Lesson 6 - Respiratory System II Flashcards
(6 cards)
Ventilation: How does breathing work?
Breathing is based on the principle of negative pressure.
Air always flows from an area of higher pressure to an area of lower pressure.
When the air pressure inside the lungs is lower than the atmospheric pressure (outside), air is forced into the lungs.
When the air pressure inside the lungs is higher than the atmospheric pressure (outside), air is forced out of the lungs.
How Does Pressure Change in the Lungs?
The lungs exist inside the thoracic cavity, which is lined with a thin layer of connective tissue called the pleural membrane (the lungs are also covered by their own pleural membrane).
The space between these membranes (pleural
cavity) is filled with fluid which prevents them from separating.
The thoracic cavity is further separated from the abdominal cavity (digestive system) by a sheet of muscle called the diaphragm.
Inhalation
During inhalation, the diaphragm contracts, making it shorter and flatter. At the same time, the muscles between the ribs, contract and pull the ribs upward and outward.
Because those pleural membranes are adhered, these actions increase the volume of the thoracic cavity which reduces the pressure inside the lungs.
As a result, the atmospheric pressure (outside) is greater than the pressure in the thoracic cavity
Due to this pressure difference, air rushes into the lungs to equalize the pressure (inhalation)!
Exhalation
During exhalation, the diaphragm relaxes and returns to its regular domed shape which pushes up on the lungs. The external intercostal muscles also relax and the ribs fall and return to their resting position.
The air pressure inside the lungs is now greater than the atmospheric pressure (outside) so air is forced out of the lungs. The elasticity of the lung tissue causes the lungs to return to their resting size, which also helps to force air out.
Fun fact: During exercise or forced exhalation, a second set of muscles (internal intercostal muscles), start contracting and relaxing. When they contract, they pull the rib cage downward, increasing the pressure inside the lungs and forcing more air out of the lungs.
Lung Capacity
Strenuous physical activity automatically
increases the rate and depth of your breathing
Total lung volume depends on biological sex,
body type, and lifestyle. Factors such as
smoking/ vaping and exercise level can influence lung volume
Total lung capacity: the maximum volume of air
that can be inhaled during a single breath
Fun fact: the average adult has a total lung capacity of ~6L but British rower and three-time Olympic gold medalist Pete Reed is reported to hold the largest recorded lung capacity of 11.68 L
We do not use out total capacity day to day.
Normal breathing does not involve a complete
exchange of the air in the lungs.
Tidal volume (TV): the volume of air inhaled or
exhaled during a normal, involuntary breath
Inspiratory reserve volume (IRV): the volume of
air that can be forcibly inhaled after a normal
inhalation
Expiratory reserve volume (ERV): the volume of
air that can be forcibly exhaled after a normal
exhalation
Even after the expiratory reserve volume
(ERV) has been expelled, the lungs are not
completely empty. This residual volume
prevents the lungs from collapsing.
During periods of high demand for oxygen
(like with strenuous exercise), the reserve
volumes (IRV/ ERV) decrease and tidal
volume (TV) increases.
The maximum tidal volume is called the vital
capacity, which is the maximum amount of air
that can be inhaled or exhaled
Oxygen Usage
The amount of oxygen reaching our cells (and how quickly it is supplied) determines how efficiently our bodies can make and use ATP. This is an indicator of the efficiency the respiratory system (the higher the better)
VO2: an estimated or measured value representing the rate at which oxygen is used in the body (mL/kg/min)
VO2max: the maximum rate at which oxygen can be used in an individual (mL/kg/min)
