Physiology 2130 Lecture 10: Phys Lecture 10
11 Feb 2017
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Module 10 – Respiratory System
INTRODUCTION
- Functions of respiratory system:
o Transport of oxygen from the air into blood
o Removal of carbon dioxide from blood into air
o Control of blood acidity – pH
o Temperature regulation
o Forming a line of defense to airborne particles
ANATOMY
- Lungs are located in the thoracic cavity – surrounded by rib case and diaphragm
- Airway consists of nasal cavity and moth – join together at the pharynx
o Pharynx leads into the larynx (voice box), then becomes the trachea
▪ Trachea divides into two main bronchi – left and right – which continually divide
into smaller and smaller bronchioles
▪ Small bronchioles continually divide and eventually end in the alveoli which are
the sites of gas exchange in the lung
ANATOMY – BLOOD VESSELS AND BLOOD
- Pulmonary artery branches to form a dense network of capillaries around each alveolus
o THIS ARTERY DELIVERS DEOXYGENATED BLOOD TO THE LUNGS
- Structure of the capillaries and blood flow characteristics maximize gas exchange
o Characteristics: thin endothelial walls, large total cross sectional area, very low blood
velocity
o In the capillaries, oxygen diffuses into the blood while carbon dioxide diffuses out
- From the capillaries, the oxygen rich blood flows back to the left side of the heart through the
pulmonary vein
ANATOMY – HISTOLOGICAL STRUCTURE OF AN ALVEOLUS
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- There are 300 million alveoli in a healthy human lung
o Each has a diameter of 0.3 mm
- Walls of the alveoli are one cell thick and composed of alveolar epithelial cells (type 1 cells)
- Type 2 cells secret surfactant (fluid) that lines the alveoli
- Large number of capillaries surround the alveoli in close proximity
- Respiratory membrane: region between the alveolar space and capillary lumen
o Can have a thickness as narrow as 0.3 microns
o Where gas exchange takes place between air and blood
- Cells of the immune system protect the body from airborne particles that male their way into the
alveoli
o Macrophages, lymphocytes
- Fibers of elastin and collagen are present in the walls of the alveoli, around blood vessel and
bronchi
PRESSURE OF THE LUNGS
- Two thin pleural membranes – one lines and sticks to the ribs (the parietal pleura) while the
other surrounds and sticks to the lungs (the visceral pleura)
o The two layers form the intrapleural space which contains a very small amount of
pleural fluid [10-15ml]
o The fluid reduces friction between the two pleural membranes during breathing
- Due to their nature and attached muscle, the ribs tend to spring outward
- The lungs tend to recoil and collapse due to the presence of elastin
PRESSURE OF THE LUNGS - ALVEOLAR AND ATMOSPHERIC PRESSURE
- Pressure inside the lungs is alveolar pressure (intrapulmonary pressure)
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o Between breaths, the alveolar and atmospheric pressures are the same at 760 mmHg
▪ 0 DIFFERENCE
- Pressure in the intrapleural space is intrapleural pressure
o Pressure is 756 mmHg
▪ 4 mmHg DIFFERENCE
- Atmospheric pressure outside the body is 760 mmHg at sea level
PRESSURE OF THE LUNG - TRANSPULMONARY PRESSURE
- Transpulmonary pressure (difference between the alveolar and intrapleural pressure) is
calculated by:
- The transpulmonary pressure is important because this difference in pressure across the alveoli
and intrapleural space holds the lungs open
- In a healthy set of lungs, the transpulmonary pressure is positive (outward) and keeps the lungs
and alveoli open
Transpulmonary Pressure = 760 mmHg – 756 mmHg = +4 mmHg
PRESSURE OF THE LUNGS – PNEUMORTHAX
- If both the alveolar and intrapleural pressures were equal, this would result in a transpulmonary
pressure of 0 mmHg
o In this case, there would be no pressure holding the lungs open and they would collapse
– produces pneumothorax
o Occurs when the intrapleural space is punctured, causing the alveolar pressure and
intrapleural pressure to become equal (both are at 760 mmHg)
o Generally, only one lung collapses because the intrapleural space of each lung is isolated
from the other
Transpulmonary Pressure = Alveolar Pressure – Intrapleural Pressure
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Document Summary
Functions of respiratory system: transport of oxygen from the air into blood, removal of carbon dioxide from blood into air, control of blood acidity ph, temperature regulation, forming a line of defense to airborne particles. Lungs are located in the thoracic cavity surrounded by rib case and diaphragm. Pulmonary artery branches to form a dense network of capillaries around each alveolus: this artery delivers deoxygenated blood to the lungs. Structure of the capillaries and blood flow characteristics maximize gas exchange: characteristics: thin endothelial walls, large total cross sectional area, very low blood velocity. In the capillaries, oxygen diffuses into the blood while carbon dioxide diffuses out. From the capillaries, the oxygen rich blood flows back to the left side of the heart through the pulmonary vein. There are 300 million alveoli in a healthy human lung: each has a diameter of 0. 3 mm. Walls of the alveoli are one cell thick and composed of alveolar epithelial cells (type 1 cells)
