Terminal ileum
Pars terminalis ilei
- Latin synonym: Ileum terminale
- Related terms: Terminal part; Ileum: Terminal part
Definition
Terminal ileum refers to the distal (final) segment of the ileum immediately proximal to the ileocaecal junction, where the small intestine joins the caecum of the large intestine. It is characterised by the presence of numerous aggregated lymphoid nodules (Peyer's patches), which appear as small lymphoid follicles within the mucosa (lamina propria) and submucosa.
Functions
The terminal ileum is the principle site for the absorption of vitamin B12 (bound to intrinsic factor) and the reabsorption of bile salts, both of which are essential for normal haematological function and the enterohepatic circulation of bile acids. The terminal ileum also plays an important role in mucosal immunity through its abundant gut-associated lymphoid tissue (GALT).
Clinical correlate
The terminal ileum is one of the most common sites affected by Crohn's disease, and diseases or resection of this region may result in vitamin B12 deficiency, bile salt malabsorption, diarrhoea, and steatorrhea.
References
Standring, S. (2015) Grays Anatomy: The Anatomical Basis of Clinical Practice. 41st edn. London: Churchill Livingstone Elsevier. Chapter 65, Small intestine.
Elsevier (n.d.) Terminal ileum. ScienceDirect Topics. Available at: https://www.sciencedirect.com/topics/medicineanddentistry/terminalileum (Accessed: 14 June 2026).
Tian C, Ranasinghe IR, Hsu R. Crohn Disease. [Updated 2025 Dec 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan. Available from: https://www.ncbi.nlm.nih.gov/books/NBK436021/
