Muscles of Inspiration
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Questions and Answers

What is the direction of the external intercostal muscles?

  • Vertically downward
  • Obliquely upward and anteriorly
  • Obliquely downward and forward (correct)
  • Horizontally forward

    • What happens to the transverse and antero-posterior diameters of the thorax when the external intercostal muscles contract?

  • They remain the same
  • They decrease
  • They are undefined
  • They increase (correct)

    • What type of inspiration requires the contraction of accessory inspiratory muscles?

  • Quiet inspiration
  • Shallow inspiration
  • Forced or deep inspiration (correct)
  • Passive inspiration

    • Which muscles lift the sternum upwards during forced inspiration?

    <p>Anterior serrati and scalene muscles</p> Signup and view all the answers

    What happens to the volume of the thorax during forced expiration?

    <p>It decreases</p> Signup and view all the answers

    What is the function of the internal intercostal muscles during forced expiration?

    <p>They depress the ribs</p> Signup and view all the answers

    What is the effect of contraction of the anterior abdominal wall muscles during forced expiration?

    <p>It increases intra-abdominal pressure</p> Signup and view all the answers

    What is the change in intra-alveolar pressure during inspiration?

    <p>It decreases by 1 cmH2O</p> Signup and view all the answers

    What is the relaxation volume of both lungs?

    <p>1 liter</p> Signup and view all the answers

    What is the primary cause of negative intrapleural pressure?

    <p>Surface tension of the fluid lining the alveoli</p> Signup and view all the answers

    What is one of the functions of intrapleural pressure?

    <p>To keep the alveoli open at the end of expiration</p> Signup and view all the answers

    What happens to the heart and mediastinum in pneumothorax?

    <p>They shift towards the opposite side</p> Signup and view all the answers

    What is the value of trans-pulmonary pressure at the end of normal inspiration?

    <p>6 cmH2O</p> Signup and view all the answers

    What is the primary function of surfactant?

    <p>To reduce surface tension in the alveoli</p> Signup and view all the answers

    What type of cells secrete surfactant?

    <p>Type II alveolar epithelial cells</p> Signup and view all the answers

    What is the condition known as tension pneumothorax?

    <p>When intrapleural pressure becomes positive</p> Signup and view all the answers

    What is the primary function of the Pneumotaxic center?

    <p>To regulate the switching between inspiration and expiration</p> Signup and view all the answers

    Which of the following muscles are supplied by the expiratory motor neurons?

    <p>Internal intercostal muscles and anterior abdominal wall muscles</p> Signup and view all the answers

    What is the primary function of the Ventral Respiratory Group (VRG)?

    <p>To integrate the inputs from the inspiratory and expiratory neurons</p> Signup and view all the answers

    What is the normal pulmonary ventilation rate in an adult at rest?

    <p>6 L/min</p> Signup and view all the answers

    What is the effect of an increase in PCO2 in the arterial blood?

    <p>It increases the activity of the respiratory center</p> Signup and view all the answers

    What is the location of the Apneustic center?

    <p>Lower part of the pons</p> Signup and view all the answers

    What is the primary function of the respiratory chemoreceptors?

    <p>To sense changes in the arterial blood gases</p> Signup and view all the answers

    What is the normal amount of O2 consumed by an adult at rest?

    <p>250 ml O2</p> Signup and view all the answers

    What is the primary function of surfactant in the lungs?

    <p>To reduce the surface tension of the fluid lining the alveoli</p> Signup and view all the answers

    What happens to the surfactant layer as the alveoli decreases in size during expiration?

    <p>It becomes thicker</p> Signup and view all the answers

    What is the consequence of high surface tension inside the alveoli?

    <p>Filtration of fluid into the alveoli leading to pulmonary edema</p> Signup and view all the answers

    What is the disease that occurs in premature infants due to surfactant deficiency?

    <p>Respiratory Distress Syndrome (RDS)</p> Signup and view all the answers

    What is the ratio of lecithin to sphingomyelin in amniotic fluid that indicates sufficient surfactant secretion?

