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Questions and Answers
What is the primary function of the respiratory system?
What is the term for the exchange of air between the atmosphere and the alveoli?
What is the name of the muscle that separates the thoracic cavity from the abdominal cavity and plays a crucial role in ventilation?
What is the law that describes the relationship between the pressure and volume of a gas?
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What is the term for the pressure difference between the atmospheric pressure and the alveolar pressure?
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What is the term for the ability of the lungs to expand and contract?
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What is the term for the resistance to airflow in the airways?
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What is the law that states that the amount of gas that dissolves in a liquid is directly proportional to the partial pressure of the gas?
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What is the term for the substance produced by the lungs that reduces the surface tension of water and helps to expand the alveoli?
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What is the term for the process of exchanging oxygen and carbon dioxide between the atmosphere and the body's tissues?
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What is the primary mechanism of gas transport in the body?
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What determines the PO2 and PCO2 levels in oxygenated blood?
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What is the effect of increased ventilation on alveolar PO2 and PCO2?
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What is the result of hyperventilation?
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What is the primary function of hemoglobin in the blood?
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What is the effect of obstructive pulmonary diseases on the PO2 of oxygenated blood?
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What is the percentage of O2 dissolved in plasma?
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What is the effect of hemoglobin on the PO2 of blood?
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What is the percentage of O2 dissolved in plasma?
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What is the characteristic of the HbO2 dissociation curve?
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What is the primary function of carbonic anhydrase in CO2 transport?
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What is the effect of the binding of O2 to one heme group on the O2 binding affinity of other heme groups?
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What is the effect of anemia on the O2 carrying capacity of blood?
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What is the primary stimulator of the respiratory reflex in response to high altitude?
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What is the role of peripheral chemoreceptors in the respiratory reflex?
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What is the effect of hyperventilation on the respiratory system?
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What is the primary cause of respiratory acidosis?
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What is the role of the diaphragm and intercostal muscles in respiration?
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What is the effect of CO poisoning on the O2 carrying capacity of blood?
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What is the primary cause of emphysema?
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Study Notes
Respiratory System and Ventilation
- The function of the respiratory system is to deliver oxygen (O2) and remove carbon dioxide (CO2) from the blood through gas diffusion at the interface between pulmonary capillaries and alveoli.
- The ventilation cycle consists of two phases: inspiration (inhalation) and exhalation.
Organization of the Respiratory System
- The respiratory system is organized into airways for air flow (conducting) and tissues for gas exchange (respiratory).
- The conducting airways include the mouth, nose, bronchioles, and bronchi.
- The respiratory airways include the alveoli, which are surrounded by capillaries for gas exchange.
Respiratory Muscles
- Skeletal muscles control the respiratory cycle, including the diaphragm and intercostal muscles.
- Contraction of the diaphragm and intercostal muscles expands the thorax and increases lung volume.
- The phrenic nerves from the brainstem initiate muscle contraction.
Thoracic Anatomy
- Alveoli are compliant sacs that cannot expand or contract without external force.
- The external force is provided by intrapleural pressure, which is created by the difference between the visceral and parietal pleura.
- The visceral pleura covers the lungs, and the parietal pleura covers the thoracic wall.
- Intrapleural fluid separates the visceral and parietal pleura, allowing the lungs to slide along the chest wall during the respiratory cycle.
Mechanics of Ventilation
- Boyle's law states that P1V1 = P2V2, which applies to the respiratory system.
- The law assumes constant temperature, sealed container, and constant number of molecules.
- The skeletal muscles expand and contract the thoracic cavity, changing the volume and pressure of the lungs.
- The decrease in thoracic pressure during inspiration increases the volume of the lungs, and the increase in thoracic pressure during exhalation decreases the volume of the lungs.
Alveolar Mechanics
- Alveoli are compliant sacs that change volume due to the transpulmonary pressure gradient.
- The transpulmonary pressure gradient is the difference between the alveolar pressure (Palv) and the intrapleural pressure (Pip).
- The change in alveolar volume is proportional to the change in transpulmonary pressure.
Elastic Recoil and Intrapleural Pressure
- Elastic recoil refers to the tendency of materials to oppose stretching or distortion.
- The elastic recoil of the chest wall and alveoli comes to equilibrium with the forces due to subatmospheric intrapleural pressure.
- The subatmospheric pressure prevents the collapse of alveoli during expiration.
Alveolar Air Flow
- Alveolar air flow is driven by the pressure gradient between the alveoli and the atmosphere.
- The flow rate is determined by the pressure difference and the resistance of the airways.
- The resistance of the airways decreases during inhalation and increases during exhalation.
Lung Compliance
- Lung compliance refers to the ability of the lungs to expand and contract.
- Decreased lung compliance requires more negative intrapleural pressure to increase inspired air volume.
- Increased lung compliance allows the alveoli to collapse during exhalation.
- Surfactants, such as soap, reduce the surface tension of water films and increase lung compliance.
Airway Resistance
- Airway resistance refers to the opposition to air flow in the airways.
- The resistance decreases during inhalation and increases during exhalation.
- The autonomic nervous system can constrict or dilate the airways to alter airway resistance and airflow.
- Asthma and bronchitis are examples of airway resistance diseases.
Gas Exchange and Transport
- Gas exchange occurs in the alveoli, where O2 is consumed, and CO2 is produced.
