H I S T O L O G Y
L E C T U R E
RESPIRATORY SYSTEM
OBJECTIVES:
Upon completion of study of this section the student should be able to:

Name the 2 divisions of the respiratory system and the components of each division.

Name the important tissues and layers of the walls of the respiratory tract and
describe the function of each.

Compare the structure of the walls of the various components of the respiratory tract.

Name 6 important cell types associated with the walls of the respiratory tract and
describe the structure and function of each.

Compare the terminal and respiratory bronchioles.

Describe the structure of the interalveolar septum.

Name the components of the blood-air barrier.

Identify the organ and the cell types present; distinguish between the various
components of the respiratory tract from a slide or photomicrograph of a section of
lung tissue.

Identify the components of the blood-air barrier and differentiate between type I and
type II alveolar cells in electron micrographs.
Respiratory System
Function of Respiratory System

is to provide oxygen to the tissues of the body in exchange for carbon dioxide.

is accomplished through two major divisions of the system:

conducting portion: airways that deliver air to the lungs.

respiratory portion: structures within the lung where gaseous exchange occurs.
1. Conducting Portion of Respiratory System

delivers air to the respiratory tissue.

conducting airways include the nose, pharynx, larynx, trachea, bronchi and
bronchioles down to and including the terminal bronchioles.

these parts of the system warm, moisten and filter the air before it reaches the
respiratory tissue.
2. Respiratory Portion of Respiratory System

is where exchange of gases take place.

includes the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.

these parts of the system are intrapulmonary and contain alveoli.
Nasal Cavity
1. Nares

nostrils, whose outermost portions are lined by extensions of skin.

this keratinized epithelium is stratified squamous and contains sweat glands, hair
follicles, and sebaceous glands.
2. Vestibule

is the first portion of the nasal cavity.

contains vibrissae (thick short hairs) that filter out large particles from the inspired
air.

posteriorly, the lining changes to respiratory epithelium (pseudostratified ciliated
columnar epithelium with goblet cells).

lamina propria is vascular (contains many venous plexuses) and has a number of
seromucous glands.
3. Olfactory Epithelium
Location

roof of nasal cavity, on either side of the nasal septum and onto the superior nasal
conchae.

consisting of a tall pseudostratified columnar epithelium with three cell types:
olfactory, supporting and basal cells.
1) Olfactory Cells
 are bipolar nerve cells characterized by a bulbous projection (olfactory vesicle)
from which several modified cilia extend.
olfactory

cilia, which acts as receptors, are nonmotile and very long.
Their proximal one-third contains a typical axoneme but their distal two-thirds is
composed of nine peripheral singlets surrounding two central singlets.
2) Supporting (sustentacular) Cells
 possess nuclei that are more apically located than those in the other two cell
types.

have many microvilli and a prominent terminal web.
3) Basal Cells
 resets on the basal lamina but do not extend to the surface and form an i
ncomplete layer of cells

are believed to be regenerative for all three-cell types.
Lamina Propria

contains many veins, unmyelinated nerves, and Bowman’s glands.
Bowman’s Glands

produce a watery serous secretion that is released onto the olfactory epithelial
surface via narrow ducts.

olfactory stimuli dissolve in this material and are carried away by the secretion to
prepare the receptors for new stimuli.
Larynx
1. Characteristics

connects the pharynx with trachea.

wall is supported by hyaline cartilages (thyroid, cricoid, lower part of arytenoids)
and elastic cartilages (epiglottis, corniculate and tips of arytenoids).

remainder of wall contains striated muscle and connective tissue with glands.
2. Vocal Cords

consists of skeletal muscle (the vocalis), the vocal ligament (formed by a band of
elastic fibers), and a covering of stratified squamous nonkeratinized epithelium.

muscles within the larynx contract and change the size of the opening between the
vocal cords, which affects the pitch of sounds caused by air passing through the
larynx.
3. Lining Epithelium

changes to respiratory epithelium at base of epiglottis, inferior to the vocal cords.

respiratory epithelium lines air passages down through trachea and primary bronchi.
4. Vestibular Fold

lies superior to the vocal cord.

