Download 1 Resp 2 Checklist Lower Respiratory Tract Lower respiratory tract

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Lower Respiratory Tract
Lower respiratory tract
The lower respiratory tract consists of the larynx,
tracheobronchial tree, and lungs.
Larynx, or voice box
The larynx, or voice box, is the beginning of the lower
respiratory tract. It consists of cartilage, laryngeal skeletal
muscles, and the vocal cords.
Most of the larynx is inferior to the hyoid bone, but a small
part of the larynx is superior to the hyoid bone. The larynx
is superior to, and connects with, the trachea.
Functions of the larynx
1. Laryngeal cartilages form a passageway for air flow.
During inspiration, air passes through the nasal cavity or
oral cavity, enters the oropharynx, goes into the larynx,
and flows on through to the lungs. During expiration, air
flows in the reverse direction.
2. Air passing through the larynx vibrates the vocal cords in
the larynx, resulting in sound production.
3. During swallowing, laryngeal muscles and cartilage close
the opening into the larynx, preventing swallowed
materials from entering the larynx.
Laryngopharynx
The laryngopharynx is posterior to the larynx. It extends to
the inferior border of the larynx and cervical vertebra C6.
The laryngopharynx connects to the superior opening of the
larynx. Air from the nasal or oral cavities can pass through
the laryngopharynx and enter the larynx.
The laryngopharynx connects to the esophagus, a tube which
conducts swallowed food and liquids to the stomach.
Laryngeal cartilages
Nine pieces of cartilage form the larynx. There are three
unpaired cartilages: the thyroid cartilage, cricoid cartilage,
and the epiglottis.
There are three paired cartilages: arytenoid, corniculate, and
cuneiform.
Thyroid cartilage
The thyroid cartilage is the largest and most prominent
laryngeal cartilage. It forms a protrusion of the throat called
the "Adams apple."
At puberty, the larynx of males becomes larger than the
larynx of females. The thyroid cartilage, in particular,
increases in size and projects anteriorly.
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During swallowing, muscles attached to the thyroid cartilage
and other parts of the larynx pull the larynx superiorly and
anteriorly. This allows the pharynx to expand and moves the
laryngeal opening out of the way of swallowed materials.
Cricoid cartilage
The cricoid cartilage (pink) forms the base of the larynx,
connecting it to the trachea.
Epiglottis
The third unpaired laryngeal cartilage is the epiglottis.
During swallowing, the larynx moves superiorly and
anteriorly. Upward movement of the epiglottis is prevented,
however, by the base of the tongue. As a result, the epiglottis
folds over the opening of the larynx. In addition, as solid
swallowed materials slide over the epiglottis, they push on it,
helping to fold it over the laryngeal opening.
Analogy: The epiglottis is like the lid on a toilet seat. When
the lid is down, nothing goes into the toilet (larynx).
In humans, the epiglottis is not essential for swallowing. The
laryngeal muscles (considered later in this lesson) prevent
materials from entering the larynx. Even if the epiglottis is
destroyed by disease, swallowing can still occur without
materials entering the larynx.
Cricothyrotomy
A cricothyrotomy is an emergency procedure used when the
larynx becomes obstructed and a person is suffocating.
The thyroid cartilage can be easily felt with a finger on the
midline of the anterior neck. Moving the finger inferiorly, an
indentation can be felt. This is the location of the
cricothyroid membrane between the thyroid and cricoid
cartilages.
In a cricothyrotomy, a small slit is made through the
cricothyroid membrane and a tube is inserted into the inferior
larynx and into the trachea, permitting air flow to occur.
Arytenoid cartilages
The paired arytenoid cartilages rest on the cricoid cartilage.
Corniculate cartilages
The paired corniculate cartilages rest on the arytenoid
cartilages.
Cuneiform cartilages
The paired cuneiform cartilages are small cartilages located in
mucous membranes.
Vestibular folds
The vestibular folds are mucous membranes covering the
vestibular ligaments, which are stretched between the thyroid
cartilage and the arytenoid cartilages.
The vestibular folds are sometimes called the false vocal
cords.
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The vestibular folds can open and close. During respiration
they open, allowing the movement of air. During swallowing,
they close to prevent the movement of swallowed materials
into the larynx.
If the epiglottis is represented by the toilet seat cover, then the
vestibular folds are the toilet seat. Unlike a toilet seat,
however, the vestibular folds can change shape.
