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The Respiratory
System
Chapter 15
The Respiratory System
• Learning
Objectives: When you have completed
this chapter you should be able to:
 Differentiate between internal, external, and
cellular respiration.
 List the secondary functions of the respiratory
system.
The Respiratory System
• List
the components of the upper respiratory tract
and describe their structure and functions.
• List
the components of the lower respiratory tract
and describe their structure and functions.
• Describe
the events that occur during inspiration
and expiration.
The Respiratory System
• List
the muscles involved in inspiration and
expiration.
• Define
the terms tidal volume, minute volume, and
residual volume.
• Describe
the processes of oxygen and carbon
dioxide exchange between the alveoli and the
blood.
The Respiratory System
• Vocabulary
Fundaments:
Be able to define, describe, or identify the terms on
pages 361 and 362.
The Respiratory System
• Respiration
is the process of bringing oxygen to all
body cells and carrying carbon dioxide in the
opposite direction.
• Types:
 External respiration
 Internal respiration
 Cellular respiration
The Respiratory System
• Secondary
functions of the respiratory system:
 Voice production
 Body temperature regulation
 Acid-base balance
 Smell
The Respiratory System
• Voice
production or “phonation” begins in the
larynx.
• The
vocal cords or vocal folds:
 Stretch across the lumen of the larynx
 The folds vibrate as air passes over them
 This produces the basic sound of an animal’s
voice
The Respiratory System
• Body
temperature regulation involves several body
systems.
• The
respiratory system utilizes superficial blood
vessels lining the nasal passages.
 Inhaled air is warmed.
 Panting uses evaporation to cool.
The Respiratory System
• Acid-base
balance is an essential homeostatic
mechanism of the body.
• Normal
acid-base is essential for normal chemical
reactions in the body.
• The
respiratory system regulates the amount of
CO2 and O2 in blood.
 The more CO2 there is, the lower (more acid) the
blood is.
 Normal blood pH = 7.4 (Range is 7.35 to 7.45)
The Respiratory System
• The
olfactory system is based on sensory
epithelium in in the upper respiratory passages of
the nose.
• The
olfactory system is covered in the chapter on
special senses.
The Respiratory System
• The
respiratory system is made up a series of
specialized tubes that connect the lungs to the
outside world.
• The
upper respiratory tract consists of all the
structures outside the lungs.
• The
lower respiratory tract consists of all the
structures in the lungs.
The Respiratory System
• The
upper respiratory tract is made up of:
 Nostrils
 Nasal passages
 Pharynx
 Larynx
 Trachea
The Respiratory System
• The
external openings of the respiratory passages
are the nostrils, most properly known as the nares.
• The
nasal passages lie between the nares and the
pharynx.
• The
midline of the passages is known as the nasal
septum.
The Respiratory System
• In
the nasal passages turbinates, or nasal conchae,
divide each passage into three main passageways:
 Ventral nasal meatus
 Middle nasal meatus
 Dorsal nasal meatus
The Respiratory System
• The
nasal passages are lined with pseudostratified
columnar epithelium, cilia, mucous, and blood
vessels.
• The
main function of the nasal passages is to
“condition” inhaled air.
• Conditioning
includes:
 Warming
 Humidifying
 Filtering
The Respiratory System
• The
sinuses are ciliated outpouchings of the nasal
passages.
• The
sinuses are names for the bones that house
them.
 Frontal sinus
 Maxillary sinus
The Respiratory System
• The
pharynx, or throat, is the common passageway
for the respiratory and digestive systems.
• The
pharynx is divided at the rostral end by the soft
palate:
 Nasopharynx (respiratory portion)
 Oropharynx (digestive portion)
• The
pharynx opens at the caudal end into the
larynx and the esophagus.
The Respiratory System
•
The larynx , or voice box, connects the pharynx with the
trachea.
•
The larynx is supported by the the hyoid bone or hyoid
apparatus.
•
The hyoid apparatus is made up of several cartilage
segments:
 Epiglottis (1)
 Artenoid cartilages (2)
 Thyroid cartilage (1)
 Cricoid cartilage (1)
The Respiratory System
• The
vocal folds are attached to the artenoid
cartilages which form the boundaries of the glottis.
• Muscles
are attached to the cartilages to adjust
tension on the folds.
• There
is a set of false vocal, or vestibular, folds in
nonruminant animals.
• The
false vocal folds are a second set of
connective tissue bands.
The Respiratory System
• The
Larynx:
 Forms part of the upper respiratory system.
 Aids in voice production.
 Helps prevent the inhalation of foreign matter.
 Helps control the flow of air into the trachea.
The Respiratory System
• The
epiglottis is the most rostral of the cartilages.
• The
epiglottis covers the larynx during swallowing.
• The
epiglottis insures that air goes into the trachea
and food goes into the esophagus.
The Respiratory System
•
The trachea is a short, wide tube made up of fibrous tissue
and smooth muscle held open by cartilage rings.
•
The trachea extends from the larynx into the thoracic cavity
where it divides into the right and left primary bronchi.
•
C-shaped rings spaced along the length of the trachea
prevent collapse during respiration.
•
The trachea has a ciliated lining and a mucous layer.
The Respiratory System
• The
lower respiratory system, also known as the
bronchial tree, is made up of:
 Bronchi
 Bronchioles
 Alveolar ducts
 Alveoli
The Respiratory System
• The
autonomic nervous system (sympathetic and
parasympathetic) controls the diameter of the
bronchial tubes by constricting and relaxing smooth
muscle fiber in their walls.
 Bronchodilation
 Bronchoconstriction
The Respiratory System
• The
alveoli are tiny, thin-walled sacs surrounded by
capillaries.
• The
sacs are lined with a think layer of fluid that
contains a surfactant.
