STRUCTURE OF THE GASTROINTESTINAL TRACT

INTRODUCTION: The GI tract is one of the most complex and important organ systems. It comprises the alimentary canal, a hollow structure extending from the mouth to the anus, and associated glandular organs that empty their contents into the canal.

LENGTH OF THE SYSTEM: The alimentary canal is 7–9 m in the adult and includes the mouth, esophagus (23–25 cm), stomach, small intestine (duodenum, jejunum, ileum; 6–7 m), large intestine (cecum and colon; 1.0–1.5 m), rectum, and anus.

CONNECTIONS AND ACCESSORY ORGANS: The canal is connected to the salivary glands, the pancreas, and the gallbladder, the sources of exocrine secretions that play an essential role in digestion.

ANATOMICAL MAKEUP OF GIT: The wall of the GI tract is composed of four main layers. From the lumen outward, these include the mucosa, submucosa, muscularis externa, and serosa. The precise structure of some of these layers, most notably the mucosa, varies from one region of the GI tract to the next. The mucosa has three components: specialized epithelial cells that line the lumen; the underlying lamina propria, a layer of connective tissue that contains small blood and lymphatic vessels, immune cells, and nerve fibers; and the muscularis mucosa, a thin layer of muscle cells. The muscularis mucosa is an important boundary in determining whether cancer of the GI tract is still localized to its site of origin or is likely to have metastasized (ie, spread to distant regions of the body). The submucosa is a layer of loose connective tissue directly beneath the mucosa containing larger blood and lymphatic vessels and a nerve plexus of the intrinsic or enteric nervous system, termed the submucosal nerve (Meissner) plexus. This nerve plexus is particularly important for secretion control in the GI tract. 

In some areas, the submucosa also contains glands and lymphoid tissue. The muscularis externa is composed of an inner circular and an outer longitudinal layer of smooth muscle and is responsible for the motility of the GI tract. Between these muscle layers lies the myenteric nerve (Auerbach) plexus, a division of the enteric nervous system that regulates motility. The serosa is an outer sheath of squamous mesothelial cells and connective tissues, where larger nerves and blood vessels travel in a bed of connective and adipose tissue.

RELATED;

1. ENTERIC NERVOUS SYSTEM  

2. DISEASES THAT AFFECT THE GIT

3.  PEPTIC ULCER DISEASE

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