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89 Cards in this Set
- Front
- Back
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2 functions of the Small Intestine:
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-Digest food material
-Absorb end products of the digestive process |
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3 regions of small intestine:
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-Duodenum
-Jejunum -Ileum |
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How much do the 3 special modifications of the intestinal surface increase its SA?
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400-600 fold
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What are the 3 specializations?
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-Plicae circulares
-Villi -Microvilli |
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What are Plicae circulares?
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Permanent mucosal folds
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What parts of the SI have plicae circulares?
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All three
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How much do the plicae circulares increase the SA of the SI?
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By a factor of 2-3
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Another function of the plicae circulares:
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Slow the movement of chyme along the alimentary canal
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What are Villi?
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Finger projections of epithelial covered lamina propria
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How much do Villi increase the SA of the intestine?
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10X
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Where are the villi greatest in number?
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In the duodenum
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How are the villi in the ileum different from the duodenum?
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Duodenum = 1.5 mm tall
Ileum = 0.5 mm tall |
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What is at the base of villi?
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Crypts of Lieberkuhn
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What are these crypts?
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Branched tubular glands
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How much do microvilli increase the SA of the intestine?
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20X
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3 layers of the small intestine's mucosa:
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-Simple columnar epithelium
-Lamina propria -Muscularis mucosa |
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What special names do we use for the surface lining cells of the small intestine?
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-Absorptive Enterocytes
-Goblet cells -Enteroendocrine cells |
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What exactly are the villi?
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Extensions of lamina propria covered in epithelial cells
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What is at the center of each villous?
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A central lacteal - lymphatic channel + Several Capillaries
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What are the most abundant cells of the SI epithelium?
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Surface absorptive - enterocytes
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What are the principle functions of enterocytes?
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Terminal digestion and absorption of water and nutrients
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What do they especially form?
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Chylomicrons
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What type of epithelial cells are enterocytes?
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Simple columnar with an elongated nucleus
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How are enterocytes linked laterally? Why?
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Via tight junctions - to prevent paracellular diffusion.
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What makes up the luminal surface of each enterocyte?
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The brush border of microvilli
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What covers the microvilli?
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A glycocalyx coat
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Functions of the glycocalyx coat:
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-Protective
-Digestion of disacchs/peptides |
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How are microvilli attached to enterocytes?
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Via Actin filaments, which attach them to the terminal web of their cytoskeletons
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What is abundant underneath the terminal web? For what?
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Smooth ER - contains enzymes for triglyceride synthesis.
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What cells are very prominently scattered among enterocytes in the small intestine?
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Goblet cells
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What do goblet cells make?
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Mucin
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What is the consistency of mucin?
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-20% protein
-80% carbohydrate |
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What happens to mucin granules after exocytosis from Goblet cells?
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They become hydrated and expand several hundred fold in volume!
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What makes goblet cells so prominent?
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The fact that they contain so much carb that they don't stain on H and E
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What does stain goblet cells?
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PAS stain
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Where can you see crypts of lieberkuhn in the SI lining?
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At the bases of villi, extending into the lamina propria.
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What cells are in the crypts?
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Base: Paneth and neuroendocrines
Surface: Enterocytes/Goblets |
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Are Paneth cells renewable as often as the rest of the intestinal epithelium?
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No, they are long lived.
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What do paneth cells secrete?
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-Lysozyme
-Defensins |
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What stains the secretory granules of paneth cells scarlet?
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Phloxine-tartrazine
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What is the core of a villus formed by?
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Lamina propria
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How far down does the lamina propria extend?
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To the muscularis mucosa
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What are the layers of the muscularis mucosa?
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-Inner circular layer
-Outer longitudinal layer |
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How does the muscularis mucosa relate to the villi?
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Some smooth fibers extend to the tip and contract during digestion to help empty the lacteal.
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What is the immune defense system in the lamina propria called?
