The document summarizes the gross structures and functions of the lower respiratory tract. It describes the trachea as a tubular passageway that branches into the two primary bronchi. The bronchi continue branching into smaller bronchioles that lead to terminal bronchioles and alveoli where gas exchange occurs. It also details the lungs, noting they are highly elastic and each has an apex, lobes divided by fissures, and a root containing bronchial tubes and vessels. The pleurae are membranes that line the thoracic wall and cover the lungs, with a potential space between that contains lubricating fluid.

1. •Gross structures and functions of the lower
respiratory tract
1

2. Gross structures and functions of the lower
respiratory tract
• Structurally, the respiratory system
consists of two parts:
I. the upper respiratory system includes
the nose, nasal cavity, pharynx,
larynx, and associated structures.
II. the lower respiratory system includes
the, trachea, bronchi, and lungs
2

3. The Trachea
3

4. The Trachea
• The trachea or windpipe, is a tubular passageway
for air that is about 12 cm long and 2.5 cm in
diameter.
• It is located anterior to the esophagus and extends
from the larynx to the superior border of the fifth
thoracic vertebra (T5), where it divides into the
right and left primary bronchi.
• It transports air to and from the lungs, Trachea
4

5. The Trachea,,,
5

6. The Trachea,,,
• The walls of the trachea are supported by 15-20 incomplete C-shaped
tracheal cartilages that hold the passageway open in spite of the air
pressure changes that occur during breathing
• The open portion of the tracheal cartilages is oriented posteriorly
against the esophagus
• This orientation allows the esophagus to expand slightly as food
passes down to the stomach.
6

7. The Trachea,,,
• This incomplete, “C” shaped cartilaginous tracheal rings (the posterior gap) is
closed by the involuntary trachealis muscle, connecting the ends of the
tracheal rings.
 Due to this the posterior wall of the trachea is flat
• A ridge on the internal aspect of the last tracheal cartilage, called the
carina, marks the point where the trachea branches into the two main
(primary) bronchi.
• The mucosa that lines the carina is highly sensitive to irritants, and the
cough reflex often originates here
7

8. The Trachea,,,
8

9. The Bronchial Tree
The collective term “bronchial tree”
refers to the bronchi and all of their
subsequent branches
The bronchi are the airways of the
lower respiratory tract.
At the level of the 3rd or 4th thoracic
vertebra, the trachea bifurcates into the
left and right main bronchi.
9

10. The Bronchial Tree,,,
Main branching structure and components:
Trachea → carina → main bronchi → lobar bronchi → segmental bronchi →
terminal bronchioles → respiratory bronchioles → alveolar duct → alveolar sac →
alveoli
 The walls of the trachea & bronchi are supported by C-shaped of cartilage
 The right main bronchi has different angle of inclination.
 The left primary bronchus diverges at a greater angle than the right primary
bronchus to reach the left lung.
10

11. The Bronchial Tree,,,
11

12. The Bronchial Tree,,,
• The left main bronchus passes inferolaterally, inferior to the arch of
the aorta & anterior to the esophagus & thoracic aorta, to reach the
hilum of the lung.
• Each primary bronchus divides into secondary lobar bronchi 2 on
the left and 3 on the right, each of which supplies each lobe of the
lung.
• Each lobar bronchus divides into several tertiary segmental bronchi
that supply the bronchopulmonary segments. 12

13. The Bronchial Tree,,,
13

14. The bronchopulmonary segments are
The largest subdivisions of a lobe.
 Pyramidal-shaped segments of the lung.
Separated from adjacent segments by connective tissue septa.
Supplied independently by a segmental bronchus and a tertiary branch of the
pulmonary artery.
 Named according to the segmental bronchi supplying them.
Drained by intersegmental parts of the pulmonary veins.
Usually 18–20 in number (10 in Rt; 8–10 in Lt).
 Surgically resectable.
14

15. Tracheobronchial tree and bronchopulmonary segments,,,
15

16. Tracheobronchial tree and bronchopulmonary segments,,,
• Beyond the tertiary segmental bronchi, there are 20 to 25 generations that
eventually end as terminal bronchioles.
• Bronchioles lack cartilage in their walls.
• Conducting bronchioles transport air but lack glands or alveoli.
• Each terminal bronchiole gives rise to several generations of respiratory
bronchioles.
• The pulmonary alveolus is the basic structural unit of gas exchange in the lung.
• Due to the presence of the alveoli, the respiratory bronchioles are involved both
in air transportation and gas exchange.
• Each respiratory bronchiole gives rise to 2–11 alveolar ducts then to 5–6 alveolar
sacs. 16

