Histology of Respiratory System
Professor Dr Ali Hassan Altimimi
Professor of Pathology & Histology MSc, PHD, MD(UK)
I.
II.
III.
Respiratory System Function
1. Gas exchange between organism & air/water
2. Requires a Moist Internal Membrane
Upper Respiratory Track
A. Nasal and Nasopharynx,
1. Nares,
a. Sebaceous and sweat glands
b. Short thick hairs (vibrissae)
c. Transition from Stratified Squamous to
Respiratory epithelium
2. Nasopharynx, Respiratory epithelium
3. Nasal septum & Conchae (3 bony projections)
a. "swell bodies" in lamina propria contain
venous plexi (swell every 20 to 30 minutes)
b. Cut air flow
c. Releave desication
d. Upper - Olfactory epithelium
e. Mid & Lower - Respiratory epithelium
4. Rich Vascular System, counter current for warming
the air
B. Protects moist membrane of lungs (Air conditioning!)
1. Warm Air
2. Filter Air
3. Moisturize Air
Respiratory Epithelium Track
. Five cell types
1. Ciliated columnar cells (~300 cilia/cell), most
abundant
2. Goblet Mucous Cells, next abundant
3. Brush cells, columnar Microvilli
a. Sensory receptors, dendritic synapses on
basal surface
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IV.
4. Basal cells, Immature cells that under go Mitosis &
differentiate
5. Small Granular cell, Endocrine like cell, same size
as basal cell, ( small granules with dense core)
A. Respiratory Epithelium changes
1. From Trachea to Alveolar Sacs
a. decrease in size
b. change in cell types
c. decrease in complexity
2. Pseudo Stratified Ciliated Columnar Epithelium,
W/goblet Cells
3. Ciliated Columnar Epithelium, No goblet Cells
4. Ciliated Cuboidal Epithelium, No goblet Cells
5. Simple Squamous Epithelium
Lower Respiratory Track
. Larynx
1. Laryngeal Cartilages held together by ligaments
a. Large(Hyaline Cartilage) &
b. Small (Elastic Cartilage)
c. Keep air way open
d. Valve to prevent food from entering the airway
e. Sound production
2. Lamina Propria
a. Epiglottis on rim of Larynx
b. False Vocal Cords 1st pair of folds
covered by respiratory epithelium
c. True Vocal Cords 2nd pair of folds
1. covered by stratified Squamous
epithelium
2. contain Vocal Ligaments, parallel
bundles of elastic fibers
3. Vocalis muscles (Skeletal) control tension of folds,
producing sounds
A. Trachea
1. Pseudostratified Ciliated Columnar Epithelium
2. Abundant Mucous goblet Cells (white arrow)
3. Lanima Propria Glands Present
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4. Rings of Hyaline Cartilage
5. Some Elastic Fibers
6. Fibro elastic Ligament binds Trachealis Muscle to
cartilage rings
B. The Root (Pulmonary) Bound in connective Tissue
1. Primary bronchus
2. Pulmonary arterys, enters
3. Pulmonary Vein , leaves
4. Lynphatic Vessels, leaves
C. Bronchial tubes
1. Pseudostratified Ciliated Columnar Epithelium
2. Mucous goblet Cells, Large, many; Medium,
present; Small, few in number
3. Smooth Muscle under epithelium, Spiral, crisscross,
bundles of smooth muscle
4. Mucous and Seromucous glands
5. Plates and Islands of Hyaline Cartilage, irregular
6. Abundant Elastic Fibers
7. Lymphoid Nodules at branch points
D. Bronchioles
1. 5mm or less
2. Pseudostratified Ciliated Columnar Epithelium
3. Scattered goblet cells
4. No Hyaline Cartilage
5. No submucosal Glands
6. Lamina propria, Smooth muscle & Abundant Elastic
Fibers
7. Smooth Muscle better developed than Bronchus
8. Autonomic neural control
E. Terminal Bronchioles
1. Ciliated Simple Columnar Epithelium
2. Clara cells, no cilia, dome shaped, secrete
glucosaminoglycans, epithelial protection
3. No Hyaline Cartilage
4. Abundant Elastic Fibers
5. Spiral bundles (crisscross)of smooth muscle
F. Respiratory Bronchioles
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1. Ciliated Simple Cuboidal Epithelium, distal portions,
No cilia
2. No Mucous Goblet Cells
3. Interrupted by alveloi (Squamous cells) Arrows
4. No glands
5. Abundant Elastic Fibers
6. Spiral bundles (crisscross)of smooth muscle
G. Alveolar ducts
1. Distal to Respiratory Bronchioles, opens into 2 or
more alveolar sacs
2. Alveoli lining walls of duct, simple squamous
3. Abundant Elastic Fibers (Important for contraction
during expiration)
4. Lamina Propria, Sphincter like bands (Knobs) of
smooth muscle
H. Alveolar sacs
1. Alveolar Sacs as Diffusion Membranes, (modified
simple Squamous cells)
2. Fused basement membrane between endothelium
and alveolar cells
3. Abundant Elastic Fibers (Important for contraction
during expiration)
4. Capillaries in walls (RBCs in photo)
I. Functional Cells in Alveolar sacs
1. ... pneumocyte Type I, simple Squamous
epithelium(diffusion)
a. 97% of alveolar surface
b. thin 25nm thick
c. organelles grouped around nucleus
d. abundant pinocytotic vessicles
e. desmosomes and occluding junctions
between cells to prevent leakage into alveolar
space
2. ... pneumocyte Type II, "Great alveolar Cells"
secretory cells
a. Cuboidal cells in groups of 2 or 3
b. organelles grouped on their free surface
c. Produce Surfactant (dipalmityl lecithin)
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d. Reduces surface tension & Prevents collapse
of Alveoli
e. Bacterialcidal effect
3. ... Dust cells, macrophages
a. develope from monocytes in the blood
b. found on the surface of the alveolus, in the
alveolar septum
c. phagocytize debris, (blood and RBCs in heart
failure)
d. carried in Surfactant up the mucocillary
elevator to the esophagus
4. ...Other cell types (in alveolar septum)
a. Fibroblasts, collagen and elastic tissue
synthesis
b. Mast cells
c. Contractile Interstitial cells, reduce volume of
alveolus
1. affected by epinephrine, histamine
(When?)
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