Question

1. What separates the hindgut from the developing urinary system.
2. How is the anal canal formed and why does its 2 halves have different blood supplies and nerve innervation?
3. Discuss the development and rotation of the stomach.
4. Discuss how the pancreas ( and its duct system) forms.
5. What are the embryological precursors for the liver, gallbladder and bile duct?
6. Discuss the development of the midgut. Which adult derivative develops from which limb of the primary intestinal loop?

no figure needed.

Answer 1

Ans 1.

The urogenital system arises during the fourth week of development from urogenital ridges in the intermediate mesoderm on each side of the primitive aorta. The nephrogenic ridge is the part of the urogenital ridge that forms the urinary system. Three sets of kidneys develop sequentially in the embryo.

Ans 2.

It is formed by the fusion of the internal anal sphincter, external anal sphincter and puborectalis muscle, and is palpable on digital rectal examination.

Modality	Above Pectinate line	Below Pectinate line
Arterial Supply	Superior rectal artery (branch of inferior mesenteric artery) Anastomosing branches from the middle rectal artery.	Inferior rectal artery (branch of the internal pudendal artery) Anastomosing branches from the middle rectal artery.
Venous Drainage	Superior rectal vein, which empties into the inferior mesenteric vein (portal venous system).	Inferior rectal vein, which empties into the internal pudendal vein (systemic venous system).
Nerve Supply	Visceral innervation via the inferior hypogastric plexus. Sensitive to stretch.	Somatic innervation via the inferior anal nerves (branches of the pudendal nerve) Sensitive to pain, temperature, touch and pressure.
Lymphatics	Internal iliac lymph nodes	Superficial inguinal lymph nodes

The superior aspect of the anal canal has the same epithelial lining as the rectum (columnar epithelium). However, in the anal canal, the mucosa is organised into longitudinal folds, known as anal columns. These are joined together at their inferior ends by anal valves. Above the anal valves are small pouches which are referred to as anal sinuses – these contain glands that secrete mucus.

Ans 3.

Stomach. ... During development the stomach rotates 90 in a clockwise direction along its longitudinal axis, placing the left vagus nerve along its anterior side and the right vagus nerve along its posterior side. Rotation of the stomach creates the omental bursa or lesser peritoneal sac.

Ans 4.

The pancreas forms during development from two buds that arise from the duodenal part of the foregut, an embryonic tube that is a precursor to the gastrointestinal tract. It is of endodermal origin. Pancreatic development begins with the formation of a dorsal and ventral pancreatic bud.

In the process of development, the organs enlarge and the ventral pancreas together with the common bile duct rotates. Then, in most cases, the pancreatic duct from the dorsal pancreas fuses with the pancreatic duct from the ventral pancreas to form the main pancreatic duct.

Ans 5.

Embryonic Development of the Liver:

The embryonic liver originates from the ventral foregut endoderm, which becomes the hepatic diverticulum, the first morphological sign of the embryonic liver. ... The STM contributes the fibroblasts and stellate cells of the liver.

The gallbladder develops from an endodermal outpouching of the embryonic gut tube. Early in development, the human embryo has three germ layers and abuts an embryonic yolk sac. During the second week of embryogenesis, as the embryo grows, it begins to surround and envelop portions of this sac.

General aspects of bile duct morphogenesis during liver development. ... The ventral foregut endoderm develops two protrusions: the cranial part leads to the formation of the intrahepatic bile ducts, while the caudal part generates the extrahepatic biliary tree.

Ans 6.

The midgut develops into the distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, and proximal 2/3 of transverse colon. The hindgut becomes the distal 1/3 of the transverse colon, descending colon, sigmoid colon and the upper anal canal.

Rotation of the midgut happens during the second month of intra-uterine life. This is the gastrointestinal tract, consisting of the foregut, the hindgut, and the midgut. ... As the midgut develops it protrudes into the body stalk forming a loop, with the superior mesenteric artery forming the axis of the loop.