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 antero-

posterior 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 cmH20

• The amount needed to hold the lungs open

• During inspiration: -7.5cmH20

As negativity increases, lung volume increases to 0.5L

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

Transpulmonary Pressure

Se-ries

1

-10

-8

-6

-4

-2

0

2

pleural PAlveolar PLung vol

Compliance

• Compliance is the extent to which lungs expand for each unit of increase in transpulmonary pressure

• = 200mL/ 1 cmH20 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 mL2. Inspiratory Reserve Volume – maximum extra

volume of air that can be inspired over and above normal tidal volume = 300 mL

Pulmonary volumes and capacities3. Expiratory Reserve Volume : maximum extra

volume of air that can be expired forcefully after end of a normal tidal expiration = 1.1L

4. Residual Volume : volume of air remaining in the lungs after most forceful expiration = 1.2L

Pulmonary volumes and capacities

• Pulmonary Capacities– Two or more volumes togethere1. Inspiratory Capacity : TV + IRV = 3.5L2. Functional Residual Capacity: ERV+RV = 2.3L3. Vital Capacity : IRV + TV + ERV = 4.6L4. Total Lung Capacity: VC + RV = 5.8L

All pulmonary volumes and capacities are about 20-25% less in women than in men.

• For the next meeting, read on Pulmonary Gas exchange and Gas transport

• Guyton Textbook of Medical Physiology