RS Physiology Quiz
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Questions and Answers

What occurs during inspiration in terms of intrathoracic volume?

  • Intrathoracic volume decreases.
  • Intrathoracic volume fluctuates.
  • Intrathoracic volume remains constant.
  • Intrathoracic volume increases. (correct)

    • Which muscles are primarily recruited during strong expiratory efforts?

  • Intercostals and abdominals. (correct)
  • Diaphragm and intercostals.
  • Abdominals and diaphragm.
  • Pectorals and abdominal obliques.

    • What is the definition of physiological dead space in the context of ventilation?

  • Volume of inspired air not participating in gas exchange. (correct)
  • Air in the alveoli undergoing gas exchange.
  • Airways beyond the respiratory bronchioles.
  • The total volume of the lungs.

    • What relationship is observed in alveolar ventilation?

    <p>Alveolar ventilation equals tidal volume minus anatomical dead space divided by respiratory rate.</p> Signup and view all the answers

    During quiet expiration, what happens to the pressures in the thorax and pleural cavity?

    <p>Pressures in thorax and pleural cavity increase.</p> Signup and view all the answers

    What is the primary effect of the diaphragm contracting during inspiration?

    <p>It decreases pleural cavity pressure, allowing air to flow in.</p> Signup and view all the answers

    What occurs to the alveolar pressure during expiration?

    <p>It becomes positive to drive air out of the lungs.</p> Signup and view all the answers

    Which component is NOT crucial for efficient ventilation?

    <p>Strength of the abdominal muscles.</p> Signup and view all the answers

    What primarily influences the distribution of blood flow in the lungs?

    <p>Gravity and muscular tone of arterioles</p> Signup and view all the answers

    What is the effect of vasoconstriction in pulmonary arterioles on blood flow?

    <p>Decreases blood flow through capillaries</p> Signup and view all the answers

    What condition can cause an increase in dead space in the lungs?

    <p>Loss of lung elasticity due to fibrosis</p> Signup and view all the answers

    In what area of the lungs is blood flow typically larger compared to airflow?

    <p>Base of the lungs</p> Signup and view all the answers

    What is a unique characteristic of the pulmonary circulation compared to systemic circulation?

    <p>Low pressure, high volume system</p> Signup and view all the answers

    Which factor does NOT significantly affect the efficiency of diffusion at the alveoli?

    <p>Temperature of inspired air</p> Signup and view all the answers

    Which of the following is most associated with reduced alveolar ventilation?

    <p>Decreased tidal volume or increased dead space</p> Signup and view all the answers

    Which condition would lead to more efficient gas exchange at the alveoli?

    <p>Increased surface area and adequate perfusion</p> Signup and view all the answers

    How does the thickness of the alveolar-capillary membrane specifically influence the diffusion of gases?

    <p>Thicker membranes decrease the rate of diffusion.</p> Signup and view all the answers

    What factor primarily drives gas movement across the alveolar-capillary membrane?

    <p>Partial pressure difference between gases in alveoli and blood.</p> Signup and view all the answers

    Which of the following statements about lung compliance is correct?

    <p>Lung compliance increases with decreased alveolar surface tension.</p> Signup and view all the answers

    Which mechanism primarily regulates the matching of ventilation and perfusion in the lungs?

    <p>Local control mechanisms within the lungs.</p> Signup and view all the answers

    What effect does exercise have on the balance of O2 and CO2 in the body?

    <p>Increased CO2 levels lead to decreased O2 levels.</p> Signup and view all the answers

    What impact does the area available for diffusion have on gas exchange efficiency?

    <p>A larger area improves the efficiency of gas exchange.</p> Signup and view all the answers

    Which of the following is NOT a factor that affects gas diffusion rates across the alveolar membrane?

    <p>Alveolar temperature.</p> Signup and view all the answers

    What role does surfactant play in the respiratory system?

    <p>Prevents collapsing of alveoli.</p> Signup and view all the answers

    Which of the following statements accurately describes the process of gas exchange in the alveoli?

    <p>Gases diffuse down their partial pressure gradients.</p> Signup and view all the answers

    What is the primary factor influencing the movement of gases across the alveolar membrane?

    <p>Partial pressure gradients of gases.</p> Signup and view all the answers

    At what arterial partial pressure of O2 (PO2) does reoxygenated blood generally reach the left atria?

    <p>95 mmHg</p> Signup and view all the answers

    What does the O2-Hb dissociation curve indicate about hemoglobin saturation at 100 mmHg of PO2?

