6.4 Gas Exchange Flashcards
What is ventilation?
The replacement of older air in the lungs with fresh air from the body’s external environment
What is ventilation essential for?
Ventilation is essential for the effective exchange of gases in the lungs
Where does gas exchange occur?
The exchange of oxygen and carbon dioxide occurs between the alveoli and the capillaries in the lungs
By what process are gases exchanged and what does this require?
Gases are exchanged by simple diffusion which requires a concentration gradient
What maintains the concentration gradient in the lungs?
This gradient is maintained by
Ventilation
The continuous flow of blood in the capillaries
What is the role of ventilation in terms of aiding gas exchange?
Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in the alveoli and blood flowing in adjacent capillaries
What does breathing in cause in terms of ventilation?
Breathing in fresh air from the surrounding environment increases the concentration of oxygen in the air inside the alveoli
What does breathing out cause in terms of ventilation?
Breathing out removes carbon dioxide
How does ventilation affect the levels of gases in the body?
This means that after ventilation, compared to the blood found in adjacent capillaries, the alveoli have
Higher oxygen levels
Lower carbon dioxide levels
Why is a concentration gradient in the alveoli necessary?
This ensures that oxygen continues to diffuse from the alveoli into the capillaries, while carbon dioxide continues to diffuse from the capillaries into the alveoli
Both gases move down their concentration gradient
How are alveoli (basic) adapted to gas exchange?
The alveoli are specifically adapted for gas exchange as they collectively have a very large surface area and the alveolar walls are only one cell thick which provides a short diffusion distance
What is another name for the alveolar wall?
The alveolar walls are also known as the alveolar epithelium
What are type 1 pneumocytes?
Type I pneumocytes are extremely thin alveolar cells which make up the majority of the alveolar epithelium
How are type 1 pneumocytes adapted?
They are adapted to maximise the rate of gas exchange by providing a short diffusion distance
How are capillaries adapted for gas exchange?
The capillary walls are also only one cell thick which means there is usually less than 0.5μm between the air in the alveoli and the blood, this maximises the rate of diffusion
What are type II pneumocytes?
Type II pneumocytes are rounded cells which secrete a solution that coats the epithelium of the alveoli
Which type of pneumocyte is more abundant?
TYPE 1
They occupy a much smaller proportion of the alveolar epithelium than the type I pneumocytes; around 5% (type II)
What do pneumocytes release?
The solution released by type II pneumocytes is pulmonary surfactant
What is pulmonary surfactant composed of?
Pulmonary surfactant contains molecules that have hydrophobic tails and hydrophilic heads
What is the structure of the pulmonayry surfactant?
The molecules form a monolayer with the hydrophobic tails facing the alveolar air
What is the role of surfactant?
Pulmonary surfactant reduces surface tension, maintaining alveolar shape and preventing the sacs sticking together
This prevents the lungs collapsing
How does surfactant aid gas exchange? both in terms of o2 and co2
The solution also aids gas exchange
The layer of moisture provided by the solution allows oxygen to dissolve before it diffuses into the blood
Carbon dioxide evaporates from the moist surface before it is removed in exhalation
Where does air enter?
Air moves in through the nose and mouth before it is carried to the lungs through the trachea
What is the trachea?
The trachea is a tube supported by rings of cartilage which help to support its shape and ensure it stays open, while allowing it to move and flex with the body
What does the trachea divide into?
The trachea divides to form the two bronchi (
What is the structure of the bronchi?
with walls also strengthened with cartilage and has a layer of smooth muscle which can contract or relax to change the diameter of the airways.
What do bronchi divide into?
Bronchioles branch off the two bronchi to form a network of narrow tubes
What are the walls of bronchioles lined with and why?
The walls of the bronchioles are lined with a layer of smooth muscle to alter the diameter of the bronchiole tubes
Why is smooth muscle necessary in the repiratory system?
This helps to regulate the flow of air into the lungs by dilating when more air is needed and constricting when e.g. an allergen is present
What is found at the end of bronchioles?
Groups of alveoli are found at the end of the bronchioles
What is each alveolus surrounded by?
Each alveolus is surrounded by an extensive network of capillaries to provide a good blood supply for maximum gas exchange
What is the general change in the chest during inhalation?
The breathing-in, or inspiration, process causes the volume of the chest to increase and the air pressure to decrease until it is lower than the atmospheric pressure
How is air forced in during inhalation?
As a result, air moves down the pressure gradient and rushes into the lungs
A gas will always move down a pressure gradient from an area of high pressure to an area of low pressure
What are the changes during inspiration i.e how do lungs increase the volume etc?
The inspiration process
The diaphragm contracts and flattens, increasing chest volume
In addition to the flattening of the diaphragm the external intercostal muscles contract, causing the ribcage to move upwards and outwards; this also increases chest volume
What mainly causes expiration?
Breathing out, or expiration, occurs mostly due to the recoil of the lungs after they have been stretched by the inspiration process, and is therefore a mainly passive process
What is the general change in pressure gradients etc during expiration?
