Biology - Unit 9: Human Gas Exchange

what are features of gas exchange surfaces in humans

• large surface area to allow faster diffusion of gases across the surface

• thin walls to ensure diffusion distances remain short

• good ventilation with air so that diffusion gradients can be maintained

• good blood supply to maintain a high concentration gradient so diffusion occurs faster

what is the percentage of gases in atmospheric air?

• oxygen = 21%

• carbon dioxide = 0.04%

• nitrogen = 78%

• other gases = 0.96%

state the characteristics of, and describe the role of, the exchange surface of the alveoli in gas exchange

• they (and the capillaries around them) have thin, single layers of cells to minimise diffusion distance

• ventilation maintains high levels of oxygen and low levels of carbon dioxide in the alveolar air space

• a good blood supply ensures a constant supply of blood high in carbon dioxide and low in oxygen

• a layer of moisture on the surface of the alveoli helps diffusion as gases need to dissolve before taking part in metabolic reactions

explain the role of the ribs, the internal and external intercostal muscles and the diaphragm in breathing in.

• external intercostal muscles contract while internal intercostal muscles relax

• ribcage moves up and out

• diaphragm contracts and flattens

• volume of thorax increases

• pressure inside thorax decreases

• air is drawn in

explain the role of the ribs, the internal and external intercostal muscles and the diaphragm in breathing out.

• external intercostal muscles relax while internal intercostal muscles contract

• ribcage moves down and in

• diaphragm relaxes and becomes dome-shaped

• volume of thorax decreases

• pressure inside thorax increases

• air is forced out

explain the role of goblet cells, ciliated cells and mucus in protecting the gas exchange system from pathogens and particles

• the passages down to the lungs are lined with ciliated epithelial cells

• cilia comes from the latin for eyelash, so unsurprisingly these cells have tiny hairs on the end of them that beat and push mucus up the passages towards the nose and throat where it can be removed

• the mucus is made by special mucus-producing cells called goblet cells because they are shaped like a goblet or cup

• the mucus traps particles, pathogens like bacteria or viruses, and dust and prevents them from getting into the lungs and damaging the cells there

how can we investigate the differences in inspired & expired