    <p>Hemoglobin is 98% saturated.</p> Signup and view all the answers

    If the partial pressure of carbon dioxide (PCO2) in the blood is higher than normal, what effect could this have on oxygen binding to hemoglobin?

    <p>It decreases the binding of oxygen to hemoglobin.</p> Signup and view all the answers

    What effect does pH have on the O2 dissociation curve?

    <p>Lower pH shifts the curve to the right, decreasing oxygen binding.</p> Signup and view all the answers

    What is the significance of pulmonary venous admixture?

    <p>It involves mixing of oxygenated and deoxygenated blood before it reaches the left atria.</p> Signup and view all the answers

    Which condition would likely result in decreased efficiency of gas exchange at the alveolar level?

    <p>Increased thickness of the alveolar membrane.</p> Signup and view all the answers

    What effect does surfactant have on alveolar stability at low lung volumes?

    <p>Equalizes pressure between alveoli of different sizes</p> Signup and view all the answers

    Which statement correctly describes the issue in premature babies lacking surfactant?

    <p>Alveoli collapse leading to infant respiratory distress syndrome</p> Signup and view all the answers

    What primarily increases airway resistance during breathing?

    <p>Decreased lung volume</p> Signup and view all the answers

    Which mechanism primarily facilitates bronchodilation?

    <p>Administration of b2 adrenergic agonists</p> Signup and view all the answers

    What happens to smaller alveoli if surfactant levels are insufficient?

    <p>They collapse due to higher internal pressure</p> Signup and view all the answers

    How does mucus accumulation influence the work of breathing?

    <p>It increases the effort needed to draw air into the lungs</p> Signup and view all the answers

    What type of nerve activity mediates bronchoconstriction in response to irritants?

    <p>Parasympathetic nerve activity</p> Signup and view all the answers

    What is the primary composition of surfactant in the lungs?

    <p>Phospholipids and proteins</p> Signup and view all the answers

    What is the primary function of Type II alveolar cells?

    <p>To produce surfactant</p> Signup and view all the answers

    What condition is characterized by excessive bronchoconstriction?

    <p>Asthma</p> Signup and view all the answers

    Which layer comprises the thin barrier for gas exchange in the alveoli?

    <p>Endothelial cells and epithelial cells</p> Signup and view all the answers

    Which mechanism primarily mediates bronchoconstriction during an allergic response?

    <p>Parasympathetic nervous system activity</p> Signup and view all the answers

    What is the contact time required for blood to be fully oxygenated in the pulmonary capillaries at rest?

    <p>0.25 seconds</p> Signup and view all the answers

    What role does surfactant play in alveolar mechanics?

    <p>Prevents alveolar collapse</p> Signup and view all the answers

    What type of muscle predominates in the bronchioles and terminal bronchioles?

    <p>Smooth muscle</p> Signup and view all the answers

    Which gas primarily diffuses from the alveoli into pulmonary capillary blood?

    <p>Oxygen</p> Signup and view all the answers

    What factor is least likely to influence the efficiency of gas diffusion across the alveolar-capillary barrier?

    <p>Concentration of hemoglobin in blood</p> Signup and view all the answers

    Which aspect is most critical for effective oxygenation and carbon dioxide removal in the lungs?

    <p>Adequate perfusion of alveoli</p> Signup and view all the answers

    What primarily determines the rate of gas transfer across the alveolar membrane?

    <p>Partial pressure gradient of gases</p> Signup and view all the answers

    In the context of perfusion in the lungs, which statement is most accurate?

    <p>Insufficient blood flow can compromise gas exchange efficiency.</p> Signup and view all the answers

    Which factor contributes most to the efficiency of gas exchange in the lungs?

    <p>Lung surface area</p> Signup and view all the answers

    How does the thickness of the alveolar-capillary membrane influence gas exchange?

    <p>Thicker membranes slow down gas diffusion rates.</p> Signup and view all the answers

    What is the relationship between ventilation and perfusion in the lungs?

    <p>Optimal gas exchange requires a matching of ventilation and perfusion.</p> Signup and view all the answers

    Which of the following statements about gas exchange efficiency is correct?

    <p>It can be hindered by poor blood flow or perfusion.</p> Signup and view all the answers

    What physiological factor is primarily responsible for regulating the respiratory rate in response to increasing levels of carbon dioxide (PCO2)?

    <p>Central chemoreceptors</p> Signup and view all the answers

    What is the formula for calculating alveolar ventilation (VA)?

    <p>TV - Dead Space x Respiratory Rate</p> Signup and view all the answers

    Which condition is characterized by an increased respiratory rate without increased depth of breathing?

