Enteroendocrine cells and GALT !
- Cell
Scattered in the gut lining are hormone-making cells and a large immune system that samples what we swallow.
Updated 2026-11-01
See it in 3D: Ileum · Appendix · Duodenum · Stomach
What it is
The gut is the largest endocrine organ and the largest immune surface of the body. Enteroendocrine cells are single cells in the epithelium that release hormones such as gastrin, cholecystokinin, secretin and serotonin into the lamina propria. Gut-associated lymphoid tissue (GALT) includes Peyer patches, isolated follicles, the appendix and countless lymphocytes and IgA plasma cells. Tumours of enteroendocrine cells cause carcinoid syndrome; GALT is the gateway for typhoid and the origin of MALT lymphoma.
Structure
- Enteroendocrine cells: pale cells near the crypt base with secretory granules toward the basement membrane, not the lumen.
- Peyer patches: groups of lymphoid follicles with germinal centres in the ileal mucosa and submucosa, under a dome of epithelium.
- M (microfold) cells in the dome epithelium carry antigens from the lumen to underlying immune cells.
- Lamina propria: plasma cells producing IgA, T cells, macrophages and dendritic cells; intraepithelial lymphocytes sit between enterocytes.
Main enteroendocrine cells
| Cell | Where | Hormone | Effect |
|---|---|---|---|
| G cell | Gastric antrum, duodenum | Gastrin | Acid secretion |
| I cell | Duodenum, jejunum | Cholecystokinin | Gallbladder contraction, pancreatic enzymes |
| S cell | Duodenum | Secretin | Pancreatic bicarbonate |
| K cell | Duodenum, jejunum | GIP | Insulin release |
| L cell | Ileum, colon | GLP-1, peptide YY | Insulin release, satiety |
| Enterochromaffin cell | Whole tract | Serotonin | Motility and secretion |
Markers
- Chromogranin A
- Synaptophysin
- IgA
- CD8 (intraepithelial lymphocytes)
Clinical notes
- Neuroendocrine (carcinoid) tumours are common in the ileum and appendix; carcinoid syndrome (flushing, diarrhoea, right-heart valve disease) appears once liver metastases release serotonin directly into the systemic circulation.
- Salmonella Typhi enters through M cells of Peyer patches; typhoid ulcers run along the long axis of the ileum.
- MALT lymphoma of the stomach is linked to chronic Helicobacter pylori infection.
- Celiac disease raises the number of intraepithelial lymphocytes.
Test yourself
Think of the answer, then tap the question to see it.
Which cell over Peyer patches transports antigens from the lumen to immune cells?
The M (microfold) cell of the dome epithelium.
Why does an ileal carcinoid usually cause carcinoid syndrome only after metastasis to the liver?
Serotonin from the gut tumour drains through the portal vein and is broken down by the liver; liver metastases release it directly into the systemic blood.
Which enteroendocrine cell secretes cholecystokinin?
The I cell of the duodenum and jejunum.
Which immunoglobulin dominates the gut mucosa?
Secretory IgA, made by plasma cells of the lamina propria and carried across the epithelium.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Small intestine: villi, crypts, enterocytes, Paneth cells; duodenum vs jejunum vs ileum
- Stomach: gastric glands, parietal and chief cells
- Large intestine, appendix and anal canal
Related conditions
Microorganisms
Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.
Sources: 23.1 Overview of the Digestive System - Anatomy and Physiology 2e | OpenStax (OpenStax (Rice University), 2022); 23.5 The Small and Large Intestines - Anatomy and Physiology 2e | OpenStax (OpenStax (Rice University), 2022); 23.4 The Stomach - Anatomy and Physiology 2e | OpenStax (OpenStax (Rice University), 2022).
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Representative model, for educational purposes only.