The oblique fissure of lung follows the 6th rib. The embryonic germ layer that gives rise to the inner lining of the respiratory tract is endoderm. Trachea is made up of hyaline cartilage. The part of lung aerated by respiratory bronchioles is called the pulmonary unit. Surfactant is produced by type 2 alveolar cells. The most anterior structure in the root of the lung is the bronchus.

1. Gross anatomy and development
of respiratory system
Dr Laxman Khanal

2. Try these……
• The oblique fissure of lung follows…………rib.
a. 5th b. 6th c. 7th d. 8th
• Which of the following embryonic germ layer
give rise to the inner lining of the respiratory
tract??
a. Ectoderm b. mesoderm c. endoderm d.
neural crest cells

3. • Trachea is made up of ….cartilage
a. Hyaline b. elastic c. fibro cartilage d. all
• Part of lung aerated by respiratory
bronchioles is called as….
a. Pulmonary unit b. broncho pulmonary unit

4. • Surfactant is produced by which alveolar
cells??
a. type1 b. type 2 c. both d. none
• Most anterior structure in root of the lung
is..
a. Pulmonary vein b. pulmonary artery
c. Bronchus d. bronchial artery

5. • Consists of respiratory and conducting zones
• Respiratory zone
– Site of gas exchange
– Consists of bronchioles, alveolar ducts, and alveoli
• Conducting zone
– Provides rigid conduits for air to reach the sites of
gas exchange
– Includes all other respiratory structures
(e.g., nose, nasal cavity, pharynx, trachea)

6. Trachea
• Also called as wind-pipe.
• Extend from end of larynx(C6) to the point of
bifurcation ( T4).
• Its about 15cm in length.
• The trachea has 15 to 20 C-shaped bars of
hyaline cartilage that prevent it from
collapsing.

8. • The carina is the upward-directed ridge seen
internally at the bifurcation and is a landmark
during bronchoscopy.
• The trachea is supplied mainly by the inferior
thyroid arteries. Its smooth muscle is supplied
by parasympathetic and sympathetic
fibers, and pain fibers are carried by the vagi.

10. Main bronchus
• Trachea divide into two main bronchus- right
and left.
• The right main bronchus is shorter, wider, and
more vertical than the left.
• Because it is in almost a direct line with the
trachea, foreign objects traversing the trachea
are more likely to enter the right main
bronchus.

12. Bronchial tree
• Main bronchi- lobar bronchi- segmental
bronchi- terminal bronchioles- respiratory
bronchioles ( duct- atrium-saccules- alveoli)
• The bronchioles are very narrow and have a
diameter of 1mm or less. Respiratory
brochioles bronchioles eventually lead into
small sac-like structures called the alveoli.

14. • Pulmonary unit
Each respiratory bronchiole aerates a small part of
the lung known as a pulmonary unit. The respiratory
bronchiole ends in microscopic passages like-
alveolar ducts, atria, air saccules and pulmonary
alveoli.
• The alveolus is the basic structural unit of gas
exchange in the lung.
• New alveoli continue to develop until the age of 8
yrs, by which there are about 300 million alveoli.

15. Pleura
• The pleura is a thin, glistening, slippery serous
membrane, inflammation of which is called
pleurisy.
• The pleura lines the thoracic wall and
diaphragm, where it is known as the parietal
pleura. It is reflected onto the lung, where it is
called the visceral pleura.
• Both are derivatives of mesoderm germ layer

16. • The pleural cavity, which is the potential space
between the two layers, contains only a thin
film of fluid.
• Air in the pleural cavity (pneumothorax)
results in collapse of the lung.
• Irritation of the parietal pleura causes pain
referred to the thoraco-abdominal wall to the
shoulder (phrenic nerve).
• Visceral pleura is pain insensitive.

17. • The parietal pleura has
costal, mediastinal, diaphragmatic parts and
a cupola.
• the cupola of the pleura and the apex of the
lung project upward into the neck, hence may
be injured in wounds of the neck.
• Their highest point is 2 to 3 cm above the level
of the medial third of the clavicle. The
sympathetic trunks and first thoracic nerves
are found posterior to the cupola.

19. Lungs
• The lungs are the essential organs of
respiration.
• The Latin word pulmo, lung, gives rise to the
adjective pulmonary.
• Each lung is attached by its root and
pulmonary ligament to the heart and trachea
but is otherwise free in the thoracic cavity.

20. • The main bronchus enters the hilum and
subdivides within the substance of the lung to
form the "bronchial tree.“
• The right lung, is heavier, shorter (the right
dome of the diaphragm being higher) and wider
(the heart bulging more to the left) than the left.

21. Lungs

22. • Each lung has an apex, three surfaces
(costal, medial, and diaphragmatic), and three
borders (anterior, inferior, and posterior).
• The right lung is divided into
upper, middle, and lower lobes by oblique and
horizontal fissures
• The left lung has usually only upper and lower
lobes, separated by an oblique fissure.