    <p>Tachypnoea</p> Signup and view all the answers

    Which of the following statements best describes the role of carbonic anhydrase in CO2 transport in blood?

    <p>It catalyzes the reaction between CO2 and water to form bicarbonate.</p> Signup and view all the answers

    What volume of air is primarily involved in dead space ventilation?

    <p>Anatomic dead space (VD)</p> Signup and view all the answers

    How does the body primarily regulate blood pH during respiration?

    <p>Through the conversion of CO2 into bicarbonate</p> Signup and view all the answers

    Which component is crucial for maintaining electrical neutrality during CO2 transport in blood?

    <p>Chloride ions</p> Signup and view all the answers

    What physiological sensation is described by dyspnoea?

    <p>A feeling of breathlessness</p> Signup and view all the answers

    What is the primary role of surfactant in the lungs?

    <p>To help stabilize alveoli at varying sizes.</p> Signup and view all the answers

    Which factor primarily contributes to increased airway resistance during breathing?

    <p>Accumulation of mucus in airways.</p> Signup and view all the answers

    How does surfactant function differently in smaller alveoli compared to larger ones?

    <p>It lowers surface tension proportionately more in smaller alveoli.</p> Signup and view all the answers

    What condition can arise in premature babies due to the lack of surfactant?

    <p>Infant respiratory distress syndrome.</p> Signup and view all the answers

    What physiological mechanism mediates bronchoconstriction in response to irritants?

    <p>Parasympathetic nerve stimulation.</p> Signup and view all the answers

    What happens to the pressure in smaller alveoli when surfactant is absent?

    <p>It becomes greater than that of larger alveoli.</p> Signup and view all the answers

    What primarily regulates airway resistance during bronchoconstriction?

    <p>Airway diameter changes.</p> Signup and view all the answers

    What stimulates bronchodilation to counteract bronchoconstriction during an asthmatic attack?

    <p>B2 adrenergic agonists.</p> Signup and view all the answers

    What is the relationship between compliance and work of breathing?

    <p>Higher compliance leads to lower work of breathing.</p> Signup and view all the answers

    Which factor significantly increases surface tension in the alveoli?

    <p>Increased liquid film thickness</p> Signup and view all the answers

    What is the effect of a decrease in surfactant on lung compliance?

    <p>Decreases lung compliance</p> Signup and view all the answers

    How does surface tension affect small alveoli compared to larger alveoli?

    <p>Smaller alveoli collapse more easily due to higher pressure.</p> Signup and view all the answers

    What best describes the effect of fibrosis on lung compliance?

    <p>Reduces lung stretchability and compliance</p> Signup and view all the answers

    What is the primary influence on the size of the alveoli?

    <p>Surface tension generated by liquid film</p> Signup and view all the answers

    What characteristic of smaller alveoli contributes to their tendency to collapse?

    <p>Higher pressure due to surface tension</p> Signup and view all the answers

    What do changes in airway pressure indicate about lung compliance?

    <p>Lower pressure suggests lower compliance.</p> Signup and view all the answers

    What is the primary function of Type I alveolar cells in the lungs?

    <p>Facilitate gas diffusion</p> Signup and view all the answers

    What is the significance of the 0.5 µm barrier in the alveolar-capillary membrane?

    <p>It enhances diffusion efficiency</p> Signup and view all the answers

    Which type of muscle predominates in the structure of trachea and bronchi?

    <p>Cartilage with minimal smooth muscle</p> Signup and view all the answers

    In conditions like asthma, what primarily occurs in the airways?

    <p>Excessive bronchoconstriction</p> Signup and view all the answers

    What type of receptor mediates bronchodilation during the sympathetic response?

    <p>Beta-adrenergic receptor</p> Signup and view all the answers

    What is the primary source of erythrocytes (RBC) in the areas surrounding the alveoli?

    <p>Pulmonary capillaries</p> Signup and view all the answers

    What is the expected contact time for blood in the pulmonary capillaries during gas exchange?

    <p>0.75 seconds</p> Signup and view all the answers

    What component is used to calculate minute ventilation in adults at rest?

    <p>Tidal Volume and Respiratory Rate</p> Signup and view all the answers

    What effect does the presence of surfactant have on smaller alveoli?

    <p>Enhances their stability</p> Signup and view all the answers

    Which of the following correctly describes hyperventilation?

    <p>Increased rate of respiration</p> Signup and view all the answers

    What is the role of peripheral chemoreceptors in respiration?

    <p>They sense oxygen and hydrogen ion concentrations</p> Signup and view all the answers

    What accurately describes the relationship between PCO2 and respiratory control?