• External
• O2
respiration takes place in the alveoli.
and CO2 are exchanged between the alveoli
and blood.
The Respiratory System
• The
lungs are cone-shaped structures with a light,
spongy consistency.
• The
base of the lungs lies directly on the cranial
surface of the diaphragm.
• The
area between the lungs is the mediastinum.
The Respiratory System
• The
lungs are divided into lobes.
• The
lobes have the same basic structure among
species:
 Left lung: cranial, middle, caudal lobes
 Right lung: cranial, middle, caudal, accessory lobes
 The horse is the exception, with a left lobe, and a right
lobe and accessory lobe.
The Respiratory System
• The
hilus of the lung is a small well defined area on
the medial side where bronchial tubes, nerves,
blood vessels, and lymph vessels enter and leave
the lungs.
The Respiratory System
• In
pulmonary circulation deoxygenated blood enters
the lungs from the right side of the heart through
the pulmonary arteries.
• The
blood vessels follow the bronchial tree and
quickly subdivide.
• These
branching's form capillary networks abound
the alveoli and O2 and CO2 are exchanges by
simple diffusion.
The Respiratory System
• The
thoracic cavity is an area bounded by the
thoracic vertebrae, the robs, the intercostal
muscles, the diaphragm, and the sternum.
• The
lungs, heart, large blood vessels, trachea,
esophagus, lymphatic vessels, lymph nodes,
nerves, and supporting tissues lie in the thorax.
The Respiratory System
• The
mediastinum contains the heart, trachea, blood
vessels, nerves, and lymphatic structures.
The Respiratory System
• The
diaphragm is a thin sheet of skeletal
(voluntary) muscle, which forms the caudal
boundary of the thorax.
• The
• The
diaphragm acts as a respiratory muscle.
diaphragm flattens when it contacts increasing
the size of the thorax, and decreases the size of the
thorax when it relaxes.
The Respiratory System
• There
is negative intrathoracic pressure in the
thorax, or a partial vacuum.
• This
allows the lungs to follow the movements of
the thoracic wall and diaphragm. This results in
inhalation and exhalation.
• This
also aids in return of blood to the heart .
The Respiratory System
• Inhalation,
or inspiration, is the process of drawing
air into the lungs.
• Inhalation
results from the enlargement of the
thoracic cavity.
• The
lungs passively follow the movement of the
thoracic walls.
• The
diaphragm and external intercostal muscles
are the main inspiratory muscles.
The Respiratory System
• Exhalation,
or expiration, is the process of pushing
air out of the lungs.
• Exhalation
is the opposite of inhalation. In
exhalation the size of the thorax is decreased, the
lungs are compressed, and air is pushed out
through the respiratory passageways.
• The
internal intercostal and abdominal muscles are
primary muscles of expiration.
The Respiratory System
• The
common standardized parameters for
describing the quantity of air involved in normal
respiration are:
 Tidal volume
 Minute volume
 Residual volume
The Respiratory System
• With
inspiration the inhaled air is high in O2 and
low in CO2.
• The
blood entering the capillaries is low in O2 and
high CO2.
• In
the alveoli high levels of O2 in air diffuses into
the blood where the level is lower, and high levels
of CO2 in blood diffuses into air where the level is
lower.
The Respiratory System
• In
exhalation the exhaled air is higher in CO2 and
lower in O2.
The Respiratory System
• The
partial pressure of a mixture of a gasses is the
sum of the pressures of each individual gas. –
Dalton
• The
pressure of each individual gas is the partial
pressure. Partial pressures also apply to gasses
dissolved in liquids.
• The
partial pressures of O2 and CO2 in blood
capillaries is the determined by the partial
pressures of the gasses in alveolar air.
The Respiratory System
• Breathing
is controlled by an area in the medulla
oblongata of the brain stem. The respiratory center
directs the timing and strength of respiratory
muscle contraction.
• There
are individual control centers for inspiration,
expiration, and breath-holding.
• Breathing
can be consciously controlled for brief
periods of time.
The Respiratory System
•
The mechanical control of breathing operates through
stretch receptors in the the lungs.
•
This is a preset and automatic system.
 Nerve impulses are sent to the respiratory center to indicate
 When the lungs are inflated to a certain point.
 The muscle contractions that produce inspiration are stopped.
 The muscle contractions that produce expiration are initiated.
The Respiratory System
 Another set of nerve impulses are sent when the
lungs deflate to a certain point.
 Expiration is stopped and the the process of
inspiration begins.
• The
net effect is normal, rhythmic, resting breathing
baseline pattern.
The Respiratory System
• The
chemical control system for breathing affects
the breathing pattern only when something is out of
balance. This will help make necessary
adjustments to maintain homeostasis.
• Chemical
receptors in the carotid artery, the aorta,
and the brain stem monitor the CO2, O2, and pH
(H+) of the blood.
The Respiratory System
• The
blood levels of CO2 and the blood pH are
usually linked.
• Increases
of CO2 in the blood deceases the pH,
makes the blood more acidotic, and triggers the
respiratory center to increase the rate and depth of
respiration. This decreases the CO2 in the blood,
increase the O2, and makes the blood more
alkalotic.
The Respiratory System
• Decreased
levels of CO2 in the blood increases the
blood pH. The blood becomes more alkalotic.
• Decreased
CO2 in the blood triggers the respiratory
center to decrease the rate and depth of
respiration.
• This
is usually measured by arterial blood gasses
or by the use of a capnograph.
The Respiratory System
• Oxygen
variations in the blood are not as clear cut
as with CO2.
• With
a slight hypoxia the respiratory center will
increase the rate and depth of respiration.
• With
a severe hypoxia neurons of the respiratory
center become so depressed that they cannot send
impulses to the respiratory muscles. This can
cause breathing to decrease or stop completely.