Muscles associated with the arytenoid cartilages cause them
to move. As a result, the attached vestibular folds change
shape and meet at the midline, thus closing the passageway
into the larynx.
Vocal folds
The vocal folds are mucous membranes covering the vocal
ligaments, which are stretched between the thyroid cartilage
and the arytenoid cartilages.
The vocal folds are sometimes called the true vocal cords.
The movement of air past the vocal folds causes them to
vibrate, producing sounds, such as speech.
The greater the movement of air, the greater the vibration, and
the louder the sound.
The pitch of the sound can be changed by altering the length
of the vocal folds. As the length of the vocal folds increases,
they stretch and are under greater tension, resulting in a
higher pitch sound.
Muscles associated with the arytenoid cartilages cause them
to move. When the muscles contract, the tension of the
attached vocal folds increases, and when the muscles relax,
the tension decreases.
Ventricle of the larynx
The ventricle of the larynx is the space between the vestibular
and vocal folds.
The ventricle of the larynx opens into a sac (laryngeal
saccule) containing numerous mucous glands. Compression
of the sac by surrounding muscles causes the secretions of
these glands to be pushed onto the vocal folds.
The secretions help to keep the vocal folds from drying out.
The vocal folds are covered with moist stratified squamous
epithelium and do not have mucous glands.
In some monkeys, the sacs are enlarged to form air sacs that
cause sounds to resonate and increase in volume. Howler
monkeys have been know to project their sounds up to a
distance of 5 miles.
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Trachea, or wind pipe
The trachea is a tube consisting of 15-20 C-shaped pieces of
cartilage connected by a fibrous membrane and smooth
muscle.
The trachea is approximately 11 cm (4.3 in) long, extending
from the larynx to the level of the fifth thoracic vertebra,
where it divides.
Functions of the trachea
1. The tracheal cartilages keep the trachea from collapsing,
thus maintaining an open passageway for the movement
of air to and from the lungs.
2. Smooth muscles within the tracheal wall can regulate the
diameter of the trachea. For example, during exercise the
muscles relax, diameter increases, and a greater volume of
air movement results.
3. The trachea is lined with pseudostratified columnar ciliate
epithelium that traps and removes inhaled debris in the
air.
Thyroid gland
An endocrine gland with two lobes located immediately
lateral to each side of the trachea. Typically, the two lobes
are connected across the anterior surface of the trachea by a
piece of thyroid tissue called the isthmus.
The thyroid gland produces thyroid hormones, which
increase metabolic rate and are essential for normal growth
and maturation.
If it is necessary to make a permanent opening into the
trachea, a tracheostomy is performed. In this procedure, an
incision is made through the skin and the muscles overlying
the trachea are retracted. If the isthmus cannot be pushed out
of the way, it is tied off and cut along the midline to expose
the trachea. Typically, the anterior part of the second tracheal
ring is removed to provide a "window" into the trachea.
A tracheostomy is not an emergency procedure and should
be performed only by individuals trained in the procedure so
as not to damage the thyroid gland.
A tracheostomy is not performed inferior to the third tracheal
cartilage because the trachea become too deep for easy
access.
Primary bronchi
The trachea branches to form two smaller tubes called
primary bronchi. The primary bronchi also branch to form
even smaller tubes. These subdivisions continue to divide
and become even smaller until they end as microscopically
small sacs.
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Tracheobronchial tree
The trachea and all of these branches are called the
tracheobronchial tree.
The tracheobronchial tree forms the passageways through
which air moves to and from the sites where gases are
exchanged between the air and the blood.
The tracheal cartilages are C-shaped pieces of cartilage.
From the anterior view, they form solid bands of cartilage
connected by a fibrous membrane. The cartilages hold the
trachea open so that air can flow uninterrupted.
Trachealis muscles
The trachealis muscles are smooth muscles that connect the
ends of the tracheal cartilages.
Contraction and relaxation of the trachealis muscles can
change the diameter of the trachea by pulling the ends of the
cartilages closer together. For example, during coughing, the
trachealis muscles contract, which decreases the diameter of
the trachea. As a result, air flows through the trachea more
rapidly, causing mucus or foreign objects to be expelled.
Esophagus
The esophagus is located between the trachealis muscles and
the vertebral column. The esophagus, which conducts
swallowed materials to the stomach, is normally flattened.
When food is swallowed, the esophagus can momentarily
expand into the trachea because the posterior part of the
trachea does not have cartilage.
