Lung
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General features
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Composed of lobes and lobules.
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Volume is mostly (85%) air
Mostly in the alveolar ducts and
alveolar sacs
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fed by bronchi and bronchioles
networks of capillaries in their
walls.
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Also present: larger blood
vessels, etc.
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1
Lung
Lung has no ability to actively inflate
or deflate
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Contraction and relaxation of
the diaphragm muscle
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thin sheet-like skeletal muscle
divides the thoracic and
abdominal cavity
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sometimes intercostals
2
Lung
lung lies directly against thoracic
body wall and diaphragm
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activities tend to increase or
decrease the volume of the
thoracic cavity
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by pulling air into, or pushing air out
of, respiratory tract.
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3
Lung
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Structural components
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Secondary bronchi
branch from 1°
bronchus in each lung
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Tertiary bronchi
branch from 2nd
bronchi
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have an inside
diameter > 1.0 mm
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4
Lung
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Lumenal epithelium
Smaller bronchi tends to have wavy
outline
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Larger secondary bronchi
pseudostratified ciliated
columnar
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Smaller secondary bronchi
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ciliated simple columnar
Larger tertiary bronchi
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ciliated simple columnar
5
Lung
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Smaller tertiary bronchi
ciliated simple columnar to
ciliated simple cuboidal
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Sometimes has scattered goblet
cells
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epithelium glandular, mucus
tubular extensions into wall to
mixed bronchial glands
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6
Lung
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LP: thin; bronchial glands.
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Spiral SMT in base of mucosa
First appears in lower parts of
primary bronchi.
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Not muscularis mucosae
Orientation intermediate between
longitudinal and circular
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contraction causes decreased
diameter and length of tube.
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7
Lung
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Peripheral to SMT
scattered hyaline cartilage and mixed
bronchial glands.
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Typical characteristics of hyaline cartilage
may be evident
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cells not be in clumped
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perilacunar matrix not basophilic
Cartilage is interconnected
cylindrical network in the wall of the
bronchi.
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Prevent collapse of the tube.
8
Lung
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Tunica adventitia: dense C.T.
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small muscular arteries and veins
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usually thin
continuous with the dense CT of
pulmonary parenchyma
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composed mainly of alveolar ducts
and sacs
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9
Lung
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Bronchioles
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Inside diameter < 1.0 mm
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Mucosa
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Lumenal epithelium
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ciliated
simple columnar or
cuboidal
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smaller bronchioles
non-ciliated simple
cuboidal
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epithelium folded in cross
section
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10
Lung
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Bronchioles
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Seromucous glands usually absent.
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LP thin
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Discontinuous Layer of SMT
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Submucosa very thin
11
Lung
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Bronchioles
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No hyaline cartilage tissue
tube held open by thick wall and
by surfactant coating on inside
surface
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Tunica adventitia: thin
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mainly dense CT
continuous with CT of
parenchyma
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12
Lung
Special types of bronchioles
Terminal bronchiole
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Not the last or smallest
bronchiole type
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A continuous wall of typical
bronchiole-wall components.
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End portions
special lumenal epithelium of
cuboidal glandular cells
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called Clara cells, Aka Club
cells or bronchiolar
exocrine cells
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secrete a special surfactantlike substance.
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13
Lung
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Respiratory bronchiole
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Last, smallest type of bronchiole
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discontinuous wall
lumenal epithelial cells in the thick-wall areas are Club cells
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14
Lung
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Respiratory bronchiole
Alveoli (singular: alveolus) compose
part of the wall as well
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Alveolus is a very tiny thin-walled,
hemispherical structure
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In the wall CT
capillary network for gasexchange (aka respiratory gas
exchange)
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with the air in the alveolus.
These bronchioles branch
15
Lung
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Alveolar ducts and sacs
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Exclusively alveoli
Compose about 95% of the lungs
volume
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compose the parenchyma
Alveoli are easily stretched
during inhalation
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almost all of the increase in
lung volume during inhalation
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due to increased volume of
the alveolar ducts and sacs
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16
http://www.udel.edu/
biology/Wags/
histopage/illuspage/
Lung
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Alveolar ducts
Alveolar ducts branch from
respiratory bronchioles
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lead to alveolar sacs
Smaller inside diameter than
alveolar sacs
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may not be evident in the
section
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Lung
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http://www.udel.edu/
17
biology/Wags/
histopage/illuspage/
Alveolar sacs
Not possible to distinguish
alveolar sacs from alveolar ducts
in the parenchyma
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occasionally you may find
such a structure with an
unusually wide lumen
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more likely an alveolar sac
18
Lung
Air in alveolar ducts and sacs is
relatively stagnant
At rest;
a pO2 about 66% of outside
air
pCO2 much higher than
outside air
Because breathing involve only
partial exchanges.
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19
Lung
Alveolar ducts and alveolar sacs
lie in all possible orientations
Adjacent alveolar ducts and
sacs have a common denseCT with capillary between
them
don't have completely
separate walls
Capillaries in that dense CT
exchange gases with the air
spaces on both sides
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20
Lung
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Structure of an alveolus
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Lumenal epithelium:
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simple squamous epithelium
monomolecular layer
surfactant substance
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eliminates water surface
tension
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would be of sufficient
strength to collapse the
alveolus
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Lung
•
http://www.udel.edu/
21
biology/Wags/histopage/
illuspage/ire/ire2.gif
Surfactant is a phospholipid
not well developed until
the last week or two of
gestation
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infants born a few to
several weeks
prematurely may have
great difficulty in inhaling.
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22
Hydrogen
bond
H
Hydrogen
bond
O
H
H
O
H
H-bonds
H-bonds
pulls water
pulls water
molecules
molecules
closer closer
Smaller
volume
Surfactant breaks up
H-bonds and surface
tension breaks up
Surfactant
H-bonds and surface tension
23
Alveolus
without water
no surface tension
(but dead cells)
high compliance
Alveolus
without water
no surface tension
(but dead cells)
high compliance
Alveolus
with water
surface tension
(but living cells)
low compliance
Alveolus
with water
surface tension
(but living cells)
low compliance
24
Alveolus
with surfactant
breaks surface tension
(but living cells)
high compliance
Alveolus
with surfactant
breaks surface tension
(but living cells)
high compliance
Smaller
volume
Alveolar type II
Alveolar type I
Alveolus
25
Lung
Lumenal epithelium is difficult to
see well even on high power, and
without special staining the
surfactant layer is not visible
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Squamous epithelial cells, aka
pneumocyte I or alveolar type I
cells
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26
25
27
Lung
Occasionally in the lumenal
epithelium
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second, scattered, non- squamous
cell type
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more spherical in shape
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Alveolar type II (septal) cell
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surfactant- secretor
Dust cell
Also, phagocytic Dust Cells, aka
alveolar macrophages (from
monocytes)
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on the lumenal surface ingesting
dust particles breathed in
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28
Lung
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Alveolar type I
Under the alveolar lumenal epithelium
Alveolar type II
thin laver of dense CT + capillary
network
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laver is about as thick as
diameter of capillaries
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lie directly against the lumenal
epithelium
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have a common basement
membrane with the lumenal
epithelium
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SMFs, sometimes in bundles
29