11 - Respiratory System Dev and Histo Flashcards
Respiratory System: 3 Principle Functions:
Air Conduction
Air Filtration
Gas Exchange (respiration)
*Olfaction in nasal cavity
Respiratory System: Upper part is associated with
development of oral cavity
Respiratory System: Lower part developed from
lung bud
Thus epithelium has endodermal origin
Olfactory Epithelium
Pseudostratified columnar epithelium
Olfactory Epithelium : Composed of
olfactory receptor cells, supporting (sustentacular) cells, basal cells,& brush cells
Olfactory Epithelium
Lacks
goblet cells
Olfactory Epithelium: Olfactory mucosa is found in the
nasal mucosa - in a small region of the roof of the nasal cavities.
It is here where there are receptors for sense of smell.
Conducting division/zone –
nasal cavities, nasopharynx, oropharynx, laryngopharynx, larynx, trachea, bronchi, bronchioles, terminal bronchioles
Respiratory division/zone
– respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli
Role of the Conducting Division:
Cleans, warms, & humidifies air
Role of the Conducting Division: Mucous & serous secretions play a
significant role
Role of the Conducting Division: Cilia of respiratory epithelium sweep the
mucous with the trapped particulate matter toward pharynx
Role of the Conducting Division: Air is conditioned as it passes through the
conducting portion:
Includes warming, moistening, and removal of particulate materials.
Mucous is from
goblet cells and mucous secreting glands.
Respiratory epithelium (ciliated pseudostratified columnar) along most of the
pathway*
Histological Characteristics of Conducting Division
Cartilage is present (varying forms)** Seromucous glands** Mucous cells** Cilia wherever mucous cells Elastic fibers in CT (except the nose) Exhibit high degree of vascularity
Mucosa
Respiratory Epithelium –
Ciliated pseudostratified columnar epithelium
ciliated columnar cells –
tall columnar cells with cilia that project into the overlying mucous
goblet cells
basal cells –
stem cells from which all other cell types arise
Lamina propria –
loose connective tissue; contains blood vessels; can contain mucous glands many with serous demilunes
Submucosa –
connective tissue slightly denser than the connective tissue of the lamina propria; contains blood vessels that may contain many glands
Adventitia –
composed of connective tissue that binds component to adjacent structures
Three parts of the pharynx:
Nasopharynx
Oropharynx
Laryngopharynx
Nasopharynx
Ciliated pseudostratified columnar epithelium
Oropharynx
Nonkeratinized stratified squamous epithelium
Laryngopharynx
Nonkeratinized stratified squamous epithelium
Laryngeal cartilages located in
lamina propria (hyaline & elastic cartilages)
Vestibular folds (aka false vocal cords) covered with
respiratory epithelium
Core contains many mucoserous glands
Vocal folds (aka true vocal cords) covered with
nonkeratinized stratified squamous epithelium (along with a large portion of the epiglottis)
Core contains elastic fibers & skeletal muscle
Cartilage rings are replaced by
plates or slivers of hyaline cartilage & will disappear
Smooth muscle within the walls of will
increase as cartilage decreases
Height of the pseudostratified columnar epithelial cells
decreases as the bronchi decrease in diameter
Bronchioles
No cartilage in walls
No glands in submucosa
Relatively thick layer of smooth muscle
Bronchioles: Epithelium height continues to get
smaller as the bronchioles divide
Changes from ciliated pseudostratified columnar epithelium to
Bronchioles
ciliated simple columnar epithelium to ciliated simple cuboidal epithelium
Bronchioles: Goblet cells present in the
largest of bronchioles but begin to decrease
Bronchioles: Goblet cells not present in the
terminal bronchioles
Relatively thick layer of
Bronchioles
smooth muscle
Terminal Bronchiole
Simple cuboidal epithelium interspersed with
non-ciliated cells called Clara cells (also known as club cells)
Terminal bronchiole: Small amount of
underlying connective tissue and smooth muscle.
Clara Cells: Represent
Represent80% of the epithelial cell populationof theterminal bronchiole
Clara Cells: Their function is to
protect the bronchiolar epithelium.
produce surfactant and other
Clara Cells: Apical surface of Clara cells are
dome-shaped and have no cilia
Clara Cells: Ciliated cells are present in
small numbers
Respiratory Division
From the terminal bronchioles of the conducting system…
Respiratory Bronchioles Alveolar Ducts Alveolar Sacs Alveoli
Respiratory Bronchiole: Cuboidal epithelium
Proximally, both
ciliated cells and Clara cells
Distally Clara cells predominate
Respiratory Bronchiole: Occasionally alveoli may extend from the
lumen of the respiratory bronchiole.
Respiratory Bronchiole proximal:
Proximally, both ciliated cells and Clara cells
Respiratory bronchiole distal
Distally Clara cells predominate
Respiratory Division: Alveolar Ducts
Almost no walls, only alveoli as peripheral boundary
Rings of smooth muscle are present in the knob-like interalveolar septa
Alveoli
150 to 250 million per adult lung
Interalveolar septademarcate and separate adjacent alveoli
Respiratory Division: Alveolar sacs
Spaces surrounded by clusters of alveoli
Typically occurs at the termination of the alveolar duct, although may occur along
Type I alveolar cells
Squamous cells
Provide minimal diffusion barrier
alveolar surface epithelial cells; squamous cells; lines 95% of alveolar surface.