- The transport of gases between the alveoli and the blood relies on carrier molecules, such as hemoglobin.
- Diffusion of gases into liquids is driven by partial pressure gradients.
Partial Pressures and Diffusion
- Partial pressure refers to the pressure exerted by a gas in a mixture.
- Henry's law states that the amount of gas that enters the liquid is directly proportional to the partial pressure of the gas.
- The partial pressure gradient between the air and the blood drives gas diffusion at the air-alveoli interface.
Alveolar Partial Pressures
- Alveolar PO2 and PCO2 are determined by three factors: atmospheric PO2, rate of ventilation, and rate of O2 consumption and CO2 production in tissues.
Gas Exchange between Alveoli and Blood
- Gas exchange occurs in the alveoli, where PO2 and PCO2 rapidly equilibrate with alveolar partial pressures.
- The rate of blood flow through the capillaries affects the gas exchange between the alveoli and the blood.
Transport of Gases in Blood
- O2 is not very soluble in water, but hemoglobin increases the O2 capacity of the blood.
- Hemoglobin consists of a soluble polypeptide (globin) with four heme groups, which bind to O2 molecules.
- The HbO2 dissociation curve shows the percentage of Hb saturation versus PO2.
I hope this helps!### Oxygen Binding to Hemoglobin
- Saturated Hb = O2 bound to Hb / total O2 binding sites
- Total O2 binding sites = 4 Hb
- Plasma PO2 shows the amount of O2 dissolved in plasma
HbO2 Dissociation Curve
- Majority of O2 remains bound to Hb under normal conditions
- Only 20% drop in O2 saturation from normal arterial PO2 (100 mm Hg) to normal venous PO2 (40 mm Hg)
- Amount of Hb in blood is large, so O2 from 20% of Hb binding sites is sufficient for normal metabolic needs
- Allows for near-saturated blood O2 even under conditions of reduced atmospheric O2 or impaired lung function
- Steep binding curve between PO2 levels of 20-40 mm Hg
- Allows for rapid O2 release under hypoxic conditions in tissues due to increased metabolism
- Approximately three times the amount of O2 will be released when PO2 drops from 40 mm Hg to 20 mm Hg compared to amount released when PO2 drops from 100 mm Hg to 40 mm Hg
Effects of Anemia and Hyperventilation
- Anemia: does not increase the amount of arterial O2, but reduces the overall O2 carrying capacity of blood
- Hyperventilation: increases the total O2 capacity, but does not increase the amount of arterial O2
Carbon Monoxide Poisoning
- Carbon monoxide has 200x higher affinity for Hb than O2
- Reduces the O2 carrying capacity of blood
- Shifts the dissociation curve to the left and increases Hb affinity for remaining O2
- Prevents O2 unbinding over appropriate PO2 levels in tissues
CO2 Transport in Blood
- CO2 is more soluble than O2 in plasma
- Hb can bind to CO2, deoxygenated Hb has increased affinity for CO2
- About 10% CO2 dissolved in plasma and 30% carried by deoxygenated Hb
- Remaining 60% is converted to bicarbonate via the reaction H2O + CO2 → H2CO3 → HCO3- + H+
- Carbonic anhydrase catalyzes the formation of carbonic acid from H2O and CO2
- Carbonic anhydrase is mainly present in RBCs, not in plasma
H+ Transport in Blood
- Deoxygenated Hb can bind H+ ions in venous blood
- Only a small number of H+ ions remain dissolved to contribute to overall blood pH
- Explains why venous blood (pH 7.35) is not much more acidic than arterial blood (pH 7.40)
- H+ ions unbind Hb in pulmonary capillaries to combine with HCO3- and form H2O + CO2 in lungs
Neural Control of Respiration
- Diaphragm and intercostals are skeletal muscles that require neural input to contract
- Input via phrenic nerves from respiratory center in brainstem
- Respiratory neurons fire rhythmically and synchronously to produce periodic muscle contraction
- Receives inputs from a host of centers to modulate respiratory rhythm or impart voluntary control on breathing
Chemoreceptors
- Peripheral chemoreceptors: located in carotid bodies and aortic arch, stimulated by decreased PO2 and pH of plasma
- Central chemoreceptors: located in brainstem, stimulated by decreased pH of cerebrospinal fluid
- Cerebrospinal fluid pH is determined by PCO2 in brain
PO2 Respiratory Reflex
- Drop in arterial PO2 below 60 mm Hg will increase ventilation rate
- Low arterial PO2 occurs due to high elevations or lung disease
- Respiratory reflexes will not increase ventilation in response to anemia or CO poisoning
- Anemia and CO poisoning reduce the capacity of Hb to carry O2, but the amount of O2 dissolved in plasma is still the same
PCO2 Respiratory Reflex
- Increase in arterial PCO2 above 40 mm Hg will increase ventilation rate
- Elevated PCO2 increases the discharge rate of peripheral and central chemoreceptors
- Largely due to increased H+ concentration via bicarbonate formation
- pH decrease due to elevated PCO2 is known as respiratory acidosis
- Stimulates brainstem respiratory neurons
- Increased ventilation rate will decrease alveolar and arterial PCO2
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Description
Test your knowledge on the functions of the respiratory system, including the exchange of oxygen and carbon dioxide, ventilation, and the organization of airways. This quiz covers chapter 13, pages 435-446 of your textbook.
