CHAPTER 2: THORAX PART II: THE THORACIC CAVITY Flashcards
OBJECTIVES
■■ To understand the general arrangement of the thoracic viscera and their relationship to one another and to the chest wall.
■■ To be able to define what is meant by the term mediastinum and to learn the arrangement of the pleura relative to the lungs. This information is fundamental to the comprehension of the function
and disease of the lungs.
■■ Appreciating that the heart and the lungs are enveloped in
serous membranes that provide a lubricating mechanism for these mobile viscera and being able to distinguish between such terms as thoracic cavity, pleural cavity (pleural space),
pericardial cavity, and costodiaphragmatic recess.
■■ To learn the structure of the heart, including its conducting system and the arrangement of the different chambers and valves, which is basic to understanding the physiologic and pathologic features of the heart.
The critical nature of the
blood supply to the heart and the end arteries and myocardial
infarction
is emphasized.
■■ To understand that the largest blood vessels in the body are located within the thoracic cavity, namely, the aorta, the pulmonary arteries, the venae cavae, and the pulmonary veins.
Trauma to the chest wall can result in disruption of these
vessels, with consequent rapid hemorrhage and death.
Because these vessels are hidden from view within the
thorax, the diagnosis of major blood vessel injury is often
delayed, with disastrous consequences to the
patie
What are the bounderies of the Chest Cavity?
The chest cavity is bounded by the chest wall and below by the diaphragm. It extends upward into the root of the neck about one fingerbreadth above the clavicle on each side (see
Fig. 3.5).
The diaphragm, which is a very thin muscle, is the only structure (apart from the pleura and the peritoneum) that separates the chest from the abdominal viscera.
The
chest cavity can be divided into a median partition, called the mediastinum, and the laterally placed pleurae and lungs (Figs. 3.1, 3.2, and 3.3).
What is the only structure (apart from the pleura and the peritoneum) that separates the chest from the abdominal viscera.
The diaphragm, which is a very thin muscle, is the only structure (apart from the pleura and the peritoneum) that separates the chest from the abdominal viscera.
The chest cavity can be divided into a :
- median partition, called the mediastinum,
- and the laterally placed pleurae andlungs (Figs. 3.1, 3.2, and 3.3).
Describe the mediastinum.
The mediastinum, though thick, is a movable partition that extends superiorly to the thoracic outlet and the root of the neck and inferiorly to the diaphragm.
It extends anteriorly to the sternum and posteriorly to the vertebral column.
The mediatstinum contains the:
It contains the remains of the thymus, the heart and large blood vessels, the trachea and esophagus, the thoracic duct and lymph nodes, the vagus and phrenic nerves, and the sympathetic trunks.
The mediastinum is divided into __________-by an imaginary plane passing from the sternalangle anteriorly to the lower border of the body of the 4th thoracic vertebra posteriorl
superior and inferior mediastina
The inferior mediastinum
is further subdivided into the ___________
- middle mediastinum
- which consists of the pericardium and heart; the anterior mediastinum, which is a space between the pericardium and the sternum
- and the posterior mediastinum,
- which lies between the pericardium and the vertebral column.
For purposes of orientation, it is convenient to remember
that the major mediastinal structures are arranged in
the following order from anterior to posterior
What are the bounderies of the Superior Mediastinum?
Superior Mediastinum
The superior mediastinum is bounded by
- front :manubrium sterni
- behind: first four thoracic vertebrae (see Fig. 3.2).
What are the contents of the Superior Mediastinum?
- (a) Thymus,
- (b) large veins,
- (c) large arteries,
- (d) trachea,
- (e) esophagus and
- thoracic duct, and
- (f) sympathetic trunks
What are the contents of the Inferior Mediastinum?
- (a) Thymus,
- (b) heart within the pericardium with the phrenic nerves on each side
- , (c) esophagus and thoracic duct,
- (d) descending aorta, and
- (e) sympathetic trunks
What are the bounderies of inferior mediastinum?
The inferior mediastinum is bounded in
- front: body of the sternum and
- behind by the lower eight thoracic vertebrae
Deflection of Mediastinum
In the cadaver, the mediastinum, as the result of the hardening effect of the preserving fluids, is an inflexible, fixed structure.
In the living, it is very mobile; the lungs, heart, and large arteries are in rhythmic pulsation, and the esophagus distends as each bolus
of food passes through it.
If air enters the pleural cavity (a condition called pneumothorax), the lung on that side immediately collapses and the mediastinum is displaced to the opposite side.
This condition reveals
itself by the patient’s being breathless and in a state of shock; on examination, the trachea and the heart are found to be displaced
to the opposite side.
Mediastinitis
The structures that make up the mediastinum are embedded in loose connective tissue that is continuous with that of the root of the neck.
Thus, it is possible for a deep infection of the neck
to spread readily into the thorax, producing a mediastinitis.
Penetrating wounds of the chest involving the esophagus may produce a mediastinitis.
In esophageal perforations, air escapes into the connective tissue spaces and ascends beneath the fascia to the root of the neck, producing subcutaneous emphysema
What is subcutaneous emphyema?
In esophageal perforations, air escapes into the connective tissue spaces and ascends beneath the fascia to the root of the neck, producing subcutaneous emphysema
Mediastinal Tumors or Cysts
Mediastinal Tumors or Cysts
Because many vital structures are crowded together withinthe mediastinum, their functions can be interfered with by an enlarging tumor or organ.
A tumor of the left lung can rapidly
spread to involve the mediastinal lymph nodes, which on enlargement may compress the left recurrent laryngeal nerve, producing paralysis of the left vocal fold.
