Exchange in lungs Flashcards
Why is the volume of oxygen and CO2 that has to be absorbed and removed in mammals large?
- They are relatively large organisms with a large volume of living cells
- They maintain a high body temperature which is due to them having high metabolic and respiratory rates
What are lungs the site of?
Gas exchange
What is one reason that lungs are located in the body due to their structure?
Air is not dense enough to support and protect these delicate structures
What is another reason that lungs are located in the body due to the body’s needs?
The body as a whole would otherwise lose a great deal of water and dry out
How are lungs supported and protected?
By the ribcage
How can ribs be moved?
By the muscles between them
What are lungs ventilated by?
A tidal stream of air, ensuring that the air within them is constantly replenished
What kind of structures are lungs?
Lobed structures
What are lungs made up of?
A series of highly branched tubules, bronchioles, which end in tiny air sacs called alveoli
What is a trachea?
A flexible airway that is supported by rings of cartilage
What does the cartilage do for the trachea?
Prevents the trachea collapsing as the air pressure inside falls when breathing in
What are the tracheal walls made up of?
Muscle, lined with ciliated epithelium and goblet cells
What are the bronchi?
2 divisions of the trachea, each leading to one lung
How are bronchi similar in structure to the trachea (mucus)?
Also produce mucus to trap dirt particles and have cilia
What do the cilia do in the bronchi?
Move dirt-laden mucus towards the throat
How are larger bronchi supported?
Supported by cartilage
What happens in terms of support as bronchi get smaller?
Amount of cartilage reduced
What are bronchioles?
A series of branching subdivisions of bronchi
What are the walls of bronchioles made of?
Muscle lined with epithelial cells
What do the muscle walls of the bronchioles allow them to do?
Constrict so that they can control the flow of air in and out of the alveoli
What are alveoli?
Minute air sacs at the end of the bronchioles
What is the diameter of the alveoli?
Between 100 micrometer - 300 micrometer
What is found between the alveoli?
Collagen and elastic fibres
What do the elastic fibres allow the alveoli to do?
To stretch as they fill with air when breathing in
What happens to alveoli when breathing out?
They spring back to their original shape in order to expel the CO2 rich air
What are the alveoli lined with?
Epithelium
What is the alveolar membrane?
The gas-exchange surface
What is the equation for pulmonary ventilation rate?
Tidal wave x breathing rate = pulmonary ventilation rate
How is the pressure change in the lungs brought about?
By the movement of 3 sets of muscles
- Diaphragm
- Intercostal muscles (there are internal and external)
What is the diaphragm?
A sheet of muscle that separates the thorax from the the abdomen
Where do the intercostal muscles lie?
Between the ribs
What happens when the internal intercostal muscles contract?
Leads to expiration
What happens when the external intercostal muscles contract?
Leads to inspiration
What is the 1st step of inspiration?
The external intercostal muscles contract, while the internal relax
What is the 2nd step of inspiration after (the external intercostal muscles contract)?
Ribs are pulled upwards and outwards, increasing volume of thorax
What is the 3rd step of inspiration after (ribs are pulled upwards and outwards)?
Diaphragm muscles contract, causing it to flatten, which also increases volume of thorax
What is the 4th step of inspiration after (diaphragm muscles contract)?
The increased volume of thorax results in reduction of pressure in the lungs
What is the final step of inspiration?
Atmospheric pressure is now greater than pulmonary pressure so air is forced into lungs
What is the 1st step of expiration?
Internal intercostal muscles contract, while external relax
What is the 2nd step of expiration after (internal intercostal muscles contract)?
Ribs move downwards and inwards, decreasing thorax volume
What is the 3rd step of expiration after (ribs move downwards and inwards)?
Diaphragm muscles relax so it is pushed up against contents of the abdomen that were compressed during inspiration
Thorax volume further decreased
What is the 4th step of expiration after (diaphragm muscles relax)?
Decreased thorax volume increases pressure in lungs
What is the final step of expiration?
Pulmonary pressure is now greater than atmospheric, so air is forced out of lungs
What is the main cause of air being forced out during normal, quiet breathing?
The recoil of the elastic tissue in the lungs
When do the various muscles play a major part in breathing?
Under more strenuous conditions
How many alveoli are there in each human lung and what is their total surface area?
Around 300 million and their total surface area is 70m^2
What is each alveolus lined with?
Epithelial cells that are only 0.05 - 0.3 micrometers thick
What surrounds each alveolus?
A network of pulmonary capillaries
Are the pulmonary capillaries narrow?
Yes
What do the red blood cells do given that the pulmonary capillaries are so narrow when exchanging gases with the alveoli?
They are flattened against the capillary walls in order to squeeze through
How thin are the walls of the pulmonary capillaries?
One cell thick
How does the movement of red blood cells cause diffusion of gases between alveoli and the blood to be very rapid?
As the pulmonary capillaries are very narrow, red blood cells are slowed as they pass though them, allowing more time for diffusion
What is also caused by the fact that red blood cells are flattened against the capillary walls in terms of diffusion?
The distance between the alveolar air and the red blood cells is reduced
Why is the distance for diffusion very short in the lungs?
Walls of both alveoli and capillaries are very thin
What is the total surface area of alveoli and pulmonary capillaries like?
Each one has a very large surface area
How do breathing movements and heart action cause diffusion of gases between alveoli and the blood to be very rapid?
- Breathing movements constantly ventilate the lungs
- Heart action constantly circulates the blood around the alveoli
- Together, these ensure that a steep concentration gradient of the gases to be exchanged is maintained
What does blood flow through pulmonary capillaries maintain?
A concentration gradient
What does COPD stand for?
Chronic obstructive pulmonary disease
What does COPD include?
Emphysema and chronic bronchitis
What are the risk factors for COPD?
- Smoking
- Air pollution, especially in heavy industry
- Genetic make-up
- Infections
- Occupation (e.g. working with harmful chemicals)
