Embryology Body Folding and Neurulation

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Questions and Answers

What is the consequence of failure of the stomach to descend into the abdominal cavity?

Congenital diaphragmatic (hiatal) hernia (correct)

Pancreatic insufficiency

Umbilical hernia

Intestinal malrotation

Which structure is formed from the fusion of two mesenteric layers draping from the stomach?

Falciform ligament

Lesser omentum

Greater omentum (correct)

Visceral peritoneum

Which blood supply primarily supports the structures of the midgut?

Superior mesenteric artery (correct)

Celiac trunk

Hepatic artery

Inferior mesenteric artery

What occurs during the development of the pancreas?

The ventral pancreas rotates in the fifth week of development Signup and view all the answers

Which condition is characterized by a protrusion of bowel through the umbilical ring and covered by skin?

Umbilical hernia Signup and view all the answers

What is the primary function of the notochord in mesoderm differentiation?

Serves as a rigid midline structure Signup and view all the answers

What do somites differentiate into?

Dermatome, myotome, and sclerotome Signup and view all the answers

Which mesodermal layer is responsible for forming urogenital structures?

Intermediate mesoderm Signup and view all the answers

What are the two layers formed from the lateral plate mesoderm?

Somatic and splanchnic layers Signup and view all the answers

How do dermatomes and myotomes relate in development?

They are formed from the same mesodermal segments Signup and view all the answers

In which direction does segmentation of somites progress?

From rostral to caudal Signup and view all the answers

What does the splanchnic mesoderm primarily surround?

Internal organs Signup and view all the answers

What does lateral folding specifically create in the abdominal region?

The coelomic cavity Signup and view all the answers

What is the result of the head fold during embryonic development?

Separation of the heart from the foregut Signup and view all the answers

How do cardiac progenitor cells reach the splanchnic mesoderm?

They migrate through the primitive streak Signup and view all the answers

What are the derivatives of the endoderm?

Inner lining of the gut tube Signup and view all the answers

How many pairs of somites are typically formed during embryonic development?

42-44 pairs Signup and view all the answers

What happens to the lateral mesoderm after body folding?

It moves ventrally during the process Signup and view all the answers

What structure is formed by the merging of two sides of the cardiac crescent?

The endocardial tube Signup and view all the answers

Which structure is formed as a result of medial mesoderm positioning during body folding?

Coelomic cavity Signup and view all the answers

What type of mesoderm do myocardial cells arise from?

Splanchnic mesoderm Signup and view all the answers

What is the role of the ventral aspect of the trilaminar disc in the development of the gut tube?

It forms the epithelial lining of the gut tube. Signup and view all the answers

Which structures do the oropharyngeal and cloacal membranes mainly serve as during gut tube development?

Closed structures marking the ends of the gut tube. Signup and view all the answers

What is the significance of the cephalocaudal folding in gut tube formation?

It places the developing heart ventrally. Signup and view all the answers

Which statement accurately describes the mesentery and its development?

It forms from a broad sheet of mesenchyme lined by serous membranes. Signup and view all the answers

How does lateral folding contribute to the gut tube structure?

It aligns the endoderm against the body wall. Signup and view all the answers

What role does the dorsal mesentery play in gastrointestinal development?

It connects the gut tube to the posterior abdominal wall. Signup and view all the answers

What germ layers contribute to the wall of the gut tube?

Splanchnic mesoderm and endoderm. Signup and view all the answers

What is the expected outcome after the rupture of the oropharyngeal membrane?

Opening of the oral cavity to the foregut. Signup and view all the answers

What does the term 'secondarily retroperitoneal' refer to?

Structures initially developing within the peritoneal cavity and later migrating retroperitoneally. Signup and view all the answers

What is characteristics of retroperitoneal organs?

They are located outside of the peritoneal cavity. Signup and view all the answers

Which of these organs is classified as secondarily retroperitoneal?

Pancreas Signup and view all the answers

What part of the gut tube does the foregut refer to?

From the oropharyngeal membrane to the liver outgrowth. Signup and view all the answers

Which of the following structures is formed from a diverticulum off the foregut?

Trachea Signup and view all the answers

What separates the trachea from the esophagus during development?

Tracheoesophageal septum Signup and view all the answers

Which statement about the esophagus is true?

Smooth muscle in the esophagus is derived from splanchnic mesoderm. Signup and view all the answers

During its development, where does the stomach begin its position?

In the thoracic cavity. Signup and view all the answers

What is the primary innervation of the muscle in the esophagus?

CN X Signup and view all the answers

Which organ is NOT considered part of the foregut proper?

Ascending colon Signup and view all the answers

What developmental characteristic distinguishes secondarily retroperitoneal organs?

They lose their dorsal mesentery and fuse with the body wall. Signup and view all the answers

Study Notes

Body Folding

Primitive streak forms along the caudal midline of the bilaminar embryonic disk, with its cranial end expanding into a primitive node.
The position of the future oropharyngeal membrane is indicated at the cranial end of the embryonic disk.
During gastrulation, epiblast cells migrate along the primitive streak, displacing the hypoblast to form the definitive endoderm.
Subsequent migrating cells form the mesoderm.
Mesoderm extends cranially from the primitive node to become the notochordal process.
Lateral mesoderm develops into paraxial, intermediate, and lateral plate mesoderm.
Lateral plate mesoderm splits into somatic and splanchnic mesoderm layers, separated by the intraembryonic coelom.
Paraxial mesoderm forms somites in the future trunk, and head mesoderm in the head region.
Oropharyngeal and cloacal membranes form, along with the neural plate, which develops into the spinal cord and brain.