    <p>More than 2</p> Signup and view all the answers

    What is one of the causes of surfactant deficiency?

    <p>Inhalation of pure oxygen for a long time</p> Signup and view all the answers

    Which hormone stimulates surfactant secretion?

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

    What is the consequence of surfactant deficiency during inspiration?

    <p>Lung expansion becomes more difficult</p> Signup and view all the answers

    What is the effect of acidosis on respiration?

    <p>It stimulates respiration</p> Signup and view all the answers

    What is the response to high PCO2?

    <p>Ventilation increases by 2 liters/minute</p> Signup and view all the answers

    What is the effect of alkalosis on respiration?

    <p>It inhibits respiration</p> Signup and view all the answers

    What is the type of hypoxia caused by inadequate oxygenation of blood?

    <p>Hypoxic hypoxia</p> Signup and view all the answers

    What is the cause of hypoxic hypoxia in high altitudes or in mines?

    <p>Low O2 tension in inspired air</p> Signup and view all the answers

    What is the effect of hypercapnia on the ventilatory response to hypoxia?

    <p>It increases the ventilatory response</p> Signup and view all the answers

    What is the type of hypoxia caused by decreased O2 utilization ability by tissues?

    <p>Histotoxic hypoxia</p> Signup and view all the answers

    What is the effect of hypoxia on the ventilatory response to high PCO2?

    <p>It increases the ventilatory response</p> Signup and view all the answers

    Study Notes

    Respiratory Muscles

    • External intercostal muscles:
      • Run obliquely downward and forward from one rib to the rib below
      • Supplied by intercostal nerves
      • Contraction elevates the ribs and pushes the sternum forward, increasing transverse and antero-posterior diameters of the thorax
    • Accessory inspiratory muscles:
      • Contract during forced or deep inspiration or increased air flow resistance
      • Include sternocleidomastoid muscles (lift sternum upwards) and anterior serrati and scalene muscles (elevate sternum and first two ribs)

    Expiration

    • Quiet expiration: passive process, no muscle contraction needed
    • Forced or deep expiration: requires muscle contraction, using accessory muscles of expiration (internal intercostal muscles and anterior abdominal wall muscles)

    Respiratory Pressures

    • Intra-alveolar pressure: drops during inspiration to -1 cmH2O
    • Intrapleural pressure:
      • Negative pressure that keeps alveoli open at end of expiration
      • Helps respiratory movements and venous return against gravity
      • Decreases during pneumothorax (air in pleural space), leading to lung collapse and chest wall expansion

    Trans-pulmonary (Transmural) Pressure

    • Difference between intra-alveolar and intrapleural pressure
    • Distending pressure of the lungs, always positive (>3 cmH2O at beginning of inspiration, increasing to 6 cmH2O at end of normal inspiration)

    Surfactant

    • Secreted by type II alveolar epithelial cells
    • Reduces surface tension, facilitating lung expansion and preventing alveolar collapse
    • Deficiency leads to difficulty in inspiration and lung collapse, seen in respiratory distress syndrome (RDS) in premature infants

    Regulation of Respiration

    • Ventral Respiratory Group (VRG): located in the medulla, containing inspiratory and expiratory motor neurons
    • Pontine centers: pneumotaxic center regulates switching between inspiration and expiration, and apneustic center drives medullary DRG

    Chemical Regulation of Respiration

    • Increase in PCO2, H+, or drop in PO2 in arterial blood stimulates respiratory center activity, increasing pulmonary ventilation
    • Chemical regulation mediated through respiratory chemoreceptors (central and peripheral)
    • Acidosis stimulates respiration, while alkalosis inhibits it

    Hypoxia

    • Oxygen deficiency at tissue level
    • Types of hypoxia:
      • Hypoxic hypoxia: most common, caused by inadequate oxygenation of blood
      • Due to low O2 tension in inspired air, pulmonary disorders, or impaired O2 utilization

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    Description

    This quiz covers the external intercostal muscles and accessory inspiratory muscles, including their functions and characteristics.

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