An expanding cyst or
tumor can partially occlude the superior vena cava, causing severe congestion of the veins of the upper part of the body.
Other pressure effects can be seen on the sympathetic trunks, phrenic nerves, and sometimes the trachea, main bronchi, and esophagus
Mediastinoscopy
Mediastinoscopy is a diagnostic procedure whereby specimens of tracheobronchial lymph nodes are obtained without opening the pleural cavities.
A small incision is made in the
midline in the neck just above the suprasternal notch, and the superior mediastinum is explored down to the region of the bifurcation of the trachea.
The procedure can be used to determine
the diagnosis and degree of spread of carcinoma of the bronchus.
FIGURE 3.1 Cross section of the thorax at the level of the eighth thoracic vertebra. Note the arrangement of the pleura and pleural cavity (space) and the fibrous and the serous pericardia.
The pleurae and lungs lie on either side of the mediastinum within the chest cavity (Fig. 3.3).
Before discussing the
pleurae, it might be helpful to look at the illustrations of
the development of the lungs in Figure 3.4.
Each pleura has two parts:
- a parietal layer
- a visceral layer
What does the parietal layer lines?
a parietal layer, which lines
the thoracic wall,covers the thoracic surface of thediaphragm
and the lateral aspect of the mediastinum and
extends into the root of the neck to line the undersurface
of the suprapleural membrane at the thoracic outlet
What is the visceral layer?
visceral layer, which completely covers the outer surfaces
of the lungsandextends into the depths of the interlobar
fissures
What is the pulmonary ligament?
The two layers of the pleura become continuous with one another by means of a cuff of pleura that surrounds the structures
entering and leaving the lung at the hilum of each lung
(Figs. 3.3, 3.4, and 3.5).
To allow for movement of the pulmonary
vessels and large bronchi during respiration, the
pleural cuff hangs down as a loose fold called the pulmonary ligament
What is pleural cavity?
The parietal and visceral layers of pleura are separated
from one another by a slitlike space, the pleural cavity
(Figs. 3.3 and 3.4).
(Clinicians are increasingly using the
term pleural space instead of the anatomic term pleural
cavity.
This is probably to avoid the confusion between the
pleural cavity [slitlike]space and thelarger chest cavity.)
What is the funciton of the pleural flurid?
The pleural cavity normally contains a small amount of tissue fluid, the pleural fluid, which covers the surfaces of the
pleuraas a thinfilm and permits the two layers to move on each other with the minimum of friction.
For purposes of description, it is customary to divide the
parietal pleura according to the region in which it lies or
the surface that it covers.
The cervical pleura extends up into the neck, lining the undersurface of the suprapleural
\ membrane (see Fig. 2.13).
It reaches a level 1 to 1.5 in. (2.5
to 4 cm) above the medial third of the clavicle.
What is costal pleura?
The costal pleura lines the :
- inner surfaces of the ribs,
- the costal cartilages,
- the intercostal spaces,
- the sides of the vertebral bodies, and
- the back of the sternum (Fig. 3.3).
What is the diaphragmatic pleura?
The diaphragmatic pleura covers the thoracic surface of the diaphragm (Figs. 3.3 and 3.5).
In quiet respiration, the
costal and diaphragmatic pleurae are in apposition to each other below the lower border of the lung.
In deep inspiration,
the margins of the base of the lung descend, and
the costal and diaphragmatic pleurae separate.
This lower
area of the pleural cavity into which the lung expands on inspiration is referred to as the costodiaphragmatic recess
(Figs. 3.4 and 3.5).
What is the mediastinal pleura?
The mediastinal pleura covers and forms the lateral
boundary of the mediastinum(see Figs. 3.3 and 3.5).
At the hilum of the lung, it is reflected as a cuff around the vessels and bronchi and here becomes continuous with the visceral pleura.
It is thus seen that each lung lies free
except at its hilum, where it is attached to the blood vessels and bronchi that constitute the lung root.
During
full inspiration, the lungs expand and fill the pleural cavities.
However, during quiet inspiration, the lungs do not
fully occupy the pleural cavities at four sites: the right and left costodiaphragmatic recesses and the right and left costomediastinal recesses.
What is the costodiaphragmatic recesses?
The costodiaphragmatic recesses are slitlike spaces
between the costal and diaphragmatic parietal pleuraethat areseparated only by a capillary layer of pleural fluid.
During inspiration, the lower margins of the lungs descend into the recesses.
During expiration, the lower margins of the
lungs ascend so that the costal and diaphragmatic pleurae
come together again.
What is the costomediastinal recesses?
The costomediastinal recesses are situated along the
anterior margins of the pleura .
They are slitlike spaces
between the costal and mediastinal parietal pleurae, which are separated by a capillary layer of pleural fluid.
During
inspiration and expiration, the anterior borders of the
lungs slide in and out of the recesses.
The surface markings of the lungs and pleurae were
described on pages 54 and 55.
Nerve Supply of the Pleura
The parietal pleura (Fig. 3.7) is sensitive to pain, temperature,
touch, and pressure and is supplied as follows:
■■ The costal pleura is segmentally supplied by the intercostal nerves.
■■ The mediastinal pleura is supplied by the phrenic
nerve.
■■ The diaphragmatic pleura is supplied over the domes by the phrenic nerve and around the periphery by the lower six intercostal nerves.
The visceral pleura covering the lungs is insensitive to stretch
but is sensitive to common sensations such as pain and
touch. It receives an autonomic nerve supply from the pulmonary
plexus
T or F
False
The visceral pleura covering the lungs is sensitive to stretch but is insensitive to common sensations such as pain and touch.