17. Gross structures and function of the lung
and pleura
17

18. Gross structures and function of the lung and
pleura,,,
The thoracic cavity is divided into 3 compartments:
Right pulmonary cavity
 Left pulmonary cavity
A central mediastinum
18

19. Gross structures and function of the lung and
pleura,,,
Transverse section of the thoracic cavity
Sagittal section of the
thoracic cavity
19

20. The pulmonary cavities
• Right and left pulmonary cavities: contain the lungs & pleurae.
• A central mediastinum: contains all other thoracic structures ,the
heart, thoracic parts of the great vessels, thoracic part of the trachea,
esophagus, thymus, and lymph nodes.
• It extends vertically from the superior thoracic aperture to the
diaphragm and anteroposteriorly from the sternum to the thoracic
vertebral bodies.
20

21. Gross structures and function of the lungs,,,
Lungs: They are the principal organs of respiration.
The most important function of the lungs is to take oxygen from the
environment and transfer it to the bloodstream.
The lungs also perform several important non-respiratory functions
that are vital for normal physiology
• Non-respiratory functions of the lungs, include:
• Filtration
• Immune defence
• Blood resevoir
• Metabolism etc
• Healthy lungs in living people are normally light, soft, and spongy.
21

22. Gross structures and function of the lungs,,,
22

23. Gross structures and function of the lungs,,,
• Lungs are highly elastic structures.
• Each lung lies free in its own pleural cavity
• Its only attachment is at its root.
• The lungs connect the with trachea by bronchii and heart by
pulmonary vessels
• The anterior, lateral, and posterior surfaces of a lung contact the ribs
and form a continuously curving costal surface 23

24. Gross structures and function of the lungs,,,
Each lung has the following parts:
An apex, superior end of the lung, a base
is concave inferior surface of the lung.
 2 or 3 lobes, created by1 or 2 fissures.
3 surfaces ;costal, mediastinal &
diaphragmatic.
3 borders; anterior, inferior & posterior.
24

25. Gross structures and function of the lungs,,,
• The right lung
• Has 2 fissures oblique &
horizontal that divide it into 3
right lobes: superior, middle &
inferior.
• Is larger and heavier than the left.
• The anterior border of the right
lung is relatively straight.
• Has 1 oblique fissure dividing it into 2
lobes, superior and inferior.
• The anterior border of the left lung has a
deep cardiac notch
• Has tongue-like process, the lingula w/c
extends below the cardiac notch& slides
in & out of the costomediastinal recess
during inspiration and expiration
•Left lung
25

26. Right lung Left lung
26
Gross structures and function of the lungs,,,

27. Gross structures and function of the lungs,,,
• Note: The costal surface of the lung is large, smooth, and convex.
• The mediastinal surface of the lung is concave.
• The mediastinal surface includes the hilum, w/c receives the root of the
lung.
• The diaphragmatic surface of the lung is concave & forms the base of
the lung.
• The concavity is deeper in the right lung b/c of the higher position of
the right lobe of the liver. 27

28. Root of the lungs
• The root of each lung is a short tubular collection of structures that
together attach the lung to structures in the mediastinum.
• The lung root is enclosed within the area of continuity b/n the
parietal & the visceral layers of pleura the pleural sleeve
(mesopneumonium).
• The vagus nerves pass posterior to the roots of the lungs, while the
phrenic nerves pass anterior to them.
28

29. Root of the lungs,,,
29

30. Root of the lungs,,,
The lung`s root has, bronchi, pulmonary artery, 2 pulmonary veins, the
pulmonary plexuses of nerves and lymphatic vessels..
If the root is sectioned before branching of the main (primary) bronchus and
pulmonary artery, its general arrangement is different on both lungs.
• Pulmonary artery: superiormost on left (the superior lobar or “eparterial”
bronchus may be superiormost on the right).
• Superior & inferior pulmonary veins: anteriormost & inferiormost,
respectively.
30

31. Root of the right lung,,,
31
NOTE HEAR!!
pulmonary
arteries are called
arteries because
they are leaving
the heart.
In this case the
pulmonary veins
are oxygen-rich.
Veins also
return blood to
the heart.

