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Objectives
After studying this chapter, you should be able to:
Trace the development of the digestive organs from their precursors in the tubiform embryo.
Summarize the blood supply and innervation of the three embryonic divisions of the digestive system: the foregut, midgut, and hindgut.
Name the specific organs that are derived from the foregut, midgut, and hindgut.
Describe the processes by which the digestive organs form, including elongation, rotation, budding, and partitioning.
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ORIGINS AND REGIONAL PATTERNS OF THE DIGESTIVE SYSTEM
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The digestive system is derived from the splanchnopleure of the tubiform embryo (Figure 5-1).
The endoderm gives rise to the epithelium of the digestive tract and the parenchyma of associated glands.
The splanchnic (visceral) mesoderm gives rise to the connective tissue and smooth muscle of the digestive system.
Neural crest cells migrate into the walls of the organs of the digestive system to form parasympathetic intramural ganglia.
The primitive gut is divided into three regions (Figure 5-2):
The foregut extends from the oropharyngeal (buccopharyngeal) membrane (Figure 5-3) through the proximal half of the duodenum, including the precursor buds of the liver, gallbladder, and pancreas.
The midgut begins at the distal half of the duodenum and continues through the proximal two thirds of the transverse colon. The midgut initially remains in communication with the yolk sac via the vitelline duct (Figure 5-3), which is later obliterated.
The hindgut begins at the distal third of the transverse colon and ends at the cloacal membrane (Figure 5-3).
During the fifth and sixth weeks of development, the lumen of the entire gut tube becomes occluded as its epithelial cells proliferate. By the eighth week, the gut tube recanalizes as epithelial cells undergo apoptosis and the gut tube diameter expands (Clinical Box 5-1).
Each embryonic region of the gut has its own mesenteries, blood supply, and innervation, as described in the following sections and summarized in Table 5-1.
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