Primary bronchi
The trachea branches to form the left and right primary
bronchi, which go to the left and right lungs.
Lung
One of two cone-shaped organs located in the thoracic cavity.
The base of the lung rests upon the diaphragm, and its apex
extends 2.5 cm (1 in) superior to the clavicle.
The adult right lung weighs about 625 gm (1.4 lb) and the
left lung 565 gm (1.2 lb).
The lungs are the organs of respiration. During inspiration,
air moves into the lungs. Oxygen in the air moves into the
blood, and carbon dioxide, produced by the body, moves
from the blood into the air. During expiration, air moves out
of the lungs.
Mediastinum
The mediastinum is the partition separating the two lungs. It
contains all of the thoracic organs, except for the lungs. The
major organs of the mediastinum include the heart, blood
vessels going to and from the heart, the trachea, and the
esophagus.
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Great vessels
The great vessels carry blood to and from the heart.
The superior vena cava returns deoxygenated blood from the
head, thorax, and upper limbs to the heart.
The aorta delivers oxygenated blood to the body.
The pulmonary trunk delivers deoxygenated blood to the
lungs.
The pulmonary trunk divides to form the left and right
pulmonary arteries, which go to the left and right lungs.
After the blood is oxygenated in the lungs, it returns to the
heart through the four pulmonary veins.
Hilum
The hilum is part of the lung where the primary bronchus
and pulmonary artery enter the lung and the pulmonary veins
exit the lung.
Lung impressions
The lungs conform to the shape of the organs with which
they come into contact.
The cardiac impression is the indentation of the lung where it
partially surrounds the left side of the heart.
The groove for the aorta is the medial indentation of the left
lung where it partially surrounds the aorta.
The diaphragmatic surface is the inferior indentation of the
lung where it partially surrounds the diaphragm.
The indentations for the superior vena cava and other blood
vessels are in the right lung.
The groove for the trachea and esophagus are in the right
lung.
Secondary bronchi
The primary bronchi branch to form the secondary bronchi.
The secondary bronchi supply subdivisions of the lungs
called lobes.
In the left lung, there are two secondary bronchi, which
supply the superior and inferior lobes.
In the right lung, there are three secondary bronchi, which
supply the superior, middle, and inferior lobes.
Tertiary bronchi
The secondary bronchi branch to form the tertiary bronchi.
The tertiary bronchi supply subdivisions of the lobes called
bronchopulmonary segments.
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In the left lung, there are nine bronchopulmonary segments.
In the right lung, there are ten bronchopulmonary segments.
The bronchopulmonary segments are separated from one
another by connective tissue partitions. Diseased
bronchopulmonary segments can be removed from the lungs
because major bronchi and blood vessels do not cross the
partitions.
Alveoli
The tertiary bronchi divide into smaller branches, which also
divide, and so on, until many small tubes are produced. The
small tubes are associated with air sacs called alveoli, which
are the site of gas exchange between the air and blood.
Mediastinum
The mediastinum is the partition separating the two lungs.
The major organs of the mediastinum are the heart,
esophagus, aorta, and azygos vein.
Pleural cavity
Each lung is surrounded by a space called the pleural cavity.
Pleural membrane
The pleural membrane forms the boundary of the pleural
cavity.
The pleural membrane is divided into two parts. The visceral
pleura covers the surface of the lungs. The parietal pleura
lines the inner surface of the thoracic wall, the diaphragm,
and the mediastinum.
Pleural membrane functions
The visceral and parietal pleurae secrete pleural fluid, which
fills the pleural cavity.
Pleural fluid is a lubricant that allows the visceral pleura to
slide past the parietal pleura as the lungs and thorax change
shape during respiration.
Pleural fluid holds the visceral and parietal pleurae together.
For example, as the thorax expands during inspiration, the
lungs also expand because they are connected through the
pleurae to the thoracic wall.
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Application Question
9. If the air passageways should become obstructed, an endoscope can be used to insert a tube
through the mouth into the trachea. Given the following list of structures, arrange them in the
order the tube would pass through or by them.
Epiglottis
Laryngopharynx
Oral cavity
Oropharynx
Vestibular folds
Vocal folds
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Application Answer
9. A tube passing through the mouth to the trachea passes through or by the following:
Oral cavity
Oropharynx
Laryngopharynx
Epiglottis
Vestibular folds
Vocal folds
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