Functional histology of intestines Flashcards
Identify the main histological features of the small intestine
Adaptations which maximise the surface area of the small intestine
- Long (6-7 cm)
- Highly folded (circular folds)
- Villi
- Microvilli
Three regions of the small intestine
duodenum
jejunum
ileum
Describe the main features of villi
Finger-like/ leaf-like projections of mucosa
Lamina propria forms the ‘core’,
Rich supply of blood vessels and lacteals (for lipid transport)
Simple columnar epithelium
Microvilli further increase surface area and create a brushborder
Crypts of Lieberkuhn open at the base of villi
What are the cells of the small intestine?
Enterocytes: main cells of villi, make up the columnar epithelium. Main function is absorption
Goblet cells: produce mucus
Enteroendocrine cells: produce peptide hormones such as secretin and cholecystokinin.
Paneth Cells: located at crypts of Leiberkuhn, produce lysozyme
Stem cells: found towards the base of intestinal glands. Allow regeneration of epithelial cells every 3-4 days
Lymphocytes: immune surveillance and protection
Where does the blood supply to the small intestine originate?
Superior mesenteric artery: has jejunal, ileal and ileocolic branched.
Proximal half of duodenum supplied by coeliac trunk
Where are Brunner’s glands found?
In the submucosal layer of the duodenum. Glands produce an alkaline secretion which neutralises the acidic chyme
Where are Peyer’s patches found?
In the lamina propria of the ileum: Large collections of lymphoid tissue
How can you distinguish between the different regions of the small intestine?
Duodenum: C-shaped structure. Simple columnar epithelium, villi, Brunner’s glands. Widest part of the small intestine, approx 25cm long. Mostly retroperitoneal
Jejunum: Intraperitoneal, prominent circular folds, thicker walled and wider lumen than ileum. The less prominent arterial arcades and longer vasa recta (straight arteries) compared to those of the ileum.
Ileum: narrowest part of small intestine, intraperitoneal, Peyer’s patches
Name two diseases which affect the small intestine and two which affect the large intestine
Small intestine: Coeliac disease, Chron’s disease
Large intestine: Appendicitis, Ulcerative colitis, diverticular disease
Features of coeliac disesase
Autoimmune disorder
Caused by intolerance to proteins in cereal crops (particularly gluten), triggers an immune reaction.
Inflammation and damage to duodenum and jejunum leads to blunting and loss of villi
Features of Chron’s disease
Inflammatory bowel disease
Patchy chronic inflammation which can affect any part of the GI tract. Commonly affects areas whith high concentration of lymphoid follicles e.g. peyer’s patches. Most common in terminal ileum.
Transmural inflammation
Causes strictures, fistula formation, symptoms due to malabsorption.
Function of small intestine
Further digestion of food and absorption into the blood
Function of large intestine
Absorption of water and formation of faeces
Distinctive features of the large intestine
Taenia coli: three thickened bands formed by condensations of longitudinal muscle layer present in the caecum and colon
Appendices epiploicae: fatty tages found on the outside of the colon
Haustrations: Visible saculations of the colon
Semilunar folds: Incomplete folds of smooth muscle