Respiratory System


Key Terms - Part 1

Bronchi - the large-bore passages that lead from the trachea to the lungs

Bronchioles - small airways extending from the bronchi into the lobes of the lungs

Alveoli - air sacs in the lungs that perform gas exchange

Gas Exchange - the process by which oxygen is extracted from inhaled air into the bloodstream, and, at the same time, carbon dioxide is eliminated from the blood and exhaled.

Diffusion - The movement of molecules from an area of high concentration to an area of low concentration

Intercostal Muscles - the muscles lying between the ribs of vertebrates that with the ribs, form the walls of the thorax

Diaphragm - the musculomembraneous partition separating the thoracic and abdominal cavities

Inhale - to draw in breathe

Exhale - to breathe out

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Key Terms - Part 2

Adaptation - a dynamic, ongoing life-sustaining process by which living organisms adjust to environmental changes

Book Lungs - a saccular respiratory organ found in some arachnids, such as spiders and scorpions, consisting of several parallel membraneous folds arranged in pages like a book

Air Sacs - cavities connected to the respiratory pathways or the oesophagus that are capable of filling with air but do not function in gas exchange in most vertebrate animals

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Respiratory Cycle

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Parts : Part 1

Nasal Chambers

  • air enters the body


  • air is warmed and moistened by mucous
  • walls covered in hair-like structures (cilia)
  • cilia trap particles to prevent infections from getting into the lungs


  • the throat, made of a smooth muscle in order to swallow


  • funnels air down
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Parts: Part 2


  • voice box, made fromsmooth muscle


  • moves air from pharynx
  • epiglottis (flap that covers respiratory/digestive system) closes when eating = stops choking
  • separates the digestion and respiratory systems



  • takes air into the lungs, keeps airways open
  • C-shaped cartilage keeps trachea open
  • smooth muscle for coughing
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Parts: Part 3


  • two sides - left and right


  • spreads air through both sides
  • cartilage rings



  • spreads air throughout lungs


  • smooth muscle
  • branching
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Parts: Alveoli



  • site of gas exchange (oxygen and carbon dioxide)
  • surrounded by capillaries to get oxygen into the blood
  • air sacs that make up a large surface area
    • gives lungs spongy appearance
  • one cell thick
  • moist to allow for gas exchange to take place easily
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Parts: Diaphragm


  • the musculomembraneous partition separating the thoracic and abdominal cavities
  • attached to the six lower ribs, at its front to the sternum, and at its back to the spine
  • the oesophagus, aorta, vena cava, and numerous nerves pass through the diaphragm
  • when relaxed it is convex, but it flattens as it contracts during inhalation, thereby enlarging the chest cavity and allowing for the expansion of the lungs
  • the large skeletal muscle at the bottom of the lungs
  • creates a vacuum in the chest cavity
  • contracts downwards when breathing in


  • relaxes and pushes up, expelling the air from the lungs
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Parts: Intercostal Muscles

  • as our lungs fill with air the chest has to expand to allow for this
  • intercostal muscles join the ribs allowing expansion
  • during the exhale the intercostal muscles relax which helps expel air from the lungs
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Parts: Air Sacs

  • do not function in gas exchange in most vertebrate animals
  • in tailless amphibians, air sacs are paired or unpaired processes in the back of the oral cavity called vocal sacs
  • in  reptiles (some turtles and lizards) air sacs are blind processes in the lungs
  • birds have five pairs of air sacs. The abdominal sacs branch off from the main bronchi and are situated between the organs of the abdominal cavity. The other four pairs are extrapulmonary prolongations of secondary bronchi:
    • cervical, lying along the oesophagus
    • clavicular, frequently merging into a single interclavicular sac
    • anterior thoracic, on the abdominal wall of the thorax
    • posterior thoracic, on the dorsal side
    • the main function of the air sacs in birds is to draw air through the lungs, especially during flight, to regulate heat and to alter the specific gravity of the birds while swimming and diving
    • many skeletal bones in birds (femur, humerus, sternum) have cavities filled with air sacs processes
    • birds also have air sacs that are not connected to bronchi; the processes of these (pharyngonasal) air sacs in some birds extend to the cranial bones, under the skin and into the anterior extremities
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Factors of Respiration

  • environmental temperature
  • metabolism
  • sleep
  • pain
  • sedation 
  • excitement
  • infection
  • exercise
  • anaethesia
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