is a fold of loose connective tissue containing glands and lymphoid aggregations.

is covered by respiratory epithelium.
Trachea and Extrapulmonary Bronchi
1. Hyaline Cartilage

supports walls of trachea and extrapulmonary bronchi.

cartilages are C-shaped, with their open ends facing posteriorly.

smooth muscle (trachealis) extends between open ends of the cartilage.

dense fibroelastic connective tissue is present, superior and inferior to each
cartilage, which facilitates the elongation of the trachea during inhalation.
2. Respiratory Epithelium

lines the lumen of the trachea and extrapulmonary bronchi.

in the human it consists of the following cell types:
Ciliated Cells

thus delicate lung tissue is protected from possible damage by inhaled particulate
matter.

have long actively motile extensions that beat in the direction of the pharynx.

ciliated cells also contain microvilli.
Mucous Cells

are of two varieties: mature goblet cells and small mucous granule cells
1) Small Mucous Granule Cell

sometimes called “brush” cell because of its many microvilli.

actively divides and thus might be able to replace desquamated cells; might also
be a goblet cell that has secreted its mucus.

contains varying numbers of small mucous granules
2) Mature Goblet cell

is best known because of its shape

is filled with large mucous droplets that are secreted to trap inhaled particles.
Short (basal) Cells

rest on the basal lamina but do not extend to the lumen, making epithelium
pseudostratified.

are able to divide.
Enteroendocrine Cells

(APUD) cells, small granule cells) also from part of the epithelium.

contain many small granules concentrated in their basal cytoplasm.

these cells exert a local affect on nearby structures and cell types (paracrine
regulation).

various types of enteroendocrine cells synthesize different polypeptide hormones.
3. Basement Membrane

is a very thick layer that underlies the epithelium.
4. Lamina Propria

a thin layer of connective tissue that lies beneath the basement membrane.

elastic fibers run longitudinally and separate the lamina propria from the submucosa.
5. Submucosa

contains many seromucous glands.
6. Adventitia

forms the outer layer of the trachea.

contains C-shaped cartilages.
Intrapulmonary Bronchi (Secondary Bronchi)
1. Origin

arise from subdivision of the primary bronchi and divide many times.

have irregular cartilage plates in their walls.

respiratory epithelium lines the lumina of the intrapulmonary bronchi.
2. Lamina Propria

is separated form the submucosa by layers of spiraling smooth muscle.
3. Glands (seromucous)

are present in the submucosa.
Bronchioles
1. General Characteristics

bronchioles measure 1 mm or less in diameter and have no cartilage in their walls.

smooth muscle replaces the cartilage plates and glands are not present.

its lining epithelium varies from ciliated columnar with goblet cells (in the primary
bronchioles) to ciliated cuboidal with secretory (Clara) cells (in terminal and
respiratory bronchioles).
2. Terminal Bronchiole

is the most distal part of the conducting portion of the respiratory system.

is lined by a simple cuboidal epithelium consisting of Clara (secretory) cells and
ciliated cells.

Clara cells also contain an abundance of smooth endoplasmic reticulum (whose
enzymes may be involved in metabolizing toxins from the inspired air).
3. Respiratory Bronchiole

marks the transition between the conducting and respiratory portion of the system.

its wall is interrupted by alveoli, which makes it the first portion of pulmonary tree in
which gaseous exchange takes place.

its remaining wall is lined by a simple cuboidal epithelial consisting of Clara cells
and ciliated cells.
Alveolar Duct
1. Characteristics

linear passageway continuous with the respiratory bronchiole.

its wall consists of closely spaced alveoli that are separated from one another only
by an interalveolar septum.

smooth muscle is present in the septum at the opening of adjacent alveoli.

alveolar duct is most distal portion of the respiratory system to contain smooth
muscle in its wall.

an attenuated simple squamous epithelium (consisting of type I and type II
pneumocytes) lines the alveolar duct.
Alveolar Sac
1. Characteristics

an expanded irregular space at the distal end of an alveolar duct, whose wall
consists of adjacent alveoli.
Alveoli
1. Characteristics

permits gaseous exchange between air and blood (oxygen from air to blood, and
carbon dioxide from blood to air).

communicate with each other via alveolar pores (of Kohn).

rims of the openings into alveoli contain elastic fibers and supportive reticular fibers.

alveoli are lined by a highly attenuated simple squamous epithelium composed of
two cell types:
Type I Pneumocyte

forms part of the blood-gas barrier.

has an extremely thin cytoplasm (can be less than 80nm in thickness).

