Humans

• Describe and explain one feature of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange. Do not refer to surface area or moisture in your answer.

  1. One cell thick;
  2. Short diffusion distance;
• Suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide between the blood and the alveoli.

  1. Less carbon dioxide is exhaled;
  2. Reduced diffusion/concentration gradient;
  3. More carbon dioxide stays in blood OR slower movement of carbon dioxide out of blood;
• Suggest how one feature of an alveolus allows efficient gas exchange to occur.

  1. Alveolar epithelium is one cell thick;
  2. Short diffusion pathway;
• Explain why the death of alveolar epithelium cells reduces gas exchange in human lungs.

  1. Reduced surface area for gas exchange;
  2. Longer diffusion pathway;
  3. Reduced rate of exchange;
• Describe the pathway taken by an oxygen molecule from an alveolus to the blood.

  1. Across the alveolar epithelium;
  2. Across the epithelium of the capillary;
• 𝘼𝙇𝙑𝙀𝙊𝙇𝙄:

  Minute air-sacs at the end of the bronchiole. They are lined with epithelium. Between the alveoli there are some collagen and elastic fibres.
• 𝘽𝙍𝙊𝙉𝘾𝙃𝙄:

  Two divisions of the trachea each leading to one lung. The amount of cartilage reduces as they get smaller. Produce mucus to trap dirt particles and have cilia to move this towards the throat.
• 𝘽𝙍𝙊𝙉𝘾𝙃𝙄𝙊𝙇𝙀𝙎:

  A series of branching subdivisions of the bronchi whose walls are made up of muscle (which constricts to control the flow of air in and out of the alveoli) lined with epithelial cells.
• 𝘿𝙄𝘼𝙋𝙃𝙍𝘼𝙂𝙈:

  A sheet of muscle that separates the thorax from the abdomen.
• 𝙀𝙓𝙋𝙄𝙍𝘼𝙏𝙄𝙊𝙉:

  A largely passive process in which external intercostal muscles relax and internal intercostal muscles contract, the ribs move downwards and inwards, and the diaphragm muscles relax, decreasing the volume of the thorax which increases the pressure.
• 𝙄𝙉𝙏𝙀𝙍𝘾𝙊𝙎𝙏𝘼𝙇:

  Muscles which lie between the ribs. There are two sets: internal, whose contraction leads to expiration, and external, whose contraction leads to inspiration.
• 𝙄𝙉𝙎𝙋𝙄𝙍𝘼𝙏𝙄𝙊𝙉:

  An active process in which external intercostal muscles contract and internal intercostal muscles relax, the ribs move upwards and outwards, and the diaphragm contracts causing it to flatten, increasing the volume of the thorax and reducing the pressure.
• 𝙇𝙐𝙉𝙂𝙎:

  A pair of lobe structures made up of a series of highly branched tubules called bronchioles, which end in tiny air sacs called alveoli.
• 𝙍𝙄𝘽𝘾𝘼𝙂𝙀:

  The bony frame formed by the ribs around the chest.
• 𝙏𝙍𝘼𝘾𝙃𝙀𝘼:

  A flexible airway that is supported by rings of cartilage, which prevent it from collapsing as the air pressure inside falls when breathing in. Its walls are made up of muscle, lined with ciliated epithelium and goblet cells.
• 𝙑𝙀𝙉𝙏𝙄𝙇𝘼𝙏𝙄𝙊𝙉:

  The process in which air is constantly moved in and out of the lungs to maintain the diffusion of gases across the alveolar epithelium (also known as breathing).
• 𝘾𝘼𝙍𝙏𝙄𝙇𝘼𝙂𝙀:

  Found in the trachea and bronchus. Provides strength to the trachea and bronchus; holds the airway open and prevents its collapse when air pressure falls.
• 𝙎𝙐𝙍𝙁𝘼𝘾𝙏𝘼𝙉𝙏:

  A phospholipid layer that coats the surface of the lungs. It maintains moisture but reduces surface tension to stop alveoli from collapsing when air pressure falls.
• 𝙎𝙈𝙊𝙊𝙏𝙃 𝙈𝙐𝙎𝘾𝙇𝙀:

  Lines the trachea to the bronchioles. Contracts to constrict (narrow) the airways.
• 𝙂𝙊𝘽𝙇𝙀𝙏 𝘾𝙀𝙇𝙇𝙎:

  Line the trachea to the bronchioles. Secrete mucus which traps particles of dust and bacteria which are breathed into the lungs.
• 𝘾𝙄𝙇𝙄𝘼𝙏𝙀𝘿 𝙀𝙋𝙄𝙏𝙃𝙀𝙇𝙄𝘼𝙇 𝘾𝙀𝙇𝙇𝙎:

