Quicktime Movie - Gastrointestinal Tract 3D stage 22

From Embryology
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width=410px|height=415px|controller=true|autoplay=false</qt> 3 Dimensional Reconstruction

Based upon a serial reconstruction from individual embryo slice images (27 mm Human embryo, Carnegie Stage 22 approximate day 56).

The endoderm and mesoderm initially contribute many structures in the gastrointestinal tract, respiratory and renal systems. Note the relative size and position of individual structures and organs at this early stage of development. Below the animation is a more complete description of each system.


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GIT Links: Introduction | Medicine Lecture | Science Lecture | endoderm | mouth | oesophagus | stomach | liver | gallbladder | Pancreas | intestine | mesentery | tongue | taste | enteric nervous system | Stage 13 | Stage 22 | gastrointestinal abnormalities | Movies | Postnatal | milk | tooth | salivary gland | BGD Lecture | BGD Practical | GIT Terms | Category:Gastrointestinal Tract
GIT Histology Links: Upper GIT | Salivary Gland | Smooth Muscle Histology | Liver | Gallbladder | Pancreas | Colon | Histology Stains | Histology | GIT Development
Historic Embryology - Gastrointestinal Tract  
1878 Alimentary Canal | 1882 The Organs of the Inner Germ-Layer The Alimentary Tube with its Appended Organs | 1902 The Organs of Digestion | 1903 Submaxillary Gland | 1906 Liver | 1907 Development of the Digestive System | 1907 Atlas | 1907 23 Somite Embryo | 1908 Liver and Vascular | 1910 Mucous membrane Oesophagus to Small Intestine | 1910 Large intestine and Vermiform process | 1911-13 Intestine and Peritoneum - Part 1 | Part 2 | Part 3 | Part 5 | Part 6 | 1912 Digestive Tract | 1912 Stomach | 1914 Digestive Tract | 1914 Intestines | 1914 Rectum | 1915 Pharynx | 1915 Intestinal Rotation | 1917 Entodermal Canal | 1918 Anatomy | 1921 Alimentary Tube | 1932 Gall Bladder | 1939 Alimentary Canal Looping | 2008 Liver | 2016 GIT Notes | Historic Disclaimer
Human Embryo: 1908 13-14 Somite Embryo | 1921 Liver Suspensory Ligament | 1926 22 Somite Embryo | 1907 23 Somite Embryo | 1937 25 Somite Embryo | 1914 27 Somite Embryo | 1914 Week 7 Embryo
Animal Development: 1913 Chicken | 1951 Frog


Movie Source: UNSW Embryology 3D Model Movie - Gastrointestinal Tract, Respiratory, Kidney

Gastrointestinal Tract

The gastrointestinal tract (GIT) develops primarily from the endoderm, with inputs from the mesoderm (splanchnic mesoderm) and the ectoderm (neural crest cells form its primary nerve plexus). After the endoderm is folded into a blind-ended tube in week 4, it begins to develop into the primary lining of the GIT, while the mesoderm provides its muscular wall and connective tissues components. The GIT is typically partitioned into 3 parts, based on their separate blood supplies: foregut, midgut and hindgut, with the allantois coming off the hindgut. A bud coming off the tract forms the liver; eventually buds appear that form gallbladder and pancreas. The rostral end of the tube ends at the buccopharyngeal membrane, where it interacts with ectoderm directly (no mesoderm in between). This area forms the future mouth. A similar endodermal-ectodermal interaction occurs at the tail the cloacal membrane. The section of the GIT here is called the cloaca. During week 4, the tube begins to dilate in a certain region, with the dorsal border growing more rapidly than the ventral. This establishes the greater and lesser curvatures of the stomach. The stomach also rotates 90o along the longitudinal axis. On day 22, a small endodermal thickening is visible on the ventral side of the duodenum this becomes the hepatic diverticulum that forms the liver over the next few days. The liver has an important in blood formation. As early as the fourth week, red blood cells production moves to the liver, as opposed to blood islands in the extraembryonic mesoderm.

Respiratory System

The respiratory system is endodermal in origin, initially "budding off" the foregut during week 3. This bud forms the respiratory diverticulum, at the level of the glottis between the adult oesophagus and trachea. It continues to bud in week 4, forming a pair of lung buds.

Kidney

The kidneys develop from intermediate mesoderm, which lies between the lateral plate mesoderm and the somites. The kidney develops in multiple stages, which occur in a rostrocaudal sequence. The earliest structure to form is the pronephros, in week 4, featuring a pronephric duct with associated nephrogenic mesenchyme. This degenerates early on, leaving only the duct system running down to the cloaca, this becomes known as the mesonephric duct, in the embryo. The next stage is the formation of the mesonephros, also in week 4. Its differentiation is induced by the pronephros. However, the mesonephros is also a transient structure. It provides a template for the adult metanephros, beginning on day 35-37.