Physiology 2130 Lecture Notes - Lecture 10: Pulmonary Surfactant, Breathing, Intrapleural Pressure

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Module #10: Respiratory System
Introduction
Functions:
- Transport of O2 from air into blood
- Removal of CO2 from blood into air
- Control of blood acidity (pH)
- Temperature regulation
- Forming defense line to airborne particles
Focus
- Anatomy and function of respiratory system
- Mechanisms of pulmonary ventilation (breathing), lung volumes, diffusion and
transport of gases, and the regulation of ventilation
Anatomy
Lungs are located in thoracic cavity, surrounded by rib cage and diaphragm
Airway consists of nasal cavity + mouth that joins at the pharynx
Order of pathway: PharynxLarynx (aka voice box) trachealeft and right
bronchibronchiolesalveoli (sites of gas exchange)
Anatomy-Blood Vessels
Pulmonary artery delivers deoxygenated blood to the lungs via branching into a
dense network of capillaries around each alveolus
Structure of capillaries and blood flow ensures maximal gas exchange
1. Thin epithelial walls
2. Large cross-sectional area
3. Low blood velocity
In capillaries, oxygen diffuses into blood while CO2 diffuses out, then blood flows
back to left side of the heart via pulmonary vein
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Anatomy- Historical Structure of Alveoli
There are ~300 million alveoli in a healthy human lung
Alveolar walls are one cell thick and composed of alveolar epithelial cells (type I
cells)
Type II cells secrete a fluid called surfactant which lines the alveoli
Region between alveolar space and capillary lumen is the respiratory membrane
- This membrane is narrow and is the location of gas exchange between lungs
and blood
Macrophages and lymphocytes protect the body from airborne particles that
enters the alveoli
Elastin and collagen fibers are present in alveolar walls around the blood vessel
and bronchi
Pressures of the lungs- Intrapleural pressure
Inspiration=inhaling, expiration=exhaling
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There are 2 pleural membranes:
1) Parietal pleura- lines and sticks to the
ribs
2) Viceral pleura- surrounds and sticks to
the lungs
Pressures of the lungs- alveolar and atmosphere
Pressure inside the lungs is called alveolar pressure (or intrapulmonary pressure)
Pressure in Intrapleural space is Intrapleural pressure
Atmospheric pressure and the alveolar pressure are the same at 760mmHg
Pressure in Intrapleural space is 756mmHg
- The chest walls and lungs moving in opposite directions cause this lower
Intrapleural pressure
Pressure of the lungs –Transpulmonary pressure
The difference between alveolar and Intrapleural pressure
In a healthy set of lungs, the transpulmonary pressure is (+), keeping the lungs
and alveoli open (Transpulmonary pressure in normal individual is usually
760mmHg-756mmHg= +4mmHg)
Pneumothrax
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