    <p>PCO2 is the main respiratory regulator affecting central chemoreceptors</p> Signup and view all the answers

    Which factor primarily determines the efficiency of gas exchange in the lungs?

    <p>Surface area available for diffusion</p> Signup and view all the answers

    During hypoventilation, which of the following occurs?

    <p>Decreased ventilation rate</p> Signup and view all the answers

    Alveolar ventilation is crucial for gas exchange because it accounts for which of the following?

    <p>Volume of air reaching the alveoli per minute</p> Signup and view all the answers

    What is the primary effect of arterial PO2 dropping below 60 mmHg?

    <p>Activation of peripheral chemoreceptors</p> Signup and view all the answers

    What is the primary role of alveolar macrophages in the lungs?

    <p>Ingesting small particles that reach the lung</p> Signup and view all the answers

    Which process involves the movement of mucus away from the lungs?

    <p>Ciliary escalator function</p> Signup and view all the answers

    What is the primary effect of reduced partial pressure of oxygen (PO2) in the alveoli at high altitudes?

    <p>Decreased diffusion of oxygen into the blood</p> Signup and view all the answers

    How does humidification occur in the upper airways?

    <p>By secretion of mucus from goblet cells</p> Signup and view all the answers

    What is the primary function of the ciliated epithelial cells in the respiratory system?

    <p>Trapping airborne pathogens and particles</p> Signup and view all the answers

    Which condition is likely to decrease the area available for gas diffusion in the lungs?

    <p>Pneumonia</p> Signup and view all the answers

    What impact does an increased blood flow have on gas exchange efficiency during high physical exertion?

    <p>Decreases time for gas equilibration</p> Signup and view all the answers

    What occurs when there is defective ciliary movement in the respiratory system?

    <p>Increased risk of lung infections</p> Signup and view all the answers

    What is the consequence of a thickened alveolar-capillary barrier on gas exchange?

    <p>Decreased diffusion rate of respiratory gases</p> Signup and view all the answers

    Which airway reflexes serve to protect the lungs during swallowing?

    <p>Closing of the glottis by the epiglottis</p> Signup and view all the answers

    What is the effect of alveolar macrophage activity on gas exchange efficiency?

    <p>Enhances clearance of pollutants</p> Signup and view all the answers

    How does a blood clot in the pulmonary arteries affect gas exchange?

    <p>Reduces blood flow to alveoli</p> Signup and view all the answers

    What does the mucous secretion in the respiratory epithelium primarily contribute to?

    <p>Humidifying incoming air</p> Signup and view all the answers

    Under what condition does the velocity of blood through the capillaries decrease, enhancing gas diffusion?

    <p>Resting state</p> Signup and view all the answers

    What is a result of decreased lung compliance?

    <p>Increased work of breathing</p> Signup and view all the answers

    What effect does a decrease in functional alveoli have on gas exchange?

    <p>Reduces surface area for diffusion</p> Signup and view all the answers

    How does the thickness of the alveolar-capillary membrane influence the rate of gas diffusion?

    <p>Thicker membranes slow down gas diffusion.</p> Signup and view all the answers

    What role does the difference in partial pressure of gases play in diffusion across the alveolar membrane?

    <p>Greater differences in pressure lead to faster diffusion.</p> Signup and view all the answers

    In healthy lungs, what effect does surfactant have on alveolar stability?

    <p>Surfactant decreases the surface tension, improving stability.</p> Signup and view all the answers

    Which factor is most likely to decrease the efficiency of gas diffusion at the alveoli?

    <p>Decreased difference in partial pressure.</p> Signup and view all the answers

    What is the primary mechanism by which O2 is transported in the blood?

    <p>Bound to hemoglobin in red blood cells.</p> Signup and view all the answers

    What determines the efficiency of gas transport in the lungs during exercise?

    <p>Higher volume of blood flow through the lungs.</p> Signup and view all the answers

    Which statement about ventilation and perfusion matching is correct?

    <p>Efficient gas exchange requires matching between ventilation and perfusion.</p> Signup and view all the answers

    Which condition could compromise the gas exchange efficiency in the alveoli?

    <p>Thickening of the alveolar-capillary membrane.</p> Signup and view all the answers

    Study Notes

    Pleural Cavity and Inspiration/Expiration

    • The pleural cavity is a crucial anatomical space located between the lungs and the chest wall. It contains a thin layer of pleural fluid, which facilitates smooth movement of the lungs during breathing.