(type I alveolar cell) covers about 95% of alveolar surface.

forms tight junctions with neighboring cells.
Type II Pneumocyte

bulging free surface contains short microvilli that are located peripherally.

(type II alveolar cell, great alveolar cell, granular pneumocyte, septal cell) is low
cuboidal and is located most often near septal intersections.

release of surfactant from the lamellar bodies produces a monomolecular film that
spreads over the alveolar surface.

synthesizes pulmonary surfactant which it stores in lamellar bodies in its cytoplasm

forms tight junctions with neighboring cells

is able to divide and regenerate both cell types in the alveolar epithelium.
1. Alveolar Macrophage

(dust cell, alveolar phagocyte) is the principal mononuclear phagocyte of the
alveolar surface.

removes inhaled dust, bacteria and other particulate matter and is a vital line of
defense in the lung.

when filled with debris it migrates to the bronchioles and is carried via ciliary action to
the upper airways and pharynx, where it is swallowed.

another exit route is to migrate into the interstitium and leave via lymphatics.
Interalveolar Septum
1. Characteristics

septum is the wall, or partition between two alveoli.

continuous capillaries occupy its central (interior) region, and an attenuated simple
squamous epithelium lines the alveoli bordering its outer surfaces.

elastin and reticular fibers are present in some of the thicker regions of the septal
wall.

elsewhere the septum constitutes the site of the blood-gas barrier.
2. Blood-Gas Barrier

is the barrier to diffusion of gases between the alveolar air and the blood.

in thinnest areas it consists of the following components:
1)
2)
3)
4)
layer of surfactant
thin epithelium of the type I pneumocyte
fused basal laminae of the type I pneumocyte and capillary endothelium
endothelium of the continuous capillary

average distance across the barrier is about 0.5 µm.

in areas where the two basal lamina fuse, to eliminate the thin interstitial space, the
distance across the barrier is reduce to 0.2 µm or less.
Vascular Supply of Lungs
1. Pulmonary Artery

carries blood to the lungs to be oxygenated.

enters the root of each lung and extends branches along the divisions of the
bronchial tree.
2. Pulmonary Veins

run independently of the arteries in the intersegmental connective tissue.

after leaving the lobules of the lung the veins come into close association with
branches of the bronchial tree.

from this point to the root of the lung the veins accompany the bronchi.

thus branches of the pulmonary artery and veins follow branches of the bronchial
tree, except within the lobules, where only arteries follow the bronchioles.
Lung Lobules
1. Characteristics

each bronchial that arises from a bronchus enters what is known as a lung lobule.

lobules are shaped somewhat like a pyramid, having an apex and a base, but they
vary greatly in size and shape.

an incomplete septum separates each lobule from its neighbor.

lymphatics run within the dense connective tissue but are not present within the
interalveolar wall.
Nerve Supply
1. Nerve Fibers

from both divisions of the autonomic nervous system innervate the smooth muscle of
bronchi and bronchioles.

axons have been demonstrated in thicker parts of the interalveolar septa.
Breathing
1. Characteristics

during inspiration the thoracic cage enlarges, becoming deeper wider and longer.

large amounts of elastic tissue within the lungs permit extensive expansion and
relaxation to occur.

each lung is enclosed in a pleural sac and the pleural space is under negative
pressure.

as thoracic wall increases in size, the visceral pleura, which is firmly attached to the
lungs, is also drawn outward.

this decreases the air pressure within the lungs and air is drawn into them.

since air has been inspired, the elastic tissue in the lungs is stretched.

