Transcript Histology of the spleen Histologie van die milt

Histology of the
Respiratory System
Department of histology, cytology and
embryology KhNMU
The respiratory system includes the lungs , system of
passages (airways) and structures of ventilating
mechanism, that link the site of gas exchange with the
external environment. It is customary to divide the respiratory
system into 3 principle regions:
1. a conducting portion, consisting of the nasal cavity,
nasopharynx, larynx, trachea, bronchi, bronchioles, and
terminal bronchioles.
2. a respiratory portion, consisting of respiratory
bronchioles, alveolar ducts, atria, alveolar sacs and alveoli.
3. ventilating mechanism , which creates pressure
differences that move air. It includes the diaphragm, rib
cage, intercostal muscles, abdominal muscles and elastic
connective tissue in the lungs.
Development of the Respiratory System
Developmental Stages (Human)
1.Embryonic phase (3-7 weeks)
Initial budding and branching of the lung buds
from the primitive foregut.
Ends with the development of the presumptive
broncho-pulmonary segements.
Presumptive -
1 : based on probability or
presumption
2 : being an embryonic precursor with
the potential for forming a particular
structure or tissue in the normal
course of development
2.Pseudoglandular phase (7-16) weeks
Further branching of the duct
system (up to 21 further orders)
generates the presumptive conducting
portion of the respiratory system up to
the level of the terminal bronchioles.
They are embedded within a rapidly
proliferating mesenchyme. The structure
has a glandular appearance.
3. Canalicular phase (16-24) weeks
The onset of this phase is marked by
extensive angiogenisis within the mesenchyme
that surrounds a dense capillary network. The
diameter of the airways increases with a
consequent decrease in epithelial thickness to
a more cuboidal structure. The terminal
bronchioles branch to form several orders of
respiratory bronchioles. The developing
respiratory tree, giving rise to chondrocytes,
fibroblasts and myoblasts.
4.Terminal sac phase (24-36) weeks
Branching and growth of the terminal sacs
or primitive alveolar ducts. Functional type I &
type-II pneumonocytes differentiate via several
intermediate stages from pluripotent epithelial
cells in the prospective alveoli. These cells
then flatten, increasing the epithelial surface
area by dilation of the saccules, giving rise to
immature alveoli. Maturation of the alveoli
continues by further enlargement of the
terminal sacs, deposition of elastin foci and
development of vascularised septae around
these foci.
5.Alveolar phase (36 weeks - term/adult)
Maturation of the lung indicated by the
appearance of fully mature alveoli begins at 36
weeks, though new alveoli will continue to form
for approximately three years.
A decrease in the relative proportion of
parenchyma to total lung volume still
contributes significantly to growth for 1 to 2
years after birth, thereafter all components
grow proportionately until adulthood.
There are changes in the
epithelial lining of the respiratory
tree as one proceeds from the
nasal cavity to the alveoli of the
lungs: Pseudostratified
Columnar Ciliated=> Simple
Columnar =>Simple Cuboidal
=> Simple Squamous
Epithelium.
Conducting Portion
 System of ducts
 Conducts air to all parts of the lungs
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Nose
Nasopharynx
Larynx
Trachea
Bronchi
Bronchioles
Preterminal bronchioles
Terminal bronchioles
Conditioning of the air
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Warming, moistening and removal of particulate materials
Trachea
20 C-shaped cartilaginous rings
 Paries membranaceus
Connective tissue that fills gap between
the two posterior ends
 Neighbouring rings
Connected by regular dense connective
tissue
Continuous with perichondrium of
cartilaginous rings
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Trachea
1. Mucosa
Pseudostratified columnar epithelium with
cilia and goblet cells
2.Lamina propria,Elastic & Collagen fibers
3.Submucosa Mixed glands and lymph
follicles
4. Fibrocartilagenous Layer Hyaline
Cartilage & SMC
5.Adventitial layer
Low Magnification of a Cross Section
Through the Trachea
1. Lumen
2. Pseudostratified
ciliated columnar
epithelium
3. Submucosa
4. Hyalin cartilage
5. Perichondrium
6. Adventitia
7. Mixed glands
8. Secretory duct
Epithelium of the Trachea
1. Lumen 2. Cilia
3. Columnar
epithelial cells
4. Basal membrane
5. Lamina propria
6. Basal cell layer
7. Goblet cell
Respiratory epithelial cell types
 1.Ciliated
columnar cells
