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Questions and Answers
The surface tension elastic force in alveoli is responsible for their expansion.
False
Surfactant is secreted by type I alveolar cells.
False
Dipalmitoylphosphatidylcholine is a protein responsible for reducing surface tension.
False
Cartilage rings are present in bronchioles.
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Bronchioles are kept expanded by cartilage plates.
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Many obstructive diseases of the lung result from excessive smooth muscle relaxation of the bronchioles.
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The sympathetic nervous system causes constriction of the bronchioles.
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Parasympathetic fibers secret norepinephrine and cause mild to moderate constriction of the bronchioles.
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Histamine and slow reactive substance of anaphylaxis cause airway dilation during allergic asthma.
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The rate of diffusion of each gas is inversely proportional to the pressure caused by that gas alone.
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The air has an approximate composition of 50 per cent nitrogen and 50 per cent oxygen.
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When the partial pressure of a gas is greater in one area than in another area, there will be net diffusion from the low-pressure area toward the high-pressure area.
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The sympathetic nervous system worsens the condition of asthma.
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All respiratory gases are complex molecules that are bound to one another.
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The rate of gas diffusion through the respiratory membrane is affected by the pressure difference of the gas between the two sides of the membrane.
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The respiratory unit is composed of a respiratory bronchiole, alveolar ducts, atria, and trachea.
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The alveolar walls are extremely thick, and capillaries are arranged as an interconnecting network.
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The diffusion coefficient of oxygen is higher than that of carbon dioxide in the respiratory membrane.
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Gas exchange between the alveolar air and the pulmonary blood occurs through the esophagus.
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The rate of alveolar ventilation is about 10 L/min in normal individuals.
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One half of the excess gas is normally removed from the alveoli in 8 seconds.
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The ventilation-perfusion ratio is expressed as QA/V.
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The rate of oxygen absorption from the alveoli is 500 ml/min in normal individuals.
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When both alveolar ventilation and alveolar blood flow are normal for a given alveolus, the ratio is abnormal.
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The rate of carbon dioxide excretion from the blood is 500 ml/min in normal individuals.
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Some areas of the lungs are always well ventilated and have excellent blood flow.
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POINT A is the normal operating point for both oxygen and carbon dioxide partial pressures in the alveoli.
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The rate of alveolar ventilation affects the partial pressure of oxygen in the alveoli.
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About 70% of carbon dioxide is transported in the form of bicarbonate ions.
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The dorsal respiratory group mainly causes expiration.
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The ventral respiratory group controls the rate and depth of breathing.
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The nucleus of the tractus solitaries is the sensory termination of both the vagal and the glossopharyngeal nerves.
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The ventral respiratory group is active during normal quiet respiration.
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The dorsal respiratory group generates rhythmical expiratory discharges to the expiratory muscles.
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Carbonic anhydrase is an enzyme that accelerates the reaction of carbon dioxide with water.
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About 23% of carbon dioxide is transported in the form of carbaminohemoglobin.
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Study Notes
Surface Tension and Surfactant
- The water surface in the alveoli tries to contract, causing the alveoli to collapse, but this is prevented by surfactant, a substance secreted by type II alveolar cells.
- Surfactant is a mixture of phospholipids, proteins, and ions, with dipalmitoylphosphatidylcholine being the most important component in reducing surface tension.
Respiratory Passageways
- The trachea, bronchi, and bronchioles have cartilage rings or plates that keep them from collapsing, allowing for sufficient motion for lung expansion.
- Intermittent smooth muscles between the cartilaginous rings of the trachea and bronchi help maintain rigidity.
- Bronchioles lack cartilage, but are kept expanded mainly by transpulmonary pressures that expand the alveoli.
- Many obstructive lung diseases result from narrowing of smaller bronchi and bronchioles due to excessive smooth muscle contraction.
Control of Bronchiolar Musculature
- Sympathetic stimulation from the adrenal medullae (norepinephrine and epinephrine) causes dilation of the bronchioles.
- Parasympathetic fibers secrete acetylcholine, causing mild to moderate constriction of the bronchioles, which worsens asthma.
Effects of Local Substances
- Histamine and slow reactive substance of anaphylaxis released in lung tissues during allergic reactions cause airway obstruction during allergic asthma.
- Smoke, dust, sulfur dioxide, and acidic elements in smog initiate local parasympathetic reflex, causing airway obstruction.
Pulmonary Capillary Dynamics
- After alveoli are ventilated with fresh air, oxygen diffuses from the alveoli into the pulmonary blood, and carbon dioxide diffuses in the opposite direction.
- The rate of diffusion of each gas is directly proportional to the pressure caused by that gas alone (partial pressure of the gas).
Physical Principles of Gas Exchange
- Pressure difference causes net diffusion of gases through fluids.
- Diffusion of gases is directly proportional to the pressure caused by that gas alone (partial pressure of the gas).
Factors Affecting the Rate of Gas Diffusion
- Thickness of the membrane
- Surface area of the membrane
- Pressure difference of the gas between the two sides of the membrane
- Diffusion coefficient of the gas in the membrane
Rate of Alveolar Ventilation
- The rate of renewal of alveolar air is about 17 seconds with normal alveolar ventilation.
- When the rate of ventilation is only half normal, one half the gas is removed in 34 seconds, and when the rate of ventilation is twice normal, one half is removed in about 8 seconds.
Oxygen and Carbon Dioxide Concentration
- The effect of alveolar ventilation on alveolar PO2 and PCO2 is shown graphically.
- Point A is the normal operating point.
Respiratory Membrane
- The alveolar walls are extremely thin, and capillaries are arranged as an interconnecting network.
- Gas exchange between the alveolar air and the pulmonary blood occurs through the respiratory membrane.
Ventilation-Perfusion Ratio
- The ratio between alveolar ventilation and alveolar blood flow is called the ventilation-perfusion ratio.
- This ratio is normally around 1, but can vary depending on factors such as ventilation and blood flow.
Transport of Carbon Dioxide
- Most carbon dioxide (about 70%) is transported in the form of bicarbonate ions after CO2 combines with water on the surface of RBC to form carbonic acid.
- About 23% of CO2 is transported in the form of carbaminohemoglobin (Hb-CO2).
- The rest (7%) is transported in a dissolved state.
Regulation of Respiration
- The respiratory center is composed of groups of neurons located bilaterally in the medulla oblongata and pons of the brain stem.
- The respiratory center is divided into three groups of neurons: dorsal respiratory group, ventral respiratory group, and pneumotaxic center.
Dorsal Respiratory Group
- Located within the nucleus of the tractus solitaries in the medulla of brain stem.
- Generates rhythmical inspiratory discharges to the inspiratory muscles (mainly diaphragm) in a ramp manner.
Ventral Respiratory Group
- Features of this group of neurons:
- Remain almost inactive during normal quiet respiration and do not participate in basic rhythm of respiration.
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Description
Learn about the surface tension in alveoli, the role of surfactant in preventing alveolar collapse, and the composition of surfactant. Understand the importance of dipalmitoylphosphatidylcholine in reducing surface tension.