    • During inspiration, the chest cavity expands, increasing intrathoracic volume

      • This is caused by contraction of the diaphragm and inspiratory chest wall muscles
      • The pressure in the thorax and pleural cavity decreases
      • The lungs expand, drawing air in

    • This is an active process

    • During quiet expiration, the chest cavity recoils, decreasing its volume

      • This is caused by relaxation of the diaphragm and inspiratory chest wall muscles
      • The pressure in the thorax and pleural cavity increases
      • The lungs recoil, pushing air out

    • This is a passive process

    Forced Ventilation

    • When ventilation is stimulated, such as during exercise, additional muscles are recruited (intercostals & abdominals)
    • This enhances the movement of the chest wall:
      • Stronger inspiratory efforts increase lung volumes
      • Stronger expiratory efforts decrease lung volumes
    • Both of these are active processes

    Alveolar Ventilation

    • Not all inspired air undergoes gas exchange because it must reach the alveoli
    • The volume of air that does not exchange with blood is called physiologic dead space
      • This includes the anatomic dead space: airways up to the respiratory bronchioles just short of the alveoli
    • The volume of air that reaches the alveoli per minute is called alveolar ventilation
    • The formula for alveolar ventilation is: (Tidal volume - Anatomic dead space) x Breaths per min

    Key Concepts in Ventilation

    • Ventilation is effected by changes in thoracic volumes and pressures
    • It requires the integrity of the lungs and pleura, muscles, and innervation
    • Alveolar ventilation is crucial for gas exchange
      • Inspired air reaches the alveoli to deliver oxygen to the blood
      • Expired air with carbon dioxide is expelled from the alveoli

    Gas Exchange at Alveoli

    • Gas exchange occurs by diffusion across the alveolar-capillary membranes
    • Diffusion is the movement of gases down their partial pressure (concentration) gradients
    • Oxygen diffuses from the alveoli into the capillaries
    • Carbon dioxide diffuses from the capillaries into the alveoli

    Overview of Respiratory Process & Partial Pressures

    • The partial pressure of oxygen in the alveoli (PAO2) is typically around 100 mmHg
    • The partial pressure of carbon dioxide in the alveoli (PACO2) is typically around 40 mmHg

    Oxygen Dissociation Curve

    • The oxygen dissociation curve shows the relationship between the partial pressure of oxygen (PO2) and the saturation of hemoglobin with oxygen
    • At a PO2 of 100 mmHg, hemoglobin is approximately 98% saturated with oxygen
    • This means that most of the oxygen carried in the blood is bound to hemoglobin

    Systemic vs Pulmonary Circulation

    • The pulmonary circulation is a low pressure, high volume system
    • It receives 100% of the cardiac output
    • Blood flow through the pulmonary capillaries is regulated by arteriolar tone

    Ventilation and Perfusion Ratios

    • Ventilation (V) refers to the amount of air that reaches the alveoli
    • Perfusion (Q) refers to the amount of blood flow through the pulmonary capillaries
    • The ventilation/perfusion (V/Q) ratio describes the matching of ventilation and perfusion
      • A high V/Q ratio indicates that there is more ventilation than perfusion
      • A low V/Q ratio indicates that there is more perfusion than ventilation

    Local Control Mechanisms

    • Local control mechanisms help to match ventilation and perfusion in the lungs
    • If there's a large airflow and a small blood flow (apex of the lungs), the blood vessels constrict to redirect blood to areas with more ventilation
    • If there's a large blood flow and a small airflow (base of the lungs), the alveoli dilate to increase ventilation

    Limitations Respiratory in Response to Disease

    • Reduced alveolar ventilation can occur due to:
      • Decreased tidal volume (volume of air inhaled/exhaled per breath)
      • Increased dead space (air that doesn't participate in gas exchange)
    • Decreased tidal volume can be caused by conditions that restrict lung or chest wall movement like pain
    • Increased dead space can be caused by conditions that affect the alveoli like fibrosis

    Summary of Gas Exchange & Perfusion

    • For efficient gas exchange, fresh air must reach the alveoli, and the alveoli must be perfused by blood
    • Diffusion at the alveoli must be efficient, which depends on:
      • Partial gas pressure (difference in pressure between the alveoli and blood)
      • Rate of blood flow
      • Diffusion barrier (alveolar-capillary thickness and surface area)

    Summary of Parts I & II: Gas Exchange & Perfusion

    • The pulmonary circulation has special properties:
      • It is a low-pressure, high-volume system
      • It is gravity-dependent
      • Blood flow can be regulated by arteriolar tone