 2.Mucous goblet cells
 3.Brush cells
 4.Basal cells
 5.Small granule cells
Bronchi
 Extrapulmonary
bronchi
Two primary bronchi
Histologically similar to the trachea
 Intrapulmonary bronchi
Secondary bronchi (Lobar) - 5
Bronchopulmonary segmental
bronchi –Tertiary (Lobular)- 20
Intrapulmonary Bronchi
Mucosa
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Pseudostratified columnar containing cilia and goblet
cells
Lamina propria - elastica changes into
longitudinally arranged elastic fibers
Smooth muscle
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Between mucosa and cartilage
Mixed glands - between muscle layer and
cartilagous plates
Cartilage
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Irregular shaped cartilaginous plates
Bronchi
Three-dimensional Representation of an Intrapulmonary Bronchus
cartilage plate
lamina propria
pseudostratified columnar epithelium with cilia
and goblet cells
smooth muscle
Bronchioles
 Branches
of bronchi
 Penetrate lung lobule at its apex
Preterminal bronchiole inside the
lobule
 Preterminal bronchiole
Branches into terminal bronchioles
Branch further
Bronchioles
Mucosa
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Epithelium in the larger bronchioles
 Simple columnar epithelium with cilia
 Tall, non-ciliated secretory cells – cells of Clara
In smaller bronchioles
 Tall cuboidal epithelium
Goblet cells have disapeared higher up in the
bronchioles
Lamina propria
 Thin elastic layer
Bronchioles
Muscle layer
Same
as that of the bronchi
Connective tissue
Attaches
bronchioles to surrounding
tissue
No
glands or cartilage are present
Terminal bronchioles – end
point of Conducting portion
Respiratory bronchioles –
beginning of Respiratory
Portion
Respiratory Portion
Consists of smaller ducts and
sacs
Respiration takes place
 Respiratory bronchioles
 Alveolar ducts
 Alveolar sacs
 Alveoli
Respiratory Bronchioles
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Respiratory
bronchioles
 Branch
from terminal
bronchioles
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Smooth muscle
respiratory bronchiole
Alveoli
 Thin
bulging sacs in
walls
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Schematic of the Respiratory
Portion of a Lung Lobule
Gas exchange takes
place
alveolar ducts
alveoli
interalveolar septum
sacculus alveolaris
High Magnification of the Lung
Demonstrating a Respiratory Bronchiole
1. High cuboidal
epithelium
2. Alveolus
3. Interalveolar
septum
4. Lumen
Alveolar Ducts, Alveolar Sacs and
Alveoli
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Alveolar ducts
 Long
passages into which respiratory bronchioles
open
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Alveolar ducts open directly into small spaces
 Alveoli
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Interalveolar septa
 Separate
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Alveolar sacs
 Air
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neighboring alveoli
spaces surrounded by clusters of alveoli
Elastic and reticular fibers
 Arranged
around the capillaries
1. Alveolar sacs
2. Alveoli
3. Interalveolar
septa
Blood – Air Barrier
Separation Between Air and
Bloodstream
 Cytoplasm
of epithelium lining the
alveoli
 Basal lamina of the epithelium
 Basal lamina of the capillary
endothelium
 Cytoplasm of capillary endothelium
Alveolar epithelium –
Pneumocytes
Simple squamous alveolar epithelial
cells – Type 1 cells -Thin cytoplasm
Large Secretory cells – Type 2
(secretory cells) - Secrete surfactant &
Decrease surface tension
Alveolar macrophages - Type 3 (dust
cells)
 Pulmonary
surfactant is a surfaceactive lipoprotein complex
(phospholipoprotein) formed by type II
alveolar cells. It is 2-layer molecular film
on the alveolar surface. The proteins and
lipids that comprise the surfactant have
both a hydrophilic region and a
hydrophobic region. The main lipid
component of surfactant, (DPPC)dipalmitoylphosphatidylcholine.
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Functions of surfactant
1.Decrease surface tension
2.To increase pulmonary
compliance
3.To prevent atelectasis (collapse
of the lung) at the end of expiration.
4.To facilitate recruitment of
collapsed airways.
Pulmonary Surfactant
Pores and Lambert-sinuses
 Alveolar
pores
Direct contact between 2 alveoli
 Infections can spread from one lobe
to another via this route
 Lambert sinuses
Short cannel
Connects terminal bronchioles with
alveoli
Acinus is a Structural and
Functional Unit of the Lung
Terminal Part of the Lungs
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