exchange surfaces

• alveoli


  tiny air sacs that serve as the primary gaseous exchange surface. They consist of a thin epithelial cell layer, collagen and elastic fibres
• breathing rate


  the number of breaths per minute
• bronchi


  divisions of the trachea that lead into the lungs. They are small tubes supported by incomplete rings of cartilage
• bronchioles


  many small divisions of the bronchi. They contain smooth muscle to restrict airflow to the lungs but do not have cartilage. They are lined with a thin layer of ciliated epithelial cells.
• cartilage 


  strong, flexible connective tissue that supports the walls of the trachea and bronchi, preventing collapse. It is found in an incomplete ring shape
• ciliated epithelial cells


  specialised cells with tiny hair-like cilia found lining the trachea that waft bacteria-containing mucus up to the back of the throat, where it is swallowed.
• counter current flow 


  an adaptation for gaseous exchange in bony fish. Blood in the gill filaments and water moving over the gills flow in opposite directions, maintaining a steep oxygen concentration gradient.
• elastic fibres


  fibres of elastin that allow the alveoli to stretch as air is drawn in and recoil back to normal size, expelling air. They are also found in the trachea, bronchi and bronchioles.
• exchange surface 


  a surface over which materials are exchanged from one region to another. An effective exchange surface has a large surface area, thin layers, a good blood supply, and ventilation to maintain a steep diffusion gradient.
• expiration 


  during expiration (exhalation) the diaphragm relaxes and reverts to a dome. The external intercostal muscles relax, moving the ribs down and in. The volume of the thorax decreases and thoracic pressure exceeds air pressure. Air moves out of the trachea
• gill filaments 


  the main site of gaseous exchange in fish, over which water flows. They are found in large stacks, known as gill plates, and have gill lamellae which provide a large surface area for exchange.
• gill lamellae 


  the fine branches of the gill filaments. They are adapted for gaseous exchange by having a large surface area and good blood supply
• gill plates 


  large stacks of gill filaments
• gills


  the organs of gaseous exchange in fish. They are contained in a gill cavity and are made up of gill lamellae, gill filaments and gill plates.
• goblet cells 


  specialised cells that secrete mucus onto the trachea lining. The mucus traps harmful substances and microorganisms, preventing their entry into the lungs.
• inspiration


  during inspiration (inhalation) the diaphragm contracts and flattens and the external intercostal muscles contract, moving the ribs up and out. The volume of the thorax increases and thoracic pressure falls below air pressure. Air moves into the trachea
• internal intercostal muscles


  muscles found between the ribs which are responsible for forced exhalation.
• mammalian gaseous exchange system 


  a complex system found in mammals in which oxygen and carbon dioxide gases are exchanged.
• operculum


  a flap that covers the gills of bony fish. It protects the gills and helps to maintain a constant stream of water over them
• smooth muscle


  an involuntary muscle found in the walls of the trachea and bronchi. It constricts the lumen of the bronchi by contracting, reducing airflow to the lungs
• spiracles 


  small, external openings along the thorax and abdomen of most insects, where air enters, and air and water leave the gaseous exchange system. Spiracle sphincters open and close the spiracles to control gas exchange.
• spirometer


  a device used to examine patterns of breathing and determine different aspects of lung volume.
• surface area to volume ratio


  the surface area of an object divided by its volume. The larger the surface area to volume ratio, the smaller the object
• tidal volume 


  the volume of air that moves into and out of the lungs during a normal breath.
• trachea (mammals)


  the primary airway which carries air from the nasal cavity down into the chest. It is a tube supported by incomplete rings of cartilage.
• tracheae (insects)


  large tubes that run from the spiracles, into and along an insect's body. They are supported by spirals of chitin. The tracheae divide further into smaller tracheoles.
• tracheal fluid 


  a fluid found at the ends of the tracheoles. The amount of fluid affects the surface area available for gaseous exchange and water loss
• tracheoles


  divisions of the tracheae that run throughout the tissues of an insect, forming a complex network. They are the main site of gas exchange and are completely permeable to gases.
• ventilation 


  the movement of fresh air into the lungs and stale air out of the lungs via inspiration and expiration.
• vital capacity 


  the largest volume of air that can be breathed in following the strongest possible exhalation.