Embryology of respiratory system Flashcards
What happens at the end of week 4
The lateral body wall folds meet and fuse to close the ventral body wall
Cranial/caudal folding occurred due to rapid growth of the head and tail region
The gut tube is completely closed except where yolk sac is connected by vitelline duct
What is gastroschisis
Failure of the body wall to close in the abdominal region resulting in intestinal loops herniating into the amniotic cavity
What is ectopia cordis
When the lateral body folds fail to close in the thoracic region causing the heart to lie on the outside of chest wall
What is bladder or cloacal exstropy
Abnormal body wall closure in the pelvic region
Cloacal extrophy is is more severe
What three regions is the gut tube divided into
Foregut
Midgut
Hindgut
When does the respiratory diverticulum appear
When the embryo is approx 4 weeks
What is the respiratory diverticulum
Outgrowth of the foregut from its ventral wall
The epithelium present on the inner lining of the larynx, trachea, bronchi and the lungs is derived from endoderm
The rest of the lung tissue is derived from the visceral layer of the mesoderm
How does the tracheoesophageal partitioning occur
Diverticulum starts to expand caudally
Causes two tracheoesophageal ridges to form
These grow towards each other and fuse to form the tracheoesophagael septum
Separating the foregut
What is fistula
An abnormal connection or passageway that connects two organs or vessels that do not usually connect
What is atresia
Absence or abnormal narrowing of an opening or passageway
Where is the internal lining and the cartilages and muscles of the larynx derived from
Internal lining - endoderm
Cartilages and muscles are derived from the mesenchyme of the 4th and 6th pharyngeal arches
What is a mesenchyme
Loosely organised, mainly mesodermal embryonic tissue that develops into connective and skeletal tissue
What does the pharyngeal arches do
Gives rise to specific skeletal and muscular components of the head and neck, supplied by a particular cranial nerve, and its own artery
How many pharyngeal arches are there
There are 5 arches
1,2,3,4 and 6
What happens are the respiratory diverticulum separates from the foregut
Trachea as well as two primary bronchial buds form
At start of week 5, bronchial buds enlarge forming right and left primary bronchi
Then form 3 secondary bronchi of the right and 2 on the left
Then form 10 tertiary bronchi on right and 8 on the left
What happens to the tertiary bronchi as lungs grow caudally
Further subdivision to form bronchioles which will continue to grow even in post natal life
What are the 4 stages of lung maturation
Pseudoglandular
Canalicular
Terminal sac
Alveolar
What is the pseudoglandular
Branching of the bronchial tree, forming many bronchioles up to terminal bronchioles
Bronchioles lined with cuboidal epithelium
Gas exchange not possible
What is the canalicular
Each terminal branch divides into two or more respiratory bronchioles
These then divide into 3 to 6 alveolar ducts that become highly vascularised with capillaries
No gas exchange
What happens at the start of terminal sac stage
Terminal sacs form
The epithelium of the terminal sacs is now a much thinner squamous epithelium
Capillaries establish close contact with the epithelium
What happens from the 28 week onward regarding foetal breathing
Ther is sufficient numbers of alveolar sacs and capillaries to allow adequate gas exchange between air and primitive alveoli
What happens in the last 2 months regarding terminal sacs
Number of terminal sacs increases
How many terminal sacs are formed by birth in each lung
20-70 million
What develops at the end of the 6th month during terminal sac stage
Type II alveolar epithelial cells develop
What is surfactante
Essential lubricant for lung function
Forms phospholipid coat on the alveolar membranes
Lowers the surface tension at the air-alveolar interface, preventing the alveoli from collapsing
What is respiratory distress syndrome
Absent or insufficient surfactant in premature babies
Primitive alveoli collapse causing respiratory distress syndrome
What happens in alveolar stage
Mature alveoli form
Have well developed contact with capillaries as the epithelium lining thinned
After birth lungs grow due to increase in number of respiratory bronchioles and alveoli
What is pulmonary hypoplasia
Reduced number of segments in the lung or alveoli
Pulmonary agenesis
Absense of one or both lungs
Respiratory diverticulum fails to split into left and right bronchial buds and to continue growing