the elastic recoil is enough to expel air from the lungs, decreasing the thoracic cage
to its initial size.
C L I N I C A L
I N T E G R A T O N
RESPIRATORY SYSTEM
Introduction:
Nasal passage until -terminal bronchiole-conducting portion {filter, warm & moisturize the inspired
air}
Respiratory bronchiole, alveolar duct, sac and alveoli – respiratory portion {gas exchange}
Respiratory epithelium - Pseudostratified ciliated columnar epithelium with goblet cells.
There is transition of epithelium progressively towards the respiratory portion. Slowly the goblet cells
disappear and replaced by clara cells, columnar cells become cuboidal and then ciliated disappear
and the simple squamous cells (pneumocytes) form the alveoli, where gas exchange takes place.
The interalveolar septum contains elastic fibers, reticular fibers, fibroblasts and immune cells and
migrating alveolar macrophages.
Respiratory Diseases:
EMPHYSEMA
KARTAGENER’S SYNDROME (Immotile cilia Syndrome)
Clinical Case 1:
Definitions:
o ACINUS – Part of the lung distal to the terminal bronchioles
o LOBULE – Cluster of 3 -5 acini
o BULLAE – enlarged air spaces more than 1 cm in diameter.
o C.O.P.D – Chronic Obstructive Pulmonary Diseases
Term used to describe 2 related lung diseases:
CHRONIC BRONCHITIS
EMPHYSEMA
Histopathogenesis:
*Chronic Bronchitis: chronic recurrent cough with excess mucous production for at least 3
consecutive months in at least 2 consecutive years. Affects both large and small airways. It is a
clinical diagnosis.
[Characterized histologically by enlargement of mucous glands, ciliary abnormality, smooth muscle
hyperplasia, inflammation and leukocyte infiltration and bronchial wall thickening> increased sputum
production and airflow obstruction.]
*Emphysema: permanent dilatation and destruction of airways distal to terminal bronchioles without
obvious fibrosis. It is morphological / histological diagnosis.
[3 morphological typesCentriacinar-only the central part (respiratory bronchioles) affected, common in smokers.
Panacinar - respiratory bronchioles to distal alveoli affected commonly in AAT (alpha 1 anti trypsin)
deficiency.
Distal acinar- distal (alveoli) mainly affected, forms bullae.]
*Both conditions can co- exists and have similar etiology.
THE INTER ALVEOLAR SEPTUM - Is present between the 2 alveoli.






