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 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
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
• = 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 mL
2. Inspiratory Reserve Volume – maximum extra
volume of air that can be inspired over and
above normal tidal volume = 300 mL
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
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 togethere
1. Inspiratory Capacity : TV + IRV = 3.5L
2. Functional Residual Capacity: ERV+RV = 2.3L
3. Vital Capacity : IRV + TV + ERV = 4.6L
4. Total Lung Capacity: VC + RV = 5.8L
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