Type II alveolar cells
Type II Alveolar Cells – also called septal cells; cuboidal cells; cover approximately 5% of alveolar surface discharge phospholipid called surfactant which keeps the alveoli from collapsing with each successive exhalation, as it lowers surface tension; these cells do not develop until the end of the 6th month of human embryonic development; alveoli do collapse with each successive exhalation in premature infants whose lungs have not developed sufficiently to produce pulmonary surfactant, causing neonatal respiratory distress syndrome (RDS).
Alveolar Macrophages – also known as
dust cells; can be found in the connective tissue of septum and in the air space of alveoli; phagocytize inhaled particulate matter and red blood cells.
Endothelial Cells –
compose wall of capillary
Fibroblasts –
produce elastic fibers
Air-Blood Barrier: composed of
- Surface lining & cytoplasm of the alveolar cells
- Fused basal laminae of the alveolar cells & capillary endothelial cells
- Cytoplasm of the endothelial cells
Respiratory diverticulum (lung bud) appears as
Approximately week 4:
outgrowth of foregut
Inner lining of larynx, trachea, bronchi, & lungs
Endoderm origin
Cartilaginous, muscular, & connective tissue components of
trachea & lungs
Splanchnic mesoderm
Lung bud is initially in
open communication with the foregut
As the bud grows caudally, tracheoesophageal ridges begin to
separate the lung bud from the foregut
Ridges will fuse to form the
tracheoesophageal septum
Dorsal portion esophagus
Ventral portion trachea & lung buds
The respiratory diverticulum maintains
s communication with the pharynx through the laryngeal orifice
Abnormalities in partitioning of esophagus & trachea by tracheoesophageal septum result in
esophageal atresia with or without tracheoesophageal fistulas (TEFs)
Most frequent abnormality is shown which occurs with the
upper esophagus ending in a blind pouch and the lower segment forming a fistula with the trachea
The respiratory diverticulum maintains communication with the pharynx through the
laryngeal orifice
Initially a sagittal slit which changes to a T-shaped opening
Laryngeal cartilages and musculature arise from
pharyngeal arch pairs 4 and 6
Mesenchyme of the 4th & 6th arch transform into:
Thyroid cartilage
Cricoid cartilage
Arytenoid cartilage
Epiglottis forms from
mesenchyme of the caudal hypopharyngeal eminence
Laryngeal mm. arising from 4th arch are innervated by
superior laryngeal n.
Laryngeal mm. arising from 6th arch are innervated by
recurrent laryngeal n.
~ Day 28: Lung bud divides to form
2 primary bronchial buds
Day 30:
Right forms 3 secondary bronchial buds
Left forms 2 secondary bronchial buds
Day 38:
Right forms 10 tertiary bronchial buds
Left forms 8 tertiary bronchial buds
This division and formation of the bronchial buds foreshadows the
lobes of each lung and the bronchopulmonary segments of each lung
As the lung buds grow in both the caudal & lateral directions, they expand into the
pericardioperitoneal canals which will gradually narrow & form the pleural cavities
Splanchnic mesoderm gives rise to
visceral pleura of the lungs
Somatic mesoderm lining thoracic body wall gives rise to the
parietal pleura
Respiratory tree produces small branches called
terminal bronchioles
Between 16-28 weeks, each terminal bronchiole divides into
two or more respiratory bronchioles
By approximately week 36,
terminal sacs (primitive alveoli) are formed
**Pseudoglandular, canalicular, & terminal sac periods are
fetal stages
***The alveolar period is a
late fetal & neonatal stage
Lung tissue appears histologically as a collection of
exocrine glands, hence pseudoglandular period
Pseudoglandular period: At this time, all the major lung structures have developed except for
most distal portions of respiratory tree where gas exchange occurs
A fetus born during Pseudoglandular period will not
survive
Canalicular period: Lung tissue becomes
highly vascular
Canalicular period:
At end of this stage,
respiration is possible. Each terminal bronchiole has split into 2 or more respiratory bronchioles, which have developed primitive alveolar ducts. Some ducts already lead into terminal sacs (primitive alveoli)
Canalicular period: A fetus born near the end of this stage may
survive, although many die as the lungs are still immature in their development
Terminal sac period: More terminal sacs (primitive alveoli) develop and are hugged by
capillaries, establishing the blood-air barrier
~ 26 weeks: lining terminal sac walls is a
single layer of simple squamous cells, most of which are type I alveolar cells through which gases diffuse
Scattered amongst the type I cells are a few
rounded type II alveolar cells
Produce, store, and secrete pulmonary surfactant
Surfactant forms film over the internal walls of the
alveolar sacs and counteracts surface tension
Facilitates expansion of the terminal sacs by preventing collapse (atelectasis)
-Production begins at 20-22 weeks
Premature babies of 24 to 26 weeks may survive, but could suffer from
respiratory distress syndrome due to insufficient surfactant
Alveolar period: Alveoli are
fully functional
Alveolar period: 95% of mature alveoli develop
postnatally (most form within first 3 years) and will continue to develop until 8 years of age
Alveolar period: The alveolar period is a
late fetal & neonatal stage
GI tube is
endoderm, thus lung bud is endoderm.
Epiglottis between
4th and 3rd pharyngeal pouch
olfactory glands in
submucosa - olfactory nerves here as well
Clara cells produce
surfactant