Volume of the chest decreases and pressure increases, causing air to be forced out down its pressure gradient
What is involved in the passive expiration process?
External intercostal muscles relax, allowing the ribcage to move down and in
Diaphragm relaxes and becomes dome-shaped
The recoil of elastic fibres in the alveoli walls reduces the volume of the lungs
Is expiration always passive?
NO
The expiration process can be active when there is a need to expel excess air from the lungs e.g. when blowing out a candle
What ar the steps in active expiration?
Internal intercostal muscles contract to pull the ribs down and in
Abdominal muscles contract to push organs upwards against the diaphragm, decreasing the volume of the chest cavity
This causes forced exhalation
Why are antagonistic muscles necessary in the respiratory system?
Muscles only carry out the work of moving the body when they are contracting, or pulling; they cannot push
As a result of this limitation muscles often operate in pairs when movement in two directions in required
What is antagonistic muscle action?
One muscle of the pair pulls in one direction and the other muscle pulls in the opposite direction
This is described as antagonistic muscle action
What are examples of antagonistic muscles in the respiratory system?
Examples of antagonistic muscle action in ventilation are:
Internal and external intercostal muscles
The diaphragm and abdominal muscles
How do intercostal muscles function in antagonistic pairs?
When the internal intercostal muscles contract, the rib cage moves down and in
When the external intercostal muscles contract, the rib cage moves up and out
How does the diaphragm and abdominal muscles function in antagonistic pairs?
When the diaphragm contracts, it flattens and moves downwards
When the abdominal muscles contract, the internal organs of the abdomen are compressed and pushed upwards, exerting upward pressure on the diaphragm
How does cancer occur?
Of all the cancers, lung cancer is the most commonly diagnosed and results in the most deaths globally
Cancer occurs if mutations affect the regulation of mitosis in cells
How do mutations result in lung cancer?
This causes uncontrolled mitosis which develops into a mass of cells in the lumen of the airways
How does the tumor become bigger and survive?
The tumour becomes larger because it has no method of programmed cell death and survives because it develops its own blood supply (vascularisation)
When does the tumour start being noticeable in the respiratory system?
The tumour then starts to interfere with the normal working of the lungs, such as by squeezing against blood vessels or cancer cells entering into the lymphatic system, where they may develop another tumour
What relationship has been established between smoking and cancer?
A causal relationship has been proven for some risk factors relating to lung cancer
How can tobacco affect lung cancer i.e what does it contain?
Tobacco in cigarette smoke has been shown to have mutagenic effects on body cells due to chemicals found in the smoke
How do mutagenic chemicals i.e carcinogens lead to the development of lung cancer?
The effects of these mutagenic chemicals can lead to cancer in smokers as well as the passive smokers inhaling their second hand smoke
What 4 factors can lead to the development of lung cancer?
Inhalation of air pollution
Tobacco
Radon has
Asbestos & Silica
How does air pollution result in lung cancer?
Inhalation of air pollution similarly, can result in lung cancer
In cities, average rates of lung cancer diagnoses are much higher due to high levels of vehicle exhaust fumes and smoke from burning organic matter
How can radon gas lead to lung cancer? Where is it found?
Radon gas is a radioactive gas which can contribute to the numbers of lung cancer in some areas more than others
Radon is released from rocks and buildings made from rocks containing high levels of radon gas
How do silica and asbestos affect lung cancer?
Various building materials, such as asbestos and silica, produce small dust particles which can cause lung cancer if they are inhaled
There are strict rules about using or working with materials, such as asbestos and silica, to minimise exposure and therefore the associated risks
What are symptoms of lung cancer?
Breathing difficulties Coughing, sometimes coughing up blood Chest pains Loss of appetite and weight loss Persistent fatigue Tumours can form in the lungs In severe cases, the primary tumours metastasize and lead to the formation of secondary tumours elsewhere in the body
What are 3 treatments for lung cancer?
Chemotherapy
Radiotherapy
Lung removal
What is emphysema an example of?
Emphysema is an example of a Chronic obstructive pulmonary disease (COPD) which also includes lung diseases such as asthma and chronic bronchitis
What is present in the lungs which can contribute to emphysema later?
In a healthy lung, some phagocytes are present as part of the non-specific immune response to protect against bacteria found in the lungs
What enzyme to phagocytes produce in the lung and why?
Phagocytes produce the protein-digesting enzyme, elastase to destroy bacteria
What does elastase break down apart from bacteria?
Elastase also breaks down proteins in the cells of the lungs, including elastin
What prevents elastase from damaging normal healthy lungs?
An enzyme inhibitor, alpha 1-antitrypsin (A1AT), is produced by lung cells to prevent damage caused by elastase
What happens to goblet cells in smokers?
In smokers, goblet cells in the ciliated epithelium become enlarged and produce more mucus which destroys the cilia in the trachea
What does the destruction of cilia lead to?
