HISTOLOGY - BIOL 4000 - LECTURE NOTES
SYSTEM TEXT - POWERPOINT
I. Respiratory system - General purpose and
A. Potentially useful links:
system histology, normal and diseased
More notes and histology
Computer imaging and radiology of respiratory system
B. Function - provide oxygen to blood and
remove CO2 from it.
C. Three principle subdivisions of the
AIR CONDUCTING PORTION
a. Nasal cavity
g. These provide a
passageway to and from lungs
h. These components
also "condition" the inspired air (i.e. moistens, removes particles
and some noxious gases, warms air)
b. aveolar ducts
c. alveole used for
MUSCULOELASTIC VENTILATION APPARATUS
- muscles, e.g. intercostals and diaphragm, used for moving air in and out of
the lungs. This third portion will be delt with more in your anatomy classes.
4. Our discussions will deal with
the first two of the above subdivisions, and more specifically with structures
below the larynx.
C. In components of the respiratory tract
including the trachea and structures below we find
various types depending on what part of the tree your in
a. Elastic fibers
associated with tissues allows expansion followed by passive contraction.
a. Smooth muscle
allows change in diameter of passageway.
5. However, the
presence or absence of the above listed
components will differ depending on which specific portion of the respiratory
tree we're talking about.
Hyaline cartilage is found at the base of the
lamina propria in the trachea, primary bronchi, and intrapulmonary bronchi.
a. This hyaline
cartilage gives support to respiratory tree.
D. Basic components of the respiratory tree -
of general structure
Trachea and primary bronchi
a. Mucosal epithelium
- the mahority of the cells form a
pseudostratified, columnar, ciliated epithelium
b. Interspersed among
the columnar, ciliated epithelial cells are,
(muscus secreting) are interspersed among the more numerous columnar ciliated
apical microvilli (may be immature goblet
Basal cells - possibly stem cells that will
divided to provide replacements for dead or laost cells of the epithelium.
contains many lymphocytes
that are supported by a meshwork of elastic and
c. A band of elastic
fibers called the membrana elastica
interna separates the mucosa from the sub mucosa.
composed of loose connective tissue and contains the secretory components of
serous and mucous glands
whose ducts empty into the traceal lumen.
the most prominent tissue layer
C-shaped rings of hyaline cartilage
(smooth muscle) fills the intervals between the cartilage rings.
cartilage and muscle make the trachea a very rigid structure.
(also called secondary
3 in right lung, 2 in left
intrapulmonary bronchi each each extend into a pulmonary lobe of the lung and
thus are sometimes called lobar
and subsequent bronchi undergo repeated branching culminating in the formation
intrapulmonary bronchi are histologically similar to the trachea and primary
Differences in the histology develop as the
bronchi become smaller.
Cartilage rings are reduced to irregular plates of cartilage.
* A band
of circular smooth muscle develops.
cells in the epithelium become less numerous.
Epithelium becomes reduced in height and simple columnar with less cilia.
Lymphatic nodules may be present in lamina
propria, particularly at branching points.
diameter 1 mm or less
Bronchioles lack cartilage
muscle layer is relatively thicker.
non-ciliated Clara cells
are present in epithelium.
Epithelium in simple columnar with fewer
No glands in lamina propria
b. 4 types of
- branch repeatedly, final branches are the terminal bronchioles
- form connection between large bronchioles and respiratory bronchioles
Epithelium becomes simple cuboidal
- form connection between terminal bronchioles and alveolar ducts
This is the transitional structure connecting the conducting zone to the
Alveoli open into this structure along its length
Clara cells become abundant
- connect directly to alveoli
Walls of the ducts consist entirely of alveolar openings.
epithelium is flat (squamous) called avleolar
Duct teminates in a cluster of alveli that share a common, dialated chamber -
called an alveolar sac.
II. Respiratory system - Cellular histology
A. THE COLUMNAR RESPIRATORY EPITHELIUM
EXHIBITS PLASTICITY. Interesting to note that changes in air flow may result in
new abrasive sites on the epithelium. The pseudostratified epithelium will
respond to this by changing into stratified squamous epithelium. Other changes
can also occur (see below).
