beathing system

• Gas exchange surface in humans


  • Large surface area to allow faster diffusion of gases across the surface
  • Thin walls to ensure diffusion distances remain short
  • Good ventilation with air so that diffusion gradients can be maintained
  • Good blood supply to maintain a high concentration gradient so diffusion occurs faster
• Lungs


  The gas exchange surface in humans
• All gas exchange surfaces have features in common which allow the maximum amount of gases to be exchanged across the surface in the smallest amount of time
• Ribs


  Bone structure that protects internal organs such as the lungs
• Intercostal muscle


  Muscles between the ribs which control their movement causing inhalation and exhalation
• Diaphragm


  Sheet of connective tissue and muscle at the bottom of the thorax that helps change the volume of the thorax to allow inhalation and exhalation
• Trachea


  Windpipe that connects the mouth and nose to the lungs
• Larynx


  Also known as the voice box, when air passes across here we are able to make sounds
• Bronchi (pl)

  Large tubes branching off the trachea with one bronchus (sin) for each lung
• Bronchioles

  Smaller tubes formed by the splitting of bronchi in the lungs
• Alveoli


  Tiny air sacs where gas exchange takes place
• Pleural cavity


  The fluid filled space between the pleural membranes which reduces friction and allows the lungs to move freely
• Cilia and mucus

  • The passages down to the lungs are lined with ciliated epithelial cells
  • Cilia cells have tiny hairs on the end of them that beat and push mucus up the passages towards the nose and throat where it can be removed
  • The mucus is made by special mucus-producing cells called goblet cells because they are shaped like a goblet, or cup
  • The mucus traps particles, pathogens like bacteria or viruses, and dust and prevents them from getting into the lungs and damaging the cells there
• Cilia


  • Extensions of the cell membrane
• Cilia are extensions of the cell membrane
• Cilia are found in the cytoplasm
• Cilia are found near the nucleus
• Cilia are found near the mitochondrion
• Cilia are found in the cell membrane
• Cilia are found in mucus
• Intercostal Muscles & Diaphragm


  • Muscles are only able to pull on bones, not push on them
  • There must be two sets of intercostal muscles to work antagonistically to facilitate breathing
• Breathing

  1. External intercostal muscles pull the rib cage up

  2. Internal intercostal muscles pull the ribcage down
• Diaphragm


  A thin sheet of muscle that separates the chest cavity from the abdomen
• Ventilation


  1. Inhalation

  2. Exhalation
• Inhalation


  1. Diaphragm contracts and flattens

  2. External intercostal muscles contract to pull ribs up and out

  3. Increases volume of chest cavity (thorax)

  4. Decreases air pressure inside lungs relative to outside

  5. Air is drawn in
• Exhalation


  1. Diaphragm relaxes and moves upwards back into domed shape

  2. External intercostal muscles relax so ribs drop down and in

  3. Decreases volume of chest cavity (thorax)

  4. Increases air pressure inside lungs relative to outside

  5. Air is forced out
• Inhalation


  1. Air pressure decreases

  2. Air is drawn into the lungs

  3. Diaphragm contracts, pulling downwards
• Breathing in


  • External intercostal muscles contract
  • Ribcage moves up and out
  • Diaphragm contracts and flattens
  • Volume of thorax increases
  • Pressure inside thorax decreases
  • Air is drawn in
• Exhalation


  1. Pressure increases

  2. Air is forced out of the lungs

  3. Diaphragm relaxes and moves up

  4. External intercostal muscles relax, allowing the ribcage to drop inwards and downwards
• Exhalation


  • External intercostal muscles relax
  • Ribcage moves down and in
  • Diaphragm relaxes and becomes dome-shaped
  • Volume of thorax decreases
  • Pressure inside thorax increases
  • Air is forced out
• Forced Exhalation


  1. External intercostal muscles work

  2. Internal intercostal muscles work

  3. Ribs pulled down and in

  4. Decrease volume of thorax

  5. Force air out more forcefully and quickly
• During strenuous activity


  Need to increase rate of gas exchange
• During strenuous activity


  Increased levels of carbon dioxide produced
• Forced exhalation


  Allows a greater volume of gases to be exchanged
• Alveoli


  • Highly specialised for gas exchange
  • Many rounded alveolar sacs which give a very large surface area to volume ratio
  • Thin, single layers of cells to minimise diffusion distance
• Ventilation


  Maintains high levels of oxygen and low levels of carbon dioxide in the alveolar air space
• Blood supply


  • Ensures constant supply of blood high in carbon dioxide and low in oxygen
• Layer of moisture


  On the surface of the alveoli helps diffusion as gases dissolve
• Smoking


  Causes chronic obstructive lung disease (COPD), coronary heart disease and increased risks of several different types of cancer, including lung cancer
• Chemicals in cigarettes


  • Tar - a carcinogen (a substance that causes cancer)
  • Nicotine - an addictive substance which also narrows blood vessels
  • Carbon monoxide - reduces the oxygen-carrying capacity of the blood