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Chapter 39. Respiratory Physiology. Mechanisms of respiration. Pulmonary ventilation Inspiration Expiration Respiratory muscles Diaphragm External intercostal Others. Mechanisms of respiration. Steps of ventilation Contraction of diaphragm and external intercostal muscles

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Chapter 39

Chapter 39

Respiratory Physiology


Mechanisms of respiration
Mechanisms of respiration

  • Pulmonary ventilation

    • Inspiration

    • Expiration

    • Respiratory muscles

      • Diaphragm

      • External intercostal

      • Others


Mechanisms of respiration1
Mechanisms of respiration

  • Steps of ventilation

    • Contraction of diaphragm and external intercostal muscles

    • Increase of thoracic volume

    • Expansion of the pleural cavities and lungs

    • Decrease of lung pressure below atmospheric pressure


Mechanisms of respiration2
Mechanisms of respiration

  • Inspiration

  • Lung pressure becomes equal to atmospheric pressure

  • Air stops to flow inside

  • Relaxation of respiratory muscles

  • Recoiling of the lung tissue


Mechanisms of respiration3
Mechanisms of respiration

  • Decrease of intrathoracic and intrapulmonary volumes

  • Increase of pulmonary pressure

  • Expiration


Mechanisms of respiration4
Mechanisms of respiration

  • Pneumothorax it is the entry of air into the pleural cavity

    • It breaks the fluid bond between the visceral and parietal pleura

    • It will cause the lung to collapse – atelectasis


Respiratory volumes and capacities
Respiratory volumes and capacities

  • Spirometry

  • Tidal volume (TV)

    • It is the amount of air inspired or expired with each breath under resting conditions

    • 500 ml


Respiratory volumes and capacities1
Respiratory volumes and capacities

  • Inspiratory reserve volume (IRV)

    • It is the amount of air that can be forcefully inspired after a normal tidal inspiration

    • 3100 ml


Respiratory volumes and capacities2
Respiratory volumes and capacities

  • Expiratory reserve volume (ERV)

    • It is the amount of air that can be forcefully expired after a normal tidal expiration

    • 1200 ml

    • It is reduced in conditions in which the elasticity of the lungs is decreased


Respiratory volumes and capacities3
Respiratory volumes and capacities

  • Vital capacity (VC)

    • It id the maximum amount of air that can be expired after a maximal inspiration

    • 4800 ml

    • VC = TV + IRV + ERV


Respiratory volumes and capacities4
Respiratory volumes and capacities

  • Residual volume (RV)

    • It is the amount of air that remains in the lung after a ERV

    • 1200 ml


Respiratory volumes and capacities5
Respiratory volumes and capacities

  • Functional residual capacity (FRC)

    • It is the amount of air that remains in the lung after a quiet respiratory cycle

    • 2400 ml

    • FRC = ERV+RV


Respiratory volumes and capacities6
Respiratory volumes and capacities

  • Total lung capacity (TLC)

    • It is the total volume of the lungs

    • 6000 ml

    • TLC = VC+RV



Respiratory volumes and capacities8
Respiratory volumes and capacities

  • Nonrecording spirometer

    • Handheld dry spirometer

      • Measures only expired air

    • Wet spirometer

      • Measures only expired air

  • Recording spirometer

    • Measures inspired and expired air


Pulmonary disorders
Pulmonary disorders

  • Obstructive

    • Bronchitis

    • Asthma

  • Restrictive

    • Tuberculosis

    • Poliomyelitis


Respiratory volumes and capacities9
Respiratory volumes and capacities

  • Forced vital capacity (FVC)

    • It is the amount of air expired after a deep inspiration and a forced and quick expiration

    • Reduced in restrictive pulmonary diseases


Respiratory volumes and capacities10
Respiratory volumes and capacities

  • Forced expiratory volume measurement (FEV1%)

    • It is the percentage of vital capacity that is exhaled during specific intervals of time

    • It is reduced in obstructive diseases


Respiratory rate and depth
Respiratory rate and depth

  • Respiratory centers

    • Medulla oblongata

    • Pons

    • Keep the RR at 12-18 respirations/minute

  • Respiratory receptors

    • Stretch receptors in the lung

    • Change RR


Respiratory rate and depth1
Respiratory rate and depth

  • Nerve vagus

  • Factors that changes the RR

    • Exercise

    • Coughing

    • Waking

    • Talking

    • Laughing, etc


Respiratory rate and depth2
Respiratory rate and depth

  • O2 concentration in the blood

    • monitored by chemoreceptors in the aortic and carotid bodies

  • CO2 concentration in the blood

    • Directly stimulates the respiratory centers

  • Blood pH

    • Monitored by chemoreceptors in the aortic and carotid bodies


Respiratory sounds
Respiratory sounds

  • Bronchial sounds

    • Heard below the larynx

  • Vesicular sounds

    • Air filling the alveolar sacs

    • Heard over the chest

  • Crepitation (crackles)

  • Wheezing – a whistling sound


Role of respiratory system in acid base balance of blood
Role of respiratory system in acid-base balance of blood

  • Blood pH

    • 7.35-7.45

    • Carbonic acid-bicarbonate buffer

      • The main body buffer


Acid base imbalance
Acid-base imbalance

  • Alkalosis

    • Blood pH above 7.45

    • Respiratory or metabolic

  • Acidosis

    • Blood pH bellow 7.35

    • Respiratory or metabolic


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