    Ventilation Terminology

    • The concept of "dead space" refers to the air that does not undergo gas exchange. This is usually mainly air in the conducting airways.
    • More forceful inspiration and expiration (vs. quiet breathing) requires more effort from the respiratory muscles

    Alveolar Area and Membrane Thickness

    • The surface area of the alveoli is critical for efficient gas exchange
    • A thinner alveolar-capillary membrane also facilitates quicker gas exchange.
    • Disease processes that decrease alveolar surface area or thicken the membrane impair gas exchange

    Lung Elastic Recoil and Compliance

    • The ability of the lung to expand and recoil is called elastic recoil
    • Lung compliance is the ease with which the lungs can be stretched
    • Surfactant, a substance that lines the alveoli, helps to maintain alveolar stability by reducing surface tension

    Surfactant

    • Surfactant is a mixture of phospholipids, lipids, and proteins
    • Surfactant lines the alveoli and reduces surface tension
    • If surfactant is absent (like in premature babies), the alveoli can collapse

    Airway Resistance

    • The resistance to airflow through the trachea, bronchi, and bronchioles
    • Narrowing of the airways increases resistance due to:
      • Smooth muscle contraction (bronchoconstriction)
      • Decreased lung volume
      • Mucus accumulation
    • Increased airway resistance increases the work of breathing

    Factors Affecting Airway Resistance

    • Bronchoconstriction is stimulated by irritants like smoke, cold air, and parasympathetic nerves
    • Bronchodilation is stimulated by drugs like b2 adrenergic agonists (e.g., epinephrine) and sympathomimetic mediators

    Oxygen and Carbon Dioxide Transport

    • Oxygen is transported in the blood bound to hemoglobin or dissolved in the plasma
    • Carbon dioxide is transported in the blood as bicarbonate (HCO3-), dissolved in the plasma, or bound to hemoglobin

    Respiratory Changes During Exercise

    • During exercise, ventilation increases to meet the increased oxygen demand
    • This is achieved by increasing both tidal volume and respiratory rate
    • The partial pressure of carbon dioxide in the blood (PaCO2) decreases during exercise due to increased ventilation

    Important Key Points:

    • Alveolar Ventilation is an important concept in lung physiology, and is crucial for gas exchange.
    • Understanding how ventilation and perfusion are controlled and how they can be affected by disease is essential for understanding lung disease.
    • The effectiveness of respiration is dependent upon the structure and function of the components of the respiratory system.

    Alveolus and Surrounding Environment

    • The alveolar-capillary membrane is the thin barrier responsible for gas exchange between air and blood, measuring approximately 0.5µm.
    • Type I alveolar cells are responsible for gas exchange within the alveoli.
    • Type II alveolar cells are responsible for producing surfactant, a phospholipid mixture which reduces surface tension and promotes alveolar stability.
    • Alveolar macrophages reside within the alveoli and fight off foreign particles.
    • Pulmonary capillaries surround the alveoli, allowing for blood to flow close to the air for gas exchange.
    • Interstitial fluid, containing monocytes, fills the space between the alveolar epithelium and the capillary endothelium.
    • Elasin fibers are present in the surrounding tissue, aiding in the expansion and contraction of the lungs.

    Gas Exchange

    • Gas exchange occurs primarily through diffusion, moving from a higher concentration to a lower concentration.
    • Oxygen diffuses from the alveoli into the blood within the capillaries.
    • Carbon dioxide diffuses from the blood in the capillaries into the alveoli.

    Perfusion of Lungs

    • Blood flow within the pulmonary capillaries is crucial for gas exchange.
    • Perfusion refers to the rate of blood flow through the alveoli.
    • The rate of blood flow must be sufficient for adequate gas exchange.

    Innervation and Musculature of Airways

    • Airways are comprised of various structures:
      • Trachea and bronchi: primarily composed of cartilage with smaller amounts of smooth muscle.
      • Bronchioles and terminal bronchioles: predominantly composed of smooth muscle.
    • Smooth muscle innervation:
      • Sympathetic nervous system: triggers bronchodilation, relaxing smooth muscle.
      • Parasympathetic nervous system: causes bronchoconstriction, contracting smooth muscle.
    • Asthma is characterized by excessive bronchoconstriction.
    • Bronchodilators, such as b2-adrenergic receptor agonists relax smooth muscle in the airways, aiding in easier airflow.

    Ventilation Terminology

    • Minute ventilation: represents the volume of air inhaled or exhaled per minute.
    • Tidal volume: the volume of air inhaled or exhaled during a normal breath.
    • Respiratory rate: the number of breaths per minute.
    • Dead space: the volume of air that does not participate in gas exchange, usually due to air remaining within airways.
    • Alveolar ventilation: represents the volume of fresh air that reaches the alveoli per minute.