It receives an autonomic nerve supply from the pulmonary
plexus
Describe the Trachea.
The trachea is a mobile cartilaginous and membranous
tube (Fig. 3.9).
Where does the trachea begins and ends?
It begins in the neck as a continuation of
the larynx at the lower border of the cricoid cartilage at the level of the 6th cervical vertebra.
It descends in the midline
of the neck.
In the thorax, the trachea ends below at
the carinabydividing into right and left principal (main)bronchi at thelevel of the sternal angle (opposite the disc between the 4th and 5th thoracic vertebrae).
During expiration,
the bifurcation rises by about one vertebral level,
and during deep inspiration may be lowered as far as the
6th thoracic vertebra
How long is the trache in adults?
In adults, the trachea is about 4 1/2 in. (11.25 cm) long
and 1 in. (2.5 cm) in diameter (Fig. 3.9).
What keeps the fibroelastic
tube of the trachea?
The fibroelastic
tube is kept patent by the presence of U-shaped bars (rings) of hyaline cartilage embedded in its wall.
What connects the posterior free
ends of the cartilage of trachea?
The posterior free
ends of the cartilage are connected by smooth muscle, the trachealis muscle.
The relations of the trachea in the neck are described on
page 651.
The relations of the trachea in the superior mediastinum
of the thorax are as follows:
■■ Anteriorly:
- The sternum,
- the thymus,
- the left brachiocephalic vein,
- the origins of the brachiocephalic and
- left common carotid arteries, and
- the arch of the aorta
(Figs. 3.6A, 3.9, and 3.30)
■■ Posteriorly:
- The esophagus and the left recurrent laryngeal nerve (Fig. 3.6A)
■■ Right side:
- The azygos vein,
- the right vagus nerve, and
- the pleura (Figs. 3.6, 3.15A, and 3.16)
■■ Left side:
- The arch of the aorta,
- the left common carotid and left subclavian arteries,
- the left vagus and left phrenic nerves,
- and the pleura (Figs. 3.6, 3.15B, and 3.17)
Blood Supply of the Trachea
The upper two thirds are supplied by the inferior thyroid arteries and the lower third is supplied by the bronchial arteries
T:UILB
Lymph Drainage of the Trachea
The lymph drains into the pretracheal and paratracheal
lymph nodes and the deep cervical nodes
Nerve Supply of the Trachea
The sensory nerve supply is from the vagi and the recurrent laryngeal nerves.
Sympathetic nerves supply the trachealis
muscle.
The pleural space normally contains _________of clear fluid, which lubricates the apposing surfaces of the visceral and
parietal pleurae during respiratory movements
Pleural Fluid
The pleural space normally contains 5 to 10 mL of clear fluid, which lubricates the apposing surfaces of the visceral and
parietal pleurae during respiratory movements.
How is the pleural fluid form?
The formation
of the fluid results from hydrostatic and osmotic pressures.
Since the hydrostatic pressures are greater in the capillaries of the parietal pleura than in the capillaries of the visceral pleura (pulmonary circulation), the pleural fluid is normally absorbed
into the capillaries of the visceral pleura.
What is pleural effusion?
Any condition that
increases the production of the fluid (e.g., inflammation, malignancy, congestive heart disease) or impairs the drainage of the fluid (e.g., collapsed lung) results in the abnormal accumulation
of fluid, called a pleural effusion.
What is the amount of fluid in costrodiaphragmatic recess in an adult that is sufficient to enable its clinical detection?
The presence of 300 mL of fluid in the costodiaphragmatic recess in an adult is sufficient
to enable its clinical detection.
What are the clinical signs of pleural effusion?
The clinical signs include
decreased lung expansion on the side of the effusion, with decreased breath sounds and dullness on percussion over the effusion (Fig. 3.8).
What is Pleurisy?
Pleurisy
Inflammation of the pleura (pleuritis or pleurisy), secondary to inflammation of the lung (e.g., pneumonia), results in the pleural surfaces becoming coated with inflammatory exudate, causing
the surfaces to be roughened.
This roughening produces friction,
and a pleural rub can be heard with the stethoscopeon inspiration and expiration.
Often, the exudate becomes invaded
by fibroblasts, which lay down collagen and bind the visceral pleura to the parietal pleura, forming pleural adhesions.
What is artificial pneumothorax?
As the result of disease or injury (stab or gunshot wounds), air can enter the pleural cavity from the lungs or through the chest wall (pneumothorax).
In the old treatment of tuberculosis, air was
purposely injected into the pleural cavity to collapse and rest the lung.
This was known as artificial pneumothorax.
What is spontaneous pneumothorax?
A spontaneous
pneumothorax is a condition in which air enters the pleural cavity suddenly without its cause being immediately apparent.
After investigation, it is usually found that air has entered from a diseased lung and a bulla (bleb) has ruptured.
What is open pneumothorax?
Stab wounds of the thoracic wall may pierce the parietal pleura so that the pleural cavity is open to the outside air.
This condition is called open pneumothorax.
Each time the
patient inspires, it is possible to hear air under atmospheric pressure being sucked into the pleural cavity.
Sometimes
the clothing and the layers of the thoracic wall combine to form a valve so that air enters on inspiration but cannot exit
through the wound.
In these circumstances, the air pressure builds up on the wounded side and pushes the mediastinum
toward the opposite side.
In this situation, a collapsed lung is
on the injured side and the opposite lung is compressed by the
deflected mediastinum. This dangerous condition is called a
tension pneumothorax.
What is tension pneumothorax?
In these circumstances, the air pressure builds up on the wounded side and pushes the mediastinum
toward the opposite side.
