Download Overview

LAB 13
Practical Histology
Respiratory system
 Overview
 Components of the Respiratory System
1. In relationship to lungs (listed in order from exterior to interior, i.e., the
path of inspired air).
Extrapulmonary
Intrapulmonary
a. Nasal cavity
a. Secondary bronchi
b. Pharynx
b. Bronchioles
c. Larynx
c. Terminal bronchioles
d. Trachea
d. Respiratory bronchioles
e. Primary bronchi
e. Alveolar ducts
f. Alveoli
2. According to function (listed in order from exterior to interior)
Conducting Portion
Respiratory Portion
(Transports air from exterior)
(Involved with gas exchange)
a. Nasal cavity
a. Respiratory bronchioles
b. Pharynx
b. Alveolar ducts
c. Larynx
c. Alveoli
d. Trachea
e. Primary bronchi
f. Secondary bronchi
g. Bronchioles
h. Terminal bronchioles
 Structure of Typical Respiratory Passageways


40
Conducting portion (nasal cavities through secondary bronchi)
1. Mucosa (mucous membrane). Faces the lumen
a. Respiratory epithelium. Pseudostratified with cilia and goblet cells.
b. Lamina propria of loose connective tissue with blood vessels and nerves.
c. Deepest layer of mucosa may consist of:
1) An elastic lamina or
2) A muscularis mucosae or
3) This layer may be absent.
2. Submucosa. Dense irregular connective tissue with mucous and serous
(mixed) glands
3. Cartilage or bone
4. Adventitia. Loose connective tissue forming the outer layer of the passageway.
Structural transitions in walls and layers of the passageways from
extrapulmonary passageways to alveoli.
1. Transitions
a. Layers become thinner as passageways decrease in diameter.
b. Epithelium decreases in height from pseudostratified to simple columnar
to simple cuboidal to simple squamous.
c. Goblet cells and mixed glands stop relatively abruptly at the junction of a
secondary bronchus with a bronchiole.
d. Cartilage decreases in size, breaks up into plates, and stops relatively
abruptly at the junction of a secondary bronchus with a bronchiole.
e. Cilia are gradually eliminated.
2. Results in the formation of the wall of an alveolus, where gas exchange
occurs.
a. Epithelium is simple squamous.
LAB 13
Practical Histology
Respiratory system
b. Connective tissue core with numerous capillaries.
 Nasal Cavities (Extra pulmonary)
1. The nasal cavities can be subdivided into two regions, the olfactory and the
non-olfactory regions.
2. Non-olfactory region
a. Vestibules. The epithelium undergoes a transition from epidermis of skin
with hairs to pseudostratified, respiratory epithelium.
b. Nasal fossae
1) Typical mucosa but deepest layer is lacking (i.e., neither a muscularis
mucosae nor an elastic lamina is present).
2) Patency maintained by bones or cartilage.
c. Olfactory region
1) Upside-down, U-shaped area in posterior, superior region of each nasal
fossa, extending over superior conchae and about 1 cm down nasal
septum.
2) Composition of wall
A. Mucosa
a) Epithelium is tall, thick, pseudostratified columnar with
nonmotile cilia composed of:
1. Olfactory cells (neurons). Bipolar neurons that respond to
odors. A single dendrite extends to the surface to form a
swelling, the olfactory vesicle, from which nonmotile cilia
extend over the surface. These cilia increase surface area
and respond to odors.
2. Support cells span the epithelium and support the olfactory
cells.
3. Basal cells are located on the basal lamina and serve as
reserve cells for the epithelium.
b) Deepest layer of mucosa is not present, so the lamina propria
blends with the submucosa. This connective tissue layer
contains Bowman’s glands, serous glands whose watery
secretions flush odorants from the epithelial surface.
B. Patency maintained by bone.
 Larynx (Extra pulmonary)
1. Composition of the wall of the larynx
a. Mucosa
1) Epithelium
a) Pseudostratified with cilia and goblet cells in most areas.
b) Stratified squamous moist over true vocal folds and much of
epiglottis because of friction incurred in these areas.
2) No muscularis mucosae or elastic lamina, so lamina propria is
continuous with submucosa.
b. Submucosa with mixed glands (except in true focal fold).
c. Cartilages maintaining patency are numerous, uniquely shaped and are
either hyaline or elastic. The larger cartilages are the epiglottis, thyroid,
and cricoid.
d. An adventitia is present.
2. Vocal apparatus. Modification in the larynx composed of two pairs of
horizontally positioned mucosal folds located on the lateral walls of the
larynx.
41
LAB 13
Practical Histology
Respiratory system
a. False vocal folds. More superior in location. Resemble the wall of a
“typical” respiratory passageway except the deepest layer of the mucosa is
absent (no muscularis mucosae nor elastic lamina).
b. The ventricle, a space, separates the false from the true vocal folds.
c. True vocal folds
1) Are lined by a stratified squamous moist epithelium and its lamina
propria
2) A vocal ligament of dense regular elastic connective tissue is located at
the edge of the fold, keeping the rim of the fold taut.
3) Vocalis muscle, skeletal muscle, lies beneath each true vocal fold. This
muscle alters the shape of the vocal fold and aids in phonation.
 Epiglottis
1. The epiglottis is a flap of tissue containing elastic cartilage, which directs
swallowed food into the esophagus and prevent it from entering the larynx.
2. Elastic cartilage has tow surfaces:
a. Anterior surface which covered by non keratinized stratified squamous
epithelial tissue.
b. Posterior surface which covered by ciliated pseudostratified columnar
epithelial tissue.
 Trachea

structure
1. Mucosa
a. Epithelium pseudostratified with cilia and goblet cells with a very
prominent basement membrane.
b. Lamina propria of loose connective tissue.
c. Elastic lamina of longitudinally arranged elastic fibers.
2. Submucosa with mixed glands.
3. C-shaped cartilage rings maintain patency; trachealis muscle (smooth)
interconnects the open ends of the tracheal rings.
4. Adventitia is present.
 Lung
1. Conducting portion consists of bronchi inside the lung and their bronchioles.
2. Respiratory portion consists of respiratory bronchioles, alveolar ducts and
alveoli.
3. Except at the hilus, the lungs are surrounded by a thin superficial connective
tissue capsule. A simple squamous mesothelium rests on this capsule.
4. Pleural mesothelial cells have sparse apical microvilli, secrete watery
lubricants into the pleural cavity, and rest on a thin basement membrane.
5. The mesothelium defines the two pleural cavity boundaries and allows the
lungs to move freely next to the body wall and diaphragm.
6. Alveolar capillaries and alveoli are held together by thin strands of connective
tissue. Where they are intimately associated, the connective tissue domain is
little more than a collagen fibril or an attenuated fibroblast process.
7. Larger connective tissue domains surround large branches of the airway. For
example, they hold bronchi and pulmonary arteries together.
8. Other connective tissue elements join veins, lymphatics, and nerves to other
lung structures, and connective tissue septa divide the bronchopulmonary
segments.
42