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