In this situation, a collapsed lung is
on the injured sideand theopposite lung is compressed by the deflected mediastinum.
This dangerous condition is called a
tension pneumothorax.
What is hydropneumothorax?
Air in the pleural cavity associated with serous fluid is known as hydropneumothorax.
What is pyopneumothorax?
Air in the pleural cavity associated with pus as pyopneumothorax.
What is hemopneumothorax?
Air in the pleural cavity associated with blood as hemopneumothorax.
What is empyema?
A collection of pus (without air) in the pleural cavity is called an
empyema.
The presence of serous fluid in the pleural cavity is
referred to as a pleural effusion (Fig. 3.9).
Fluid (serous, blood, or
pus) can be drained from the pleural cavity through a wide-bore
needle, as described on page 45.
In hemopneumothorax, blood enters the pleural cavity.
It can
be caused by stab or bullet wounds to the chest wall, resulting in bleeding from blood vessels in the chest wall, from vessels in the
chest cavity, or from a lacerated lung.
Where does the trachea bifurcates?
The trachea bifurcates behind the arch of the aorta into the right and left principal (primary or main) bronchi
(Figs. 3.9, 3.18, and 3.19).
What is the division of bronchi?
The bronchi divide dichotomously,
giving rise to several million terminal bronchioles
that terminate in one or more respiratory bronchioles.
Each respiratory bronchiole divides into 2 to 11 alveolar
ducts that enter the alveolar sacs.
The alveoli arise from the
walls of the sacs as diverticula (see page 71
Describe the right principal (main) bronchus.
The right principal (main) bronchus (Fig. 3.11) is wider,
shorter, and more vertical than the left(Figs. 3.9, 3.18,
and 3.19) and is about 1 in. (2.5 cm) long.
Before entering
the hilum of the right lung, the principal bronchus gives
off the ______________
Before entering
the hilum of the right lung, the principal bronchus gives
off the superior lobar bronchus.
On entering the hilum,
it divides into a middle and an inferior lobar bronchus.
Describe the left principal bronchus.
The left principal (main) bronchus is narrower, longer,
and more horizontal than the right and is about 2 in.
(5 cm) long.
It passes to the left below the arch of the aorta
and in front of the esophagus.
On entering the hilum of
the left lung, the principal bronchus divides into a superior
and an inferior lobar bronchus.
On entering the hilum of
the left lung, the principal bronchus divides into a :
- superior and
- an inferior lobar bronchus.
On entering the hilum, the right principal bronchus will divide into:
a middle and an inferior lobar bronchus.
What is Tracheitis or Bronchitis?
Tracheitis or Bronchitis
The mucosa lining the trachea is innervated by the recurrent laryngeal nerve and, in the region of its bifurcation, by the pulmonary
plexus.
A tracheitis or bronchitis gives rise to a raw,
burning sensation felt deep to the sternum instead of actual pain.
Many thoracic and abdominal viscera, when diseased,
give rise to discomfort that is felt in the midline (see page 224).
It seems that organs possessing a sensory innervation that is not under normal conditions directly relayed to consciousness display this phenomenon.
The afferent fibers from these organs
traveling to the central nervous system accompany autonomic
nerves.
Where does Inhaled Foreign Bodies mostly dislodged and why?
Inhaled Foreign Bodies
Inhalation of foreign bodies into the lower respiratory tract is common, especially in children.
Pins, screws, nuts, bolts, peanuts,
and parts of chicken bones and toys have all found their way into the bronchi.
Parts of teeth may be inhaled while a
patient is under anesthesia during a difficult dental extraction.
Because the right bronchus is the wider and more direct continuation of the trachea (Figs. 3.18 and 3.19), foreign bodies tend to enter the right instead of the left bronchus.
From there, they
usually pass into the middle or lower lobe bronchi.
What is Bronchoscopy?
Bronchoscopy
Bronchoscopy enables a physician to examine the interior of the trachea; its bifurcation, called the carina; and the main bronchi
(Figs. 3.12 and 3.13).
With experience, it is possible to examine
the interior of the lobar bronchiand thebeginning of the first segmental bronchi.
By means of this procedure, it is also possible
to obtain biopsy specimens of mucous membrane and to remove inhaled foreign bodies (even an open safety pin).
Lodgment of a foreign body in the larynx or edema of the mucous membrane of the larynx secondary to infection or trauma may require
immediate relief to prevent asphyxiation.
A method commonly used
to relieve complete obstruction is tracheostomy (see page 654
What is carina?
bifurcation of the trachea, called the carina
During life, the right and left lungs are soft and spongy
and very elastic.
- *If the thoracic cavity were opened,** the
- *lungs would immediately shrink to one third or less in
volume. **
What is the appearance of lungs in childs?
In the child, they are pink.
What is the appearance of the lungs when we age?
, but with age, they
become dark and mottledbecause of the inhalation of
dust particles that become trapped in the phagocytes of the lung.
This is especially well seen in city dwellers and
coal miners. The lungs are situated so that one lies on
each side of the mediastinum.
They are therefore separated
from each other by the heart and great vessels and
other structures in the mediastinum.
What is the shape of the lungs?
Each lung is conical,
covered with visceral pleura, and suspended free in
its own pleural cavity, being attached to the mediastinum
only by its root (Fig. 3.4).
What is the appearance of the apex of the lungs?
Each lung has a blunt apex, which projects upward into the neck for about 1 in. (2.5 cm) above the clavicle;
What is the appearance of the base of the lungs?
a concave
base that sits on the diaphragm;
What is the shape of the costal surface of the lungs?
a convex costal surface,
which corresponds to the concave chest wall
What is the shape of themediastinal surface of the lungs?
concave mediastinal surface, which is molded to the pericardium and other mediastinal structures (Figs. 3.20 and 3.21).
