gross anatomy of respiratory system

1. GROSS ANATOMY OF PLEURA
& LUNGS
By Dr. Sumaira Abbasi
PGT

2. TRACHEA
 The trachea is a mobile cartilaginous
and membranous tube, about 4½ in.
(11.25 cm) long and 1 in. (2.5 cm) in
diameter.
 It begins in the neck as a continuation
of the larynx at the lower border of the
cricoid cartilage at the level of the
sixth cervical vertebra.
 It descends in the midline of the
neck.

3.  In the thorax the trachea ends below at the carina by
dividing into right and left principal (main) bronchi at the level
of the sternal angle between the fourth and fifth thoracic
vertebrae.
 The fibroelastic tube is kept patent by the presence of U-
shaped bars (rings) of hyaline cartilage embedded in its wall.
The posterior free ends of the cartilage are connected by
smooth muscle, the trachealis muscle.

4. RELATIONS OF THE TRACHEA
 IN THE NECK:
 Anteriorly: Skin, fascia, isthmus of the
thyroid gland, inferior thyroid vein, jugular
arch, thyroidea ima artery.
 Posteriorly:
 Laterally: Lobes of the thyroid gland and
the carotid sheath and contents

5.  SUPERIOR MEDIASTINUM:
 Anteriorly: The sternum, thymus, left
brachiocephalic vein, brachiocephalic ,left
common carotid arteries, and the arch of
the aorta.
 Posteriorly: esophagus and the left
recurrent laryngeal nerve.
 Right side: The azygos vein, the right
vagus nerve, and the pleura.
 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.

6. NEUROVASCULATURE OF TRACHEA
 Nerve Supply of the Trachea:
The sensory nerve supply is from the vagi and the
recurrent laryngeal nerves.
 Blood Supply of the Trachea:
The upper two thirds is supplied by the inferior thyroid
arteries and the lower third is supplied by the
bronchial arteries.

7. LYMPH DRAINAGE OF THE TRACHEA
 Into the pretracheal and paratracheal lymph nodes
and the deep cervical nodes

8. BRONCHI
 The trachea bifurcates behind the arch of
the aorta into the right and left principal
(primary, or main) 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.

9. PRINCIPAL BRONCHI
 The right principal (main) bronchus is wider, shorter,
and more vertical than the left and is about 1 in. (2.5
cm) long.
 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.

10.  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.

12. LUNGS
 Right and left lungs are soft, spongy and very
elastic.
 If the thoracic cavity were opened, the lungs
would immediately shrink to one third or less in
volume.
 In the child, they are pink, but with age, they
become dark and mottled because of the
inhalation of dust particles that become trapped
in the phagocytes of the lung.
 The lungs are situated so that one lies on each
side of the mediastinum.
 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.

13.  Each lung has a blunt apex, which projects upward into the
neck for about 1 in. (2.5 cm) above the clavicle; a concave
base that sits on the diaphragm.
 SURFACES: A convex costal surface, which
corresponds to the concave chest wall; and a concave
mediastinal surface, which is molded to the pericardium
and other mediastinal structures.
 BORDERS: The anterior border is thin and overlaps the
heart , posterior border is thick and lies beside the
vertebral column.

14.  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.

15. LOBES AND FISSURES
 Right Lung
 The right lung is slightly larger than the
left and is divided by the oblique and
horizontal fissures into three lobes: the
upper, middle, and lower lobes.
 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 inches below the apex.
 The horizontal fissure runs horizontally
across the costal surface at the level of
the fourth costal cartilage to meet the
oblique fissure in the midaxillary line.

16. Left Lung:
 The left lung is divided by a
similar oblique fissure into two
lobes: the upper and lower lobes.

17. BRONCHOPULMONARY SEGMENTS
 The bronchopulmonary segments are
the anatomic, functional, and surgical
units of the lungs.
 Each lobar (secondary) bronchus,
which passes to a lobe of the lung,
gives off branches called segmental
(tertiary) bronchi.
 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.

18.  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.

19.  On entering a bronchopulmonary segment, each
segmental bronchus divides repeatedly.
 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.
 The smallest bronchi divide and give rise to bronchioles,
which are less than 1 mm in diameter- respiratory
bronchiole.
 The respiratory bronchioles end by branching into alveolar
ducts, which lead into tubular passages with numerous
thin-walled outpouchings called alveolar sacs.

20.  The alveolar sacs consist of several alveoli opening
into a single chamber. 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.

21.  Main characteristics of a bronchopulmonary
segment are as:
 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.

22. 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.
 The bronchial veins (which communicate with the
pulmonary veins) drain into the azygos and
hemiazygos veins.

24. LYMPH DRAINAGE OF THE LUNGS
 The lymph vessels originate in superficial and deep plexuses;
they are not present in the alveolar walls.
 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.

26. 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.