    Control of Respiration

    • Chemical control:
      • Carbon dioxide (CO2) is the primary respiratory regulator, acting on central chemoreceptors, stimulating increased breathing to expel CO2.
      • Hydrogen ion (H+) concentration is monitored by peripheral chemoreceptors located in the carotid and aortic bodies.
      • Oxygen (O2) levels are also monitored by peripheral chemoreceptors, becoming active when arterial PO2 falls below 60 mmHg.
    • Physical control:
      • Stretch receptors in the lungs send signals to the brain stem to adjust the rate and depth of breathing.
    • Nervous control:
      • The respiratory center in the brainstem dictates involuntary breathing.
      • Higher brain areas (cerebral cortex) can voluntarily adjust breathing patterns (holding your breath, singing, etc.).

    Factors Influencing Gas Exchange

    • Partial pressures of gases: The driving force for gas diffusion across the alveolar-capillary membrane depends on differences in partial pressure.
    • Thickness of barrier: A thinner barrier allows for faster diffusion.
    • Surface area: Larger surface area allows for faster diffusion.
    • Blood flow: The rate of blood flow through the alveoli contributes to the efficiency of gas exchange.
    • Perfusion of alveoli: Efficient gas exchange requires an adequate blood supply to every alveolus.

    Work of Breathing: Compliance of Lungs and Chest Wall

    • Compliance refers to the stretchability of the lungs and chest wall.
    • It is influenced by surface tension within the alveoli.
    • Compliance is measured as the change in lung volume per unit change in airway pressure (ΔV/ΔP).
    • Lower compliance means less stretchability and requires more effort to breathe.
    • Surfactant reduces surface tension, promoting compliance and reducing the work of breathing.
    • Infant respiratory distress syndrome (IRDS) occurs when premature babies lack sufficient surfactant, leading to collapsed alveoli.

    Work of Breathing: Airway Resistance

    • Airway resistance is the opposition to airflow caused by the narrowing of airways.
    • Bronchoconstriction (narrowing of airways) increases resistance due to smooth muscle contraction, leading to increased work of breathing.
    • Bronchodilators help relax smooth muscle in the airways, decreasing resistance and improving breathing.
    • Stimulants such as smoke and cold air can trigger bronchoconstriction.
    • Sympathetic nervous system can induce bronchodilation.
    • Parasympathetic nervous system can induce bronchoconstriction.

    Alveolus and Surrounding Environment

    • Alveolus is a small air sac in the lungs where gas exchange occurs.
    • The alveolar-capillary membrane is a 0.5µm barrier separating air and blood.
    • Alveolar macrophages reside in the alveolus, responsible for engulfing foreign particles.
    • Type I alveolar cells provide a thin barrier for gas exchange.
    • Type II alveolar cells produce surfactant, a substance that reduces surface tension in the alveoli.
    • Pulmonary capillaries surround the alveoli, facilitating gas exchange.

    Gas Exchange

    • Gas exchange occurs by diffusion across the 0.5µm alveolar-capillary membrane.
    • Diffusion occurs from areas of high partial pressure to low partial pressure.
    • Blood in the pulmonary capillaries spends about 0.75 seconds in contact with the alveoli, allowing for complete oxygenation at rest.

    Innervation & Musculature of Airways

    • The trachea and bronchi primarily consist of cartilage with minimal smooth muscle.
    • Bronchioles, up to the terminal bronchioles, are primarily composed of smooth muscle.
    • The autonomic nervous system innervates smooth muscle in the bronchi and bronchioles.
    • Sympathetic stimulation causes bronchodilation, while parasympathetic stimulation causes bronchoconstriction.
    • Asthma is characterized by excessive bronchoconstriction.

    Protective Mechanisms of Airways

    • The respiratory epithelium (mucosa) is protected by humidifying the air in the upper passages and secreting mucus.
    • The lungs are protected by the mucociliary trapping of foreign matter, the ciliary escalator, alveolar macrophages, and airway reflexes.

    The Ciliary Escalator

    • The epithelium of the upper airways, trachea, bronchi, and bronchioles contain cilia.
    • The epithelium is covered by mucus.
    • Cilia beat to move particles away from the lungs, a process known as the ciliary escalator.
    • Macrophages ingest small particles that reach the lungs.