At about the middle of this surface is the hilum, a
depression in which the bronchi, vessels, and nerves that form the root enter and leave the lung.
Where can you find the cardiac notch?
The anterior border is thin and overlaps the heart; it is
here on the left lung that the cardiac notch is found.
The posterior border is thick and lies beside the vertebral column
Which is larger, right or left lung?
The right lung is slightly larger than the left
The right lobe of the lung is divided by what fissures?
and is divided by the oblique and horizontal fissures into three lobes:
- the upper,
- middle, and
- lower lobes (Fig. 3.20).
Where does the oblique fissure runs?
The oblique
fissure runs from the inferior border upward and backward
across the medial and costal surfaces until it cuts the
posterior border about 2.5 in. (6.25 cm) below the apex.
Where does the horizontal fissure runs?
The horizontal fissure runs horizontally across the costal
surface at the level of the 4th costal cartilage to meet the
oblique fissure in the midaxillary line.
Describe the middle lobe of the right lung?
The middle lobe is
thus a small triangular lobe bounded by the horizontal and oblique fissures.
The left lung is divided by a _____________
similar oblique fissure into two lobes:
the upper and lower lobes (Fig. 3.21).
- *There is no**
- *horizontal fissure in the left lung.**
What are the bronchopulmonary segments?
The bronchopulmonary segments are the anatomic, functional, and surgical units of the lungs.
Each segmental bronchus passes to a structurally and
functionally independent unit of a lung lobe called a
bronchopulmonary segment, which is surrounded by
connective tissue (Fig. 3.22).
What is segmental (tertiary) bronchi ?
Each lobar (secondary)
bronchus, which passes to a lobe of the lung, gives off
branches called segmental (tertiary) bronchi (Fig. 3.18).
Each segmental bronchus passes to a **structurally and functionally independent unit of a lung lobe called a bronchopulmonary segment**, which is surrounded by connective tissue (Fig. 3.22).
The segmental bronchus is
accompanied by a branch of the pulmonary artery, but
the tributaries of the pulmonary veins run in the connective tissue between adjacent bronchopulmonary segments.
Each segment has its own lymphatic vessels and autonomic
nerve supply.
On entering a bronchopulmonary segment, each segmental bronchus divides repeatedly (Fig. 3.22).
As the bronchi
become smaller, the U-shaped bars of cartilage found
in the trachea are gradually replaced by irregular plates of
cartilage, which become smaller and fewer in number.
What are bronchioles?
The
smallest bronchi divide and give rise to bronchioles, whichare <1 mm in diameter (Fig. 3.22).
Bronchioles possess no
cartilage in their walls and are lined with columnar ciliated
epithelium.
The submucosa possesses a complete layer of
circularly arranged smooth muscle fibers.
What are terminal bronchioleS?
The bronchioles then divide and give rise to terminal
bronchioles (Fig. 3.22), which show delicate outpouchings rom their walls.
What are respiratory bronchioles?
Gaseous exchange between blood and
air takes place in the walls of these outpouchings, which explains the name respiratory bronchiole.
The diameter of
a respiratory bronchiole is about 0.5 mm.
What are alveolar sacs?
The respiratory
bronchioles end by branching into alveolar ducts, which lead into tubular passages with numerous thin-walled outpouchings called alveolar sacs
Alveolar sacs consist of?
. The alveolar sacs consist
of several alveoli opening into a single chamber (Figs. 3.22 and 3.23).
Where does gaseous exchange happens?
Each alveolus is surrounded by a rich network
of blood capillaries.
Gaseous exchange takes place between
the air in the alveolar lumen through the alveolar wall into the blood within the surrounding capillaries
Gaseous exchange between blood and
air takes place in the walls of these outpouchings, which explains the name respiratory bronchiole. The diameter of a respiratory bronchiole is about 0.5 mm.
The respiratory
bronchioles end by branching into alveolar ducts, which lead into tubular passages with numerous thin-walled outpouchings called alveolar sacs.
The main characteristics of a bronchopulmonary
segment
may be summarized as follows:
■■ It is a subdivision of a lung lobe.
■■ It is pyramid shaped, with its apex toward the lung
root.
■■ It is surrounded by connective tissue.
■■ It has a segmental bronchus, a segmental artery, lymph vessels, and autonomic nerves.
■■ The segmental vein lies in the connective tissue between adjacent bronchopulmonary segments.
■■ Because it is a structural unit, a diseased segment can be removed surgically
The main bronchopulmonary segments (Figs. 3.24 and
3.25) are as follows
■■ Right lung
- Superior lobe: Apical, posterior, anterior
- Middle lobe: Lateral, medial
- Inferior lobe: Superior (apical), medial basal, anterior basal, lateral basal, posterior basal
The main bronchopulmonary segments (Figs. 3.24 and
3.25) are as follows
■■ Left lung
- Superior lobe: Apical, posterior, anterior, superior lingular, inferior lingular
- Inferior lobe: Superior (apical), medial basal, anterior basal, lateral basal, posterior basal
Although the general arrangement of the bronchopulmonary segments is of clinical importance, it is unnecessary to memorize the details unless one intends to specialize in
pulmonary medicine or surgery
Describe the root of the lung.
The root of the lung is formed of structures that are
entering or leaving the lung.
It is made up of the bronchi,
pulmonary artery and veins, lymph vessels, bronchial
vessels, and nerves.