32. Relations of root of the lung
•On the mediastinal surface of the
right lung the major grooves are :
1. Groove for arch of azygos vein
2. Groove for 1st rib
3. Groove for superior vena cava
4. Groove for inferior vena cava
5. Groove for esophagus
6. Groove for brachiocephalic vein
32

33. Other relations of root of the lung
33
On the mediastinal surface of
the left lung the major grooves
are
1. Groove for arch of aorta
2. Groove for descending aorta
3. Groove for 1st rib
4. Groove for subclavian artery
and others.

34. The Pleurae
• Around each lung is a flattened
sac whose walls consist of a
serous membrane called
pleura.
• The outer layer of this sac is
the parietal pleura, whereas
the inner layer, directly on the
lung, is the visceral pleura.
34

35. The Pleurae,,,
The parietal pleura lines the pulmonary cavities, adhering to the thoracic wall,
the mediastinum, and the diaphragm.
• The pleural cavity is a potential space b/n visceral and parietal pleurae that
contains serous pleural fluid.
• This fluid lubricates the pleural surfaces and allows the layers of pleura to slide
smoothly over each other during respiration.
• In the area where these vessels enter the lung, the parietal pleura is continuous
with the visceral pleura, which covers the external lung surface
35

36. The visceral pleura
• The visceral pleura is continuous with the parietal pleura at the hilum of
the lung.
• The visceral pleura closely covers the lung & adheres to all its surfaces,
including those within the horizontal and oblique fissures
• In cadaver dissection, the visceral pleura cannot usually be dissected
from the surface of the lung.
• The visceral pleura is innervated by visceral afferent nerves that
accompany bronchial vessels.
36

37. The parietal pleura
The parietal pleura consists of 4
parts:
Costal,
Mediastinal
Diaphragmatic and
Cervical pleura
37

38. The parietal pleura,,,
• The costal pleura lines the inner surfaces of the
ribs, the costal cartilages, the intercostal spaces,
the vertebral bodies & the back of the sternum.
• The mediastinal part covers the lateral aspects of
the mediastinum.
• It is continuous with costal pleura anteriorly and
posteriorly, and with the diaphragmatic pleura
inferiorly.
38

39. The parietal pleurae,,,
• At the hilum of the lung, it is the mediastinal
pleura that reflects laterally onto the root of
the lung.
• The diaphragmatic part of the parietal
pleura covers the superior surface of the
diaphragm, except along its costal
attachments and where the diaphragm is
fused to the pericardium.
39

40. The parietal pleurae,,,
• A thin, more elastic layer of endothoracic fascia, the phrenicopleural fascia,
connects the diaphragmatic pleura with the muscular fibers of the
diaphragm
• The cervical pleura covers the apex of the lung.
• It is a superior continuation of the costal & mediastinal parts of the parietal
pleura.
• The cervical pleura forms pleural cupula, cover the apex that reaches 2–3 cm
superior to the level of the medial third of the clavicle at the level of the neck
of the 1st rib.
40

41. The parietal pleurae,,,
 The cervical pleura is
reinforced by a fibrous
extension of the endothoracic
fascia, the suprapleural
membrane(Sibson fascia).
 The membrane attaches to the
internal border of the 1st rib
and the transverse process of
C7 vertebra.
41

42. Pleural recesses
• The lungs do not completely occupy the pleural
cavities especially during expiration.
• The potential pleural spaces are the
costodiaphragmatic recesses.
• Similar but smaller pleural recesses are the
costomediastinal recesses.
• The potential costomediastinal recesses; the
left recess is potentially larger (less occupied)
because of the cardiac notch in the left lung.
• The inferior borders of the lungs move farther
into the pleural recesses during deep
inspiration. 42

43. Innervation of the pleurae
• The parietal pleura: The costal, cervical &
the periphery of the diaphragmatic portion
are innervated by the intercostal nerves.
The mediastinal &central part of the
diaphragmatic pleura are innervated by the
phrenic nerves.
• The visceral pleura & the lung itself
receives innervation from the autonomic NS.
43

44. Vasculature of lungs and pleurae,,,
• Each lung has a pulmonary artery
supplying blood to it & 2
pulmonary veins draining blood
from it .
• The Rt & Left pulmonary arteries
arise from the pulmonary trunk at
the level of the sternal angle &
carry poorly oxygenated (venous)
blood to the lungs for oxygenation 44