    Functions of the Respiratory System

    • Gas Exchange: Pulmonary circulation transports blood from the body to the lungs for gas exchange and back to the heart for distribution. Gas exchange occurs between blood in alveolar capillaries and air in alveoli.
    • Immunological & Protective Functions: The respiratory system plays a role in immunity and protection against foreign particles.
    • Endocrine Functions: The respiratory system participates in endocrine function, for instance, producing angiotensin II.
    • Voice Production: The respiratory system is involved in voice production.
    • Water and Heat Loss: The respiratory system contributes to water and heat loss from the body.

    Ventilation

    • Ventilation refers to the movement of air into and out of the respiratory tract.
    • Minute ventilation is calculated by multiplying tidal volume (TV) by the respiratory rate.
    • Normal minute ventilation at rest is around 6 liters/minute, while it increases significantly during exercise.
    • Hyperventilation: Increased ventilation.
    • Hypoventilation: Decreased ventilation.
    • Tachypnoea: Increased rate of respiration.
    • Dyspnoea: Distressful sensation of breathing.

    Alveolar Ventilation

    • Alveolar ventilation (VA) is the volume of air that reaches the alveoli per minute.
    • Not all air breathed in reaches the alveoli, as some remains in the dead space.
    • VA is calculated by subtracting the dead space volume (VD) from tidal volume (TV) and multiplying the result by the respiratory rate.

    Control of Respiration

    • CO2 Transport in Blood:
    • CO2 is transported in the blood in three forms:
      • Dissolved CO2 (7%)
      • Carbaminohemoglobin (23%)
      • Bicarbonate ions (HCO3-) (~70%)
    • Chemoreceptor Control:
      • Central chemoreceptors in the medulla are sensitive to changes in PCO2.
      • Peripheral chemoreceptors (carotid and aortic bodies) are sensitive to changes in both PO2 and H+.

    Chemical Control of Breathing

    • PCO2: The primary respiratory regulator, acting primarily on central chemoreceptors. CO2 can pass the blood-brain barrier, while H+ cannot.
    • [H+]: Monitored by the carotid and aortic bodies.
    • PO2: Monitored by the carotid and aortic bodies, stimulating peripheral chemoreceptors when arterial PO2 drops below 60 mmHg.

    Factors Affecting Gas Diffusion

    • Difference in Partial Pressure: Gases diffuse from higher to lower partial pressure; a larger difference in partial pressure leads to faster diffusion.
    • Diffusion Barrier: A thicker alveolar-capillary barrier slows down diffusion.
    • Area Available for Diffusion: A smaller area for diffusion results in slower diffusion.
    • Diffusion Properties of Gas: More soluble gases in blood diffuse faster (e.g., CO2 > O2).

    Abnormal Diffusion

    • Decreased Pressure Difference: Decreased partial pressure difference across the membrane can lead to reduced diffusion.
    • Thickened Barrier: Abnormal thickening of the alveolar-capillary barrier (due to fibrosis, edema) slows down diffusion.
    • Reduced Alveolar Volume: Decreased alveolar volume or fewer functional alveoli decrease the area for diffusion.

    Gas Exchange at Alveoli: Diffusion vs. Blood Flow

    • Decreased Blood Flow: Reduced blood flow (e.g., pulmonary embolism) leads to decreased gas exchange.
    • Increased Blood Flow: Increased blood flow (e.g., during exercise) can also lead to decreased gas exchange due to less time for equilibration, especially in diseased alveoli with thickened membranes.

    Work of Breathing

    • Compliance: Compliance refers to the ease with which the chest wall and lungs can stretch.
    • Airway Resistance: Resistance to airflow in the respiratory passages can influence the work of breathing.

    Summary

    • Ventilation is essential for gas exchange in the lungs.
    • Alveolar ventilation specifically refers to the volume of air reaching the alveoli per minute.
    • The control of respiration is primarily regulated by CO2 through central chemoreceptors and peripheral chemoreceptors sensitive to both PO2 and H+.
    • Gas diffusion is influenced by differences in partial pressure, barrier thickness, available area, and gas solubility.
    • Abnormal diffusion can occur due to factors like reduced pressure difference, thickened barriers, and reduced alveolar volume.
    • Blood flow also affects gas exchange, with decreased flow reducing gas exchange and excessive flow potentially leading to incomplete equilibration in diseased alveoli.
    • The work of breathing is affected by compliance (ease of stretching) and airway resistance.

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    RS Physio 3 Lect Combined (PDF) - Respiratory System Lecture Notes

    Description

    Test your knowledge on the pleural cavity, inspiration, and expiration processes. This quiz covers the mechanics of breathing, including active and passive respiration, as well as forced ventilation during exercise. Challenge yourself to understand these essential respiratory concepts.

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