size and SA to vol. ratio
small objects have relatively large SA - therefore no large single celled organisms
important for exchange
- cells/ organisms need to exchange materials/heat with enviro.
- more chem. reactions every sec with larger vol. ---> more O2, nutrients, waste products, heat exchanged across membrane of cells ---> larger vol. becomes inc problem
structure of the thorax
lungs have large gas exchange SA
- larger animals have complex blood systems + lungs to provide larger SA for efficient diffusion
- alveoli: gas exchange takes place in tiny air sacs
alveoli adaptions for efficiency
- sigle thin layer - faster due to short distance for molecules
- higher concen in alveoli than in blood - allows faster diffusion due to bigger concen. diff. due to blood carrying away O2
- fully permeable walls - O2 + CO2 pass easily through cell membranes to epithelial cells
breathing in and breathing out
why do we need to breathe?
- ventilation allows air with higher concen of O2 taken to lungs + higher concen. of CO2 removed
- maints high concen. gradients between air + blood inc. diffusion rate
if vol. inc. pressure dec.
- lungs suspended in airtight throax
- inc vol ---> dec pressure below atmospheric level ---> air flows in until equal in alveoli
- intercostal muscles + diaphragm contract ---> throax vol inc. ---> dec pressure
- intercostal muscles + diaphragm relax ---> throax vol dec. ---> inc pressure