The root is surrounded by a tubular
sheath of pleura, which joins the mediastinal parietal
pleura to the visceral pleura covering the lungs (Figs. 3.5,
3.15, 3.16, and 3.17).
What makes up the root of the lung?
It is made up of the :
- bronchi,
- pulmonary artery and veins,
- lymph vessels,
- bronchial vessels, and nerves.
Blood Supply of the Lungs
What does bronchial artery supply?
Blood Supply of the Lungs
The bronchi, the connective tissue of the lung, and the visceral pleura receive their blood supply from the bronchial arteries, which are branches of the descending aorta.
Bronchial Artery is a brach of:
Descending aorta
Where does bronchial vein drain?
The bronchial veins (which communicate with the pulmonaryveins) drain into the azygos and hemiazygos veins.
How does the blood exchange in alveoli happens?
The alveoli receive deoxygenated blood from the terminal
branches of the pulmonary arteries.
The oxygenated
blood leaving the alveolar capillaries drains into the tributaries
of the pulmonary veins, which follow the intersegmental
connective tissue septa to the lung root.
Two
pulmonary veins leave each lung root (Fig. 3.15) to empty
into the left atrium of the heart.
How many pulmonary veins leave each lung root?
Two
pulmonary veins leave each lung root (Fig. 3.15) to empty
into the left atrium of the heart.
The lymph vessels originate in_____________(Fig. 3.26); they are not present in the alveolar walls.
superficial and deep plexuses
The superficial (subpleural) plexus lies beneath the visceral pleura and drains over the surface of the lung toward
the hilum, where the lymph vessels enter the bronchopulmonary
nodes.
The deep plexus travels along the bronchi
and pulmonary vessels toward the hilum of the lung, passing through pulmonary nodes located within the lung substance; the lymph then enters the bronchopulmonary nodes
in the hilum of the lung.
All the lymph from the lung leaves
the hilum and drains into the tracheobronchial nodes and then into the bronchomediastinal lymph trunks.
Nerve Supply of the Lungs
At the root of each lung is a pulmonary plexus composed
of efferent and afferent autonomic nerve fibers.
The plexus
is formed from branches of the sympathetic trunk and
receives parasympathetic fibers from the vagus nerve.
The sympathetic efferent fibers produce bronchodilatation
and vasoconstriction.
The parasympathetic efferent
fibers produce bronchoconstriction, vasodilatation, and
increased glandular secretion
Afferent impulses derived from the bronchial mucous
membrane and from stretch receptors in the alveolar walls pass to the central nervous system in both sympathetic and parasympathetic nerves.
Respiration consists of two phases—
inspiration and expiration— which are accomplished by the alternate increase and decrease of the capacity of the thoracic cavity.
The rate varies between 16 and 20 per minute in normal resting patients and is faster in children and slower in the elderly.
Quiet Inspiration
Compare the thoracic cavity to a box with a single entrance at the top, which is a tube called the trachea (Fig. 3.29).
The
capacity of the box can be increased by elongating all its diameters, and this results in air under atmospheric pressure entering the box through the tube.
Consider now the three diameters of the thoracic cavity
and how they may be increased (Fig. 3.29).
- Vertical Diameter
- Anteroposterior Diameter
- Transverse Diameter
Describe the Vertical Diameter during Quiet Inspiration.
Vertical Diameter
Theoretically, the roof could be
raised and the floor lowered.
The roof is formed by the
suprapleural membrane and is fixed.
Conversely, the floor
is formed by the mobile diaphragm.
When the diaphragm contracts, the domes become flattened and the level of the
diaphragm is lowered
Describe the Anteroposterior Diameter during quiet inspiration.
Anteroposterior Diameter
If the downward-sloping
ribs were raised at their sternal ends, the anteroposterior diameter of the thoracic cavity would be increased and the lower end of the sternum would be thrust forward
(Fig. 3.29).
This can be brought about by fixing the 1st rib
by the contraction of the scaleni muscles of the neck and contracting the intercostal muscles (Fig. 3.10).
By this
means, all the ribs are drawn together and raised toward the first rib.
Descirbe the tranvers diameter in Quiet inspiration.
Transverse Diameter
The ribs articulate in front with
the sternum via their costal cartilages and behind with the vertebral column.
Because the ribs curve downward as well
as forward around the chest wall, they resemble bucket handles (see Fig. 3.29).
It therefore follows that if the ribs are
raised (like bucket handles), the transverse diameter of the thoracic cavity will be increased.
As described previously,
this can be accomplished by fixing the 1st rib and raising the other ribs to it by contracting the intercostal muscles (Fig. 3.10).
An additional factor that must not be overlooked is
the effect of the descent of the diaphragm on the abdominal viscera and the tone of the muscles of the anterior abdominal wall.
As the diaphragm descends on inspiration,
intra-abdominal pressure rises. This rise in pressure is
accommodated by the reciprocal relaxation of the abdominal wall musculature.
However, a point is reached when no
further abdominal relaxation is possible, and the liver and other upper abdominal viscera act as a platform that resists further diaphragmatic descent.
On further contraction,
the diaphragm will now have its central tendon supported from below, and its shortening muscle fibers will assist the intercostal muscles in raising the lower ribs (Fig. 3.10).
Apart from the diaphragm and the intercostals, other
less important muscles also contract on inspiration and assist in elevating the ribs, namely, the levatores costarum muscles and the serratus posterior superior muscles
What is forced inspiration?
In deep forced inspiration, a maximum increase in the
capacity of the thoracic cavity occurs.
Every muscle that
can raise the ribs is brought into action, including the
scalenus anterior and medius and the sternocleidomastoid.
