Exchange Surfaces

• Why is diffusion alone enough to supply the needs of single-celled organisms?

  • The metabolic activity of a single-celled organism is usually low, so oxygen demand and carbon dioxide production is low.
  • The surface are to volume ratio of the organism is large, increasing the speed at which exchange occurs.
  • The distance between supply and cells is short, so efficient diffusion can occur.
• How do you calculate the surface area to volume ratio?


  Surface area divided by volume.
• What are specialised exchange surfaces?

  These are surfaces within large, multicellular organisms, that allow for increased efficiency of the exchange of substances obtained and removed.
• What are the key characteristics of specialised exchange surfaces?

  Increased surface area, thin layers, good blood supply, good ventilation.
• What are some examples of specialised exchange surfaces?


  Root hair cells, villi, alveoli, gills.
• What is the benefit of increased surface area?

  This provides the area needed for exchange and overcomes the limitations of the smaller surface area to volume ratio of larger organisms.
• What is the benefit of thin layers?

  The distances that substances have to diffuse are short, making the process fast and efficient.
• What is the benefit of good blood supply?

  The steeper the concentration gradient, the faster diffusion takes place, so having a good blood supply ensures substances are constantly delivered to and removed from the exchange surface, and maintains the concentration gradient.
• What is the benefit of good ventilation?

  Specifically for gases, a strong ventilation system also helps maintain concentration gradients, making the process more efficient.
• What are the key features of the human gaseous exchange system?

  The nasal cavity, trachea, bronchus, bronchioles, alveoli.
• What are key features is the nasal cavity?

  1. A large surface area with good blood supply, which warms the blood to body temperature.
  2. A hairy lining which secretes mucus to trap dust and bacteria, protecting the lung tissue from irritation and infection.
  3. Moist surfaces which increase the humidity if the incoming air, reducing evaporation from the exchange surface.
• What is the trachea?

  The main airway carrying clean, warm, moist air from the nose into the chest, and a wide tube supported by incomplete rings of cartilage, allowing food to move down the oesophagus.
• What is the trachea lined with?

  Ciliated epithelial cells, with goblet cells between and below the ciliated epithelial cells.
• What are goblet cells?

  Specialized cells found in the respiratory and digestive tracts that secrete mucus, trapping dust and microorganisms that have escaped the nose lining.
• What are ciliated epithelial cells?

  Cells with hair-like structures called cilia on their surface, the cilia beat and move mucus, along with any trapped substances, away from the lungs; with most entering the throat where it swallowed and digested.
• What is the bronchus?

  This is what the trachea divides into within the chest cavity, with the right bronchus leading to the right lung, and the left bronchus leading to the left lung, and a structure similar to the trachea with the same supporting rings of cartilage but smaller.
• What are the bronchioles?

  These are what the bronchi divide into, and due to being smaller have no cartilage, but have smooth muscle lining their walls, and a thin layer if flattened epithelium which makes some gaseous exchange possible. When the muscle contracts, the bronchioles constrict, and when the muscle relaxes the bronchioles dilate; altering the amount of air reaching the lungs.
• What are the alveoli?

  These are tiny air sacs which the main gas exchange surfaces of the body, and are unique to mammalian lungs, with each consisting of a layer of flattened epithelial cells, along with some collagen and elastic fibres (elastin).
• What is the purpose of elastic tissues in the alveoli?

  They allow the alveoli to stretch as air is drawn in, and when they return to their resting size, they help squeeze the air out; a process known as the elastic recoil of the lungs.
• What are the adaptations of the alveoli?

  • Large surface area for efficient diffusion of gases.
  • Thin layers of both the alveoli and surrounding capillaries, being only a single epithelial cell thick, reducing the diffusion distance between the air in the alveolus and blood in the capillaries.
  • Good blood supply from a strong capillary network, providing a constant blood flow and maintaining a strong concentration gradient for carbon dioxide and oxygen between the alveoli and capillaries.
  • Good ventilation of air in and out of the alveoli, helps again maintain a steep concentration gradient.
• What mixture is the inner surface of the alveoli covered in?

