Questions and Answers
Which structure connects the greater and lesser sacs?
How many layers of visceral peritoneum does the greater omentum have?
Which nerve supplies the foregut?
Which of the following organs does not develop from the foregut?
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In which week of development does the stomach begin to form?
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Pain in which region is associated with the foregut?
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What is the stage of lung development where the respiratory bronchioles and primitive alveoli develop?
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Which embryonic layer gives rise to the glands of the respiratory tract?
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What is the function of the saccular stage of lung development?
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What is the stage of lung development where the trachea and primary bronchial buds form?
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Which structure is formed from the somatopleuric layer of the mesoderm?
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What is the final stage of lung development where the number of alveoli and capillaries increases?
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What is the origin of the bronchial tree during embryonic development?
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Which structure is not formed during the embryonic stage of lung development?
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During which weeks of conception does the embryonic gut tube form?
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What are the three sections of the embryonic gut tube?
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What is the result of the tracheoesophageal grooves failing to fully close in the midline?
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What happens to the lung bud as it grows out and down?
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What is the result of the trachea bifurcating into the right and left bronchial buds?
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What is the characteristic of the pseudoglandular stage of respiratory system development?
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What is bronchopulmonary sequestration?
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What is the consequence of tracheal atresia?
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What type of innervation is present in the anal canal above the pectinate line?
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What is the blood supply to the anal canal below the pectinate line?
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What is the result of a failure in septation of the cloaca during development?
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What is the genetic mutation associated with Hirschsprung disease?
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What sensations can be detected in the anal canal above the pectinate line?
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What is the term for the abnormal connections between the anus and bladder?
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What occurs during the development of the stomach due to the posterior wall growing more quickly than the anterior wall?
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What is the result of the smaller rotation of the stomach around the anteroposterior axis?
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What is the fate of the caudal part of the foregut in the development of the duodenum?
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What is the clinical relevance of failure of the lumen to fully recanalize during duodenal development?
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What forms from the caudal side of the hepatic diverticulum?
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What is the result of the connection between the caudal bud and the gallbladder?
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What is the source of blood supply to the part of the duodenum derived from the cranial part of the midgut?
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What occurs to the duodenal lumen during the 5th week of development?
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Study Notes
Embryology of the Respiratory System
- The respiratory system consists of the upper respiratory tract (nose, nasal cavity, paranasal sinuses, laryngo-pharynx, and larynx) and the lower respiratory tract (trachea, bronchi, and lungs)
- Lung development consists of 5 stages: embryonic, pseudoglandular, canalicular, saccular, and alveolar
Embryonic Stage
- Development of the bronchial tree begins in the embryonic stage, with budding of the embryonic gut tube to form the larynx, trachea, and lungs by the end of the stage
- The embryonic layers and their associated bronchial tree structures are:
- Endoderm: respiratory epithelium, glands of the respiratory tract
- Mesoderm (splanchnopleuric layer): visceral pleura, connective tissue, bronchial musculature, cartilage
- Mesoderm (somatopleuric layer): parietal pleura
- The bronchial tree develops off of the foregut of the embryonic gut tube, which forms from the laterally folded endoderm layer and is surrounded by mesoderm
- The lung bud buds off of the ventral side of the foregut around week 4 and grows out ventrally and down caudally, including both endoderm and surrounding splanchnopleuric mesoderm
- The tracheoesophageal groove appears as lateral indentations between the new lung bud and the foregut, which move in medially, "pinching off" the lung bud and forming the tracheoesophageal septum
- Defects at this stage can cause tracheoesophageal fistula (TEF), esophageal atresia, tracheal atresia, or bronchopulmonary sequestration
Pseudoglandular Stage
- Weeks 8-16: the conducting portion of the airways continues to develop, forming bronchioles from the tertiary bronchi
- At this point, the mesoderm that will develop into alveoli has not completed development, so there are no formed alveoli
Foregut Development
- The foregut is supplied by the coeliac trunk and the greater splanchnic nerve (T5-9 nerve roots)
- Pain in these organs will localize to the epigastric region (T5-9 dermatomes)
- Organs that develop from the foregut are:
- Oesophagus
- Stomach
- Pancreas
- Liver
- Gallbladder
- Portion of the duodenum that is proximal to the entrance of the bile duct
Development of the Stomach
- Development begins around the 4th week
- Fusiform dilation of the foregut: site of primordial stomach
- The lengthening oesophagus places the stomach below the diaphragm
- Posterior wall grows more quickly than anterior wall → develops a C shape
- Posterior wall → greater curvature
- Anterior wall → lesser curvature
- 90-degree rotation clockwise around longitudinal axis:
- Greater curvature (dorsal): rotates anteriorly and to the left
- Lesser curvature (ventral): rotates posteriorly and to the right
Development of the Duodenum
- Development begins in the 4th week
- Above the ampulla of Vater: derived from caudal part of the foregut → supplied by the celiac artery
- Below the ampulla of Vater: derived from cranial part of the midgut → supplied by SMA
- Elongates and forms C-shaped loop
- Joins together with the developing pancreas attached to the posterior body wall
Duodenal Obliteration and Recanalization
- Week 5: rapid cell proliferation in its walls leads to complete obstruction of the duodenal lumen
- By the end of week 8: vacuoles form within the duodenum, grow and merge → lumen recanalization
- Clinical relevance: failure of the lumen to fully recanalize results in duodenal stenosis or duodenal atresia
Liver and Biliary Ducts
- Development begins in the 3rd-4th week
- Appears from the caudal portion of the foregut as the hepatic diverticulum, which goes on to form the liver (endoderm differentiates into hepatocytes), intrahepatic ducts, and extrahepatic portions of the hepatic ducts
- A smaller bud grows off the caudal side of the hepatic diverticulum: forms the gallbladder and connection between the caudal bud and the gallbladder → cystic duct
Hindgut Abnormalities
- If there are issues in septation of the cloaca or rupture of the membrane, this can cause abnormalities in the adult anatomy
- Imperforate Anus – the cloacal membrane does not rupture and so persists, meaning there is no outlet from the gastrointestinal tract and therefore no anus
- Fistulae – if there are holes in the septum, there can be abnormal connections between the anus and the bladder as they are not properly separated in development
- Anorectal Agenesis – a severe defect where there is no development of the anus or rectum rather than simply no outlet
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Description
This quiz covers the development of the upper and lower respiratory tracts, including the formation of the trachea, bronchi, and lungs. It also explores the 5 stages of lung development, from embryonic to canalicular.