Gas exchange in Humans: Lungs Flashcards
Why do humans need a specialised system for gas exchange?
They have a small SA:V ratio due to being a larger animal
What is the specialised system for gas exchange in humans?
The lungs
What is the site of gas exchange in humans?
Alveoli
Why are lungs a suitable specialised system?
Provide a large surface area to volume ratio
What’s the trachea?
Also known as the windpipe, it’s a tube-like structure which brings oxygen from the mouth to the lungs, branching into two bronchi supplying oxygen to the lungs. These branch into bronchioles which at their tips contain air sacs called alveoli
Movement of O2 in lungs
Trachea -> Bronchi -> Bronchioles -> Alveoli
Difference between the two lungs
They are asymmetrical, left lung is slightly smaller to make room for the heart
Alveoli structure + adaptations for effective gas exchange
•Extremely large surface area
•Rich blood supply -> Ensures a large concentration gradient between gases in alveoli (high conc of O2) and surrounding capillaries (low conc of O2)
•Deoxygenated blood brought to the lungs by the pulmonary artery but returns oxygenated via pulmonary vein
•Gases in alveoli are separated from blood by alveolar epithelium and endothelium of capillary
•Alveolar epithelium is one cell thick -> Provide a short diffusion distance for a faster rate
•CO2 and O2 both non polar so cross via simple diffusion, so epithelium membrane is therefore permeable
What is ventilation?
The mechanism of breathing air in and out of the lungs, the process needed to get oxygen into lungs. It’s a result in pressure difference between the lungs and air outside the body
How is pressure inside the lungs changed?
By changes in the lung volume brought about by muscular contractions of the diaphragm and intercostal muscles
What occurs during inhalation?
1) External intercostal muscles contract pulling the ribcage up
2) Diaphragm contracts and flattens
3) Thoracic cavity volume increases
4) Pressure in lungs lower than the atmospheric pressure
5) Air moves into lungs down a pressure gradient
What occurs during exhalation?
•External intercostal muscles relax and ribcage moves down. Internal intercostal muscles contract
•Diaphragm relaxes and moves up
•Thoracic cavity volume decrease
•Pressure in lungs greater than atmospheric pressure
•Air moves out of the lungs down a concentration gradient
What is the interaction between internal and external intercostal muscles?
Antagonistic interaction, one contracts as the other relaxes
Pulmonary ventilation equation
Pulmonary ventilation (dm3min-1) = tidal volume (dm3) x breathing rate (min-1)
