Special Histology and Embryology: Practical Course - V. K. Napkhanyuk 2001

Digestive System

The human Digestive System (systema alimentarium) integrates several Organs that collectively ensure the assimilation of substances from the external environment, which are essential for meeting the body's plastic and energy needs.

The human digestive system consists of the alimentary canal and associated glands located outside its walls (Salivary Glands, Liver, and Pancreas), whose secretions participate in the digestive process.

Digestion is The process of chemical and mechanical food Processing followed by the absorption of breakdown products, occurring sequentially in various sections of the alimentary canal.

Structure/19.html">The Importance of the digestive system as an open biological system in The Human Body is immense. It provides the intake of substances that supply the body with necessary energy and building Materials for the continuous restoration of structures that break down and die off.

The digestive system is conventionally divided into three main sections:

1) the anterior section, which includes the Oral Cavity with all its structures, the Pharynx, and the Esophagus;

2) the middle section, consisting of The Stomach, small and large intestines, liver, and pancreas;

3) the posterior section, which represents the caudal part of the rectum and ensures the evacuation of undigested food residues from the digestive tract.

Throughout any of its sections, the alimentary canal shares a General structural plan consisting of an inner mucous membrane (mucosa); a submucosa; a muscular layer (muscularis); and an outer layer, which is either a serosa or an adventitia.

The mucous membrane (tunica mucosa) typically consists of three layers—the epithelium, the lamina propria, and the muscularis mucosae.

The submucosa (tela submucosa) is formed by loose Connective Tissue, which provides mobility to the mucous membrane and allows for fold formation.

The muscular layer (tunica muscularis) is formed by two layers of Muscle tissue—an inner circular layer and an outer longitudinal layer. These muscle layers are separated by connective tissue containing Blood and Lymphatic vessels, as well as an intermuscular nerve plexus. In the anterior and posterior sections, the muscle tissue is predominantly striated, whereas in the middle section it is smooth.

The serous membrane (tunica serosa) is formed by the visceral Peritoneum, consisting of a connective tissue layer containing Blood Vessels and nerve elements, and covered by mesothelium.

The esophagus and part of the rectum lack a serous membrane. Externally, they are covered by an adventitial layer (tunica adventicia) formed exclusively by connective tissue.