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Questions and Answers
What causes the decrease in vascular resistance after birth?
What causes the decrease in vascular resistance after birth?
Where are the alveoli most likely to be overventilated?
Where are the alveoli most likely to be overventilated?
What is a primary consequence of rapid ascent during diving due to decreased PN2?
What is a primary consequence of rapid ascent during diving due to decreased PN2?
What is the role of the I neurons in the brain stem respiratory centers?
What is the role of the I neurons in the brain stem respiratory centers?
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Which center in the pons antagonizes the apneustic center?
Which center in the pons antagonizes the apneustic center?
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What monitors changes in blood PCO2, PO2, and pH?
What monitors changes in blood PCO2, PO2, and pH?
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What occurs during inspiration in terms of pressure differences?
What occurs during inspiration in terms of pressure differences?
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According to Boyle's Law, how does an increase in lung volume affect intrapulmonary pressure?
According to Boyle's Law, how does an increase in lung volume affect intrapulmonary pressure?
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What term describes the ease with which the lungs can expand?
What term describes the ease with which the lungs can expand?
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What does the Law of Laplace state about the pressure in alveoli?
What does the Law of Laplace state about the pressure in alveoli?
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How does surfactant affect surface tension in the lungs?
How does surfactant affect surface tension in the lungs?
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What happens to elastic tension during inspiration and expiration?
What happens to elastic tension during inspiration and expiration?
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What is the primary role of the diaphragm in respiration?
What is the primary role of the diaphragm in respiration?
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Which of the following describes the function of alveolar type II cells?
Which of the following describes the function of alveolar type II cells?
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What is the main purpose of mucus in the conducting zone of the respiratory system?
What is the main purpose of mucus in the conducting zone of the respiratory system?
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How does gas exchange occur in the lungs?
How does gas exchange occur in the lungs?
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What is the approximate total surface area of the alveoli in the lungs?
What is the approximate total surface area of the alveoli in the lungs?
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What characterizes the intrapleural pressure within the thoracic cavity?
What characterizes the intrapleural pressure within the thoracic cavity?
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Which of the following structures is part of the respiratory zone?
Which of the following structures is part of the respiratory zone?
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What physiological process is primarily responsible for the movement of carbon dioxide from the blood to the air?
What physiological process is primarily responsible for the movement of carbon dioxide from the blood to the air?
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What impact does chronic progressive lung disease have on bronchioles during expiration?
What impact does chronic progressive lung disease have on bronchioles during expiration?
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What is primarily disrupted in pulmonary fibrosis?
What is primarily disrupted in pulmonary fibrosis?
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What does Dalton's Law state about gas mixtures?
What does Dalton's Law state about gas mixtures?
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What is the contribution of water vapor to the partial pressure in humidified oxygen?
What is the contribution of water vapor to the partial pressure in humidified oxygen?
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What does Henry’s Law describe about the behavior of gases?
What does Henry’s Law describe about the behavior of gases?
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What is the approximate P0 level of oxygen in arterial blood?
What is the approximate P0 level of oxygen in arterial blood?
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What is a role of pulmonary arterioles in response to decreased alveolar P0?
What is a role of pulmonary arterioles in response to decreased alveolar P0?
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What characterizes pulmonary circulation compared to systemic circulation?
What characterizes pulmonary circulation compared to systemic circulation?
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What does a higher vascular resistance in the fetal pulmonary circulation indicate?
What does a higher vascular resistance in the fetal pulmonary circulation indicate?
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Why does low pressure in pulmonary circulation avoid pulmonary edema?
Why does low pressure in pulmonary circulation avoid pulmonary edema?