27. PLEURAE
 Each lung is invested by and enclosed in a serous pleural sac
that consists of two continuous membranes,
 The visceral pleura (pulmonary pleura) covers the lungs and
is adherent to all its surfaces, including the surfaces within the
horizontal and oblique fissure.
 The parietal pleura lines the pulmonary cavities, adhering to
the thoracic wall, the mediastinum, and the diaphragm.
 The root of the lung is enclosed within the area of continuity
between the visceral and parietal layers of pleura the pleural
sleeve. Inferior to the root of the lung, this continuity between
parietal and visceral pleura forms the pulmonary ligament
extending between the lung and the mediastinum.

28.  The pleural cavity is the potential space between the
visceral and the parietal layers of pleura contains a
capillary layer of serous pleural fluid, which lubricates
the pleural surfaces and allows the layers of pleura to
slide smoothly over each other during respiration.
 Its surface tension also provides the cohesion that
keeps the lung surface in contact with the thoracic wall;
consequently, the lung expands and fills with air when
the thorax expands while still allowing sliding to occur,
much like a layer of water between two glass plates.

29. PARIETAL PLEURA
 Consists of four parts:
1. Costal part (pleura) covers the internal surfaces of
the thoracic wall (sternum, ribs, costal cartilages,
intercostal muscles and membranes, and side of
thoracic vertebrae) and is separated from the wall
by endothoracic fascia.
2. Mediastinal part (pleura) covers the lateral
aspects of the mediastinum (the central
compartment of the thoracic cavity).

30. 3. Diaphragmatic part (pleura) covers the superior or
thoracic surface of the diaphragm on each side of the
mediastinum.
4. Cervical pleura extends through the superior thoracic
aperture into the root of the neck 2–3 cm superior to the
level of the medial third of the clavicle at the level of the
neck of the 1st rib, forming a cup-shaped dome over the
apex of the lung. It is reinforced by a fibrous extension of the
endothoracic fascia, the suprapleural membrane (Sibson
fascia) spanning between the 1st rib and C7 vertebra.

32. PLEURAL REFLECTION
 The relatively abrupt lines along which the parietal pleura
changes direction from one wall of the pleural cavity to
another are the lines of pleural reflection.
 The sternal line of pleural reflection is sharp or abrupt and
occurs where the costal pleura becomes continuous with the
mediastinal pleura anteriorly.
 The costal line of pleural reflection is also sharp and
occurs where the costal pleura becomes continuous with the
diaphragmatic pleura inferiorly.
 The vertebral line of pleural reflection is a much rounder,
gradual reflection where the costal pleura becomes
continuous with the mediastinal pleura posteriorly.

34. MECHANICS OF RESPIRATION
 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.

35. Lung Changes on Inspiration:
 In inspiration, the root of the lung descends and the level of
the 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.

36.  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.

37. 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.

38. TYPES 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 - abdominal type of
respiration.
 After the second year of life, the ribs become more oblique,
and the adult form of respiration is established.
 In the adult a sexual difference 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 - thoracic type of respiration. The
male uses both the thoracic and abdominal forms of
respiration, but mainly the abdominal form.

40. NEUROVASCULATURE OF LUNGS
 Each lung has a large pulmonary artery supplying blood to
it and two pulmonary veins draining blood from it.
 The right and left pulmonary arteries arise from the
pulmonary trunk at the level of the sternal angle.
 pulmonary arteries carry poorly oxygenated blood to the
lungs for oxygenation.
 The pulmonary veins, two on each side, carry well-
oxygenated blood from the lungs to the left atrium of the
heart.
 A main vein drains each bronchopulmonary segment,
usually on the anterior surface of the corresponding
bronchus.

41.  The bronchial arteries supply blood to the structures
making up the root of the lungs, the supporting tissues of
the lung, and the visceral pleura.
 The left bronchial arteries arise from the thoracic aorta.
 Right bronchial artery may arise from: superior posterior
intercostal artery.
 The distal most branches of the bronchial arteries
anastomose with branches of the pulmonary arteries in the
walls of the bronchioles and in the visceral pleura.

42.  The bronchial veins drain only part of the blood supplied to
the lungs by the bronchial arteries, primarily that distributed
near and more proximal part of the root of the lungs.
 The remainder of the blood is drained by the pulmonary
veins.
 The right bronchial vein drains into the azygos vein, and the
left bronchial vein drains into the accessory hemiazygos
vein or the left superior intercostal vein.

44. LYMPHATIC DRAINAGE
 The superficial lymphatic plexus lies deep to the visceral
pleura and drains the lung parenchyma (tissue) and visceral
pleura.
 Lymphatic vessels from the plexus drain into the
bronchopulmonary (hilar) lymph nodes in the hilum of the lung.
 The deep lymphatic plexus is located in the submucosa of the
bronchi and in the peribronchial connective tissue.
 It is largely concerned with draining structures that form the root
of the lung.
 Lymphatic vessels from this plexus drain into the pulmonary
lymph nodes located along the lobar bronchi. At the hilum of the
lung, they drain into bronchopulmonary (hilar) lymph nodes .

