell like snail, meet the challenges of dehydration by behavioral adaptation that restricts them to only humid environments and night activities.
However a more common solution is anatomical: an internalized respiratory epithelium. Human lungs are enclosed within the chest cavity to limit their contact with the outside world. Internalization creates a humid environment for the exchange of gases with the blood and protects exchange surface from damage. Internalized lungs create another problem, however: how to exchange air between the atmosphere and the exchange surface deep within the body. Air flow requires a muscular pump to create the pressure gradients. Thus in more complex animals, the respiratory system, consists of two separate components, a muscular pump and a thin moist exchange surface. In humans the pump is the musculoskeletal structure of the thorax, and the lungs themselves consists of the exchange epithelium and the associated blood vessels.
Functions:
The primary function of the respiratory system are :
- Exchange of gases between the atmosphere and blood: Oxygen is brought into the body for distribution to the tissues, and carbon dioxide wastes produced by metabolism are eliminated.
- Homeostatic regulation of body pH.
- Protection from inhaled pathogens and irritating substances.: Like all epithelia that contact the external environment, the epithelium found in the respiration system is well supplied with mechanisms to trap and destroy potentially harmful substances before they can enter the body.
- Vocalization: Air moving across the vocal cords creates vibrations used for speech, singing, and other forms of communication.
In addition to serving these functions, the respiratory system is also a source of a significant losses of water and heat from the body.