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Study Notes
Transpulmonary Pressure
- The pressure difference between the inside of the lungs and the space between the lungs and the chest wall
- Keeps the lungs in contact with the chest wall
Intrapulmonary and Intrapleural Pressures
- During inspiration, atmospheric pressure is greater than intrapulmonary pressure
- During expiration, intrapulmonary pressure is greater than atmospheric pressure
Boyle's Law
- Changes in lung volume cause changes in intrapulmonary pressure
- The pressure of a gas is inversely proportional to its volume
- Increasing lung volume decreases intrapulmonary pressure, allowing air to flow in
- Decreasing lung volume increases intrapulmonary pressure, forcing air out
Physical Properties of the Lungs
- Ventilation occurs due to pressure differences created by changes in lung volume
- Lung function is impacted by: compliance, elasticity, and surface tension
Compliance
- The ability of the lungs to expand is known as distensibility
- Measured as the change in lung volume per change in transpulmonary pressure (∆V/∆P)
- Lungs are 100 times more distensible than a balloon
- Factors increasing resistance to distension reduce compliance
Elasticity
- The tendency of the lungs to return to their original size after expansion
- High elastin protein content makes the lungs elastic and resistant to distension
- The elastic tension increases during inspiration and is reduced by recoil during expiration
Surface Tension
- The force exerted by the fluid lining the alveoli that resists distension
- This film of fluid causes surface tension
- Fluid absorption is driven by active Na+ transport
- Fluid secretion is driven by active transport of Cl- out of the alveolar epithelial cells
- Water molecules at the surface are attracted to each other, creating inward force and increasing pressure in alveoli
Law of Laplace
- Pressure in the alveoli is directly proportional to surface tension and inversely proportional to the radius of the alveoli
- If surface tension were the same, pressure in a smaller alveolus would be greater than in a larger one
Surfactant
- A phospholipid produced by alveolar type II cells
- Lowers surface tension
Respiration
- Includes: ventilation, gas exchange, and O2 utilization
Ventilation
- The mechanical process of moving air in and out of the lungs
- Oxygen diffuses from the air in the lungs to the blood, as the concentration of oxygen is higher in the lungs than in the blood
- Carbon dioxide diffuses from the blood to the air, moving down its concentration gradient
Gas Exchange
- Occurs entirely through diffusion
- Fast due to the large surface area and small diffusion distance
Alveoli
- Polyhedral in shape and clustered like honeycomb
- ~300 million air sacs (alveoli)
- Large surface area (60–80 m2)
- Each alveolus is one cell layer thick, with a total air barrier of two cells (2 ∝m)
- Two types of cells: alveolar type I (structural) and alveolar type II (secrete surfactant)
Respiratory Zone
- Region of gas exchange between air and blood
- Includes respiratory bronchioles and alveolar sacs
- Must contain alveoli
Conducting Zone
- Structures air passes through before reaching the respiratory zone
- Warms and humidifies inspired air
- Filters and cleans
- Mucus traps particles in inspired air
- Cilia moves mucus for expectoration
Thoracic Cavity
- Diaphragm separates the anterior body cavity into two parts:
- Thoracic cavity above diaphragm (heart, large vessels, trachea, esophagus, thymus, lungs)
- Abdominopelvic cavity below diaphragm (liver, pancreas, GI tract, spleen, genitourinary tract)
- Intrapleural space is between visceral and parietal pleurae, containing a thin film of fluid
- Lungs stay in contact with the chest wall, expanding and contracting with it
Intrapulmonary and Intrapleural Pressures
- Intrapulmonary pressure: pressure in the alveoli (intra-alveolar pressure)
- Intrapleural pressure: pressure in the intrapleural space
- Negative pressure in the intrapleural space due to lack of air
Chronic Obstructive Pulmonary Disease (COPD)
- Progressive condition that reduces surface area for gas exchange
- Decreases ability of bronchioles to stay open during expiration
- Cigarette smoke stimulates macrophages and leukocytes to secrete protein-digesting enzymes that damage tissue
Pulmonary Fibrosis
- Normal lung structure disrupted by accumulation of fibrous connective tissue proteins
- Anthracosis is a type of pulmonary fibrosis caused by coal dust inhalation
Gas Exchange in the Lungs
- Dalton's Law: total pressure of a gas mixture is the sum of the individual pressures each gas would exert independently
- Partial pressure: the pressure a specific gas exerts independently
- PATM = PN2 + PO2 + PCO2 + PH2O = 760 mm Hg
- PO2 (humidified) = 105 mm Hg
- PH2O contributes to partial pressure (47 mm Hg)
- PO2 (sea level) = 150 mm Hg
- PCO2 = 40 mm Hg
Partial Pressures of Gases in Inspired Air and Alveolar Air
- Chart showing the partial pressures of gases in inspired air vs. alveolar air