2 thin squamous epithelial cells layers between which lie capillaries, CT matrix, cells, reticular &
numerous elastic fibers. Elastic fibers are important in the recoil of lungs(expiration)
Phases of respiration:
Inspiration (active process)
Expiration (passive process)
Neutrophils and macrophages in the interalveolar septum (esp. inflammation) release elastase
among other proteolytic enzymes.
Elastase – destroy micro organisms, also digests elastic fibers in the interstitium
Alpha 1 anti trypsin (AAT) –protein produced in the liver - function is to neutralize elastase &
protect the interstitium from enzymatic breakdown (elastolysis)
Protease – Anti protease balance.
EMPHYSEMA
Protease – Anti protease imbalance.
Etiology is related to
 AAT deficiency-alpha 1 anti trypsin deficiency
 Smoking
 both
Pathophysiology:
Permanently dilated airways distal to the terminal bronchioles
Associated destruction of the alveolar walls and decrease in the number of alveoli {loss of lung
parenchyma}
Alpha 1 antitrypsin – a glycoprotein produced in the liver and transported to the lungs. Inhibits the
enzyme elastase {anti elastase activity}. Protectective agent keeps most of the elastin intact.
Inactivated by free radicals presents in cigarette smoke
Deficiency- congenital or functional.
SMOKING:
Reactive free radicals in smoke:-
Inhibit alpha 1 anti trypsin activity.
Attracts macrophages and neutrophils that release lots of elastase (protease)
Proteases are enzymes that are capable of digesting lung tissue and these chemicals are
responsible for the damage seen in emphysema.
A persistent stimulus (smoking) increases the # of leucocytes (increased proteolytic activity) or
lowers the level of AAT > unchecked elastic tissue destruction > dilated airways > hyper inflated
lungs >emphysema
KARTAGENER’S SYNDROME (Immotile cilia syndrome)
Normal cilia have a core of 9 pairs of microtubules and central two microtubules. But in patients with
Kartagener’s syndrome, one of the paired microtubule is deficient, thereby causing abnormal
movement of the cilia > impairment of mucociliary clearance.
Therefore immotile cilia cannot sweep the mucus leading to build up of mucus which leads to chronic
respiratory tract infections. Associated situs inversus may be present.
[Organization of micro tubules leads to proper development of tail of spermatozoa. Therefore
abnormal micro tubular arrangement or their absence can lead to infertility in the males].
*Other Clinical Considerations:
Hyaline membrane disease (Infant respiratory distress syndrome)
Asthma
Asbestosis
Carbon monoxide poisoning
Lung cancer
Hyaline membrane disease:
Infant respiratory distress syndrome. Premature infants< 28weeks old are deficient in surfactant.
Labored breathing secondary to difficulty in alveolar expansion secondary to high surface tension in
lungs. If detected earlier, can be prevented by glucocorticoids to the mother a few days prior to
delivery to help induce synthesis of surfactant.
Asthma:
Widespread constriction of smooth muscle in the bronchioles causes decrease in the diameter:
Associated with extreme difficulty in expiration of air, accumulation of mucus in the passage ways
and infiltration of inflammatory cells.
Therefore treated with medications to relax the smooth muscles to dilate the passageways and with
corticosteroids as anti inflammatory.
Asbestosis:
Pulmonary disease caused by inhalation of asbestos fibers. Small particles are phagocytosed but
larger ones enter the interstitium and induce alveolar macrophages to release inflammatory
mediators – interstitial pulmonary fibrosis in the walls of respiratory bronchioles, alveolar ducts and
alveoli.
Carbon Monoxide Poisoning:
CO is an odorless tasteless gas that binds to hemoglobin in red blood cells with greater affinity than
does oxygen. Co poisoning can lead to symptoms of nausea, headache and sleepiness. Death may
occur as oxygen is not effectively delivered to the vital organs. Treatment is by exposing the patient
to 100% oxygen until all CO is displaced.
Lung cancer:
Leading cause of death from cancer in men and women. 90% is a consequence of cigarette
smoking. 2 types-squamous cell and small cell (oat cell) carcinoma. Squamous cell carcinoma arises
in the bronchi where the respiratory epithelium changes to stratified squamous epithelium due to
chronic irritation. Initial metaplasia leads to dysplasia and then to carcinoma (Malignant). Small cell
(oat cell) carcinoma is of bronchial origin whose incidence is greatly increased in smokers.
H I S T O L O G Y
L A B O R A T O R Y
Respiratory System
OBJECTIVES:
At the completion of this section the student will be able to:

Characterize each subdivision of the respiratory conducting portions (larynx, trachea,
bronchus, bronchioles, and alveolar ducts).

Identify each of the cell types and matrix components that are involved with
respiratory conduction and conditioning of the inspired air.

Describe the structure and function of each of the components of the alveolar
septum. Include the alveolar macrophages, Type I and II epithelial cells, capillaries,
fibroblasts, mast cells and matrix fibers (collagen III and elastin).

Identify the air passages found in the lungs. These include the respiratory
bronchioles, alveolar ducts, and alveoli.
ANNOTATIONS
Respiratory System

The respiratory system is designed to interface atmospheric oxygen with the blood in
order to effect an exchange between 02 and C02. The system is subdivided into two
main portions: a conduction system and a site for respiration.

Conduction. Air is internalized in a series of tubular conduits. Properties of the air
pathway include: maintenance of an open lumen, ability to accommodate expansion
and contraction activity warming, moisturizing and filtering of the inspired air.