Folding and Neurulation

The process of folding begins at the start of the fourth week.
The embryo forms a three-dimensional shape.
The neural tube closes and the primitive streak disappears.

Primary Germ Layers

Ectoderm
Mesoderm
Endoderm

Ectoderm Characteristics

After body folding, surface ectoderm surrounds the embryo and forms the epidermis.

Mesoderm Differentiation in the Trunk

Notochord is the midline mesoderm structure that gives rise to the vertebral bodies and nucleus pulposus of intervertebral discs.
Notochord induces neurulation.
Paraxial mesoderm segments into somites (from occipital to coccygeal regions) differentiating into dermatome, myotome, and sclerotome.
Each myotome and dermatome retain their innervation from their segment of origin.
Dermatome and myotome migrate together to form skin and muscle tissues.
Intermediate mesoderm forms the urogenital structures (gonadal ridge and mesonephric system).

Lateral and Longitudinal Folding in Mesoderm

Lateral folding brings the lateral aspects of the embryo ventrally and wraps the amniotic cavity around the embryo, creating the coelomic cavity.
Longitudinal folding brings the developing heart ventrally and caudally, and creates the foregut and hindgut.

Cardiogenic Mesoderm Development

Cardiac progenitor cells migrate through the primitive streak to the splanchnic mesoderm.
Cardiogenic mesoderm migrates to become the endocardial tube (from the cardiac crescent).
Myocardial cells originate from splanchnic mesoderm.

Somitomeres and Somites

Somites are formed in the cephalic region, with initial somitomeres disappearing, leaving 42-44 pairs of somites(occipital, cervical, thoracic, lumbar, sacral, and coccygeal).

Body Folding Outcomes

Medial mesoderm remains dorsal, while lateral mesoderm shifts ventrally.
Amniotic cavity surrounds the embryo.

Coelomic Cavity and Endoderm Derivatives

The coelomic cavity forms within the embryo.
Endoderm lines the gut tube.
Endoderm also forms respiratory epithelium, tonsils, thymus, thyroid, parathyroid, auditory canal, tympanic membrane, liver, gallbladder, pancreas, urinary bladder, and urethra.

Gut Tube Formation

In the fourth week, the ventral aspect of the trilaminar disc internalizes to form the epithelial lining of the gut tube.
Simultaneous cephalocaudal and lateral folding forms the gut tube.
The tube starts as a closed structure with oropharyngeal and cloacal membranes.

Primary Germ Layer Contributions to Gut Tube

Stomodeum (ectoderm-lined invagination) is cranially located to the oropharyngeal membrane.
Proctodeum (ectoderm-lined invagination) is caudally located to the cloacal membrane.

Cephalocaudal Folding of Gut Tube

Forms the head fold, placing the heart ventrally.
Creates the foregut.
Brings the septum transversum ventrally to create the hindgut.

Septum Transversum

Septum transversum divides the developing heart from the foregut, contributing to the development of the diaphragm and other structures.

Lateral Folding of Gut Tube

Lateral folding positions the developing organs and structures and establishes the primitive gut tube's final shape.

Mesentery Development

Dorsal mesentery connects the gut tube to the posterior abdominal wall.
Dorsal mesentery maintains the proper location of the gut tube.
Ventral mesentery forms from the mesenchyme of the septum transversum.
Intraperitoneal organs are suspended from dorsal mesentery,
Retroperitoneal organs are located outside the peritoneal cavity
Secondarily retroperitoneal organs originate within the peritoneal cavity and lose their mesenteric connection through fusion with the posterior body wall.

Gut Tube Derivatives

The gut tube gives rise to the foregut, midgut, and hindgut.
Foregut forms the esophagus, stomach, and proximal duodenum.
Midgut forms the distal duodenum, jejunum, ileum, cecum, ascending colon, proximal transverse colon.
Hindgut forms the distal transverse colon, descending colon, sigmoid colon, rectum, and upper anal canal.

Foregut Development

Foregut runs from the oropharyngeal membrane to the liver outgrowth, including the major duodenal papilla.
Pharyngeal gut forms the esophagus, stomach, and proximal duodenum, as well as tracheoesophageal septum, and lung buds.
Foregut esophagus is dorsal to the respiratory primordium, which develops further into the respiratory diverticulum.
Stomach begins in the thoracic cavity, rotating caudally.

Liver and Gallbladder Development

Hepatic plate forms a diverticulum, which develops into the liver bud and gallbladder.
Endoderm forms liver cords.

Pancreas Development

Pancreas develops from two buds (ventral and dorsal).
Ventral pancreas rotates to the fifth week.
Ventral pancreas and hepatic duct merge into the hepatopancreatic ampulla.

Anal Canal Development

The anal canal is subdivided by the urorectal septum into superior (hindgut) and inferior (proctodeum) portions with different embryological origins and nerve/vascular supply from the inferior mesenteric artery.

Summary of GI Development

During week 4, the gut tube forms.
The liver, gallbladder, pancreas form as buds from the duodenum.
The stomach rotates and expands.
Midgut herniates through the umbilical ring to rotate.
The cloaca separates into structures like the urogenital sinus and the anorectal canal, and surrounding membranes rupture.

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Description

This quiz explores the processes of body folding and neurulation during embryonic development. It covers key structures like the primitive streak, mesoderm formation, and the development of membranes and the neural plate. Test your knowledge on these crucial stages of embryonic development!