6.4 Gas exchange Flashcards
What does ventilation maintain?
Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries
What is gas exchange?
The process in which organisms absorb one gas from the environment and release a different one
How do humans use gas exchange?
Human absorb oxygen for use in cell respiration and release the carbon dioxide produced by this process
Where do gas exchange occur in humans and in terrestrial organisms?
Humans: In small air sacs called alveoli inside the lungs
Terrestrial organisms: exchange gases with the air
How does gas exchange happen by?
By diffusion between air in the alveoli and blood flowing in the adjacent capillaries
How does the gases only diffuse during gas exchange?
The gases only diffuse because there is a concentration gradient
Describe the concentration gradient involving the alveolus and the blood in the capillary?
The air in the alveolus
* higher conc. of oxygen
* Lower conc. of CO2
… compared to the blood in the capillary
How do humans maintain the concentration gradient between oxygen and CO2?
- Fresh air must be pumped into the alveoli
- Stale air must be removed
This process is called ventilation
What is the process of maintaining the concentration between oxygen and Co2 called?
Ventilation
What are type I pneumocytes?
extremely thin alveolar cells that are adpated to carry out gas exchange
What does the lung contain huge numbers of?
Alveoli
What is the purpose of having huge numbers of alveoli in the lungs?
For a very large total surface area for diffusion. Diffusion for gas exchange
What is the wall of each alveolus consist of?
A thin layer of cells, called the epithelium
What type are most of the cells in the epithelium of each alveolus?
Type I pneumocytes
What do type I pneumocytes look like?
Flattened cells, with the thickness of only about 0.15 micrometer
What do the walls of the adjacent capillaries also consist of?
A single layer of very thin cells
Therefore the air in the alveolus and the blood in the alveolar capillaries are less than 0.5 micrometer apart
How does the distance between the air in the alveolus and the blood in the alveolar capillaries affect gas exchange?
The distance over which oxygen and carbon dioide has to diffuse is therefore very small, which is an adaptation to increase the rate of gas exchange
What is the adaptation of having a thin layer of cells as the wall for alveolus and capilliaries?
Short diffusion pathways -> increase the rate of gas exchange
What are type II pneumocytes?
Rounded cells that occupy about 5% of the alveolar surface area
What do type II pneumocytes secrete?
A solution containing surfactant that coats the inner surface of the alveoli
What does the film of moisture from the solution secreted by type II pneumocytes allow for?
- Allows oxygen in the alveolus to dissolve and then diffuse to the blood in the alveolar capillaries
- It also provides an area from which carbon dioxide can evaporate into the air and be exhaled
What does the fluid secreted by the type II pneumocyte contain?
A pulmonary surfactant
What is similar of the molecules in the pulmonary surfactant and phospholipids?
Its molecules have a similar structure with phospholipids in cell membranes .
What does the pulmonary surfactant do?
It forms a monolayer on the surface of the moisture lining the alveoli, with the hydrophilic heads facing the water and the hydrophobic tails facing the air.
How does surfactant prevent the collapse of the lung?
- reduces the surface tension and prevents the water from causing the sides of the alveoli to adhere when air is exhaled from the lungs
- due to the hydrophilic tails
How is the pulmonary surfactant positioned to stop the sides of the alveoli to adhere when air is exhaled from the lung?
The hydrophilic heads facing the water and hydrophobic tails facing the air.
What do premature babies suffer from when they are born without insufficient pulmonary surfactant?
Infant respiratory distress syndrome
How is infant respiratory distress syndrome treated?
- giving the baby oxygen
- one or more doses of surfactant, extracted from animal lungs
Where does air enter the ventilation system?
through the nose or mouth, then passes down the trachea
What does the rings of cartilage do in the trachea?
To keep it open even when air pressure inside is low or pressure in surrounding tissues is high
What does the trachea divide to form?
Two bronchi, with walls strengthened with cartilage
What does one bronchus lead to?
each lung
Inside the lung, what do the bronchi do?
They divide repeatedly to form a tree-like strucutre of narrower airways, called bronchioles.
What do bronchioles have in their walls?
Smooth muscle fibres, allowing the width of these airways to vary
What is found at the end of the narrowest bronchioles?
A group of alveoli, where gas exchange occurs
What happens to the pressure when the volume increases or decreases?
Increase volume = decrease pressure
Decreased volume = increased pressure
If a gas is free to move, where will it flow from and to?
It will always flow from regions of higher pressure to regions of lower pressure
During ventilation, what causes the pressure inside the thorax to drop below atmospheric pressure?
Muscle contractions
What is the consequence of muscle contractions during ventilation?
The contraction of respiratory muscles changes the volume of the thoracic cavity (i.e. the chest)
What happens when the volume of the thoracic cavity increases and decreases?
Increase = pressure in the thorax decreases
Decrease = pressure in the thorax increases
What effect does muscle contractions have during expiration?
They cause the pressure inside the thorax to rise above atmospheric, so air is forced out from the lungs to the atmosphere
When the pressure in the chest is greater than the atmospheric pressure, air will move out of the lungs (expiration)
What effect does muscle contractions have during inspiration?
