Physiology 1020 Lecture Notes - Lecture 2: Internal Intercostal Muscles, External Intercostal Muscles, Pulmonary Surfactant
11 Apr 2016
School
Department
Course
Professor
Respiratory System
Responsible for:
• Transport of O2 from the air into the blood
• Removal of CO2 from blood into the air
• Control of pH
• Temperature regulation
• Line of defense against airborne particles
Anatomy
• Located within the thoracic cavity surrounded by the rib cage and diaphragm
• Branched airway network: trachea → bronchi → bronchioles → alveoli (gas
exchange)
Anatomy- Blood Vessels
• Pulmonary artery delivers deoxygenated blood to the lungs
• Capillaries surround alveoli
• Capillaries are thin and have a large cross sectional area which allow for
maximal diffusion
Anatomy- Structure of Alveolus
• Walls of the alveoli are 1 cell thick and are composed of alveolar epithelial
cells- type 1 cells
• Type 2 cells secrete a fluid called surfactant that lines the alveoli
• Large numbers of capillaries surround the alveoli
• Respiratory membrane- region between the alveolar space and the capillary
lumen
o This membrane is where gas exchange occurs between air and blood
• Macrophages and lymphocytes, cells of the immune system, protect body
from airborne particles that make their way into the alveoli
Pressure of the Lungs- Intrapleural Pressure
• The lungs are separated from the ribs by two thin pleural membranes
• Parietal pleura- lines and sticks to the ribs
• Visceral pleura- surrounds and sticks to the lungs
• Intrapelural space contains fluid that reduces friction during breathing
• Pleural fluid- cushions the lungs from the ribcage and helps prevents the
lungs from collapsing from inhalation and exhalation
• Gas pressures of the lungs:
o Atmospheric = 760 mmHg
o Intrapulmonary/alveolar = 760 mmHg
o Intrapleural = 756 mmHg→ pressure inside the pleural fluid and
keeps the lungs open
o All of these conditions and numbers are when the lungs are at rest
• Lungs are elastic in nature → want to collapse as alveolar = atmospheric
pressure
• Kept open as intrapleural pressure is less than alveolar pressure
• Transpulmonary pressure is the difference in pressure across the alveoli and
intrapleural space
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• Transpulmonary pressure = Alveolar Pressure – Intrapleural
o In healthy lungs = +4 mmHg → more pressure inside the lungs
pushing outwards than inside the pleural fluid pushing outwards
o Positive pressure pushes outwards → maintains open lungs at rest
• If the intrapleural space was punctured then the intrapleural pressure =
atmospheric pressure → 760 mmHg
o Transpulmonary pressure = 0 mmHg
o Lung would collapse
o Pneumothorax
Ventilation
• Boyle’s Law → Pressure 1/volume
• Intrapulmonary/Alveolar pressure increases as lung volume decreases
o Inverse relationship
• Moving air into the lungs requires an air pressure gradient
• Air moves down its pressure gradient
o High pressure → low pressure
• To inhale the pressure within the lungs (alveolar/intrapulmonary pressure)
needs to be less than atmospheric pressure
• To exhale the alveolar pressure needs to be greater than atmospheric
• Outside pressure cannot change, so alveolar pressure must
Mechanisms of Inspiration
• Alveolar pressure must be less than atmospheric pressure (760 mmHg)
• To decrease the alveolar pressure (intrapulmonary) pressure, the lung
volume must increase
o Through movement of rib cage and diaphragm
• Diaphragm contracts, moves down, while external intercostal muscle of the
rib cage move out an up → increased lung volume → decreased alveolar
pressure = 759 mmHg → inhale
• Contraction of these muscles is an active process that relies on signals from
the brain
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Mechanisms of Expiration
• Diaphragm and external intercostal muscles relax → decreased lung volume
→ increased alveolar pressure = 761 mmHg → exhale
• During exercise abdominal and internal intercostal muscles contract →
further decrease lung volume → increase alveolar pressure = 763 mmHg →
stronger exhale
• Exhalation is only an active process during exercise- active process when
abdominal and internal intercostal muscles are activated
• When muscles contract they further decrease the volume creating a larger
pressure gradient which forces air out
Pulmonary Compliance
• Stretchability of the lungs = more stretchable more compliant
• How compliant the lungs are determines the ease of breathing
• Pulmonary compliance = (V/P)
o Greater compliance = easier inhalation
• Pulmonary compliance influenced by two major factors:
1. Elastin fibres
• Arrangement of fibres allow elastin fibres to be easily stretched, but collagen
cannot
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find more resources at oneclass.com
Document Summary
Responsible for: transport of o2 from the air into the blood, removal of co2 from blood into the air, control of ph, temperature regulation, line of defense against airborne particles. Anatomy: located within the thoracic cavity surrounded by the rib cage and diaphragm, branched airway network: trachea bronchi bronchioles alveoli (gas exchange) Anatomy- blood vessels: pulmonary artery delivers deoxygenated blood to the lungs, capillaries surround alveoli, capillaries are thin and have a large cross sectional area which allow for maximal diffusion. Pressure of the lungs- intrapleural pressure: the lungs are separated from the ribs by two thin pleural membranes, parietal pleura- lines and sticks to the ribs, visceral pleura- surrounds and sticks to the lungs. If the intrapleural space was punctured then the intrapleural pressure = atmospheric pressure 760 mmhg: transpulmonary pressure = 0 mmhg, lung would collapse, pneumothorax. Ventilation: boyle"s law pressure 1/volume, inverse relationship. Mechanisms of expiration: diaphragm and external intercostal muscles relax decreased lung volume.
