Respiratory System
• The respiratory system is divided
into two major components:
• The air-conducting components
• The respiratory or gas-exchange
components
Air Conducting Portion
• Consists of the:
– nasal cavities
– Pharynx
– Larynx
– Trachea
– Extrapulmonary bronchi
– Intrapulmonary bronchi and
bronchioles
– Terminal bronchioles
Three layers
1) Mucosa:
---epithelium: pseudostratified ciliated columnar
epithelium
---lamina propria: CT, contain LC, PC, BV, LV
Pseudostratified ciliated columnar epi.
• ciliated cell: columnar, cilia
• goblet cell
• basal cell:
-pyramidal, basally-located
-undifferentiated cell→ciliated cell or goblet cell
• brush cell:
-columnar, microvilli,
-EM: RER
-function: not very clear
• diffuse neuro-endocrine cell:
-less, pyramidal
-function: secret hormones to regulate contract of
SM and secretion of gland
Cilia on the surface of trachea Ciliated cell
Goblet cell
2) Submucosa:
LCT, with BV, LV and N
• tracheal gland: mixed
• diffuse LT and LN
• S Ig A = secretory component (secreted by epi.
cell) + Ig A ( produced by plasma cell)
3) Adventitia:
• cartilage ring: 16-20 “C ” shaped
• circular ligament: elastic F
• SM- posterior part (membrane part): SM,
elastic F, tracheal gland
Air Conducting Portion
functions:
----- Filters, moistens, and warms air before it enters lungs.
-----Olfactory functions to examine air and to protect
against breathing in harmful substances.
-----Mucous tends to trap foreign substances and then the
cilia (of pseudostratified ciliated columnar epithelium)
clear the foreign substances from the trachea and bronchi
of lungs.
----Cartilages found in trachea and bronchi play an
important role in keeping airway open.
Air Conducting Portion
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Bronchial Tree – upside down tree with the trachea
serving as the trunk of the tree and the bronchi as
the primary branches
Many smaller branches ending is small twigs
(bronchioles)
The leaves would represent the millions of alveoli.
Extra-pulmonary bronchi are the left and right
bronchi that branch off of the trachea and then enter
the lungs.
The intrapulmonary bronchi are the branches that
form within the lungs.
The larger sizes have hyaline cartilage which
decreases with smaller bronchi. Eventually the
cartilage is replaced with smooth muscle.
Bronchioles have diameters of less than 5 mm.
Terminal bronchioles have intact but greatly
reduced amounts of smooth muscle in the wall.
When this wall becomes incomplete, and contact
with alveoli becomes evident, then the bronchiole
changes to become a respiratory bronchiole.
① from lobar bronchi to small bronchi
---Regulation of simplification: (gradually)
mucosa:
-epi. : become thinner
-goblet cell ↓
-lamina propria: thinner, SM ↑
• submucosa: gland ↓
• adventitia: cartilage→cartilage →decreasing
② bronchiole: D < 1mm
---continuous to change
• goblet cell, Gland, cartilage ↓ or disappear
• smooth muscle ↑,circular mucosa plica ↑
③ terminal bronchiole: D < 0.5 mm
---goblet cell, gland, cartilage disappear
---SM: form a whole layer of circumferential SM
---Wall:
• simple columnar epi.: two types of cells
• A layer of SM
Simple columnar epi:
Clara cell
i. ciliated cell
ii. secreting cell: Clara cell
EM:
Ciliated cell
• dome-shaped apical
• SER
• Secreting G: contains proteolytase and
oxidase
function:
• dissolve the mucus, secrete surfactant.
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biological transformation
undifferentiated cell → ciliated cell
Respiratory Components
• The respiratory components
consist of:
• Respiratory bronchioles
• Alveolar ducts
• Alveolar sacs
• Alveoli
Respiratory Components
• Respiratory bronchioles have incomplete walls such that
alveoli make direct contact. This allows for gas exchange
to occur.
• Alveolar ducts are where respiratory bronchioles branch.
There is much greater space with alveoli exposed.
• Alveolar sacs are clusters of alveoli .
