4.2 Gas Exchange

-the diffusion distances from the outside to the innermost areas are very small -the surface area in contact with the the outside is very large relative to the volume of the inside of the organism- its surface area to volume ratio is large -metabolic demands are low, the organisms do not regulate their own temperature and the cells do not use much oxygen and food or produce much carbon dioxide

-the bigger the organism the smaller the surface area to volume ratio

-substances need to travel long distances from the outside to reach the cytoplasm of cells, simple diffusion would not transport nutrients and oxygen fast enough to sustain the processes of life -the metabolic rate of larger organisms especially animals tends to be higher than smaller organisms -the demands of each cell for oxygen and food and the amount of waste produced is much larger

-the surface area- the larger the surface area the more particles can be exchanged at the same time -the concentration gradient of particles diffusing- the steeper the concentration gradient the faster they move across -the distance over which diffusion is taking place- the shorter the distance the faster diffusion can take place

-a large surface area giving sufficient gas exchange to supply all the needs of the organism and compensating for the relatively small surface area to volume ratio of the organism -thin layers to minimize the diffusion distance -in animals a rich blood supply to the respiratory surfaces as the blood is involved in the transport of the respiratory gases to and from the site of gas exchange helping to maintain a steep concentration gradient -moist surfaces as diffusion takes place with the gases in solution -permeable surfaces that will allow free passage of the respiratory gases

-the main route by which air enters the gas exchange system -the passages have a relatively large surface area but no gas exchange takes place here -the passages have a good blood supply raising the temperature of the air if necessary and the lining secretes mucus and is covered in hairs meaning the external air is prepared before entering the rest of the system -the hairs and mucus filter out most of the dust, small particles and pathogens that you breathe in -the moist surfaces increase the level of water vapor in the air

-air can enter here but misses out on the cleaning, warming and moistening effects of the nasal route

-a flap of tissue that closes over the glottis in a reflex action when food is swallowed -this prevents food from entering the gas exchange system

-the voice box which uses the flow of air across it to produce sounds

-a major airway to the bronchi lined with cells including mucus-secreting cells -cilia on the surface move mucus and any trapped microorganisms and dust away from the lungs

-prevent the trachea and bronchi from collapsing but allow food to be swallowed and moved down the oesophagus

-tubes leading to the lungs and are similar in structure to the trachea but narrower and divide to form bronchioles -bronchioles are small tubes that spread through the lungs and end in alveoli -for tubes with diameter less that 1mm there is no cartilage and they collapse quite easily -their main function is still as an airway but little gas exchange may occur

-the organ where gas exchange takes place

-tiny air sacs where most of the gas exchange occurs by a process of simple diffusion between the alveolar air and the deoxygenated blood in the caplillaries -made of a single layer of flattened epithelial cells (squamous) -the capillaries that run close to the alveoli also have a wall that is only one cell thick -between the two is a layer of elastic tissue which helps to force air out of the lungs and stretches when you breathe in -this is known as the elastic recoil of the lungs

-a special phospholipid known as lung surfactant that coats the alveoli and makes breathing easier

-a protective bony cage around the gas exchange system

-found between the ribs and important in breathing

-space between the pleural membranes usually filled with a thin layer of lubricating fluid that allows the membranes to slide easily with breathing movements

-broad sheet of tissue that forms the floor of the chest cavity -also important in breathing movements

-large surface area for the gas exchange of gases -a short diffusion distance- one cell thick as are the capillaries that run beside them -a steep concentration gradient- blood is continuously flowing through the capillaries exchanging gases maintaining the gradient ion the capillary side, the air within the alveoli is constantly being refreshed with air from outside from breathing -have macrophages which are phagocytic white blood cells that engulf bacteria

-an active process where the muscles around the diaphragm contract and as a result it is lowered and flattened -the intercostal muscles also contract raising the ribcage upwards and outwards resulting in the volume of the chest cavity increasing reducing the pressure in the cavity -the pressure writhin the chest cavity is now lower than the atmospheric air outside so air moves in through the trachea, bronchi and bronchioles into the lungs to equalize the pressure

-a passive process where the muscles surrounding the diaphragm relax so that it moves up into its resting dome shape -the intercostal muscles relax so the ribs move down and in and the elastic fibers around the alveoli of the lungs return to their normal length -the volume of the chest cavity decreases causing an increase in pressure greater than the outside air so air moves up of the lungs through the bronchioles, bronchi and trachea

-when you force air out of your lungs more rapidly than passive exhalation allows -the internal intercostal muscles contract pulling the ribs down and in and the abdominal muscles contract forcing the diaphragm upwards -this increases the pressure in the chest cavity causing exhalation -singers use this to achieve a powerful voice and to maintain long notes and free divers do this before diving to fill their lungs with as much air as possible -coughing is an exaggerated form of forces exhalation which is used to force mucus out of the respiratory system

-the respiratory system produces a lot of mucus that lines the airways and traps tiny particles and organisms -mucus is usually very runny so it is easily moved up the airways by cilia that sweep upwards to the back of your throat -here the majority of mucus is swallowed and the acid in the stomach and the digestive enzymes digest the mucus and everything carried in it