45. Vasculature of lungs and pleurae,,,
• The right & left superior lobar arteries arise
before entering the hilum.
• Lobar arteries divide into tertiary segmental
arteries.
• The arteries & bronchi are paired in the lung.
• Consequently, a paired secondary lobar artery
and bronchus serves each lobe.
 Each pulmonary artery becomes part of the root of the
corresponding lung& divides into secondary lobar arteries.
45

46. Vasculature of lungs and pleurae,,,
• Superior & inferior pulmonary vein on each side, carry oxygen-rich
blood from corresponding lobes of each lung to the left atrium of the heart.
• The middle lobe vein is a tributary of the right superior pulmonary vein.
• The pulmonary veins run independently of the arteries and bronchi in the
lung.
• Bronchial arteries supply blood for nutrition of the structures making
up the root of the lungs, the supporting tissues of the lungs, and the visceral
pleura.
46

47. Vasculature of lungs and pleurae,,,
• Left bronchial arteries arise from the
superior thoracic aorta.
• The origin of the right bronchial
artery is variable; it may arise:
1. from the right 3rd posterior
intercostal artery.
2. from a common trunk shared with the
left superior bronchial artery.
3. directly from the aorta
47

48. Vasculature of lungs and pleurae,,,
48

49. Vasculature of lungs and pleurae,,,
• The small bronchial arteries provide branches to the upper esophagus.
• The small bronchial aas pass along the posterior aspects of the main bronchi, as
far distally as the respiratory bronchioles.
• The most distal branches of the bronchial arteries anastomose with branches
of the pulmonary arteries in the walls of the bronchioles and in the visceral
pleura.
• The parietal pleura is supplied by the arteries that supply the thoracic wall.
49

50. Vasculature of lungs and pleurae,,,
• The bronchial veins drain the more proximal
capillary beds supplied by the bronchial arteries.
• The right bronchial vein drains into the azygos
vein, and
• The left bronchial vein drains into the accessory
hemi-azygos vein or the left superior intercostal
vein.
• Bronchial veins also receive some blood from
esophageal veins.
50

51. Vasculature of lungs and pleurae,,,
• The pulmonary lymphatic plexuses communicate freely.
• The superficial lymphatic plexus lies deep to the visceral pleura & drains lymph
from surface of the lung & visceral pleura then drain into the
bronchopulmonary(hilary) lymph nodes.
• The deep bronchopulmonary lymphatic plexus is located in the submucosa of the
bronchi, they initially drain into the intrinsic pulmonary lymph nodes then continue
to follow the bronchi and pulmonary vessels to the hilum of the lung.
• From both the superficial & deep lymphatic plexuses drains to the superior and
inferior tracheobronchial lymph nodes.
51

52. Vasculature of lungs and pleurae,,,
52

53. Vasculature of lungs and pleurae,,,
• Lymph from the tracheobronchial lymph nodes passes to the right
and left bronchomediastinal lymph trunks, the major lymph
conduits draining the thoracic viscera.
• These trunks usually terminate on each side at the venous angles
• The left bronchomediastinal trunk may terminate in the thoracic duct.
• Lymph from the parietal pleura drains into the lymph nodes of the
thoracic wall (intercostal, parasternal, mediastinal, and phrenic).
53

54. Nerves of the lungs
The nerve supply of the lungs is derived from anterior & posterior pulmonary
branches of the vagus which are joined by rami of 2nd, 3r & 4th thoracic
sympathetic nerves to form the pulmonary plexus.
• These plexus contain parasympathetic, sympathetic & visceral afferent fibers.
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).
54

55. Nerves of the lungs,,,
• The sympathetic fibers are:
 Inhibitory to the bronchial muscle (bronchodilator),
 Motor to the pulmonary vessels (vasoconstrictor) and
Inhibitory to the alveolar glands of the bronchial tree.
• The visceral afferent fibers are either reflexive or nociceptive.
• Reflexive visceral afferent fibers with cell bodies in the sensory
ganglion of the vagus nerve (CN X) accompany the parasympathetic
fibers
55

56. Nerves of the lungs,,,
Reflexive visceral afferent fibers conveying impulses centrally from nerve
endings associated with the:
Bronchial mucosa, probably in association with tactile sensation for cough
reflexes.
Bronchial muscles, possibly involved in stretch reception.
Pulmonary arteries, serving pressor receptors (receptors sensitive to blood
pressure).
Pulmonary veins, serving chemoreceptors (receptors sensitive to blood gas
levels). 56

57. Innervation of the lungs,,,
57

58. The end!!!
58