The Respiratory System II
Physiology
Physiology
• The major function of the respiratory system
is to supply the body with oxygen and to
dispose of carbon dioxide
• Events happening during respiration:
1. Pulmonary ventilation: Air must move into
and out of the lungs; this process is
commonly known as breathing
2. External respiration: Gas exchange between
the pulmonary blood and alveoli must take
place
Physiology
3. Respiratory gas transport: Oxygen and
carbon dioxide must be transported to and
from the lungs and tissue via the blood
stream
4. Internal respiration: Gas exchange between
the blood and tissue cells
Mechanics of Breathing
• Volume changes leads to pressure change,
which leads to the flow of gases to equalize
the pressure
• Inspiration: air is flowing into the lungs
• Expiration: air is leaving the lungs
• Inspiratory muscles: diaphragm and external
intercostals
Inspiration
• At the end of a
normal inspiration:
- Chest is expanded
- Rib cage is elevated
- Diaphragm is
depressed and
flattened
Expiration
• At the end of a
normal expiration:
- Chest is depressed
- Rib cage is descended
- Diaphragm is
elevated and domeshaped
Forced expiration
• Forced expiration: the internal intercostal
muscles are activated to help depress the rib
cage, and the abdominal muscles contract
- Asthma: the respiratory passageways are
narrowed by spasms of the bronchioles
- Pneumonia: the respiration passageways are
clogged with fluid or mucus
Respiratory Volumes and Capacities
• Tidal volume (TV): the
amount of air into and
out of the lungs when
breathing normally and
quietly (approximately
500 ml of air)
• Inspiratory reserve
volume (IRV): the
amount of air that can
be taken in forcibly
over the tidal volume
(approximately 21003200 ml of air)
Respiratory Volumes and Capacities
• Expiratory reserve volume
(ERV): The amount of air
can be forcibly exhaled
after a tidal expiration
(approximately 1200 ml)
• Residual volume (RV):
Even after the most
strenuous expiration,
about 1200 ml of air still
remains in the lungs, and
it can not be voluntarily
expelled
• Vital Capacity (VC): the
total amount of
exchangeable air (
TV+IRV+EVR)
Dead Space Volume
• The amount of air remains in the conducting
zone passageways and never reaches the
alveoli
Respiratory Sounds
• Bronchial sounds: are produced by air rushing
through the large respiratory passageways
• Vesicular sounds: occurs as air fills the alveoli
Respiration
External Respiration:
• It is the actual
exchange of gases
between the alveoli
and the blood
• Gas exchanges in the
body occur according
to the laws of diffusion
Internal Respiration:
• It is the exchange of
gases that takes place
between the blood
and the tissue cells
Oxygen Transport in the Blood
• Oxygen is transported in the blood in two
ways:
- Most attaches to hemoglobin molecules inside
the red blood cells to form oxyhemoglobin
- A very small amount of oxygen is carried
dissolved in the plasma
Carbon Dioxide Transport in the Blood
• Most carbon dioxide is transported in plasma
as the bicarbonate ion (HCO3-)
• A smaller amount (between 20%-30%) is
carried inside the red blood cells bound to
hemoglobin
- Carbon dioxide attaches to hemoglobin at a
different site than oxygen does, so it does not
interfere in any way with oxygen transport
Carbon Dioxide Transport in the Blood
• Before carbon dioxide can diffuse out of the
blood into the alveoli, it must:
- Combine with hydrogen ions (H+) to form
carbonic acid (H2CO3)
- carbonic acid (H2CO3) quickly splits to form
water and carbon dioxide
- Carbon dioxide then diffuses from the blood
and enters the alveoli
- HCO3- + H+  H2CO3  CO2 + H2O