7. Respiratory System.pdf

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Naveen Sooknanan McGill Fall 2011
Respiratory System:
The function of the respiratory system is to provide oxygen
and remove carbon dioxide from the blood. There are three
segments of the respiratory system:
Conduction portion:
o Consists of the nasal cavity, nasopharynx,
oropharynx, larynx ,trachea, bronchi and
Includes regular and terminal
We will only look at the system
starting at the trachea
The transitional portion is made up of respiratory
bronchioles, which have a discontinuous wall
The conducting portion consists of the alveolar duct, alveolar sac and lung alveoli
The conducting portion is meant to warm, humidify and clean the air of any debris
It possesses glands which secrete liquids, to humidify, and mucous, to cling on to any
floating debris
Ciliated cells also help remove any foreign particles
The transitional portion has an intermediate function between conducting and respiratory
Some gas exchange occurs because of the discontinuous walls, but it also has the same
functions as for the conduction portion
This marks the beginning of gas exchange (no gas exchange occurs in the conducting
The respiratory portion is where the most gas exchange occurs
Like in blood vessels, many of the peripheral components of the “general “respiratory
structure will be missing, allowing for easier transfer of gases
If a particle was missed by the conducting system, it will be ingested by a macrophage in
the lungs, and we can see these in histological slides
We will make a general structural plan for
the respiratory system with the trachea,
which contains all of the necessary
components. As we go deeper, these
components will start to go missing.
Working from the trachea lumen out:
o A pseudostratified ciliated
columnar epithelium with
goblet cells
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Naveen Sooknanan McGill Fall 2011
The cilia act as hairs to trap particles
The goblet cells secrete liquid which keeps the surface moist
Goblet cells are very pale staining
o Lamina propria
Loose CT with fibroblasts and fibrocytes, elastic fibers and capillaries
Loose CT has more cells, less fibers
Elastic fibers allow extension and retraction of the tissue as you
Capillaries bring by warm blood which warms the air
o Loose and dense irreg. CT
o Serous and mucous glands (we will see what they are in a bit)
o An outer layer of hyaline cartilage shaped like a horseshoe
Connecting the two ends of cartilage is a region of smooth muscle known
as the Trachealis muscle
The opening of the cartilage is at the posterior (back) end
Remember, no elastin fibers in hyaline cartilage
o The same as other adventitias; dense irreg. CT (type I collagen) with BVs
The adventitias are all continuous with one another, and are generally
made of the same materials
o As the trachea branches out into deeper layers, these components are lost
Looking closer at the wall of the trachea, we can see that there are 2 types of glands located in
the submucosa. Both types of glands here are acinus (we will go over glandular structure later
There are two types of secretion: serous
and mucous
o Serous secretion is thin and
aqueous, meant to humidify the
air as it comes into the system
o Mucous is thick and slimy, and is
meant to cover and protect the
epithelium, as well as stick to
foreign material
Serous acinus glands are the smaller of
the two glands
o They are very acidophilic,
meaning they stain a very dark
o They have 1 layer of pyramidal cells which have a round nucleus located either in
the middle or towards the outer base
o Surrounded by myoepithelial cells which contract and squeeze, just like the sweat
o They have aqueous (watery) secretion
Mucous acinus glands are much larger than serous glands
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Naveen Sooknanan McGill Fall 2011
o They stain very poorly in H&E, making them appear very faded in slides
This is due to the presence of many glycoproteins
Just by this feature, they can be easily distinguished from serous cells
o They also have 1 layer of pyramidal cells, but the cells are larger and paler
o The nuclei are flattened and pushed towards the base of the cell
o Thick, mucous secretion
Both of these glands may appear disconnected from the surface because of place of
o In reality, they all connect and secrete into the lumen of the trachea
The pseudostratified columnar ciliated epithelium contains 5 types of cells with different
First off, the BM under the epithelium in the respiratory system is visible. The only other
place we see this is in the hair follicle
The ciliated cells are the actually epithelial cells
o They are tall and mature, and
have many cilia projecting out
of its surface
o All of the ciliated cells touch
the BM membrane even
though it may not appear like
it (that’s why it’s called
Goblet cells are very pale staining (as
we saw in the slide) because they
have glycoproteins
o They also secrete mucous
fluid, but a DIFFERENT type
than the mucous acinus glands
o Therefore, there are 2 types of
mucous secretions
o These cells are not ciliated
Trachea at low mag.
Trachea mucosa at high mag.
Pseudostratified ciliated
columnar epithelium
Lamina Propria
Dense CT less
cells more fibers
Serous acinus
Mucous acinus
Perichondrium, followed by
hyaline cartilage
Cilia (hairs)
columnar epithelium
Lamina Propria
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