3.1.1 - exchange surfaces

• what is an exchange surface 


  • allows molecules/ions to move into and out of the cell/organism as quickly as possible
  • molecules/ions move in and out by diffusion/osmosis/active transport/ facilitated diffusion
• give some examples of an exchange surface

  • gut endothelial lining (vili/ microvilli)
  • root hair cells
  • alveolar epithelium
  • capillary endothelium
• what are the features of a good exchange surface 


  • large SA
  • short diffusion pathway
  • good blood supply - maintains conc gradient
  • good ventilation - maintains conc gradient
  • large SA:vol
  • moist surface
  • counter current system
• why do unicellular organisms not require specialised exchange surfaces 


  • large surface area to volume area
  • diffusion of gasses is fast enough to meet the organisms metabolic needs
• why do multicellular organisms require specialised exchange surfaces 


  • smaller SA:vol
  • longer distance for gasses to diffuse to reach cells art centre of the organism
  • more metabolically active = higher oxygen demand more carbon dioxide to remove
  • diffusion is too slow to meet metabolic requirements
• what is the function of the pharynx 


  • warms the air
  • hairs/mucus - trap bacteria and dust
  • moist surface - increases air humidity
  • reduces the evaporation of water from surface of alveoli
• what is the larynx 


  voice box
• fiction of the rings of cartilage

  • prevents the trachea collapsing during inspiration when pressure inside is low it also prevents the oesophagus from pressing against it when swallowing
• function of alveoli 


  • site of gas exchange
• function of plural membranes 


  • contains a fluid that provides lubrication between the lungs and the ribcage
• rib cage function 


  • protects the lungs and the heart
  • able to move to change the volume of the thorax and thus the pressure inside the lungs
• trachea function 


  • transports air from the mouth to the bronchi
  • allows air to flow through without obstruction
  • less resistance to air flow
  • lining contains ciliated epithelial cells and goblet cells
• function of the bronchus 


  transports air into each lung

  lining contains ciliated epithelial cells and goblet cells
• function of external muscles 


  • muscles that are located between the ribs
  • contraction of these muscles causes the rib cage to move up and outwards during inspiration
  • relax during expiration
• function of internal intercostal muscles 


  • muscles located between ribs
  • contraction of these muscles causes ribcage to move down and inwards
  • these muscles contracted during forced exhalation
  • don't contract during normal ventilation
• bronchioles function 


  narrow airways that transport the air into the alveoli
• function of diaphragm 


  • sheet of muscle located underneath the ribcage
  • contracts and flatters during inhalation to increase the volume of the thorax
  • relaxes and becomes dome shaped during exhalation
• name a few ways that the thorax is adapted to have a short diffusion pathway 


  • each alveolus wall is made up of a single layer of squamous epithelial cells
  • the wall of the capillary is made up of a single layer of squamous endothelial cells
  • each alveolus is in close contact with a network of capillaries
• name a few ways that the thorax is adapted to have a large SA:Vol 


  • each individual alveolus is very small
• name a few ways that the thorax is adapted to have a steep conc gradient 


  • the walls of the alveoli and capillaries are permeable to oxygen and carbon dioxide
  • each capillary is narrow - meaning rbc are flattened against capillary wall
  • blood is constantly moving through the network of capillaries
  • air within each alveolus is constantly being refreshed through ventilation
• how is the alveoli adapted so that gasses dissolve efficiently 


  surface is moist
• function of human respiratory system 


  • trachea, bronchi and bronchioles allow smooth passage of air during ventilation
  • alveoli for gas exchange
• what are the two layers that make up the pleural membrane 


  • the visceral or pulmonary pleura covers outside of each lung
  • the parietal or costal pleura lines the inside of the chest wall
• what do pleural membranes do 


  secrete pleural fluid which allows them to move freely against each other during ventilation
• what is ricks law of diffusion 


  • rate of diffusion is proportional to = surface area x difference in conc divided by length of diffusion path
• what is surfactant 


  • it coats the inner surface of the alveoli
  • it prevents alveoli from collapsing after expiration
  • this reduces surface tension on the surface of the alveoli
• what is surface tension 


  • when water molecules on the surface of the alveoli are attracted to each other
  • water molecules pull together which creates an inwards force on the surface of the alveoli
  • this causes walls of alveoli to pull together reducing SA
  • causes alveoli to collapse after expiration
  • suficient reduces surface tension
• what structures are present in the trachea 


  • cartilage
  • smooth muscle
  • elastic fibres
  • ciliated epithelium
  • goblet cells
  • mucous glands
• what structures are present in the bronchi

  • cartilage
  • smooth muscle
  • elastic fibres
  • ciliated epithelium
  • goblet cells mucous glands
• what structures are present in largest bronchioles

  • smooth muscle
  • elastic fibres
  • ciliated epithelium
  • goblet cells
• what structures are present in smaller bronchioles

  smooth muscle

  elastic fibres
• what structures are in the smallest bronchioles 


  • smooth muscle
• what structures are found in alveoli 


  elastic fibres

  squamous epithelium
• What is the primary function of the trachea?


  Allows air to flow through without obstruction
• How does the structure of the trachea reduce resistance to airflow?


  It allows air to flow through without obstruction
• What prevents the trachea from collapsing during inspiration?


  1. shaped rings of cartilage
• Why are the C-shaped rings of cartilage positioned at intervals in the trachea?


  To allow flexibility and movement
• How do the rings of cartilage in the trachea aid in swallowing?


  They allow the oesophagus to expand without rubbing against the cartilage
• What role do smooth muscle and elastic fibers play in the trachea?


  They control movements of air into and out of the alveoli
• What happens to the tracheal lumen when the smooth muscle contracts?


  The lumen constricts, reducing airflow to the alveoli