3. Embryology Flashcards
When do the trachea and lungs begin to develop?
Beginning of 4th week
What does the laryngotracheal tube develop from?
Splanchnic mesoderm
What develops from the larygotracheal tube?
Tracheal buds
What is present at the end of the 4th week?
Bronchial buds
What is present at 8 weeks?
Trachea with bronchial buds and lungs split into lobes
What does the tubular outgrowth from the foregut develop into?
Trachea and lungs
Before the lungs buds begin to proliferate , what must happen to the trachea?
It must separate from the oesophagus
How are the pleural cavities and visceral and parietal pleuras formed?
The proliferating lung buds will invaginate the pleural cavities laterally forming them
What will begin to develop between the thorax and abdomen?
A transverse septal shelf
How many components is the septal shelf made up of?
4 components
What do the 4 components of the septal shelf fuse to form?
The diaphragm
How do congenital abnormalities affecting the respiratory system occur?
Things go wrong with the embryonic tracheal, lung and diaphragmatic formation
What does the visceral pleura form from?
The mesoderm which covers the outside of the lung
What does the parietal pleura develop from?
The somatic mesoderm covering the body wall from the inside
What are the stage of differentiation of lung buds?
- Embryonic
- Pseudo Glandular
- Canalicular
- Saccular
- Alveolar
What does the septum transversum form?
Tendinous part of the diaphragm
What do the 2 pleuroperitoneal membranes form?
Muscular part of the diaphragm
What does the peripheral body wall muscle form?
Muscular part of the diaphragm
What does the mesentery of the oesophagus form?
Crura of diaphragm
What does folding of the embryo give rise to?
Primitive gut tube
What does the gut tube form from?
Endoderm
What is the relationship between the trachea/larynx and the oesophagus?
Trachea and larynx are always located anterior to the oesophagus
What does the respiratory primordium start as?
A median outgrowth (larnygotracheal groove/ diverticulum) from the anterior part of the foregut
How does the diverticulum form the trachea and lung buds?
It becomes invested with mesoderm on its outside and enlarges
What develops between the trachea and oesophagus?
Oesophagotracheal septum
Fistula
-An abnormal or surgically made passage between a hollow or tubular organ and the body surface,
OR
-Between 2 hollow or tubular organs
What is a common congenital abnormality?
Trachoesophageal fistula
Atrasia
A condition in which an orifice or passage in the body is closed or absent
What does the visceral pleura develop from?
The splanchnic mesoderm
What does the parietal pleura form from?
Somatic mesoderm
When do the lungs appear?
Around 26 days
What is the first form the lungs take?
Form in the respiratory diverticulum in the ventral part of the digestive tract
What does the respiratory diverticulum create?
A median trachea and 2 lateral pockets
Where do the pulmonary arteries individuate?
The 6th aortic arch
What happens during the pseudo glandular period?
Setup of all pulmonary structures except elements needed for gas exchange
What happens during the canalicular stage?
- The terminal bronchioles give rise tubes that make up respiratory part of the lung.
- Differentiation of epithelium into cuboidal secretory cells which will synthesise surfactant and flat cells.
What happens during the saccular stage?
Formation of alveolar sacs separated by primary septa. The alveolar sacs will be progressively divided into smaller subunits by secondary septs leading to the formation of alveoli.
When does the pseudoglandular stage take place?
7-17 weeks
When does the canalicular stage take place?
17-27 weeks
When does the saccular stage take place?
27-40 weeks
When does the alveolar stage take place?
32 weeks -8 years
What happens during the alveolar stage?
- Formation of alveoli from terminal sacs
- Alveoli enlarge
- Number of respiratory bronchioles (and alveolar ducts and alveoli) increase as lungs enlarge.
What percentage of adult-like alveoli are formed postnatally?
About 95%
What is another name for respiratory distress syndrome?
Hyaline membrane disease
What is surfactant a mixture of?
Phospholipids and proteins
What secretes surfactant?
Type II pneumocytes
What does surfactant do?
Counteracts surface tension at air-alveolar surface
What is a major cause of RDS?
Surfactant deficiency
Give examples of respiratory congenital conditions?
- RDS
- Accessory lobes
- Lobe of Azygous vein
- Agenesis of lung
Where is the septum transversum initially located?
Opposite C3-C5
What is the root value of phrenic nerves?
C3-C5
As the septum transversum migrates caudally what does it take with it?
Spinal nerves C3-C5
What are the 3 major defects involved in congenital abnormalities of the diaphragm?
- Failure of the diaphragm to completely close during development
- Herniation of the abdominal contents into the chest
- Pulmonary hypoplasia
Hernia
General term used to describe a bulge or protrusion of an organ through the structure or muscle that usually contains it
What are examples of diaphragmatic hernias?
- Posterolateral Bochdalek hernia
- Anterior Morgagni hernia
- Central hernia
What are examples of hiatal hernias?
- Sliding hiatus hernia
- Paraesophageal hiatus hernia (rolling hiatus hernia)
