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Recognize the Functions of the respiratory system.
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Understand Mechanism of Inspiration and Expiration.
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Recognize Surface tension and role of Surfactant.
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Understand Pressure and Volume Changes During Breathing.
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I. Pulmonary ventilation *
1.Mechanisms of pulmonary ventilation
2.Indexes of pulmonary ventilation function
II. Pulmonary gas exchange and Tissue gas exchange
1. Principles of gas exchange *
2. Pulmonary gas exchange *
3. Tissue gas exchange
III. Gas transport in the Blood
1. Transport forms of oxygen and carbon dioxide in the blood
2. Oxygen transport *
3. Carbon dioxide transport *
IV. Respiratory Regulation
1. Respiratory centers and formation of respiratory rhythm
2. Reflex regulation of respiration *
V. Role of the lungs in regulation of acid-base balance

Overview of lung function and structure
Lung Functions
 Lungs are a site for gas exchange with the external environment.
 Regulate acid-base balance.
 Lungs have a defense mechanism.
 Lungs are a blood reservoir.
 Serve a biosynthetic function (Angiotensin II, surfactant)

 Respiration is the exchange of gas between the body and the environment.
 External respiration : the exchange of gases between pulmonary blood and the external environment, which involves not only diffusion across the lung capillaries
（ pulmonary gas exchange, but also the bulk movement of gases in and out of the lungs (pulmonary ventilation).
 Internal respiration : the exchange of gases between the tissue cells and the systemic capillaries. The diffusion of gases between the interstitial fluid and the cytoplasm.
 Gas transport in the blood : physical solvation and chemical constitution.

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Region of gas exchange between air and blood.
Includes respiratory bronchioles and alveolar sacs.
Must contain alveoli.

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All the structures air passes through before reaching the respiratory zone.
Warms and humidifies inspired air.
Filters and cleans:
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Mucus secreted to trap particles in the inspired air.
 Mucus moved by cilia to be expectorated.
Insert fig. 16.5

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 Cup-shaped outpouching
 Alveolar sac – 2 or more alveoli sharing a common opening
 2 types of alveolar epithelial cells
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Type I alveolar cells – form nearly continuous lining, more numerous than type II, main site of gas exchange
Type II alveolar cells (septal cells) – free surfaces contain microvilli, secrete alveolar fluid
(surfactant reduces tendency to collapse)
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Respiration (gas exchange) steps
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Pulmonary ventilation/ breathing
Inhalation and exhalation
Exchange of air between atmosphere and alveoli
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External (pulmonary) respiration
Exchange of gases between alveoli and blood
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Internal (tissue) respiration
Exchange of gases between systemic capillaries and tissue cells
Supplies cellular respiration (makes ATP)
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 Pressure inside alveoli lust become lower than atmospheric pressure for air to flow into lungs
 760 millimeters of mercury (mmHg) or 1 atmosphere (1 atm)
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Achieved by increasing size of lungs
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Boyle’s Law – pressure of a gas in a closed container is inversely proportional to the volume of the container
Inhalation – lungs must expand, increasing lung volume, decreasing pressure below atmospheric pressure
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Inhalation is active – Contraction of
 Diaphragm – most important muscle of inhalation
 Flattens, lowering dome when contracted
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 Responsible for 75% of air entering lungs during normal quiet breathing
External intercostals
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Contraction elevates ribs
25% of air entering lungs during normal quiet breathing
 Accessory muscles for deep, forceful inhalation
When thorax expands, parietal and visceral pleurae adhere tightly due to subatmospheric pressure and surface tension – pulled along with expanding thorax
As lung volume increases, alveolar (intrapulmonic) pressure drops
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 Pressure in lungs greater than atmospheric pressure
 Normally passive – muscle relax instead of contract
 Based on elastic recoil of chest wall and lungs from elastic fibers and surface tension of alveolar fluid
 Diaphragm relaxes and become dome shaped
 External intercostals relax and ribs drop down
 Exhalation only active during forceful breathing
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Diaphragm is the main muscle of inspiration
Dome-shaped

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