In respiratory distress, the action of all the muscles
already engaged becomes more violent, and thescapulae are fixed by the trapezius, levator scapulae, and rhomboid muscles, enabling the serratus anterior and the pectoralis minor to pull up the ribs.
If the upper limbs can be
supported by grasping a chair back or table, the sternal origin of the pectoralis major muscles can also assist the process
What are the lung changes during inspiration?
In inspiration, the root of the lung descends and the level ofthe bifurcation of the trachea may be lowered by as much
as two vertebrae.
The bronchi elongate and dilate and the
alveolar capillaries dilate, thus assisting the pulmonary circulation.
Air is drawn into the bronchial tree as the result
of the positive atmospheric pressure exerted through the upper part of the respiratory tract and the negative pressure on the outer surface of the lungs brought about by the increased capacity of the thoracic cavity.
With expansion of
the lungs, the elastic tissue in the bronchial walls and connective tissue are stretched.
As the diaphragm descends, the
costodiaphragmatic recess of the pleural cavity opens, and the expanding sharp lower edges of the lungs descend to a lower level
Discuss Quiet expiration?
Quiet expiration is largely a passive phenomenon and is
brought about by the elastic recoil of the lungs, the relaxation of the intercostal muscles and diaphragm, and an increase in tone of the muscles of the anterior abdominal wall, which forces the relaxing diaphragm upward.
The serratus
posterior inferior muscles play a minor role in pulling
down the lower ribs.
Discuss force expiration.
Forced expiration is an active process brought about by the forcible contraction of the musculature of the anterior abdominal wall.
The quadratus lumborum also contracts
and pulls down the 12th rib.
It is conceivable that
under these circumstances some of the intercostal muscles may contract, pull the ribs together, and depress them to the lowered 12th rib (Fig. 3.10).
The serratus posterior
inferior and thelatissimus dorsi muscles may also play a minor role
Lung Changes on Expiration
In expiration, the roots of the lungs ascend along with
the bifurcation of the trachea.
The bronchi shorten and
contract.
The elastic tissue of the lungs recoils, and the
lungs become reduced in size.
With the upward movement
of the diaphragm, increasing areas of the diaphragmatic
and costal parietal pleura come into apposition, and the costodiaphragmatic recess becomes reduced in
size.
The lower margins of the lungs shrink and rise to
a higher level
Types of Respiration
- abdominal type of respiration.
- thoracic type of respiration
What is abdominal type of respiration?
In babies and young children, the ribs are nearly horizontal.
Thus, babies have to rely mainly on the descent of the
diaphragm to increase their thoracic capacity on inspiration.
Because this is accompanied by a marked inward and
outward excursion of the anterior abdominal wall, which
is easily seen, respiration at this age is referred to as the
abdominal type of respiration
What is thoracic type of respiration?
After the second year of life, the ribs become more
oblique, and theadult form of respiration is established.
In the adult, a sexual difbference exists in the type of respiratory movements.
The female tends to rely mainly on
the movements of the ribs rather than on the descent of the diaphragm on inspiration.
This is referred to as the
thoracic type of respiration.
The male uses both the thoracic and abdominal forms of respiration, but mainly the
abdominal form.
In the adult, a sexual difbference exists in the type of respiratory movements.
What type of breathing does the female uses?
The female tends to rely mainly on
the movements of the ribs rather than on the descent of the diaphragm on inspiration.
This is referred to as the
thoracic type of respiration.
In the adult, a sexual difbference exists in the type of respiratory movements.
What type of breathing does the male uses?
The male uses both the thoracic and abdominal forms of respiration, but mainly the
abdominal form.
Physical Examination of the Lungs
For physical examination of the patient, it is helpful to remember
that the upper lobes of the lungs are most easily examined from
the front of the chestand thelower lobes from the back.
In the
axillae, areas of all lobes can be examined.
Trauma to the Lungs
A physician must always remember that the apex of the lung projects up into the neck (1 in. [2.5 cm] above the clavicle) and can be damaged by stab or bullet wounds in this area.
Although the lungs are well protected by the bony thoracic cage, a splinter from a fractured rib can nevertheless penetrate the lung, and air can escape into the pleural cavity, causing a
pneumothorax and collapse of the lung.
It can also find its way into
the lung connective tissue.
From there, the air moves under the
visceral pleura until it reaches the lung root. It then passes into the
mediastinum and up to the neck.
Here, it may distend the subcutaneous
tissue, a condition known as subcutaneous emphysema.
The changes in the position of the thoracic and upper abdominal viscera and the level of the diaphragm during different phases of respiration relative to the chest wall are of considerable
clinical importance.
A penetrating wound in the lower part
of the chest may or may not damage abdominal viscera, depending
on the phase of respiration at the time of injury.
Lung tissue and the visceral pleura are devoid of pain-sensitive nerve endings, so that pain in the chest is always the result of conditions affecting the surrounding structures.
T or F
True
Lung tissue and the visceral pleura are devoid of pain-sensitive nerve endings, so that pain in the chest is always the result of conditions affecting the surrounding structures. In tuberculosis
or pneumonia, for example, pain may never be experienced.
When does a lung disease becomes a prominent feature of pain?
Once lung disease crosses the visceral pleura and the pleural cavity to involve the parietal pleura, pain becomes a prominent feature.
Lobar pneumonia with pleurisy, for example, produces a severe tearing pain, accentuated by inspiring deeply or coughing.
Because the lower part of the costal parietal pleura receives its sensory innervation from the lower five intercostal nerves, which also innervate the skin of the anterior abdominal wall, pleurisy in this area commonly produces pain that is referred to
the abdomen.
