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 To
continue functioning, body cells must
obtain oxygen and eliminate carbon
The Functions of the
Respiratory System
1. Moving air to and
from exchange
surfaces where
diffusion can occur
between air and
circulating blood
2. Defending the
respiratory system
and other tissues
from pathogens
3. Permitting vocal
4. Helping control
body fluid pH.
 The
respiratory system includes the
nose, nasal cavity, and sinuses as well
as the pharynx, larynx, trachea, and
conducting passageways leading to the
surfaces of the lungs.
Respiratory Tract
 The
respiratory tract consists of the
conducting passageways that carry air
to and from the alveoli
The Nose
 Air
normally enters the respiratory
system via the external nares, which
open into the nasal cavity.
 The vestibule is guarded by hairs that
screen out large particles.
 The
hard palate separates the oral and
nasal cavities.
 The soft palate separates the superior
nasopharynx from the rest of the
 The internal nares connects the nasal
cavity and nasophaarynx.
Much of the
epithelium is ciliated
and produces
mucus that traps
incoming particles.
Pharynx and Larynx
The pharynx is a chamber shared by the
digestive and respiratory systems.
 Inhaled air passes through the glottis en route
to the lungs.
 The larynx surrounds and protect the glottis.
 The epiglottis projects into the pharynx
 Exhaled air passing through the glottis
vibrates the true vocal cords and produces
The Trachea
 The
wall of the trachea (windpipe)
contains C-shaped tracheal cartilages,
which protect the airway.
 The posterior tracheal wall can distort to
permit large masses of food to pass.
The Bronchi
The trachea branches within the mediastinum
to form the right and left primary bronchi
 The primary bronchi, secondary bronchi,and
their branches form the bronchial tree.
 As the tertiary bronchi branch within the lung,
the amount of cartilage in their walls
decreases and the amount of smooth muscle
The Bronchioles
 Each
terminal bronchiole delivers air to
a single pulmonary lobule.
 Within the lobule, the terminal
bronchiole branches into respiratory
The Alveolar Ducts and Alveoli
 The
respiratory bronchioles open into
alveolar ducts, which end at alveolar
 Many alveoli are interconnected at each
alveolar sac.
The Respiratory Membrane
 The
 1.
respiratory membrane consists of
A simple squamous alveolar epithelium
 2. A capillary endothelium
 3. Their fused basement membranes.
 Surfactant
cells produce an oily
secretion that keeps the alveoli from
 Alveolar macrophages engulf foreign
The Lungs and Pleural
 The
lungs are made up of five lobes;
three in the right lung and two in the left
 Each lung occupies a single pleural
cavity lined by a pleura (serous
Respiratory Physiology
 Respiratory
physiology focuses on a
series of integrated processes:
 Pulmonary
ventilation or breathing.
 Gas exchange or diffusion between the
alveoli and circulating blood and between
the blood and interstitial fluids
 Gas transport between the blood and
interstitial fluids.
Pulmonary Ventilation
 A single
breath, or respiratory cycle,
consists of an inhalation (inspiration)
and exhalation (expiration)
 The relationship between the pressure
inside the respiratory tract and
atmospheric pressure determines the
direction of airflow.
 The
diaphragm and the external
intercostal muscles are involved in quiet
breathing, in which exhalation is
 Accessory muscles become active
during the active inspiratory and
expiratory movement of forced
breathing in which exhalation is active.
 The
vital capacity includes the tidal
volume plus the expiratory reserve
volume and the inspiratory reserve
 The air left in the lungs at the end of
maximum expiration is the residual
Gas Exchange
 Gas
exchange involves external
the diffusion of gases between the blood
and alveolar air across the respiratory
 Internal
 The
diffusion of gases between blood and
interstitial fluid across the single
endothelial cells of capillary walls.
Gas Transport
 Blood
entering peripheral capillaries
delivers oxygen and absorbs carbon
 The transport of oxygen and carbon
dioxide in the blood involves reaction
that are completely reversible.
 Over
the range of oxygen pressures
normally present in the body, a small
change in plasma PO2 will mean a large
change in the amount of oxygen bound
or released by hemoglobin
Aerobic metabolism in peripheral tissues
generates carbon dioxide.
 Roughly 7 percent of the CO2 transported in
the blood is dissolved in the plasma
 23% is bound as carbaminohemoglobin
 The rest is converted to carbonic acid which
dissociates into a hydrogen ion and a
bicarbonate ion.
The Control of Respiration
 Large-scale
changes in oxygen demand
require the integration of cardiovascular
and respiratory responses.
Local Control of Respiration
 Arterioles
leading to alveolar capillaries
constrict when oxygen is low and
bronchioles dilate when carbon dioxide
is high
The Respiratory Centers of
the Brain
The respiratory center include three pairs of
nuclei in the reticular formation of the pons
and medulla oblongata.
 These nuclei regulate the respiratory muscles
and control the respiratory rate and the depth
of breathing.
 The respiratory rhythmicity centers in the
medulla oblongata set the basic pace for
The Reflex Control of
The inflation reflex prevents overexpansion of
the lungs during forced breathing.
 The deflation reflex stimulates inspiration
when the lungs are collapsing.
 Chemoreceptor reflexes respond to changes
in the pH PO2 and PCO2 of blood and
cerebrospinal fluid.
Control by Higher Centers
 Conscious
and unconscious thought
processes can affect respiration by
affecting the respiratory centers or the
motor neurons controlling respiratory
Respiratory Changes at Birth
 Before
delivery, the fetal lungs are fluidfilled and collapsed.
 After the first breath, the alveoli
normally remain inflated for the life of
the individual.
Aging and the Respiratory
 The
respiratory system is generally less
efficient in the elderly because:
 Elastic
tissue deteriorates, lowering the
vital capacity of the lungs
 Movements of the chest cage are restricted
by arthritic changes and decreased
flexibility of costal cartilages
 Some degree of emphysema is normal in
the elderly.