Tubo digestivo I

Introduction to the Digestive System

Overview of the Digestive Tract

• Fernando Pérez introduces the topic, focusing on the first part of the digestive tube, which extends from the esophagus to the anus and involves nervous, endocrine, and psychic coordination.

• The digestive system includes accessory glands such as the liver and pancreas. It consists of four tunics: mucosa, submucosa, muscularis, and serosa.

Structure of the Mucosa

• The mucosa features a unique structure with two layers of smooth muscle: an inner circular layer and an outer longitudinal layer that are characteristic across all digestive organs.

• The mucosal layer is supported by a loose connective tissue lamina propria beneath its epithelium.

Esophagus Anatomy and Function

Layers of the Esophagus

• The esophagus has a mucosal lining made up of stratified squamous non-keratinized epithelium supported by loose connective tissue.

• The second tunic (submucosa) contains dense connective tissue with blood vessels, lymphatics, nerves, and esophageal glands that aid in lubrication.

Muscle Composition

• The muscularis layer consists of two muscle types: striated muscle in the upper third, mixed striated and smooth in the middle third, and only smooth muscle in the lower third.

• Between these muscle layers lies Auerbach's myenteric plexus which regulates peristalsis.

Functions of the Esophagus

Role in Digestion

• The primary function is to transport swallowed food from the oropharynx to the stomach while protecting its mucosal surface through secretions from esophageal glands.

Histological Features

Microscopic Structure

• Histological images show stratified squamous epithelium with connective tissue papillae extending into it; this aids in structural integrity.

• Additional images highlight glandular structures within submucosa contributing to lubrication via mucus secretion.

Stomach Anatomy

Structural Characteristics

• The stomach is described as a dilated organ with three layers of muscle: an additional oblique layer complements circular and longitudinal layers found throughout other digestive organs.

Mucosal Layer Details

• Stomach mucosa features simple columnar epithelium rich in mucus-producing cells known as gastric pits or crypts where gastric glands open.

Digestive Functions of Stomach

General Functions

Esophageal and Gastric Structure Overview

Transition from Esophagus to Stomach

• The transition from the esophagus to the stomach is marked by a significant change at the cardiac point, where stratified squamous epithelium shifts to gastric mucosa.

• The stomach consists of three structurally glandular regions, each with distinct tubular glands that vary in secretion types.

Regions of the Stomach

• The first region adjacent to the cardia is known as the cardiac region; it features simple or branched tubular glands.

• The body or fundus of the stomach contains glands that secrete gastric juice, while the pyloric region near the duodenum has different secretory functions.

Glandular Structures and Secretions

• Cardiac glands release a bicarbonate-rich mucus, while fundic glands produce gastric juice rich in enzymes and hydrochloric acid.

• Surface epithelium secretes mucus that protects against acidity; gastric pits contain neck cells that add soluble mucus.

Cellular Composition of Gastric Glands

• Parietal cells located in upper gland regions are responsible for producing hydrochloric acid and intrinsic factor.

• Intermediate zones feature both parietal and chief (zymogenic) cells which secrete pepsinogen, activated into pepsin by acid.

Endocrine Functions within Gastric Tissue

• Enteroendocrine cells found deeper in gastric glands release various hormones like somatostatin, influencing digestive processes.

Gastric Glands and Their Functions

Structure and Function of Gastric Glands

• The stomach contains unicellular enteroendocrine glands that produce a bicarbonate-rich, slightly soluble secretion. The fundus region has extensive gastric juice-producing glands, while the cardiac region primarily secretes mucus rich in bicarbonate to prevent reflux.

• Mucus secreted in the cardiac region neutralizes gastric acid, protecting the esophageal mucosa from acidity. This is crucial as the gastric secretion moves towards the small intestine, which lacks protection against acidic pH.

Histological Features of Gastric Glands

• The left image illustrates simple or branched tubular glands in the antrum, showing a homogeneous behavior with a single type of cell producing mucus rich in vital components. These glands are located deep within the mucosa.

• A longitudinal section reveals layers including mucosa, muscularis mucosae, submucosa, and external muscular tunics. Notably observed are arteries, veins, lymphatic vessels, and a central nerve plexus (submucosal plexus).

Nervous System Components in Gastric Function

• The second nervous plexus identified is the myenteric plexus (Auerbach's), situated between muscle layers. Neurons exhibit large nuclei with loose chromatin characteristics.

• In the stomach's final portion (antrum and pylorus), there are significant changes as it transitions to the duodenum. This area features bicarbonate-producing glands essential for digestion.

Transition from Stomach to Duodenum

• At the pylorus, two key changes occur: transformation from gastric to intestinal mucosa and gland relocation into submucosal areas. Some pyloric glands remain above while others penetrate through muscularis mucosae.