Each of these functional attributes is supported by a structural organization of cells
and matrices. Identify each of the following mucosal structures and provide its
function:
Epithelium
Function in Air Conduction
Ciliated cells
Goblet cells
Basal cells
Brush cells
Mucus gland
Serous glands
_______________________________________
_______________________________________
_______________________________________
_______________________________________
_______________________________________
_______________________________________
Lamina propria
Function in Air Conduction
Fibroblasts
Endothelial vessels
Smooth muscle
Collagen I fibers
Elastic fibers
Hyaline cartilage
_______________________________________
_______________________________________
_______________________________________
_______________________________________
_______________________________________
_______________________________________

Within the lung, the structures of the alveoli provide for efficient and rapid exchange
of atmospheric gases. Most of the cells and structures are at the level of resolution of
the microscope and are not readily evident in our lab material. Find as many of the
listed structures as you can. Identify the function of each of the following structural
elements present in the alveolar septum:
Alveolar Septum
Epithelium
Function in Respiratory Exchange
Squamous alveolar (Type I ) _____________________________________
Great alveolar (Type II)
Surfactant
Mesenchyme
_____________________________________
_____________________________________
Function in Air Conduction
Endothelial cells
_______________________________________
Mast cells
_______________________________________
Fibroblasts
_______________________________________
Reticular fibers
_______________________________________
Elastic fibers
_______________________________________
Alveolar macrophage_______________________________________
MICROSCOPIC STUDIES
There will be 5 slides used in this exercise:
1. Larynx l.s.
2. Trachea x.s. & l.s.
Lung, latex injection 5. Lung
3. Bronchus x.s.
4.
1. Larynx, I.s. MAZ Trichrome (Harris Biol. H.8-4):

Scan the organization at low power. You should be able to identify each of the
epithelial and mesenchymal tissue types. How does each function in supporting the
activities of the larynx. The larynx will be dissected in gross lab. In the center of the
section you will see a large central lumen with tissue folds on either side.

At higher magnification, focus on clear cross- and longitudinal-sections of the
muscles. One of the primary considerations in describing mesenchyme tissues is to
identify which of the components, cells, fibers or ground substance, is lending the
tissue its character.
Though ground substance and fibers are necessary to support muscle
tissue function, it is the cellular component that characterizes this tissue.
These folds are the true and false vocal folds (use your atlas for
orientation).

Focus on the epithelium lining the lumen. Under high power, examine the
organization of the respiratory epithelium (pseudostratified ciliated columnar
epithelium with goblet cells). The goblet cell population declines as you move from
top to bottom of the larynx. Regions of the epithelium in the vicinity of the vocal folds
are stratified squamous because of the mechanical vibration they experience in
producing sound.

The supporting cartilages in the mucosa are primarily hyaline, however in the region
of the vocal folds the arytenoid cartilages are elastic. Though the section is not
stained, the fibrous nature of the elastic cartilage can be distinguished from the
homogeneous matrix in the hyaline cartilage.
Identify and check-off each of the following:
 Ciliated cells
 Stratified squamous epithelium
 Mucus and seromucous glands
 Hyaline cartilage
 Perichondrium
 Goblet cells
 Vascular bed beneath epithelium
 Skeletal muscle
 Elastic cartilage
2. Trachea, I.s. & x.s. H&E.

In those slides with two sections, the longitudinal section has two or more oval
portions of hyaline cartilage surrounded by a fibrous perichondrium.

The epithelium is the typical pseudostratified ciliated columnar with goblet cells.
Mucus and serous glands lie between the epithelium and the cartilage rings.

Adipose tissue will be evident within the loose connective tissue of the lamina
propria. Dense collagen fibers deep to the cartilage serve to anchor the trachea to
the surrounding tissue.

In the cross-section the hyaline cartilage can be seen in its ring configuration. The
loose connective tissue beneath the epithelium condenses into a fibro-elastic band
adjacent to the perichondrium.
Identify and check-off each of the following:
 Respiratory epithelium
 Hyaline cartilage
 Loose irregular CT
 Serous and mucus glands
 Perichondrium
 Vascular bed beneath epithelium
3. Bronchus, l.s. & x.s. MAZ Trichrome (Harris Biol. H.8-6.2):

At low magnification identify the lumen and examine the structure of the respiratory
epithelium. The organization of the lamina propria is virtually the same as that in the
trachea. A primary difference is related to the presence of smooth muscle bundles,
which are active in regulating the diameter of the lumen. The smooth muscle is
organized as helical entwined bundles.

