Embryology - Respiratory system

Question 1

the respiratory diverticulum is the ‘beginning point’ of the respiratory system.

where does it come from?

Answer 1

RD arises as a VENTRAL OUT-POUCHING of the foregut endoderm

grows CAUDALLY by endodermal proliferation

Question 2

describe how the RD develops into the bronchial tree.

which germ layer is it surrounded by?

Answer 2

RD endoderm proliferation contributes to branching

• grows laterally, caudally splanchnic mesoderm surrounds it
• branches into primary, secondary, tertiary bronchi, into the pericardio-peritoneal canal
• 18 more divisions after tertiary bronchi
• dichotomous branching, if not accessory lobes

Question 3

how many more divisions after birth?

Answer 3

6 more divisions

Question 4

describe the process of tracheo-oesophageal septation

Answer 4

by the FUSION of tracheo-oesophageal folds, resulting in seperation of the ventral trachea and dorsal oesophagus

Question 5

what is tracheo-oesophageal fistula

Answer 5

results from incomplete septation of the oesophagus and trachea

• GI content and milk can be aspirated from lungs or trachea
• can lead to pneumonitis

Question 6

how does the intraembryonic cavity arise and what structures arise from it

Answer 6

• fusion of cavities within the LATERAL PLATE mesoderm = U-shaped intraembryonic coelem
• gives rise to 2x pleural cavities, 1x peritoneal and pericardial cavity

Question 7

describe 3 main process of separating the cavities in the intraembryonic coelem

Answer 7

1. pleuropericardial FOLD: fusion, separates the primitive pericardial cavity from 2x pleural cavity
2. Pleural cavity connected to the peritoneal cavity via pericardioperitoneal canal
3. pleuroperitoneal membranes grows from dorsal body wall towards each other, fuse with septum transversum
   - > closes the pericardioperitoneal canal

Question 8

what is diaphragmatic hernia and the outcome of such condition

Answer 8

• failure of fusion of the pleuroperitoneal membrane with septum transversum
• pericardioperitoneal canal not closed
• peritoneal content enters thorax

outcomes:

• heart pushed anteriorly
• intestinal loop, stomach, spleen, parts of liver enters
• pulmonary hypoplasia

Question 9

4 stages of lung maturation and their main points

Answer 9

1. pseudoglandular period (5-17 weeks): tall coumnar epithelium. no gas exchange as no respiratory bronchiole or alveolar sac etc
2. canalicular period (16th - 24 weeks)
   - over laps because cranial end mature faster
   - respiratory bronchiole and alveolar duct present = gas exchange at the end of period
   - cuboidal epithelium
3. terminal sac period: (24th week - birth)
   - flattened cuboidal cells
   - terminal sacs formed
   - close association between sacs and lymph and blood capillaries
4. alveolar period (32th week - 10 years old)
   - well established endothelium-epithelial contact
   - primitive alveoli present
   - rapid maturation and growth of the respiratory system

Question 10

what is respiratory distress syndrome and the treatment, histology

Answer 10

• condition that is common in premature babies, due to lack of surfactant production
• 28th week: mostly death
• 32th week: glucocorticoid to encourage surfactant production + given surfactant + intense ventilatory support
• alveolar under inflate = collapses = damage structure
• hyaline membrane present