  A thing layer of a solution of water, salts, and lung (pulmonary)

  surfactant.
• What is the role of lung (pulmonary) surfactant?

  As the alveoli increase in size during inspiration, the surfactant becomes more spread out, reducing surface tension and allowing the alveoli to stay open, making it easier for the lungs to inflate.
• What is ventilation?


  The movement of air in and out of the lungs as a result of pressure changes in the thorax due to breathing movements.
• What is the rib cage?

  A semi rigid case that surrounds the chest cavity.
• What is the diaphragm?

  A broad, domed sheet of muscle that forms the floor of the thorax.
• What is the internal and external intercostal muscle?

  Muscle found between the ribs.
• What is the thorax?

  The chest cavity, lined by pleural membranes which surround the lungs, which contains a space between them called the pleural cavity, that usually contains a thing layer of lubricating fluid so the membranes can slide easily over each other as you breathe.
• What occurs during inspiration?

  This is an energy using process, whereby the diaphragm contracts, flattening and lowering, the external intercostal muscle relax, causing the ribs to move up and outward, and the elastic fibres of the alveoli stretch. The volume of the thorax increases so the pressure is reduced, and is now lower than the pressure of the atmospheric air, causing air to be drawn through the nasal passages, trachea, bronchi, and bronchioles into the lungs, until the pressure is equalised.
• What occurs during expiration?

  This is a passive process, whereby the diaphragm relaxes, moving upwards into its resting dome position, the external intercostal muscle relaxes, causing the ribs to move down and inwards, and the elastic fibres of the alveoli return to their normal length. The volume if the thorax decreases so the pressure is increased, and is now higher than the pressure of the atmospheric air, causing air to move out of the lungs until the pressure is equalised.
• How can you forcibly exhale?

  Using energy, the internal intercostal muscles contract, pulling the ribs down hard and fast, and the abdominal muscles contract forcing the diaphragm up to increase the pressure in the lungs rapidly.
• What occurs during asthma attacks?

  The cells lining the bronchioles release histamines, chemicals that make epithelial cells inflated, stimulate goblet cells to produce excess mucus, and the smooth muscle of bronchiole walls to contract, causing the airways to become narrow and mucus filled.
• What are the treatments of asthma?

  • Relievers, chemicals similar to adrenaline that attach to active sites the surface membranes of smooth muscle cells in the bronchioles, making them relax, and dilating the airways.
  • Preventers, steroids taken everyday to reduce the sensitivity of the airway lining.
• How can we measure the capacity of the lungs?

  A peak flow meter, vitalograph, and spirometer.
• What is a peak flow meter?

  A device that measures the rate at which air can be expelled from the lungs.
• What is a vitalograph?

  Complex version of a peak flow meter, in which the patient blows out as quickly as possible through a mouthpiece, and the instrument produces a graph of the amount of air they breathe out and how quickly it is breathed out, from which the forced expiratory volume can be calculated.
• What is a spirometer?

  A device used to measure different aspects of lung volume, as well as breathing patterns, done through an individual wearing a nose clip and breathing in and out of an airtight chamber filled with oxygen, until the oxygen runs out, causing the chamber lid to move up and down, and leaving a trace on a revolving drum that can be interpreted.
• What is used to remove carbon dioxide from the airtight chamber?

  A canister of soda lime is attached to remove carbon dioxide.
• What are the components of lung volume?

  Tidal volume, vital capacity, inspiratory reserve volume, expiratory reserve volume, residual volume.
• What is tidal volume?

  The volume of air that moves in and out of the lungs with each resting breath.
• What is the vital capacity?

  The maximum volume of air that can inhaled or exhaled in a single breath, which varies depending on age, gender, and size.