Partial Pressures of Gases in Blood
- When a liquid or gas (blood and alveolar air) are at equilibrium, the amount of gas dissolved in the fluid reaches a maximum (Henry's Law)
- Depends on solubility of the gas, temperature of the fluid, and partial pressure of the gas
- The amount of gas dissolved in a fluid is directly proportional to its partial pressure in the gas mixture
Significance of Blood PO2 and PCO2
- PO2 arterial blood is about 100 mm Hg, indicating good lung function
- PO2 systemic veins is about 40 mm Hg
- PCO2 systemic veins is 46 mm Hg
Pulmonary Circulation
- Blood flow through the pulmonary circulation equals blood flow through the systemic circulation
- Driving pressure is about 10 mm Hg
- Pulmonary vascular resistance is low, leading to less net filtration compared to systemic capillaries, helping to prevent pulmonary edema
- Autoregulation: pulmonary arterioles constrict when alveolar PO2 decreases, matching ventilation/perfusion ratio
Pulmonary Circulation (continued)
- In a fetus, pulmonary circulation has higher vascular resistance due to partially collapsed lungs
- Vascular resistance decreases after birth:
- Opening of vessels due to subatmospheric intrapulmonary pressure
- Physical stretching of the lungs
- Dilation of pulmonary arterioles in response to increased alveolar PO2
Lung Ventilation/Perfusion Ratios
- Alveoli at the apex are underperfused (overventilated)
- Alveoli at the base are underventilated (overperfused)
Disorders Caused by High Partial Pressures of Gases
- Nitrogen narcosis: nitrogen is inert at sea level, but under hyperbaric conditions it can dissolve slowly and cause effects resembling alcohol intoxication
- Decompression sickness: as a diver surfaces, the amount of dissolved nitrogen decreases, potentially forming bubbles in tissues and blood, causing "the bends"
Brain Stem Respiratory Centers
- Neurons in the reticular formation of the medulla oblongata form the rhythmicity center, controlling automatic breathing
- Consists of interacting neurons that fire during inspiration (I neurons) or expiration (E neurons)
Brain Stem Respiratory Centers (continued)
- I neurons stimulate spinal motor neurons innervating respiratory muscles
- Expiration is passive when I neurons are inhibited
- I and E neurons activity varies reciprocally
Rhythmicity Center
- I neurons in dorsal respiratory group (DRG) regulate phrenic nerve activity
- I neurons project to and stimulate spinal interneurons that innervate respiratory muscles
- E neurons in ventral respiratory group (VRG) control motor neurons to internal intercostal muscles
- E neurons inhibit I neurons
- Pacemaker neurons may be responsible for I and E neurons rhythmicity
Pons Respiratory Centers
- Medullary rhythmicity center activity is influenced by pons:
- Apneustic center promotes inspiration by stimulating I neurons in the medulla
- Pneumotaxic center antagonizes the apneustic center, inhibiting inspiration
Chemoreceptors
- Two groups monitor changes in blood PCO2, PO2, and pH:
- Central: medulla
- Peripheral: carotid and aortic bodies
Hemoglobin
- Each heme group contains one iron atom that can bind to one oxygen molecule
- Oxyhemoglobin: normal heme with reduced iron (Fe2+) bound to oxygen
- Deoxyhemoglobin: oxyhemoglobin that has dissociated, releasing oxygen, but the heme iron remains in the reduced form
- Methemoglobin: iron in the oxidized form (Fe3+) cannot bind to oxygen, normally present in small amounts
- Carboxyhemoglobin: reduced heme bound to carbon monoxide, a bond 210 times stronger than the bond with oxygen, impairing oxygen transport to tissues
Hemoglobin (continued)
- Oxygen-carrying capacity depends on hemoglobin concentration
- Anemia: below normal hemoglobin
- Polycythemia: above normal hemoglobin
- Erythropoietin controls hemoglobin production, stimulated by low PO2 delivery to the kidneys
- Loading/unloading of oxygen depends on environment's PO2 and affinity between hemoglobin and oxygen
Oxyhemoglobin Dissociation Curve
- Graph illustrating the percentage of oxyhemoglobin saturation at different PO2 values
- Reflects both loading and unloading of oxygen
- Steep portion of the curve means small PO2 changes produce large saturation differences, allowing for more oxygen unloading
- Decreased pH, increased temperature, and increased 2,3-DPG decrease hemoglobin's affinity for oxygen, shifting the curve to the right, causing greater oxygen unloading
Effects of pH and Temperature
- Loading and unloading of oxygen is influenced by hemoglobin's affinity for oxygen
- Affinity decreases with decreased pH (Bohr effect)
- Increased temperature and 2,3-DPG shift the curve to the right
Effect of 2,3 DPG on O2 Transport
- Anemia: RBCs produce more 2,3-DPG due to lower hemoglobin concentration
- Since RBCs lack nuclei and mitochondria, they generate ATP through anaerobic metabolism
- Fetal hemoglobin (hemoglobin f): has two γ-chains instead of β-chains, cannot bind to 2,3-DPG, and has a higher affinity for oxygen
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