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exchange surfaces and breathing (specialised exchange surfaces (thin…
exchange surfaces and breathing
ventilation in fish
the mouth opens and the floor of the buccal cavity lowers which increases the volume and decreases the pressure causing water to move into the buccal cavity. the opercular cavity valve is shut and the opercular cavity expands which lowers the pressure, the floor of the buccal cavity moves up increasing the pressure causing water to move from the buccal cavity to the opercular cavity over the gills. the mouth closes and the sides of the opercular cavity move inwards which increases the pressure moving water over the gills
gills
the gill arch supports the structure of the gills, efferent blood vessels carry blood away from the gills in the opposite direction of the water and afferent blood vessels bring deoxygenated blood into the system. gill filaments are in stacks and are made up of gill lamellae, the sire of gaseous exchange
have a large surface area, good blood supply, and thin layers, they are covered by the operculum
countercurrent - water flowing over the gills and the blood in the gills flow in opposite directions which maintains a steep concentration gradient
ventilation in insects
trachea lead away from the spiracles and into the body, lined with chitin which keeps them open under pressure, they divide to form tracheoles which have no chitin so are permeable to gas exchange. the tracheal fluid limits the amount of gas exchange, when the insect requires more oxygen lactic acid build up results in water moving out of the tracheoles by osmosis allowing more gas exchange to take place
insects that have high energy demands can use mechanical ventilation where air is actively pumped into the system by the thorax or abdomen using the change in pressure. They can also have collapsable trachea or air sacs which are used as air stores to increase the amount of air moved through the system
they have spiracles along the thorax and abdomen which air and water pass through, closed and opened by sphincters
mammalian gaseous exchange
ventilation
expiration - is a passive process, the diaphragm relaxes so it moves up, the external intercostal muscles relax moving the ribs in and up. This reduces the volume of the thorax and increases the pressure moving the air out of the lungs
forced expiration - internal intercostal muscles contract moving the ribs down hard and fast, the abdominal muscles contract forcing the diaphragm up the increase the pressure and force the air out
inspiration - diaphragm contracts and lowers, the external intercostal muscles contract moving the ribs up and out. The volume of the thorax increases reducing the pressure so air is drawn in to equalise the pressure
key structures
bronchus - trachea splits to form left and right bronchus
trachea - supported by incomplete rings of thick flexible cartilage which stop it from collapsing and lined with goblet cells which secrete mucus to trap dust and ciliated epithelium which beat to move the mucus away
bronchioles - bronchi divide to form smaller bronchioles which have no cartilage, the walls contain smooth muscle which contracts to constrict and dilate the bronchioles to change the amount of air entering, also are lined with a thin layer of flattened epithelium for gaseous exchange
nasal cavity - moist surface which increases the humidity of incoming air reducing evaporation from the exchange surface, a hairy lining that secretes mucus to trap dust and bacteria
alveoli - ting air sacs which are the main sire of gaseous exchange, made up of flattened epithelial cells, collagen and elastic fibres for elastic recoil
specialised exchange surfaces
thin layers reduces diffusion distance
increases surface area overcomes limitations of small surface area to volume ratio
good blood supply means substances and constantly being delivered to and removed from the exchange surface so the concentration gradient is maintained
ventilation to maintain the concentration gradient