Embryology 2

Question 1

Describe the folding of the embryo ( week 3)

Answer 1

• Embryo folds forming the primitive gut tube. Gut tube forms ( from endoderm> midgut, hindgut)
• trachea and lungs are formed from the foregut

Question 2

When + where does the development of the trachea and lungs occur?

Answer 2

• At 4 weeks of gestation

- from ventral wall of foregut

Question 3

What does the respiratory primordium(early stage of organ) start of as?

Answer 3

-starts as a median outgrowth (diverticulum=blind tube leading to cavity) - laryngotracheal groove - from ventral (=anterior) part of the gut

Question 4

Describe the development of the diverticilum and septum.

Answer 4

Diverticulum( = endoderm) becomes covered with mesoderm on its outside and enlarges to form the trachea and lung buds.
-A septum ( oesophageotracheal septum) develops between the oesophogus and trachea + seperates them into trachea ventrally and oesophogeal dorsally

Question 5

What is a tracheoosophogeal fistula?

Answer 5

• abnormal/surgical made passage between a tubular organ and the body surface/between 2 hollow or tubular organs
• common congenital abnormality

Question 6

Describe the development of the pleural cavities

Answer 6

• develop from the mesoderm
• as the lungs develop, itacquires a layer of visceral pleura from the splanchnic mesoderm.
• The thoracic wall becomes lined by a layer of parietal pleura derived from the somatic mesoderm.
• Gap inbetween parietal and visceral pleura = pleuroperitoneal canals ( which eventually develops into pleural cavities)
• pleuropericardial folds form around primitive heart seperating pleural cavities from pericardial cavities

Question 7

Describe the development of the pleural cavities

Answer 7

• Lung buds ‘pushes’ intot he visceral mesoderm.
• Visceral pleura is formed from the splanchnic mesoderm and parietal pleura is derived from the somatic mesoderm.
• There is now a gap between parietal and visceral pleura = pleuroperitoneal canals ( eventually develops into pleural cavities)
• pleuropericardial folds forms around primitive heart separating pleural cavities from pericardial cavities

Question 8

Describe the differentiation of pleural membranes

Answer 8

• Lung buds ‘‘punch’ into the visceral mesoderm. Mesoderm ( covering the outside of lung) develops into visceral pleura. The somatic mesoderm covering body wall from inside = parietal pleura.
• The space between =pleural cavity

-expansion of the lung buds into the pericardioperitoneal canals. The canals are now in communication with the peritoneal and pericardial cavities.

Question 9

State the stages of differentiation of lung buds

Answer 9

• Embryonic>Pseudoglandular>canalicular>saccular> alveolar
• foetal period>postnatal period
• Alveolar phase normally post natal period
• PECSA

Question 10

Pseudoglandular phase

Answer 10

-(7-17wks) sets up all pulmonary structures except elements required for GE

Question 11

Canalicular stage

Answer 11

• ( 17-27wks).
• Terminal bronchioles form tubes that make up respiratory part of the lung
• Differentiation of epithelium into type 2 pneumocytes (makes surfactant )+ flat cells(type 1 pneumocytes

Question 12

Saccular stage (Prenatal)

Answer 12

• 27-40wks

- formation of alveolar sacs which will divide into smaller subnits(alveoli)

Question 13

Alveolar stage

Answer 13

• 32wks-8yrs
• formation of alveoli from terminal sacs
• alveoli enlarges
• number of respiratory bronchioles, alveolar ducts + alveoli) increases

Question 14

Other congenital conditions

Answer 14

Formation of accessory lobes - 1/more lobes which are smaller than the largest.

Azygous lobe - zygos lobe formed due to displaced azygos vein creating deep pleural fissure into the apical segment of the right upper lobe during E development.

Agenesis of lung - failure of primitive lung bud to develop + results in unilateral/bilateral absence of lung tissue.

Question 15

Describe the development of the diaphragm

Answer 15

• develops from surrounding the 4 embryonic components:
  1. Septum transversum>central tendon
  2. Pleuroperitoneal membrane> primitive diaphragm
  3. Dorsal mesentery of oesophogus > median portion + crura of diaphragm
  4. Muscular ingrowth from lateral body walls > peripheral parts of diaphragm

Question 16

Where is the septum transversum located? State its development

Answer 16

• opposite C3-C5

- migrates caudually(inferiorly) during development of the diaphragm + brings down with its spinal nerves (C3-5)

Question 17

Congenital abnormalities of the diaphragm

Answer 17

3 major defects:

• failure of diaphragm to completely close during development
• herniation of the abdominal contents into the chest
• pulmonary hypoplasia

Question 18

What is a hernia?

Answer 18

-general term used to describe a bulge/protusion of an organ through the structure/muscle that usually contains it

Question 19

Types of hernia - congenital abnormalities

Answer 19

-diaphragmatic + hiatal herniae