human gas exchange

how does the change in the thorax allow for inspiration?

pressure difference between lungs and atmosphere creates a gradient
so air is forced into the lungs

how does change in the thorax allow for expiration?

increased pressure forces air out of the lungs

inspiration?

• diaphragm muscles contract + flatten

• external intercostal muscles contract, internal relax

• ribcage moves up + out

• thorax vol increases + pressure decreases lower than atmosphere

• air moves in down pressure gradient

expiration?

• diaphragm muscles relax + move upwards

• internal intercostal muscles contract, external relax

• ribcage moves down + inwards

• thorax vol decreases + pressure increases greater than atmosphere

• air leaves down pressure gradient

why is expiration passive at rest?

internal intercostal muscles dont usually need to contract

expiration aided by elastic recoil in alveoli

what is a spirometer?

device used to measure lung volume

how is a spirometer used?

person breathes in and out of an airtight chamber, causing it to move up and down
leaving a trace on a graph to be interpreted

vital capacity?

max. volume that can be exhaled/inhaled in one breath

tidal volume?

volume of air we breath in and out for each breath at rest

when can tidal volume be exceeded?

when lots of oxygen is required eg. when exercising

residual volume?

vol. of air always present in the lungs

expiratory volume?

max vol. air breathed out in one second

role of cartilage?

• supports trachea + bronchi

• prevents lungs from collapsing when pressure drops during inspiration

• maintains open airway for uninterrupted airflow

where is ciliated epithelium found?

bronchi, bronchioles + trachea

role of ciliated epithelium?

moves mucus along to prevent lung infection by moving it towards the throat to be swallowed

where are goblet cells found?

in the trachea, bronchi and bronchioles

role of goblet cells?

secrete mucus to trap bacteria and dust to reduce the risk of infection
assisted by lysozymes that digest bacteria

role of smooth muscle?

contract to constrict airway, so can control its diameter and the flow of air to and from the alveoli

role of elastic fibres?

stretch for exhalation
recoil for inhalation
controlling flow of air

how does gas exchange take place in the alveoli?

O2 from alveoli diffuses into capillaries via epithelium
CO2 diffuses into alveoli from the capillaries

how is the epithelium adapted to gas exchange?

many alveoli → large SA

very thin → short diffusion pathway

each alveolus surrounded by network of capillaries maintaining conc. gradient

folded → large SA

permeable → allow CO2/O2 diffusion

moist → gases dissolve for diffusion

how can lung diseases reduce gas exchange?

• thickened alveoli tissue (fibrosis0 → increased diffusion pathway

• break down of alveolar wall → decreased SA

• decreased lung elasticity → lungs expand/recoil less, reducing conc gradient of O2/CO2

how can lung diseases affect ventilation?

• reduced lung elasticity → expand/recoil less, reducing tidal vol and vital capacity

• narrow airways reduce airflow in/out → decreasing expiratory volume

• less gas exchange → increased ventilation to compensate for less oxygen in blood

how does lung disease cause fatigue?

cells receive less O2

rate of aerobic respiration decreases

producing less ATP