  Line the trachea to the bronchioles. Beat regularly to waft mucus up the airways towards the mouth to be removed. They help to keep the airways clear and prevent infections. They contain lots of mitochondria to provide the energy required to move cilia.
• 𝙀𝙇𝘼𝙎𝙏𝙄𝙉 (𝙋𝙍𝙊𝙏𝙀𝙄𝙉):

  Lines the airways and alveoli. Allows lung tissue to stretch when breathing in and filling up the lungs, and to recoil when breathing out to help force air out of the lungs. Allows the alveoli to return to their original shape after exhaling.
• 𝙎𝙌𝙐𝘼𝙈𝙊𝙐𝙎 𝙀𝙋𝙄𝙏𝙃𝙀𝙇𝙄𝙐𝙈:

  Line the alveoli. Flattened, thin membranes providing a short diffusion distance pathway for oxygen and carbon dioxide in the alveoli for a rapid rate of diffusion.
• 𝗦𝗧𝗥𝗨𝗖𝗧𝗨𝗥𝗘:

  The lungs of mammals are highly adapted to have a very large surface area in contact with the bloodstream to sustain a high rate of gas exchange required to maintain a high metabolic rate.
• 𝗔𝗜𝗥𝗙𝗟𝗢𝗪:

  Air flows in through the mouth and nose then down the trachea.

  The trachea then splits into two bronchi which branch off further into smaller tubes known as bronchioles.

  Bronchioles end in small air sacs known as alveoli.

  Alveoli are surrounded by capillaries; this is where gas exchange takes place.
• Each lung is surrounded by a membrane and the space (pleural cavity) is filled with pleural fluid. This lubricates the lungs and helps the lungs adhere to the walls of the thoracic cavity by water cohesion. This allows the lungs to expand with the chest during inhalation.
• 𝗔𝗗𝗔𝗣𝗧𝗔𝗧𝗜𝗢𝗡𝗦:

  1. 𝘵𝘩𝘪𝘯 𝘦𝘱𝘪𝘵𝘩𝘦𝘭𝘪𝘶𝘮 𝘰𝘧 𝘢𝘭𝘷𝘦𝘰𝘭𝘪 𝘢𝘯𝘥 𝘤𝘢𝘱𝘪𝘭𝘭𝘢𝘳𝘪𝘦𝘴 - shortens diffusion distance
  2. 𝘭𝘢𝘳𝘨𝘦 𝘯𝘶𝘮𝘣𝘦𝘳 𝘰𝘧 𝘢𝘭𝘷𝘦𝘰𝘭𝘪 - increases the surface area for gas exchange
  3. 𝘭𝘢𝘳𝘨𝘦 𝘯𝘶𝘮𝘣𝘦𝘳 𝘰𝘧 𝘤𝘢𝘱𝘪𝘭𝘭𝘢𝘳𝘪𝘦𝘴 𝘢𝘳𝘰𝘶𝘯𝘥 𝘢𝘭𝘷𝘦𝘰𝘭𝘪 - circulation constantly removes oxygenated blood to maintain a steep concentration gradient
  4. 𝘤𝘰𝘯𝘴𝘵𝘢𝘯𝘵 𝘷𝘦𝘯𝘵𝘪𝘭𝘢𝘵𝘪𝘰𝘯 - ensures the concentration of O2 in alveoli is higher and the concentration of CO2 is lower than in the blood, maintaining a steep concentration gradient
• 𝗜𝗡𝗛𝗔𝗟𝗔𝗧𝗜𝗢𝗡/𝗜𝗡𝗦𝗣𝗜𝗥𝗔𝗧𝗜𝗢𝗡:

  1. the diaphragm contracts (flattens, moves down)
  2. external intercostal muscles contract, moving the ribcage up and out
  3. volume of the thoracic cavity is increased, reducing the air pressure
  4. air moves into the trachea down the pressure gradient (high to low)
  5. active process - requires energy
• 𝗘𝗫𝗛𝗔𝗟𝗔𝗧𝗜𝗢𝗡/𝗘𝗫𝗣𝗜𝗥𝗔𝗧𝗜𝗢𝗡:

  1. the diaphragm relaxes (moves up)
  2. external intercostal muscles relax, and the ribcage moves in and down
  3. the volume of the thoracic cavity decreases, increasing the air pressure
  4. air moves out of the trachea down the pressure gradient
  5. normal expiration (not forced) is a passive process