Gas exchange in humans Flashcards
How does gas exchange work in humans?
Gas exchange in humans
As you breathe in, air enters trachea which spilts into two bronchi (each leading to a lung)
Each bronchus branches off into bronchioles
Bronchioles end in alveoli, where gases are exchanged
Thr ribcage, intercostal muscles and diaphragm all work together to move air in and out
Internal and external intercostal muscles
Process of inspiration
Gas exchange in humans
During inspiration, external intercostal and diaphragm muscles contract
Causes ribcage to move upwards and outwards and diaphragm falttens, increasing volume of thoracic cavity
As vol of thoracic cavity increases, lung pressure decreases to below atmospheric pressure
Air will always flow from area of high press to area of low press
Inspiration is an active process - requires energy
Process of expiration
Gas exchange in humans
During expiration, external intercostal and diaphragm muscles relax
Ribcage moves downwards and inwards and diaphragm curves upwards again (dome shaped)
Volume of thoracic cavity decreases, causing air press to increase to above atmospheric press
AIr is forced down press grad and out of lungs
Normal expiration is passive
Forced expiration - external intercostal relax and interal intercostal contract, pulling ribcage further down and in
Movement of two intercostal muscles is antagonistic
Alveoli structure
Gas exchange in humans
Wall of each alveolus made from a single layer of thin, flat cells called alveolar epithelium
Walls of capillaries are made from capillary endothelium
Walls of alveli contain elastin - which is elastic, this helps alveoli to recoil to normal shape after inhaling and exhaling air
How is gas exchanged in alveoli?
Gas exchange in humans
O2 diffuses out of alveoli, across alveolar epithelium and capillary endothelium and into a haemoglobin in the blood
CO2 diffuses into the alveoli from blood
How are alveoli adapted for faster diffusion?
Gas exchange in humans
Thin exchange surface - alveolar epithelium is only one cell thick
Large SA - millions of alveoli
Steep conc grad of O2 and CO2 between alveoli and capillaries - constantly maintained by flow of blood and ventilation
