Functional Anatomy of the Respiratory System Dr Megangela

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

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

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

Diaphragm Movement • During INSPIRATION: – 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

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

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

Pleural Presure • Pressure of fluid in the narrow space between lung pleura and chest wall pleura • Slightly negative pressure • At beginning of inspiration: -5 cm. H 20 • The amount needed to hold the lungs open • During inspiration: -7. 5 cm. H 20 As negativity increases, lung volume increases to 0. 5 L

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 1 cm. H 20 = 0. 5 L of air

Transpulmonary Pressure 2 1 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 pleural P Alveolar P Lung vol

Compliance • Compliance is the extent to which lungs expand for each unit of increase in transpulmonary pressure • = 200 m. L/ 1 cm. H 20 change in transpulmonary pressure

Work of breathing • Equivalent to Work of Inspiration • 3 fractions: 1. That required to expand the lungs against the lung and chest elastic forces = compliance work 2. That required to overcome the viscosity of the lung and chest wall structures =tissue resistance work 3. The required to overcome airway resistance during the movement of air into the lungs = airway resistance work

Pulmonary volumes and capacities • Spirometry – process of studying pulmonary ventilation, recording the volume movement of air into and out of lungs • Pulmonary Volumes: 1. Tidal Volume: vol. of air inspired/expired with each normal breathing = 500 m. L 2. Inspiratory Reserve Volume – maximum extra volume of air that can be inspired over and above normal tidal volume = 300 m. L

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. 1 L 4. Residual Volume : volume of air remaining in the lungs after most forceful expiration = 1. 2 L

Pulmonary volumes and capacities • Pulmonary Capacities – Two or more volumes togethere 1. Inspiratory Capacity : TV + IRV = 3. 5 L 2. Functional Residual Capacity: ERV+RV = 2. 3 L 3. Vital Capacity : IRV + TV + ERV = 4. 6 L 4. Total Lung Capacity: VC + RV = 5. 8 L All pulmonary volumes and capacities are about 2025% less in women than in men.

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