This prevents cilia from sweeping mucus, containing bacteria, dust and other microorganisms away from the lungs, this leads to infections in the lungs
What does the increased amount of mucus (containing pathogens) cause?
Infections attract more phagocytes to the lungs and the phagocytes release elastase
Why does elastase cause damage in the lungs with empehsyma, and not in healthy lungs?
A1AT is not effective against the increased levels of elastase and so the enzyme damages the elasticity of the alveolar walls
What happens when alveoli lose elasticity?
Without enough elastin, the alveoli break down and may burst, creating large air spaces in the alveoli with an insufficient surface area to volume ratio
What in emphysema decreases diffusion rates?
Thickening of the alveolar walls increases the diffusion distance for gas exchange
What does a decreased efficiency for gas exchange cause in emphesyma?
This reduces the efficiency of gas exchange, causing emphysema where less oxygen is carried in blood (making exercise difficult)
What do people need in end stage emphesyma?
Once the disease progresses, people often need a constant supply of oxygen to stay alive
Can emphysema be reversed?
NO
Damage to the alveoli which result in emphysema, is irreversible
What is the overall result of emphysema in terms of blood composition?
It leads to low blood oxygen levels and high carbon dioxide levels in patients
What are the symptoms of emphysema?
Shortness of breath or laboured ventilation
A chronic or persistent cough
Chest tightness
Wheezing and difficulty breathing when exercising or during any physical activity
Lack of energy
How do lungs increase overall rate of gas exchange?
The lungs are also structured to have a very large surface area, so as to increase the overall rate of gas exchange
What are the 4 adaptations of alveoli?
thin epithelial layer
rich capillary network
spherical in shape
surfactant
How does the spherical shape of alveoli help in gas exchange?
They are roughly spherical in shape, in order to maximise the available surface area for gas exchang
Why is the internal surface of capillaries covered with a layer of fluid?
Their internal surface is covered with a layer of fluid, as dissolved gases are better able to diffuse into the bloodstream
What shape are type I pneumocytes?
They are squamous (flattened) in shape and extremely thin (~ 0.15µm) – minimising diffusion distance for respiratory gases
What connects type I pneumocytes?
Type I pneumocytes are connected by occluding junctions, which prevents the leakage of tissue fluid into the alveolar air space
How can more type I pneumocytes be produced?
Type I pneumocytes are amitotic and unable to replicate, however type II cells can differentiate into type I cells if required
What shape are type II pneumocytes?
They are cuboidal in shape and possess many granules (for storing surfactant components)
What is surface tension
Surface tension is the elastic force created by a fluid surface that minimises the surface area (via cohesion of liquid molecules)
Give 2 steps of how surfactant helps reduce surface tension?
As an alveoli expands with gas intake, the surfactant becomes more spread out across the moist alveolar lining
This increases surface tension and slows the rate of expansion, ensuring all alveoli inflate at roughly the same rate
What can the degradation of alveoli in emphysema also lead to in terms of surface area?
The loss of elasticity results in the abnormal enlargement of the alveoli, leading to a lower total surface area for gas exchange
How may the structure of alveoli be affected in emphysema?
The degradation of the alveolar walls can cause holes to develop and alveoli to merge into huge air spaces (pulmonary bullae)
When does ventilation change?
Ventilation in humans changes in response to levels of physical activity, as the body’s energy demands are increased
What does ATP Production produce?
ATP production (via cellular respiration) produces carbon dioxide as a waste product (and may consume oxygen aerobically)
What detects changes in blood CO2?
Changes in blood CO2 levels are detected by chemosensors in the walls of the arteries which send signals to the brainstem
Why does exercise lead to increased ventilation?
As exercise intensity increases, so does the demand for gas exchange, leading to an increase in levels of ventilation
In what two ways does exercise influence ventilation (basic)
Increase ventilation rate
Increase tidal volume
Why does ventilation rate increase alongside exercise?
a greater frequency of breaths allows for a more continuous exchange of gases
Why does tidal volume increase alongside exercise?
increasing the volume of air taken in and out per breath allows for more air in the lungs to be exchanged
In what 3 ways can ventilation be observed in humans?
via simple observation
chest belt and pressure meter
spirometer
How can simple observation be used to measure ventilation?
counting number of breaths per minute
How can chest belt and pressure meter be used to measure ventilation?
recording the rise and fall of the chest
How can spirometer be used to measure ventilation?
recording the volume of gas expelled per breath
What does spirometry involve?
Spirometry involves measuring the amount (volume) and / or speed (flow) at which air can be inhaled or exhaled
What is a spirometer?
A spirometer is a device that detects the changes in ventilation and presents the data on a digital display
What is more simplistic alternative to spirometry?
A more simplistic method involves breathing into a balloon and measuring the volume of air in a single breath
How can the volume of air be determined when using a balloon?
The volume of air can be determined by submerging the balloon in water and measuring the volume displaced (1ml = 1cm3)
