Function of the Lungs

• Primary - to provide a means of gas exchange between environment and body

• Secondary - maintenance of acid-base balance and as a resevoir for blood

Ventilation vs. Diffusion

• Ventilation - moving air into and out of the lungs– oxygen is moved into the lungs and CO2 is

moved out during ventilation

• Diffusion - random movement of molecules from area of high concentration to low concentration– because O2 concentration is high in the lungs,

and low in the blood, O2 diffuses into the blood from the lungs (converse for CO2)

Structure

• Conductive zone - area where no gas exchange occurs, air is simply moved through (eg. trachea, bronchii)

• Respiratory zone - area where gas exchange does occur (eg. alveoli)

Major Organs of the Respiratory System

Position of the Pleura and Mediastinum

Pathway of Air to Alveoli

Alveolus at Microscopic Level

Mechanics of Breathing• Bulk Flow

– movement of air from the environment to the lungs

– occurs due to pressure differences at end of system

Cont’d

• Inspiration – major muscle involved is the diaphragm– (diaphragm only skeletal muscle in body

considered essential for life)– intrapulmonary pressure reduced below

atmospheric– during exercise

• external intercostals, pectoralis minor, scalene, sternomastoids increase volume of thorax

More

• Expiration – intrapulmonary pressure exceeds atmospheric– passive at rest– during exercise

• rectus abdominus, internal obliques involved

Mechanics of Inspiration and Expiration

• Pulmonary - ventilation (breathing) and gas exchange in the lungs

• Cellular - O2 utilization and CO2 production in the tissues

Muscles Involved in Respiration