• Alveoli are single bubble like structures.
① respiratory bronchiole
---similar to terminal bronchioles:
• simple ciliated columnar epi.
• smooth muscle
---place where connect with alveoli: gradual changing
• simple cuboidal epi. →simple squamous epi.
• less SM, elastic F
② alveolar duct: 20-60 alveoli connect with it
---wall: hard to see- opening part between two alveoli
• simple cuboidal epi. or squamous epi.
• SM: single, EF- knob-liked structure
③ alveolar sac:
---many alveoli open to it
---no proper wall, no knob-liked structure
④ alveoli
Respiratory Components
• The lungs have an abundant blood supply.
• Capillary beds are abundant within the spaces
adjacent to the alveoli.
• Alveoli walls consist of simple squamous
epithelial cells which allow for rapid exchange
of gases (diffusion).
• The many millions of alveoli produce a very
large surface area (1/2 of a tennis court)
• Most abundant cells are the endothelial cells of
the capillaries. These usually have small,
elongated nuclei.
④alveoli:
---polygonal, with opening sac- 0.2mm in D, 300-400 million/per
lung, total area: 70-80mm2
---wall:
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epi. and basal lamina
alveolar septum: CT with BV, EF
a.alveolur epi:
---type I alveolar cell:
LM: flattened, 0.2um, N: round
EM:
•
plasmalemmal vesicles
•
tight junction
Function: constitute the blood-air barrier
---type II alveolar cell: scattered, 5-8/per alveoles
LM:
•
cuboidal or round, with round N
•
paler- stained, foamy cytoplasm
EM:
•
secreting granules: Osmiophilic multilamellar
body
-0.1-1.0 um
-contains: phospholipid, glycosaminoglycan and protein
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microvilli, mito, lysosome, RER, Golgi
Function:
i. secreting surfactant
ii. differentiated into type I alveolar cell
neonatal respiratory distress syndrome
b. alveolar septum: CT
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EF
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Fibroblast, macrophage, plasma cell, mast cell
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LV, N
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capillary: endothelium + basement membrane
* Blood-air barrier: the structure through which the gaseous exchange
takes place
---0.2-0.5 um
---components:
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a layer of liquid
•
type I alveolar cell and basement M
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CT
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capillary endothelial cell and BM
c. alveolar pore: 10-15 um
---equalize( balance) the air-pressure between alveoli
---lober pneumonia- bacteria or inflammatory spread through
the pore
d. alveolar marcophage: monocytes- MPS
---dust cell: macrophage which phagocytose carbon or duct particles
---heart failure cell: when lung congested(edema), the alveolar
marcophage phagocytose RBC, digest the hemoglobin into
hemosiderin(pigment) and accumulated them within macrophage
Trachea
Epithelium
Hyaline cartilage
Mucous acini
Perichondrium
Serous acini
Adventitia
fibrosa
Pseudostratified
Ciliated columnar
Epithelium
Blood vessel
Hyaline
cartilage
cl = cilia, gc = goblet cell, bm = basement membrane
Trachea – trachealis muscle between hyline cartilage
Trachealis muscle
Bronchus contains hyaline cartilage
Cartilage
Smooth muscle that
Serves for bronchoconstriction
Serous acini
Intrapulmonary bronchus
Bronchus with cartilage
Pulmonary
vein
Intrapulmonary bronchus
Intrapulmonary bronchus
Intrapulmonary bronchus
With cartilage
Terminal bronchiole
Terminal bronchiole
Alveolar duct
Respiratory
bronchiole
Pulmonary artery and vein
bronchiole (no cartilage)
Branching of bronchiole (no cartilage vissible)
b=respiratory bronchiole with alveolus (a) in its wall,
c and d = alveolar ducts which are lined almost entirely with alveoli,
e= individual alveoli, f= blood vessel.
a = two alveoli separated by thin interalveolar septa,
b = smooth muscle in bronchiole, c= blood vessel
d = bronchiole no cartilage
Alveoli separated by the thin
interalveolar septa. Reddish spots
are RBC and dark spots are nuclei
of simple epithelium of capillaries or
alveoli.