Cause the pressure inside the thorax to drop below atmpspheric pressure and air is drawn into the lungs from the atmosphere
When the pressure in the chest is greater than the atmospheric pressure, air will move out of the lungs (expiration)
What effect does muscle contractions have during inspiration?
Cause the pressure inside the thorax to drop below atmpspheric pressure and air is drawn into the lungs from the atmosphere
When the pressure in the chest is greater than the atmospheric pressure, air will move out of the lungs (expiration)
Compare the pressure during inspiration and expiration?
- When the pressure in the chest is less than the atmospheric pressure, air will move into the lungs (inspiration)
- When the pressure in the chest is greater than the atmospheric pressure, air will move out of the lungs (expiration)
What two states can muscles be in?
Contracting and relaxing
How do muscles do work?
When they contract by exerting a pulling force (tension) that causes a particular movement. They become shorter when they do this
What happens to muscles when they are relaxing?
Muscles lengthen passively when relaxing - they do not lengthen themselves.
* Most muscles are pulled into an elongated state by the contraction of another muscle - they do no exert a pushing force (compression) while relaxing
Why can muscles only cause movement in one direction?
Because the opposite movement is required by a second muscle contracting while the other one relaxes.
if movement in opposite directions is needed at different times, what is needed?
Two muscles will be required
What is an antagonistic pair of muscles?
When muscles work together for two opposite movements.
* When one muscle contracts and causes a moement, the second muscle relaxes and is elongated by the first.
* The opposite movement is caused by the second muscle contracting while the first relaxes.
How are antagonistic pair of muscles related to gas exchange?
Inspiration and expiration involve opposite movements, so different muscles are required, working as antagonistic pairs
What are the examples of antagonisitic muscle action in ventilation?
- External and internal intercoastal muscles
- Diaphram and abdominal muscles
What do ventilation need two pairs of opposite movements for?
to change the volume. andtherefore the pressure inside the thorax
What happens to the diaphram and ribcage during inspiration and expiration?
How does volume and pressure change during inspiration and expiration?
How does the diaphragm and abdomen wall muscles influence the movement of the diaghragm during inspiration and expiration?
How does the external and internal intercostal muscles influence the movement of the ribcage during inspiration and expiration?
What does tobacco smoke contain lots of?
Mutagenic chemicals
How does passive smoking cause 3% of lung cancer cases?
This happens when non-smokers inhale tobacco smoke exhaled by smokers
How does air pollution probably cause about 5% of lung cancers?
The sources of air pollution that are most significant are diesel exhaust fumes, nitrogen oxides from all vehicles exhaust fumes and smoke from bruning coal, wood or other organic matter
How does Radon gas cause significant number of cases?
Radon gas is a radioactive gas that leaks out of certain rocks such as granite.
It accumulates in badly ventilated buildings and people then inhale it
How does Asbestos, silica and some other solid cause lung cancer?
If dust or other particles of them are inhaled. This usually happens on construction sites or in quarries, mines or factories
What are some symptoms of lung cancer?
- difficulties with breathing
- persistent coughing
- coughing up blood
- chest pain
- loss of appetite
- weight loss
- general fatigue
What is emphysema?
a lung condition whereby the walls of the alveoli lose their elasticity due to damage to the alveolar walls
How does the alveoli of emphysema patients compare to a healthy lung?
- Smaller number of larger air sacs with much thicker walls
- Huge air space (pulmonary bullae)
- total surface area for gas exchange is considerably reduced
- Distance over which diffusion of gases occurs is increased
= gas exchange is much less effective
= lung is less elastic, so ventilation is more difficult
What happens when a lung is less elastic?
Ventilation is more difficult
What do phagocytes ustually do inside aleveoli?
normally prevent lung infections by:
* engulfing bacteria
* producing elastase, a protein-digesting enzyme, to kill them inside the vesicles formed by endocytosis
What prevents elastase and other proteases form digesting lung tissue?
An enzyme inhibitor called alpha 1-antitrypsin (A1AT)
* Elastase activity can be blocked by an enzyme inhibitor (α-1-antitrypsin), but not when elastase concentrations are increased
What would you expect of the phagocytes in smokers?
The number of phagocytes in the lungd increases and they try to produce more elastase
How does smoking cause damage to alveolar walls
The damage to lung tissue leads to the recruitment of phagocytes to the region, which produce an enzyme called elastase
This elastase, released as part of an inflammatory response, also breaks down the elastic fibres in the alveolar wall
How does smoking cause damage to alveolar walls
The damage to lung tissue leads to the recruitment of phagocytes to the region, which produce an enzyme called elastase
This elastase, released as part of an inflammatory response, also breaks down the elastic fibres in the alveolar wall
How does genetic factors play a role in emphysema?
- affect the quantity and effectiveness of A1AT produced in the lungs
Why is emphysema a chronic disease?
The damage to alveoli is usually irreversible
* It causes low oxygen saturation in the blood and higher than normal carbon dioxide concentrations.
What explains an emphysema patients lack o energy?
Low oxygen saturation in the blood and higher than normal CO2 conc.
* Ventiation is laboured and tends to be more rapid than normal