In addition the hyaline cartilage is organized as multiple plates rather than a single
C-shaped ring. Peripheral to the cartilage the “webbed” tissue is a portion of the lung.
The thin-walled alveoli can be distinguished from the bronchioles that are lined with
cuboidal to low columnar simple epithelium. Do not spend much time on the lung
portion since the next two slides cover that. However the alveoli are important in
diagnostics since they indicated the tissue is within the lung.
Identify and check-off each of the following:
 Respiratory epithelium
 Hyaline cartilage
 Loose irregular CT
 Smooth muscle bundles
 Bronchioles
 Serous and mucus glands
 Perichondrium
 Vascular bed beneath epithelium
 Alveoli
4. Lung, t.s. Latex injected (Harris Biol. H.8-6.2):

This lung tissue has had its vasculature injected with red latex. The vascularity of the
alveolar septum is readily apparent. The large pulmonary vessels filled with latex
standout at low magnification.

Bronchioles are evident because of their cuboidal to low columnar epithelium.
Respiratory bronchioles (revealing both a cuboidal epithelium and alveolar sacs) and
alveolar ducts are present among the alveoli.

At higher magnification examine the alveoli. The alveolar epithelial cells are hard to
discriminate. Identify macrophages in the alveolar lumen, they are rounded and
possess large pale nuclei. Some macrophages contain carbon (dust) particles and
are visible in the connective tissue matrix.
Identify and check-off each of the following:
 Bronchioles
 Alveoli
 Alveolar macrophages
 Alveolar ducts
 Respiratory bronchioles
 Alveolar septa
 Pulmonary vessels
5. Lung, Human H&E (Carolina Biol. H7745)
This preparation is not preserved well, but the same elements described in the preceding slide
may the same structures as above.
Summary table of Respiratory System
Division
Region
Skeleton
Nasal Cavity
Vestibule
Hyaline
cartilage
Respiratory
Olfactory
Pharynx
Nasal
Oral
Larynx
Trachea &
extrapulmonary
(primary)
bronchi
Intra-pulmonary
conducting
Secondary
bronchi
Bronchioles
Terminal
bronchiole
Glands
Epithelium
No
Goblet Features
cells
No
Vibrissae
Yes
Yes
Large venous plexus
Yes
No
Yes
Yes
Basal cells; sustentacular
cells; olfactory cells; nerve
fibers
Pharyngeal tonsil;
eustachian tube
No
No
Palatine tonsils
Yes
Yes
Vocal cords; epiglottis;
some taste buds
Yes
Yes
Trachealis muscle; elastic
lamina
Pseudostratified Yes
ciliated
columnar
Simple
Yes
columnar to
simple cuboidal
Yes
Two helically oriented
ribbons of smooth muscle
Only
in
larger
bronchiole
None
Clara cells
Sebaceous & Stratified
sweat glands squamous
keratinized
Bone &
Seromucous Pseudostratified
hyaline
ciliated
cartilage
columnar
Nasal con- Bowman’s
Pseudostratified
chae (bone glands
ciliated
columnar
Muscle
Seromucous Pseudostratified
glands
ciliated
columnar
Muscle
Seromucous Stratified
glands
squamous nonkeratinized
Hyaline & Mucous &
Stratified
elastic
seromucous squamous noncartilage
glands
keratinized &
Pseudostratified
ciliated
columnar
C-rings of Mucous &
Pseudostratified
hyaline
seromucous ciliated
cartilage
glands
columnar
Plates of
hyaline
cartilage
Smooth
muscle
Seromucous
glands
Smooth
muscle
None
`None
Simple
cuboidal
Cilia
Some
Less than 0.5 mm in
diameter; Clara cells
Respiratory
Respiratory
bronchiole
Some
smooth
muscle
None
Alveolar
duct
None
None
Alveolus
None
None
Simple
cuboidal &
simple
squamous
Simple
squamous
Some
None
Outpocketings of alveoli
None
None
Simple
squamous
None
None
Outpocketings of alveoli;
type I pneumocytes; type II
pneumocytes; dust cells
Type I pneumocytes; type II
pneumocytes; dust cells