1. All of the following are developed from the mesogastrium of Stomach except?
Reference: Keith L Moore, The Developing Human, 8th edition, pages 213-224, 244.
Answer is D Kidney
The stomach is suspended from the dorsal wall of the abdominal cavity by a dorsal mesentery—the primordial dorsal mesogastrium. This mesentery is originally in the median plane, but it is carried to the left during rotation of the stomach and formation of the omental bursa or
lesser sac of peritoneum. The primordial ventral mesogastrium attaches to the stomach. The ventral mesogastrium also attaches the duodenum to the liver and the ventral abdominal wall.
• The liver arises as a ventral outgrowth (hepatic diverticulum) from the caudal or distal part of the foregut early in the fourth week . Based on recent research findings, it has been suggested that both the hepatic diverticulum and the ventral bud of the pancreas develop from two cell populations in the embryonic endoderm.
• Hepatic diverticulum extends into the septum transversum, a mass of splanchnic mesoderm between the developing heart and midgut. The septum transversum forms the ventral mesentery in this region.
The pancreas develops between the layers of the mesentery from dorsal and ventral pancreatic buds of endodermal cells, which arise from the caudal or dorsal part of the foregut . Most of the pancreas is derived from the dorsal pancreatic bud. The larger dorsal pancreatic bud appears first and develops a slight distance cranial to the ventral bud. It grows rapidly between the layers of the dorsal mesentery”.
• The spleen is unique in respect to its development within the gut. While most of the gut viscera are endodermally derived (with the exception of the neural-crest derived suprarenal gland), the spleen is derived from mesenchymal tissue. Specifically, the spleen forms
within, and from, the dorsal mesentery.
• Development of the spleen is described with the digestive system because this organ is derived from a mass of mesenchymal cells located between the layers of the dorsal mesogastrium.
• During the fifth week of gestation, the mesonephric duct develops an outpouching, the ureteric bud, near its attachment to the cloaca.
• This bud, also called the metanephrogenic diverticulum, grows posteriorly and towards the head of the embryo.
• The elongated stalk of the ureteric bud, called the metanephric duct, later forms the ureter.
• As the cranial end of the bud extends into the intermediate mesoderm, it undergoes a series of branchings to form the collecting duct system of the kidney. It also forms the major and minor calyces and the renal pelvis.
• The portion of undifferentiated intermediate mesoderm in contact with the tips of the branching ureteric bud is known as the metanephrogenic blastema.
• The metanephrogenic blastema develops into the renal tubules.
• As the renal tubules grow, they come into contact and join with connecting tubules of the collecting duct system, forming a continuous passage for flow from the renal tubule to the collecting duct.
• Simultaneously, precursors of vascular endothelial cells begin to take their position at the tips of the renal tubules. These cells differentiate into the cells of the definitive glomerulus.
• In humans, all of the branches of the ureteric bud and the nephronic units have been formed by 32 to 36 weeks of gestation. However, these structures are not yet mature, and will continue to mature after birth. Once matured, humans have an estimated one million nephrons (approximately 500,000 per kidney) or more.