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Functional Anatomy of the Respiratory System

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1 Functional Anatomy of the Respiratory System
Dr. Meg-angela Christi Amores

2 Pulmonary Ventilation
Pulmonary Ventilation – inflow and outflow of air between the atmosphere and the lungs Muscles for Respiration: Diaphragm External Intercostal muscles Sternocleidomastoid Muscles Anterior Serrati Scalene muscles Abdominal Rectus musles Internal Intercostals

3 Lung Expansion and Contraction
2 ways: Diaphragm Movement or – lengthen or shorten chest cavity Ribs Elevate or depress – increase or decrease antero-posterior diameter of chest cavity Normal quite breathing is accomplished almost entirely by first method.


5 Diaphragm Movement During INSPIRATION: During EXPIRATION:
Diaphragm contracts and pulls lower surface of the lung downward During EXPIRATION: Diaphragm relaxes accompanied by elastic recoil of lungs, chest wall and abdominal structures During heavy breathing, extra force is achieved mainly by contraction of abdominal muscles

6 Ribs Movement During INSPIRATION
Ribs project almost entirely forward from an original downward position Sternum also moves forward away from spine Anteroposterior (AP) diameter increases to 20% Muscles that elevate ribs: External intercostals Sternocleidomastoid Anterior Serratus Scalene Muscles


8 PRESSURES Lungs are “elastic” – collapses like a balloon when there is no force to keep it inflated There are no attachments between the lungs and the ribcage except at hilum Lungs float in pleural fluid Lymphatics provide slight suction between visceral surface of lung pleura and parietal surface of thoracic cavity

9 Pleural Presure Pressure of fluid in the narrow space between lung pleura and chest wall pleura Slightly negative pressure At beginning of inspiration: -5 cmH20 The amount needed to hold the lungs open During inspiration: -7.5cmH20 As negativity increases, lung volume increases to 0.5L

10 Alveolar Pressure Pressure of air inside the lung alveoli
Open glottis – pressures are equal at 2 atm For inspiration – inward flow of air into alveoli the pressure must fall to a value slightly below atmospheric pressure (below 0) During inspiration: alv pressure drops to -1cmH20 = 0.5 L of air

11 Transpulmonary Pressure

12 Compliance Compliance is the extent to which lungs expand for each unit of increase in transpulmonary pressure = 200mL/ 1 cmH20 change in transpulmonary pressure

13 Work of breathing Equivalent to Work of Inspiration 3 fractions:
That required to expand the lungs against the lung and chest elastic forces = compliance work That required to overcome the viscosity of the lung and chest wall structures =tissue resistance work The required to overcome airway resistance during the movement of air into the lungs = airway resistance work

14 Pulmonary volumes and capacities
Spirometry – process of studying pulmonary ventilation, recording the volume movement of air into and out of lungs Pulmonary Volumes: Tidal Volume: vol. of air inspired/expired with each normal breathing = 500 mL Inspiratory Reserve Volume – maximum extra volume of air that can be inspired over and above normal tidal volume = 300 mL

15 Pulmonary volumes and capacities
3. Expiratory Reserve Volume : maximum extra volume of air that can be expired forcefully after end of a normal tidal expiration = 1.1L Residual Volume : volume of air remaining in the lungs after most forceful expiration = 1.2L

16 Pulmonary volumes and capacities
Pulmonary Capacities Two or more volumes togethere Inspiratory Capacity : TV + IRV = 3.5L Functional Residual Capacity: ERV+RV = 2.3L Vital Capacity : IRV + TV + ERV = 4.6L Total Lung Capacity: VC + RV = 5.8L All pulmonary volumes and capacities are about 20-25% less in women than in men.

17 For the next meeting, read on Pulmonary Gas exchange and Gas transport
Guyton Textbook of Medical Physiology

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