BIOL125 Lecture Notes - Lecture 10: Phrenic Nerve, No Air, Skeletal Muscle
BIO week 10 LC Pulmonary Ventilation
Learning Objectives:
- Discuss the gross anatomy and functions of the rib cage, pleura and diaphragm
- Explain the relevance of Boyle’s law to breathing
- Define ventilation and explain its elementary steps
- Define the significance of diaphragm in pulmonary ventilation
- List and explain the significance of the expiratory muscles
- Discuss the origin and significance of the spontaneous recoil tendency of the lungs
Respiration
- The process that provides the body’s cells with O2 and removes the waste product
CO2
- Respiration includes five separate processes:
1. Pulmonary Ventilation
oMovement of air in and out of the lungs
2. External respiration (pulmonary gas exchange)
oGas exchange between alveolar air and blood
3. Gas transport
oTransport of O2 and CO2 in blood
4. Internal respiration (tissue gas exchange)
oGas exchange between blood and tissues/cells
5. Cellular respiration
oThe process of oxidising food molecules to CO2 and water
Pulmonary Ventilation
- Has two phrases:
oInspiration (ie. Breathing in = air moves into lungs)
oExpiration (ie. Breathing out = air moves out of lungs)
- Air is driven by a pressure gradient
- Air always moves from high pressure to low pressure
- Therefore, to ensure that air moves into and out of the lungs, there must be a
pressure difference between the atmosphere and the lungs ie. (intra-)alveolar or
intrapulmonary space
- To create a pressure difference between the atmosphere and intra-alveolar space,
the pressure inside the lungs (ie. Alveolar pressure) needs to be reduced below and
then increased above atmospheric pressure
How can we change the pressure inside the lungs?
- Boyle’s law (1662)
o“as volume increases, the pressure of the gas decreases in proportion. In
contrast, as volume decreases, the pressure of the gas increases in
proportion”
oP1 x V1 = P2 x V2, where P is pressure and V is volume
oVolume changes occur because of thoracic cavity
oPressure gradient from atmosphere to lungs – therefore air rushes into lungs
oPressure gradient from lungs to atmosphere – therefore air rushes out of
lungs into atmosphere
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Pulmonary Ventilation
- Therefore, pulmonary ventilation necessitates volume changes:
oWhen intra-alveolar volume increases pressure goes down becomes
lower than atmospheric pressure inspiration
oWhen intra-alveolar volume decreases pressure goes up exceeds
atmospheric pressure expiration
Problems
- Lungs cannot expand on their own (due to lack of relevant muscles)
oSkeletal muscles of the thoracic cavity/wall need to be exploited
- However, none of the skeletal muscles of the thoracic cavity/wall is attached to the
lungs directly
- In fact, the lungs are not even attached to the thoracic wall
- Enter pleura and intrapleural space…
The Pleura
- Makes pleural fluid that fills the cavity
- If anything gets into pleural cavity, eg. Blood, then lung can collapse
Inspiratory Muscles
- Diaphragm
oSkeletal muscle (voluntary control)
oWhen relaxed, diaphragm bulges into the thoracic cavity
oThe major outflow of the phrenic nerve is C4 this will be crucial when it
comes to the effect of spinal cord injury on breathing
oWhen diaphragm contracts:
It moves down and becomes flat
Thoracic volume increases
Pressure in the thoracic cavity decreases
Abdominal volume reduces
Pressure in the abdominal cavity increases
oWhen diaphragm relaxes:
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Document Summary
Explain the relevance of boyle"s law to breathing. Discuss the gross anatomy and functions of the rib cage, pleura and diaphragm. Define ventilation and explain its elementary steps. Define the significance of diaphragm in pulmonary ventilation. Discuss the origin and significance of the spontaneous recoil tendency of the lungs. List and explain the significance of the expiratory muscles. The process that provides the body"s cells with o2 and removes the waste product. Respiration includes five separate processes: pulmonary ventilation, movement of air in and out of the lungs, external respiration (pulmonary gas exchange, gas exchange between alveolar air and blood, gas transport. 4: transport of o2 and co2 in blood. Internal respiration (tissue gas exchange: gas exchange between blood and tissues/cells, cellular respiration, the process of oxidising food molecules to co2 and water. Has two phrases: inspiration (ie. breathing in = air moves into lungs, expiration (ie. breathing out = air moves out of lungs)
