Gas exchange in humans.

what features do gas exchange surfaces have?

• large surface area - gives more space for diffusion to take place thereby speeding up the rate of diffusion and maximising gas exchange

• thin surface - reduces the diffusion distance across which gases must diffuse

• good blood supply - ensures good concentration gradients are always maintained

• good ventilation w/ air - this also ensures that a good concentration gradient is maintained

diagram of lungs, diaphragm, ribs, intercostal muscles, larynx, trachea, bronchi, bronchioles, alveoli and associated capillaries

why is the trachea lined with rings of cartilage

• keep trachea open

• prevent trachea from collapsing

• allows flexibility, can breathe even when bent

inspiration

act of breathing in

during inspiration:

• the external intercostal muscles contract

• the internal intercostal muscles relax

• this pulls the ribcage upwards and outwards

• diaphragm contracts and moves downwards

• volume of thorax increases

• air pressure inside lungs decreases

• air moves from outside to into the lungs down a pressure gradient

expiration

act of breathing out:

• the external intercostal muscles relax

• the internal intercostal muscles contract

• this pulls the ribcage downwards and inwards

• the diaphragm relaxes and moves back upwards

• volume of thorax decreases

• air pressure inside of lungs increases

• air moves from the lungs into the outside down a pressure gradient

composition of expired and inspired air

oxygen - 21% inspired air. 16% expired air.

why: Only 5% of oxygen absorbed. The concentration of oxygen of the blood surrounding the alveoli is lower than the inspired air. Oxygen used in aerobic respiration. Oxygen diffuses through the partially permeable membranes of the alveoli and enters into the bloodstream down a concentration gradient.

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carbon dioxide - 0.04% inspired. 4% expired - The concentration of carbon dioxide of the blood surrounding the alveoli is higher than the inspired air. carbon dioxide is released by respiration Carbon dioxide diffuses out of the bloodstream through the partially permeable membrane of the alveoli into the outside down a concentration gradient.

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water vapour - less in inspired. more in expired. - the body’s warmth causes water in the alveoli surface to evaporate into the expired air. water vapour increases, produced in respiration

why does breathing rate and depth increase during exercise

exercise causes the body’s cells to respire faster, to release more energy. this produces more CO2, so there is an increased CO2 concentration in the blood. this is detected by the brain, which signals the body to increase the rate and depth of breathing. this in turn allows gas exchange to happen more rapidly. therefore, CO2 is removed faster from the body, and there is an increased intake of oxygen, which is supplied to the respiring cells faster

protecting the breathing system

• a thin layer of mucus lines the respiratory tract

• this mucus is produced by goblet cells

• the mucus traps pathogens and dust particles.

• this prevents the entry of pathogens into the lungs

• the respiratory tract is also lined with ciliated epithelial cells

• these cells have tiny hairs called cilia

• the cilia beat and waft the mucus upwards towards the throat, where it can be swallowed