Endodermal Derivatives of the Developing Chick Embryo
33-hour Chick Embryo Transverse Sections
Foregut: The part of the gut that has so far been formed at the 33- hour embryo is an epithelium-lined dorsoventrally flattened cavity ventral to the brain. This is separated from the stomodaeum by the oral plate
Thyroid: This is seen as a median shallow depression of the foregut just above the dorsal mesentery suspending the heart.
Anterior intestinal portal: As you trace the foregut posteriorly in your slide, this is seen as the opening of the gut into the yolk
Midgut: This is the floorIess gut
48-hour Chick Embryo Transverse Sections
Preoral Gut: This is the anteriormost portion of the foregut. In the transverse sections this is a small oval cavity between the pair of big blood vessels, the first pair of aortic arches.
Pharynx: Posteriorly, the preoral gut forms a bigger cavity, the pharynx. The pharynx has left and right arms, the 1st pair of pharyngeal pouches. Note the ectodermal invaginations or grooves between arches and the closing plates, fused ectoderm and endoderm between visceral arches.
Oral plate or pharyngeal membrane: This is the double membrane of outer ectoderm and inner endoderm separating the stomodeum and the pharynx.
Endoderm lining of the first visceral or mandibular arch: The mandibular arches are large masses of mesenchyme on each side of the oral plate. The inner lining is of endodermal origin.
Second pharyngeal pouches: These lateral evaginations of the pharynx are at about the level of the thyroid, a V-shaped ventral diverticulum of the pharynx.
Third pharyngeal pouches: These are large diverticulae of the pharynx immediately posterior to the third pair of visceral arches.
Laryngotracheal groove: Posteriorly, the pharynx becomes constricted and forms the esophagus. A deep V-shaped depression in the floor is the laryngotracheal groove.
Pleural recesses: Beside the esophageal region, note the presence of two lateral cavities, parts of the coelom that will later become the pleural cavity.
Lung buds: Primordia of the lung buds are seen as slight ventro-lateral evaginations of the splanchnic mesoderm into the pleural cavities/recesses.
Liver diverticula: These primordia of the liver are found in the transverse septum that separates the pleural cavity from the peritoneal cavity.
Dorsal diverticulum: This is the outpocketing appearing as dark oval structure lying dorsal to a big blood vessel, the ductus venosus.
Ventral diverticulum: This is a dark ventral outpocketing of the duodenum flanked by the vitelline veins. Trace the slide porteriorly and note how they connect to the gut.
72-hour Chick Embryo Transverse Sections
Go quickly through the endoderm derivatives of the 72-hour chick embryo. Essentially the structures are in the same positions but observe closely changes in development such as the appearance of new structures.
Trace the serial sections posteriorly until you see the oculomotor nerves arising from the mesencephalon floor. Look for the following paired structures associated with the foregut:
First pharyngeal furrow and pouch: Observe the first pharyngeal furrow as an ectodermal indentation between the first and the second pharyngeal arches. The first pharyngeal pouch is an endodermal evagination between the two mentioned arches.
First visceral or mandibular arch: This is the mass of mesenchyme anterior to the first furrow.
Oral plate or pharyngeal membrane: This is a thin double membrane connecting the pair of mandibular arches and between the pharynx and the stomodaeum.
Second pharyngeal furrow and pouch: The second pharyngeal unit, appearing posterior to the second pharyngeal arch
Second pharyngeal or hyoid arch: the mesenchyme mass between the first or hyomandibular pouch and furrow and the second cleft.
Third pharyngeal furrow and pouch: These lie posterior to the third pharyngeal arches.
Thyroid: Observe the ventral diverticulum from the floor of the pharynx at the level of the second pair of pouches.
Fourth pharyngeal furrow and pouch: These are found posterior to the fourth arch. Is a cleft present?
Laryngotracheal groove: Trace the pharynx posteriorly until it becomes a ventrally elongated narrow tube. The ventral V-shaped region is the laryngo-tracheal groove. The dorsal portion is the putative esophagus.
Lung buds: After the esophagus separates from the laryngo-tracheal groove, a pair of lateraI diverticula the bronchi are formed at the posterior end of the laryngotracheal groove. Tracing the bronchi, they lead to thick- walled bodies, the lung buds.
Stomach: The stomach is the enlarged endodermal tube formed as you trace the esophagus posteriorly.
Duodenum: Keep on tracing the stomach posteriorly until a vertical oval, the duodenum is formed and enclosed by a large blood vessel, the ductus venosus.
QUESTIONS:
- Does the gut extend into the tail?
- What is the fate of the postanal gut?
Step by step
Solved in 2 steps