This has sometimes resulted in a mistaken diagnosis
of an acute abdominal lesion.
When does a lung disease can produce a referred pain on the shoulders?
In a similar manner, pleurisy of the central part of the diaphragmatic pleura, which receives sensory innervation from the phrenic nerve (C3, 4, and 5), can lead to referred pain over the shoulder because the skin of this region is supplied by the supraclavicular
nerves (C3 and 4).
Surgical Access to the Lungs can done by:
Surgical access to the lung or mediastinum is commonly undertakenthrough an intercostal space (see page 46).
Special rib
retractors that allow the ribs to be widely separated are used.
The
costal cartilages are sufficiently elastic to permit considerable bending.
Good exposure of the lungs is obtained by this method.
When do you do Segmental Resection of the Lung?
Segmental Resection of the Lung
A localized chronic lesion such as that of tuberculosis or a
benign neoplasm may require surgical removal.
If it is restricted to a bronchopulmonary segment, it is possible carefully to dissect out a particular segment and remove it, leaving the surrounding
lung intact.
Segmental resection requires that the
radiologist and thoracic surgeon have a sound knowledge of the bronchopulmonary segments and that they cooperate fully to
localize the lesion accurately before operation.
Bronchogenic Carcinoma
Bronchogenic carcinoma accounts for about one third of all cancer deaths in men and is becoming increasingly common in women.
It
commences in most patients in the mucous membrane lining the larger bronchi and is therefore situated close to the hilum of the lung.
The neoplasm rapidly spreads to the tracheobronchial and bronchomediastinal nodes and may involve the recurrent laryngeal nerves, leading to hoarseness of the voice.
Lymphatic spread via
the bronchomediastinal trunks may result in early involvement in the lower deep cervical nodes just above the level of the clavicle.
Hematogenous spread to bones and the brain commonly occurs.
Conditions That Decrease Respiratory Efficiency
- Constriction of the Bronchi (Bronchial Asthma)
- Loss of Lung Elasticity
- Loss of Lung Distensibility
What disease that cause Loss of Lung Distensibility?
Many diseases of the lungs, such as emphysema and pulmonary fibrosis, destroy the elasticity of the lungs, and thus the lungs are unable to recoil adequately, causing incomplete expiration.
The
respiratory muscles in these patients have to assist in expiration, which no longer is a passive phenomenon.
What diseases cause Loss of Lung Distensibility?
Loss of Lung Distensibility
Diseases such as silicosis, asbestosis, cancer, and pneumonia interfere with the process of expanding the lung in inspiration.
A decrease in the compliance of the lungs and the chest wall then occurs, and a greater effort has to be undertaken by the inspiratory muscles to inflate the lungs.
What is Postural Drainage?
Postural Drainage
Excessive accumulation of bronchial secretions in a lobe or segment of a lung can seriously interfere with the normal flow of air into the alveoli.
Furthermore, the stagnation of such secretions
is often quickly followed by infection.
To aid in the normal drainage
of a bronchial segment, a physiotherapist often alters the position of the patient so that gravity assists in the process of drainage.
Sound knowledge of the bronchial tree is necessary to determine the optimum position of the patient for good postural drainage.
Development of the Lungs and Pleura
A longitudinal groove develops in the entodermal lining of the floor of the pharynx.
This groove is known as the laryngotracheal
groove.
The lining of the larynx, trachea, and bronchi
and the epitheliumof the alveoli develop from this groove.
The
margins of the groove fuse and form the laryngotracheal tube (Fig. 3.27).
The fusion process starts distally so that the lumen
becomes separated from the developing esophagus.
Just behind the developing tongue, a small opening persists that will become the permanent opening into the larynx.
The laryngotracheal tube
grows caudally into the splanchnic mesoderm and will eventually lie anterior to the esophagus.
The tube divides distally into the surrounding the tube, and the upper part of the tube becomes
the larynx, whereas the lower part becomes the trachea.
Each lung bud consists of an entodermal tube surrounded by splanchnic mesoderm; from this, all the tissues of the corresponding
lung are derived.
Each bud grows laterally and projects
into the pleural part of the embryonic coelom (Fig. 3.27).
The
lung bud divides into three lobes and then into two, corresponding to the number of main bronchi and lobes found in the fully
developed lung.
Each main bronchus then divides repeatedly in
a dichotomous manner, until eventually the terminal bronchioles
and alveoli are formed. The division of the terminal bronchioles,
with the formation of additional bronchioles and alveoli, continues
for some time after birth.
Each lung will receive a covering of visceral pleura derived from the splanchnic mesoderm.
The parietal pleura will be
formed from somatic mesoderm. By the seventh month, the capillary loops connected with the pulmonary circulation have
become sufficiently well developed to support life, should premature birth take place. With the onset of respiration at birth, the
lungs expand and the alveoli become dilated. However, it is only
after 3 or 4 days of postnatal life that the alveoli in the periphery
of each lung become fully expanded.
Esophageal Atresia and Tracheoesophageal Fistula
If the margins of the laryngotracheal groove fail to fuse adequately, an abnormal opening may be left between the laryngotracheal
tube and the esophagus.
If the tracheoesophageal
septum formed by the fusion of the margins of the laryngotracheal
groove should be deviated posteriorly, the lumen of
the esophagus would be much reduced in diameter.
The different
types of atresia, with and without fistula, are shown in
Figure 3.28. Obstruction of the esophagus prevents the child from swallowing saliva and milk, and this leads to aspiration into the larynx and trachea, which usually results in pneumonia. With early diagnosis, it is often possible to correct this serious anomaly
surgically