23. • The bronchi and pulmonary vessels, which
extend from the trachea and
heart, respectively, collectively form the root
of the lung.
• The part of the medial surface where these
structures enter the lung is known as the
hilum of lung.

24. Roots and hila of lungs

25. • The inferior limit of the lung crosses rib 6 in
the midclavicular line and rib 8 in the
midaxillary line and then proceeds toward the
10th thoracic vertebra.
• Inferior limit of pleura is rib 8 in MCL, rib 10 in
MAL and 12th thoracic vertebra along para-
vertebral line.

26. • The oblique fissure follows approximately the
line of rib 6 as far as the inferior border of the
lung.
• The horizontal fissure begins at the oblique
fissure near the midaxillary line (of the right
side), at about the level of rib 6.
• Important for localization of particular lobe
during chest injury.

27. Right lung
– related
structures

28. Left lung
– related
structures

29. Bronchopulmonary segment
• A bronchopulmonary segment is the area of lung
supplied by a segmental bronchus and its
accompanying pulmonary artery branch.
• Tributaries of the pulmonary vein tend to pass
intersegmentally between and around the
margins of segments.
• A bronchopulmonary segment is the
smallest, functionally independent region of a
lung and the smallest area of lung that can be
isolated and removed without affecting adjacent
regions.

32. Clinical importance
• The normal respiratory rate is 12 - 20 breaths
per minute. A faster breathing rate is called
tachypnoea. Tachypnoea is an important sign
of respiratory disease.
• If the breathing rate is increased for a long
period of time, dehydration can occur. So it is
important to give fluids to patients with
respiratory disease or tachypnoea from other
causes.

33. • Types of respirations
Abdominal type of respiration
Thoracic type of respiration
• Bronchogenic carcinoma
Begins by involving the glands around the
large bronchi.
May cause hoarseness in voice.

34. • Chronic obstructive pulmonary disease
(COPD): Damage to the lungs results in
difficulty blowing air out, causing shortness of
breath. Smoking is by far the most common
cause of COPD.
• Pleural effusion: Fluid builds up in the pleural
space. If large, pleural effusions can cause
problems with breathing.
• Pneumothorax: Air in the pleural space .

35. Development of respiratory system
Formation of lung bud ( respiratory
diverticulum).
• Its an outgrowth from the ventral aspect of
foregut ( endodermal tube ).
• This give rise to the larynx, trachea, bronchi
and lungs.
• Hence epithelium of the internal lining of the
larynx, trachea, and bronchi, as well as that of
the lungs, is entirely of endodermal origin.

36. • cartilaginous, muscular, and connective tissue
components of the trachea and lungs are derived
from splanchnic mesoderm surrounding the
foregut.
• When the diverticulum expands two longitudinal
ridges, the tracheoesophageal ridges, separate it
from the foregut. when these ridges fuse to
form the tracheoesophageal Septum, the
foregut is divided into a dorsal portion, the
esophagus, and a ventral Portion, the trachea
and lung buds.

37. Abnormalities in partitioning of oesophagus and
trachea by tracheoesophageal septum results in
esophageal atresia and tracheoesophageal
fistula.

39. • During separation from foregut, lung bud forms
trachea and two lateral out pocketing, bronchial
buds.
• Each of these buds enlarges to form right and left
main bronchi. Later right one divide into 3 and
left into 2 secondary bronchi.
• During further development, secondary bronchi
divide repeatedly forming tertiary (segmental)
bronchi, creating the bronchopulmonary
Segments Of The adult lung.

41. Growth of the lungs after birth is primarily due to an
increase in the number of respiratory bronchioles
and alveoli and not to an increase in the size of the
alveoli. New alveoli are formed during the first 10
years of postnatal life.

42. • After a pseudoglandular and canalicular
phase, cells of the respiratory bronchioles
change into thin, flat cells, type I alveolar
epithelial cells, intimately associated with
capillaries. In the seventh month, gas
exchange between the blood and air in the
primitive alveoli is possible.

43. • Before birth, the lungs are filled with fluid
with surfactant, which is produced by type II
alveolar epithelial cells which forms a
phospholipid coat on the alveolar membranes.
At the beginning of respiration, the lung fluid
is reabsorbed except for the surfactant
coat, which prevents the collapse of the
alveoli during expiration by reducing the
surface tension at the air– blood capillary
interface.

44. Queries ???

45. Try these……
• The oblique fissure of lung follows…………rib.
a. 5th b. 6th c. 7th d. 8th
• Which of the following embryonic germ layer
give rise to the inner lining of the respiratory
tract??
a. Ectoderm b. mesoderm c. endoderm d.
neural crest cells

46. • Trachea is made up of ….cartilage
a. Hyaline b. elastic c. fibro cartilage d. all
• Part of lung aerated by respiratory
bronchioles is called as….
a. Pulmonary unit b. broncho pulmonary unit

47. • Surfactant is produced by which alveolar
cells??
a. type1 b. type 2 c. both d. none
• Most anterior structure in root of the lung
is..
a. Pulmonary vein b. pulmonary artery
c. Bronchus d. bronchial artery