45.  Lymph from the superficial and deep plexuses drains from
the bronchopulmonary lymph nodes to the superior and
inferior tracheobronchial lymph nodes.
 Lymph from the tracheobronchial lymph nodes passes to
the right and left bronchomediastinal lymph trunks.
 Right bronchomediastinal trunk may first merge with other
lymphatic trunks, converging here to form the right
lymphatic duct.
 left bronchomediastinal trunk may terminate in the thoracic
duct.

47.  The nerves of the lungs and visceral pleura derive from
the pulmonary plexuses located anterior and (mainly)
posterior to the roots of the lungs.
 These nerve networks contain parasympathetic fibers from
the vagus nerves and sympathetic fibers from the
sympathetic trunks.
 The parasympathetic fibers are motor to the smooth
muscle of the bronchial tree (bronchoconstrictor),
inhibitory to the pulmonary vessels (vasodilator), and
secretory to the glands of the bronchial tree
(secretomotor).

48.  The visceral afferent fibers of CN X are distributed to the:
 Bronchial mucosa and are probably concerned with tactile
sensation for cough reflexes.
 Bronchial muscles, possibly involved in stretch reception.
 Pulmonary arteries serving pressor receptors (blood
pressure) and pulmonary veins serving chemoreceptors
(blood gas levels).

49. CLINICALS

50. ASPIRATION OF FOREIGN BODIES
 Because the right bronchus is wider and shorter and
runs more vertically than the left bronchus, aspirated
foreign bodies are more likely to enter and lodge in it
or one of its branches.
 A potential hazard encountered by dentists is an
aspirated foreign body, such as a piece of tooth,
filling material, or a small instrument.
 Such objects are also most likely to enter the right
main bronchus.

51.  Pneumothorax, Hydrothorax, Hemothorax, and Chylothorax
 Entry of air into the pleural cavity – pneumothorax resulting from
a penetrating wound of the parietal pleura or rupture of a lung
from a bullet.
 results in partial collapse of the lung.
 Hydrothorax accumulation of a significant amount of fluid in the
pleural cavity – hydrothorax may result from pleural effusion
(escape of fluid into the pleural cavity).
 With a chest wound, blood may also enter the pleural cavity
(hemothorax); this condition results more often from injury to a
major intercostal vessel than from laceration of a lung. Lymph
from a torn thoracic duct may also enter the pleural cavity
(chylothorax). Chyle, a pale white or yellow lymph fluid in the
thoracic duct containing fat absorbed by the intestines

52.  Pleuritis
 During inspiration and expiration, the normally
moist, smooth pleurae make no sound detectable
by auscultation (listening to breath sounds);
however, inflammation of the pleurae—pleuritis
(pleurisy)—makes the lung surfaces rough. The
resulting friction (pleural rub) may be heard with a
stethoscope. Acute pleuritis is marked by sharp,
stabbing pain, especially on exertion, such as
climbing stairs, when the rate and depth of
respiration may be increased even slightly.

53.  Injury to Pleurae
 The visceral pleura is insensitive to pain because its
innervation is autonomic (motor and visceral afferent). The
autonomic nerves reach the visceral pleura in company with
the bronchial vessels. The visceral pleura receives no nerves
of general sensation. The parietal pleura is sensitive to pain,
particularly the costal pleura, because it is richly supplied by
branches of the somatic intercostal and phrenic nerves.
Irritation of the parietal pleura produces local pain and referred
pain to the areas sharing innervation by the same segments of
the spinal cord. Irritation of the costal and peripheral parts of
the diaphragmatic pleura results in local pain and referred
pain along the intercostal nerves to the thoracic and
abdominal walls. Irritation of the mediastinal and central
diaphragmatic areas of the parietal pleura results in pain that
is referred to the root of the neck and over the shoulder
(C3–C5 dermatomes).

54.  Pulmonary Embolism
 Obstruction of a pulmonary artery by a blood clot (embolism)
is a common cause of morbidity (sickness) and mortality
(death). An embolus in a pulmonary artery forms when a blood
clot, fat globule, or air bubble travels in the blood to the lungs
from a leg vein. The embolus passes through the right side of
the heart to a lung through a pulmonary artery. The embolus
may block a pulmonary artery—pulmonary embolism—or
one of its branches. The immediate result is partial or
complete obstruction of blood flow to the lung. The obstruction
results in a sector of lung that is ventilated but not perfused
with blood. When a large embolus occludes a pulmonary
artery, the person suffers acute respiratory distress because of
a major decrease in the oxygenation of blood owing to
blockage of blood flow through the lung. A medium-size
embolus may block an artery supplying a bronchopulmonary
segment, producing a pulmonary infarct, an area of necrotic
(dead) lung tissue.