Small Intestine Histology: Key Points
Overview of the Small Intestine
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Length and Structure:
- It is the longest portion of the gastrointestinal (GI) tract, approximately 6 meters long in adults.
- Primary site for digestion and absorption in the body.
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Segments:
- Duodenum: Most proximal, shortest segment. Connects with the jejunum at the duodenojejunal junction.
- Jejunum: Approximately 2.5 meters long, transitions to the ileum.
- Ileum: About 3.5 meters long, leads to the cecum of the large intestine at the ileocecal junction.
Histological Structure
- Layers of the Small Intestine:
- Mucosa: Innermost layer composed of the epithelium, lamina propria, and muscularis mucosae.
- Submucosa: Contains blood vessels, lymphatic vessels, and nerves.
- Muscularis propria: Consists of smooth muscle cells arranged in inner circular and outer longitudinal layers.
- Serosa: Outermost connective tissue layer, allows movement within the abdomen.
Microscopic Features
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Villi:
- Finger-like projections into the lumen, tallest in the duodenum and jejunum, shorter and broader in the ileum.
- Lined with enterocytes (simple columnar cells with microvilli) and goblet cells (secrete mucus).
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Crypts of Lieberkühn:
- Glands located at the base of the villi.
- Contain stem cells for epithelial cell renewal, including enterocytes and goblet cells.
- Paneth cells present, providing innate immune defense.
Functions of Cells
- Enterocytes: Increase surface area for absorption due to microvilli.
- Goblet Cells: Secrete mucus for lubrication and protection of intestinal epithelium.
- Paneth Cells: Contain eosinophilic granules, aid in immune defense against pathogens.
Summary
- The small intestine plays a critical role in nutrient absorption. Its histological structure includes distinct layers and specialized cells facilitating digestion and immune protection.
These notes provide a concise yet comprehensive overview of the small intestine's histology, focusing on structure, function, and cellular composition.