The document discusses the segmental anatomy of the lungs and secondary lobule. It notes that there are approximately 23 generations of dichotomous branching from the trachea to the alveolar sacs. The secondary lobule is described as the basic anatomic unit of pulmonary structure and function, measuring 1-2 cm and containing 5-15 pulmonary acini. It is supplied by a terminal bronchiole in the center and surrounded by connective tissue septa and two lymphatic systems. Diseases typically manifest in either the centrilobular or perilymphatic areas based on how they enter the lungs.

2. Segmental Anatomy of Lungs ,
Anatomy of Mediastinum and
Secondary Lobule
Gamal Rabie Agmy, MD, FCCP
Professor of chest Diseases,
Assiut university

3. There are approximately 23
generation of dichotomous
branching From trachea to the
alveolar sac
HRCT can identify upto 8th order
central bronchioles

4. An
App
An
Ap
P
 App = Apicoposterior
 An = Anterior
 P = Posterior

5. 1 1
2
3
2
&
3

7. Upper lobe
Lower lobe

8. An
App
SL
Ap
P An
SL
 SL = Superior LL
 An = Anterior
 App = Apicoposterior
 P = Posterior

9. 1 1
4 4

11. Middle lobe
Lower lobe
Lingula
Lower lobe

12. SL
S
I
L
M
SL
AN PL
AN
L,MP
 SL = Superior LL
 AN = Anterior LL
 P = Posterior LL
 L,M = Lateral, Medial LL

14. 7
6 5
8
99
10 10
1111
12

17. M 44Y with malignant liver
F 45Y with post irradiation changes
after radical mastectomy
Atelectasis in the middle lobe
Post irradiation scarring in
the right upper lobe

18. 35Y male with fever and expectoration
Pneumonic consolidation in the left upper lobe

19. 45Y male with chest pain and hemoptysis
Bronchogenic carcinoma in the left lower lobe

20. 43Y male with acute chest pain
and hemoptysis
Multiple infarcts in the lingula as
well as the left lower lobe

29. Secondary lobule
• The secondary lobule is the basic anatomic
unit of pulmonary structure and function.
Interpretation of interstitial lung diseases is
based on the type of involvement of the
secondary lobule.
It is the smallest lung unit that is surrounded
by connective tissue septa.
It measures about 1-2 cm and is made up of
5-15 pulmonary acini, that contain the alveoli
for gas exchange.

30. Secondary lobule
Basic anatomic unit of pulmonary
structure and function.
1-2 cm and is made up of 5-15
pulmonary acini
Supplied by a small bronchiole
(terminal bronchiole) in the
center, that is parallelled by the
centrilobular artery.
Pulmonary veins and lymphatics
run in the periphery
Two lymphatic systems:
 central network
 peripheral network

31. • The secondary lobule is supplied by a small
bronchiole (terminal bronchiole) in the
center, that is parallelled by the
centrilobular artery.
Pulmonary veins and lymphatics run in the
periphery of the lobule within the
interlobular septa.
Under normal conditions only a few of
these very thin septa will be seen.

32. There are two lymphatic systems: a
central network, that runs along the
bronchovascular bundle towards the
centre of the lobule and a peripheral
network, that is located within the
interlobular septa and along the pleural
linings.

33. The terminal bronchiole in the center divides into respiratory
bronchioli with acini that contain alveoli.
Lymphatics and veins run within the interlobular septa

34. Centrilobular area
It is the central part of the secondary
lobule.
It is usually the site of diseases, that
enter the lung through the airways (
i.e. hypersensitivity pneumonitis,
respiratory bronchiolitis, centrilobular
emphysema ).

35. Centrilobular area in blue
perilymphatic area in yellow

36. Perilymphatic area
Perilymphatic areais the peripheral part
of the secundary lobule.
It is usually the site of diseases, that are
located in the lymphatics of in the
interlobular septa ( i.e. sarcoid,
lymphangitic carcinomatosis, pulmonary
edema).
These diseases are usually also located in
the central network of lymphatics that
surround the bronchovascular bundle.

37. Raoof, S. , CHEST 2006; 129:805

39. 40

40. A group of terminal bronchioles
41

41. Unit of lung (0.5-3 cm)
Irregularly polyhedral
Supplied by a group of terminal bronchioles
and accompanying pulmonary arterioles
surrounded by lymph vessels
Demarcated by “interlobular septa”
pulmonary veins
pulmonary lymphatics
connective tissue stroma

42. Accompanying pulmonary arterioles
43

43. Surrounded by lymph vessels
44

44. Pulmonary veins
45

45. Pulmonary lymphatics
46

46. 47
Connective Tissue Stroma

48. HRCT
PATTERN
INCREASED
LUNG
ATTENUATION
LINEAR AND
RETICULAR
OPACITIES
NODULESAND
NODULAR
OPACITIES
PARENCHYMAL
OPACIFICATION
consolidation
Ground glass
DECREASED
LUNG
ATTENUATION
CYSTIC LESIONS,
EMPHYSEMA,AND
BRONCHIEACTASIS
MOSAIC
ATTENUATION AND
PERFUSION
AIR TRAPPING ON
EXPIRATORY
SCANS
49