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THE RESPIRATORY
SYSTEM
CHAPTER 15
Introduction
 To
continue functioning, body cells must
obtain oxygen and eliminate carbon
dioxide.
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
communication

4. Helping control
body fluid pH.
Organization
 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
pharynx.
 The internal nares connects the nasal
cavity and nasophaarynx.

Much of the
respiratory
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
sound.
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
increases.
The Bronchioles
 Each
terminal bronchiole delivers air to
a single pulmonary lobule.
 Within the lobule, the terminal
bronchiole branches into respiratory
bronchioles.
The Alveolar Ducts and Alveoli
 The
respiratory bronchioles open into
alveolar ducts, which end at alveolar
sacs.
 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
collapsing.
 Alveolar macrophages engulf foreign
particles.
The Lungs and Pleural
Cavities
 The
lungs are made up of five lobes;
three in the right lung and two in the left
lung.
 Each lung occupies a single pleural
cavity lined by a pleura (serous
membrane)
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
passive.
 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
volume.
 The air left in the lungs at the end of
maximum expiration is the residual
volume.
Gas Exchange
 Gas
exchange involves external
respiration,

the diffusion of gases between the blood
and alveolar air across the respiratory
membrane,
 Internal
 The
respiration
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
dioxide.
 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
respiration.
The Reflex Control of
Respiration

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
muscles.
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
system
 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.