Histology · MU Sofia

Small intestine (duodenum + mesenteric)

Covers the histology of the duodenum, the first part of the small intestine, going through its four wall layers from the mucosa with villi, enterocytes and goblet cells, to the submucosa with Brunner's glands, the muscularis and the adventitia. It then describes the mesentery, a double peritoneal fold, and its loose connective tissue, vessels, lacteals, autonomic nerves and lymphoid elements.

Inside: 3 sections · 4 labelled pictures · 20 flashcards · 3 min

Topic 11 of 17 in the MU Sofia syllabus for Histology (Medicine, Year 2). The free AceMed note covers it in 3 sections, about 501 words (3 min of reading), with 20 flashcards.

In this note

  1. Introduction
  2. Duodenum
  3. Mesentery

Duodenum

  • The duodenum is the first section of the small intestine, immediately following the stomach. It is a C-shaped, approximately 25-30 cm (10-12 inches) long, and plays a crucial role in the digestive process.

Microscopic (histologic) description

The duodenum is composed of the four layers characteristic of the gastrointestinal tract.

  • (or mucous membrane)
  • - tall, slender finger-like projections that extend into the lumen.
  • Absorptive Cells (or Enterocytes) - simple columnar cells with microvilli (or brush border) to expand the absorptive surface.
  • Goblet Cells - secrete mucus for lubrication.
  • - intestinal glands found at the base of villi.
  • - separates the intestinal crypts in the mucosa from the Brunner's glands in the submucosa.
  • - only in the esophagus and the duodenum does the submucosa contain glands.
  • - secrete alkaline mucus.
  • - two orthogonal layers of smooth muscle (inner circular and outer longitudinal).
  • Adventitia - loose connective tissue (absent in this specimen).

Mesentery

  • The mesentery is a double layer of peritoneum (a membrane) that attaches the intestines to the posterior abdominal wall, providing support and containing blood vessels, nerves, and lymphatics that supply the intestines.

Microscopic (histologic) description

  • Mesothelial Layer:
  • Structure: The outermost layer is lined by mesothelial cells, which are a type of simple squamous epithelium.
  • Function: These cells secrete serous fluid, which reduces friction between the mesentery and other organs, allowing smooth movements.
  • Connective Tissue:
  • Loose Connective Tissue: Just beneath the mesothelial layer, this loose connective tissue contains collagen and elastic fibers, which provide support and flexibility. It houses various cell types, including fibroblasts, macrophages, mast cells, and adipocytes (fat cells).
  • Adipose Tissue: Fat cells are abundant in the mesentery, storing energy and providing cushioning and insulation for the blood vessels and nerves.
  • Vascular Structures:
  • Arteries: The mesentery contains branches of the superior mesenteric artery, which supply oxygenated blood to the intestines. These arteries are lined with endothelial cells and surrounded by smooth muscle cells.
  • Veins: Venous structures include branches of the superior mesenteric vein, which drain deoxygenated blood and nutrients from the intestines. These veins also have an endothelial lining and are less muscular than arteries.
  • Capillaries: Numerous capillaries facilitate the exchange of gases, nutrients, and waste products between the blood and intestinal tissues.
  • Lymphatic Vessels:
  • Structure: The mesentery contains numerous lymphatic vessels, including lacteals, which are specialized for the absorption of dietary fats. These vessels have an endothelial lining and valves that prevent backflow of lymph.

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