Exchange Surfaces & Breathing

• Small organisms have a large surface area to volume ratio
• Large organisms have a small surface area to volume ratio
• The three main factors that affect the need for an exchange system:

  • size
  • surface area to volume ratio
  • level of activity
• Why do active organisms need specialised exchange surfaces?

  They need energy for movement and keeping themselves warm via aerobic respiration which needs a good supply of oxygen
• The features of a good exchange surface:

  • large surface area
  • thin barrier
  • good blood supply
  • steep concentration gradient
• What's the formula for the surface area of a sphere?

  $4πr^2$
• What's the formula for the volume of a sphere?

  $4/3 π r^3$
• To calculate surface area to volume ratio:

  divide both values by the value of the volume
• Outline why multicellular organisms require specialised gas exchange surfaces?

  • small surface area to volume ratio
  • longer diffusion distance
  • higher metabolic rate = higher demand for oxygen to respire
  • regulate body temperature = remove heat quickly
  • some cells are not in contact or able to remove/uptake substances
• In all surface area to volume ratio, volume is always expressed as 1
• Define Alveoli:

  Tiny air sacs, lined with thin epithelium cells, where gas exchange take place
• Describe how the alveoli is adapted for gas exchange:

  • small = large surface area to volume ratio
  • permeable walls = gases can dissolve easily in the moisture
  • secrete a surfactant = reduces the surface tension of the water lining, prevent them from collapsing, maintains large surface area
  • steep concentration gradient between the alveoli and the surrounding capillaries
  • extensive blood supply
  • one cell thick membrane = squamous epithelium cells
  • millions of cells
  • elastic fibres
• Why do the alveoli have permeable walls?

  gases can easily dissolve in the moisture
• Why do the alveoli have a thin membrane?

  to shorten the diffusion distance
• Why do the alveoli secrete a surfactant?

  to reduce the surface tension of the water lining, prevent them from collapsing, maintains their large surface area
• How is there a steep concentration gradient between the alveoli and the surrounding capillaries?

  There is a difference in the concentration of oxygen and carbon dioxide in blood

  This is maintained through ventilation
• How do the alveoli have an extensive blood supply?

  they are surrounded by capillaries
• Give two examples of substances that are transported out of the body:

  • urea
  • carbon dioxide
• Why do the walls of the alveoli contain elastic fibres?

  • To expand during inspiration so more oxygenated air can move in
  • For elastic recoil during passive exhalation to push deoxygenated air out
  • strength
• In the alveoli, carbon dioxide diffuses in and oxygen diffuses out
• Ventilation ensures that:

  • the concentration of oxygen in the air of the alveoi remains higher than in the blood in the capillaries
  • the concentration of carbon dioxide in the air of the alveoli remains lower than in the blood in the capillaries
• Describe the process of Inspiration (Inhalation):

  • requires energy
  • diaphragm contracts to move down and flattens = displaces the digestive organs downwards
  • external intercostal muscles contracts = raises the ribcage up and outwards
  • while the internal intercostal muscles relax
  • the volume of the chest increases
  • the pressure in the chest cavity decreases below the atmospheric pressure = creates an air pressure gradient
  • causing air to move into the lungs
• Define the Intercostal Muscles:

  The muscles found between the ribs
• Describe the process of Expiration (exhalation):

  • diaphragm relaxes and rises up to reverts into a dome by the digestive organs underneath
  • internal intercostal muscles contract
  • while the external intercostal muscles relaxes = lowering the ribcage down and inwards
  • the volume of the chest decreases
  • the pressure in the chest cavity increases above the atmospheric pressure = creates an air pressure gradient
  • causing air to move out of the lungs
• Define Ventilation:

  The movement of air in and out of the lungs via inspiration and expiration
• Which main three structures make up the airways and allow the passage of air into and out of the lungs?

  • trachea
  • bronchi
  • bronchioles
• The trachea and bronchi walls have similar structure, however, the bronchi are narrower than the trachea
• Name and explain the use of cartilage in the trachea, bronchi, and larger bronchioles?

  • Structure : C-shaped cartilage - surrounds the front of the trachea for flexibility so that it does not constrict the oesophagus when food travels down
  • Protection : prevents the walls from collapsing during inspiration
• How is cartilage used for structure in the trachea?

  They are C-shaped and surround the front of the trachea for flexibility so that it does not constrict the oesophagus when food travels down
• How is cartilage used for protection in the airways?

  It prevents the walls from collapsing during inspiration
• Define Goblet Cells:

  Cells that secrete mucus to trap dust and bacteria to reduce the risk of infection
• What is the role of the ciliated epithelium tissues in the respiratory system?

  to move trapped dust and bacteria in mucus along the airways with the cilia
• Describe and explain the use of smooth muscle in the walls of the bronchi and bronchioles.

  • contracts involuntarily to constrict the airways = narrows the lumen to restrict airflow to and from the alveoli
• Name two reasons why smooth muscle in the walls of the airways contract?

  • allergic reaction
  • to prevent harmful substances in the air from entering the alveoli/lungs
• Outline the uses of elastic tissue in the walls of the airways.

  • to stretch when inhaling
  • to recoil when exhaling
• Ciliated epithelium tissues have hair-like extensions called cilia
• What kind of tissue helps the smooth muscle revert to its original shape when it relaxes from contraction?

  Elastic tissue
• What is the double membrane of the lungs called?

  Pleura membrane
• Each of the lungs is enclosed in a double membrane known as the pleural membrane. The space between the two membranes is called the pleural cavity, and is filled with a small amount of pleural fluid.
• What are the roles of the pleural fluid?

  • To lubricate the lungs
  • to adhere to the outer walls of the lungs by water cohesion, so that the lungs expand with the chest while breathing.