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