3 Substance exchange- Gas exchange (humans) Flashcards
Where does human gas exchange take place?
Lungs- specialised organs for the quick exchange of O2 & CO2 with the bloodstream
What structures do the lungs consist of?
Trachea, bronchi, bronchioles and alveoli
What is the structure and function of the trachea?
-Entrance to human gas exchange system
-Breathe in; air flows through trachea
-Ridges of cartilage surround the front to provide protection and structure; none at the back so that oesophagus isn’t constricted
What is the structure and function of the bronchi?
-Divide into 2 from trachea
-Air flows along each bronchus to a lung
-Made from cartilage and smooth muscle
What is the structure and function of the bronchioles?
-Many smaller bronchioles divide from each bronchus
-Branch throughout lungs into small air-sacs, alveoli
What is the structure and function of the alveoli?
-Sacs, fill with air when you breathe in
-Oxygen in alveoli diffuses into bloodstream and CO2 from bloodstream diffuses into alveoli
-Millions in the lungs
-Provide large surface area for gas exchange
How is ventilation controlled?
-Controlled by ribcage, intercostal muscles and diaphragm
-When you breathe in, these move so that lungs fill with air
-When you breathe out, these move so air can leave the lungs
What is the structure and function of the capillaries?
-Capillary network surrounds each alveolus
-Provide large surface area for gas exchange between alveoli and bloodstream
What is the structure and function of the alveolar epithelium?
-Single layer of epithelial cells, line walls of alveoli.
-Provide very short diffusion distance from alveoli to capillaries: maximises rate of gas exchange
How is a steep concentration gradient maintained?
-Capillaries supply CO2 to alveoli and O2 is rapidly carried away from alveoli
-Quick transport of gases in bloodstream maintains steep concentration gradient of O2 and CO2
-Allows quick diffusion of gases into and out of bloodstream
What are the steps involved in breathing in/ inspiration?
Air flows into lungs, O2 diffuses into bloodstream
- The external intercostal muscles (surrounding ribcage) contract
Diaphragm contracts, moves downwards
Energy is required to power this
2.External intercostal muscles move ribcage upwards and outwards. Diaphragm moves downwards. Volume of thoracic cavity increases - Pressure in lungs decreases due to increasing volume in thoracic cavity. Pressure gradient created- outside and inside of the lungs
- Air flows inside the lungs down the pressure gradient, and down the trachea into the alveoli
What are the steps involved in breathing out/expiration ?
Air flows out of lungs, CO2 diffuses out of bloodstream
1.External intercostal muscles relax, internal intercostal muscles contract and diaphragm relaxes, moves upwards
2.Internal intercostal muscles move rib cage downwards + inwards, diaphragm moves upwards. Volume of thoracic cavity decreases
3. Pressure in the lungs increases due to decreasing pressure in thoracic cavity, creating a pressure gradient between the outside and inside of the lungs
4.Air flows out of the lungs down the pressure gradient, and out of the alveoli up the trachea
What does lung disease affect and how?
The ability of the lungs to exchange gases over their surface. Can be direct tissue damage or reduced ability to ventilate
What are some examples of lung diseases?
Asthma
Pulmonary fibrosis
Tuberculosis
Emphysema
What are the causes of gas exchange problems?
The exchange system is damaged, causes of problems can include;
-Decreased surface area
-Increased diffusion distance
-Decreased concentration gradient
