Lecture 11: Intestine microanatomy Flashcards
What is the name of the folds in the digestive tract?
Plicae circularis
What increases the SA of the digestive tract?
Plicae circularis, Villi and microvilli
Describe an isolated villus
Can be divided into villus and intestinal glands/crypts of leiberkhan
Whats the function of smooth muscle found in the villus?
- Increased squeeze of lacteal - Increased localised movement
What are some conditions that impacts the villus?
1) Decreased blood flow in elderly can lead to malabsorption 2) Celiacs disease = villous atrophy and malabsorption IBS, Crohns etc too
What is the epithelium of the villus like?
Columnar epithelium with brush border
How are fats transported in the lacteals?
No smooth muscle, therefore rely on contractions of the muscularis mucosae. Eventually drain into venous system.
Whats transported in the submucosae venules of the digestive tract?
CHO, Proteins, Water and electrolytes. Venules in the submucosa are tributaries of the hepatic portal vein
What cells are found in the mucosa of the SI?
Columnar absorptive cells (Enterocytes) Goblet cells Enteroendocrine cells Undifferentiated cells (Stem cells for epithelium, up/down movement) Paneth cells EGEUP (Every Gut Enjoys Unique Poops)
What is the function of enterocytes?
- Absorbs small molecules from digestion (membrane studded with enzymes i.e Enterokinase (actives gut enzymes) and Glycosidases (breakdown CHO)
What is found on enterocytes?
Brush border, microvilli that increase SA and are connected to an actin cytoskeleton for localised movement (stirring of luminal contents) Also, a glycocalyx biofilm is found on top of the brush border. Attracts/protects desired/unwanted molecules.
What is the function of goblet cells?
Found in the squamous epithelium No brush border Contains mucinogen granules Secretes mucus
What is the function of enteroendocrine cells?
Secretes hormones through basal lamina into capillaries of lamina propria.
Give some examples of enteroendocrine cells and their hormones
Specific entero-endocrine cells;
- I cells; Detect FA/AA release CCK
- S cells; Detect pH release Secretin
- Enterochromaffin cells; Senses food/irritation Release serotinin (Gut motility or vomiting)
Consult lecture 19 for more specificity
Describe CCK function;
CCK stimulates pancreatic enzyme release
CCK stimulates bile release
CCK inhibits gastric emptying
Describe secretin function;
Increase pH-Enteroentocytes = Secretin,
Increase HCO3 release from pancreas.
Increase HCO3 release from brunners glands
Inhibits gastric acid release. (Somatosatin, Inhibts gastrin)
Describe the function of serotonin;
Increased smooth muscle contraction and peristalsis
Describe somatostatin function;
-ive feedback, inhibits gastrin release
What is the function of the paneth cells?
TNF-alpha (inflam response to bacteria and parasites) Lysozyme (Bacteriacidal, destroys bac. mem.) Defensins (Increases ion channels in cell membranes of invading microbes, thus, increased permiability)
Describe the regional specialisation of the duodenum;
Contains brunners glands (unique to first part of duodenum) HCO3 rich mucous to neutralise the acid in the chyme coming from the stomach
What else is present in the duodenum to aid acidity neutralisation?
Enterocytes- stimulate Bile enzymes and HCO3 production
What are unique about the jejenum villi?
No specialisations
Whats unique about the ilium?
Contains peyers patches, Lymphatic patches, macroscopically visible.
Difference between cilia and microvilli?
Cilia = Motile Microvilli = Not motile
Give a brief overview of the large intestine;
Soft muscular tube, ~1.5m long, minor digestive, major absorptive role
Describe the ceacum;
Expanded pouch, beginning of compaction process. Ilioceacal valve. Appendix off end. Lymphoid nodules.
What unique features are found on the large intestine?
Haustra Tenae coli
Describe the gross features of the large intestine?
Ceacum Ascending colon Right clonic (heaptic) flecture Transverese colon Left clonic (splenic) flecture Descending colon Sigmoid colon
Describe the mucosa of the large intestine;
Smooth; No plicae or villi Mucosal glands (crypts of leiberkhan) are numerous.
What are the cells in the mucosa of the large intestine?
Two cell types predominate; Columnar absorptive cells (like enterocytes in SI) - Absorb water and electrolytes - Absorbs vitamins produced by bacteria (B and K) Goblet cells; - Secretes mucous for lubrication (Increases towards end) Enteroendocrine cells; not visible on routine sections Undifferentiated cells; Base of glands.
What are the specialisations of the lamina propria in the large intestine?
- Dense collagen immediately beneath epithelium, numerous lymphatic nodules extending down to sub-mucosa. No lymphatic vessels till muscularis mucosae (thus some large intestine metastasis take ages to spread)
What are the specialisations of the muscularis externa in the large intestine?
Circular and longitudinal muscle layers. Outer longitudinal forms three distinct strips/bands running along the colon (teniae coli) = Allows independent segment contraction. These contractions form little pouches (haustra coli).
What is the large intestine covered by externally?
Adventitia occurs on the post./ surface of the large intestine. Elsewhere is serosa (refer to peritoneum for guidance)
Describe the structure of the anus;
Final portion; Anal canal (mucosa contains long. folds called anal columns) Distal margins; Transverse folds (Marks boundary between columnar epithelium -> stratified squamous. Anal spincters; Internal = (smooth muscle) and external (skeletal muscle) End = ANUS