1. For those of you that smoke,
this means that the pseudostratified epithelium of your respiratory tract has a
greater number of goblet cells than normal in order to provide additional
mucous to clear your airway of particulates in the cigarette smoke.
2. Unfortunately, as a result,
there are fewer ciliated cells so the mucus does not move as rapidly as it
should (smoking also has a detrimental effect on the cilia).
3. Portions of your respiratory
epithelium will change from pseudostratified columnar to stratified squamous.
This also reduces the number of cilia, as well as the area of ciliation.
4. This causes your lungs to be
more prone to congestion, i.e. the bronchioles are more likely to be clogged
5. The increased mucus also
reduces the diameter of the air passages smaller making your lungs less
6. As a result, respiratory
problems like colds and hay fever cause smokers more problems than if they
7. If you quit smoking, the
damage is reversible because the respiratory epithelium can regenerate.
B. SEVEN TYPES OF CELLS FOUND IN RESPIRATORY
a. Mucus secretion.
b. Plentiful in
portions of respiratory tree above the smaller bronchi.
c. Function - mucus
collects particulate matter and absorbs some noxious gases.
Ciliated columnar cells
a. In components
above the smaller respiratory bronchioles
b. 300 cilia/cell.
move mucus back toward oral area
c. Function - to move
inhaled debri trapped in mucous out of respiratory tract.
Columnar brush cells
microvilli on surface
b. Some have
dendritic synapses on basal surface
c. Function - thought
to be sensory.
Basal (short) cells
a. Small basal cells
on basal lamina that do not extend to surface of epithelium.
b. Function - thought
to be stem cells for other cell types.
Small granule cells
a. Look like basal
cell, but have granules in cytoplasm.
b. Function - thought
to be APUD cells that secrete hormones.
a. Secretory cell
b. Function -
possibly secrete surfactants that decrease surface tension of fluid that
moistens the surface of lung epithelia.
Alveolar cells - Type I
Alveolar cells - type II
III. The alveolus
A. The alveoli are lined by an
B. Between the epithelia of adjacent alveoli
1. The endothelial lining of
capillaries - continuous, non-fenestrated endothelium.
2. Basal laminas of epithelium of
aveolar type I cells and capillary endothelial cells that are fused at some
3. Smooth muscle
5. Elastic and reticular fibers
6. Pores between adjacent alveoli
C. Cells of the alveolar wall
Alveolar type I squamous epithelial cells
a. Presumably the
cells across which gaseous transfer occurs, possibly at the sites of fusion
between this cells basal lamina and that of the capillary endothelial cells.
b. Compose about 40%
of the alveolar cells, but cover about 95% of the alveolar surface area.
Alveolar type II cells (also called septal
a. These are roughly
cuboidal with many microvilli on their free surface
b. Thought to
synthesize a phospholipid, dipalmitan lecithin that acts as a
i.e. it reduces surface tension across the squamous epithelium of the alveoli
and thus reduces the force needed to inflate the lungs.
3. Also find alveolar macrophages
called dust cells - usually free in the alveolar lumen.
a. These cells act to
clean fine inhaled debri from the alveolar free surface of cells by
b. They are critical
to lung function. Deficiency in function increases the incidence and
seriousness of lung disorders.
1. This refers to the cellular
structures that lie between the air in the alveolar sacs and the blood in the
a. Starting in the
alveolar lumen this barrier consists of,
Mostly type I alveolar cells
lining the alveolus
of both alveolar cells and capillary endothelial cells (fused in some areas)
Non-fenestrated (continuous) endothelium
areas where basal lamina of the two endothelial layers are not fused,
reticular and elastic fibers
b. The blood-air
barrier prevents air in gaseous form from mixing with the blood.
c. In certan
situations, the blood air barrier may be broken
result in the release of gaseous oxygen into the blood circulatory system
air bubbles can cause blockage of blood circulation in the brain that results
in paralysis and/or death.