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GALT
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2 types of lymphoid lumps in the GALT:
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-Peyers patches
-Lymphoid nodules |
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What is at the center of a lymphoid nodule?
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Germinal center
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What is in germinal centers?
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Proliferating lymphoblasts that generate IgA producing B-cells
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Are B-cells the only thing in germinal centers?
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No they also have T-cells, APCs, and Dendritic cells.
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What special cells are in the epithelium covering lymphoid nodules (thank you alicia)?
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Mcells
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What do MCells do?
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Endocytose Ags from the gut lumen and pass them via transcytosis to APCs that present to lymphocytes.
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What diseases result from uncontrolled chronic inflammation of the gut mucosa?
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-IBD
-Crohn's -Ulcerative Colitis |
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What is NOD2?
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The susceptibility gene for IBD
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So the function of the muscularis mucosa of the small intestine is:
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To help digestion by contracting and shortening villi several times per minute
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What are the layers of the muscularis mucosae?
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-Outer longitudinal
-Inner circular |
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What does the submucosa of the SI consist of?
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-Moderately dense CT
-Small numbers of adipocytes |
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How is the duodenal submucosa unique?
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It contains Brunners Glands!
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2 Things that mark the junction of the stomach and duodenum:
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1. Pyloric sphincter
2. Presence of Brunner's glands in the submucosa |
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What are the structures of Brunner's Glands called?
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Tubuloalveolar
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What do the Brunner's Glands secrete? Intended for what?
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ALKALINE mucous that protects the duodenal mucosa from acidic chyme from the stomach.
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How does the alkaline mucus from Brunner's Glands get to the lumen of the duodenum?
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Their ducts cross through the submucosal layer and empty into the lumen.
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Do the Brunner's Glands secretions only have alk mucus?
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No - also epidermal growth factor
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How much fluid does the small intestine secrete per day?
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1 L/day
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What controls the small intestinal secretion?
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-Mainly Submucosal plexus
-CCK -Secretin |
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What is the function of the Muscularis Externa?
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To move chyme along the intestine
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What is the muscularis externa composed of?
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-Inner circular layer
-Outer longitudinal layer of smooth muscle of course |
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What lies between the two layers of muscle?
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Auerbach's myenteric plexus
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2 types of movement associated with the small intestine:
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1. Mixing contractions
2. Propulsive contractions |
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What do mixing contractions do?
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Expose chyme to digestive juice
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What do propulsive contractions do?
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Move chyme along the intestine at about 2 cm/min
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What does the myenteric plexus mediate peristaltic movement in response to?
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Gastric distention
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What happens when Enteritis causes irritable substances to assault intestinal mucosa?
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Peristaltic rush
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What is the result of a peristaltic rush?
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Diarrhea
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Which is the smallest segment of the SI? how long?
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Duodenum - 25 cm
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What flows into the duodenum?
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-Bile from liver
-Digestive enzymes from pancreas |
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Where does the common bile duct flow into the duodenum?
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At the duodenal papilla
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How are the villi in the duodenum different from in the jejunum and ileum?
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-Taller
-Broader -More numerous/unit area |
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How are the glands in the duodenum unique?
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-Less goblets
-Brunners in submucosa |
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Features of jejunum:
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-No brunners
-More goblets -Shorter/narrower/fewer villi |
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Features of the ileum:
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-Fewest
-Narrowest -Shortest VILLI |
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What does the lamina propria of the ileum house?
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Peyers patches
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What digests dietary fat in the duodenum?
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Pancreatic lipase
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What happens to the FFAs in micelles that diffuse into the enterocytes after being digested in the duodenum?
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They are re-esterified into triglycerides, then packaged into chylomicrons.
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Where do chylomicrons go?
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Into lacteals of the villi
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What is Chyle?
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The milky white emulsion of lipid that fills up the lymphatics during digestion.
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What is Celiac disease?
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An autoimmune disease of the gut caused by allergy to GLUTEN (jen allen)
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How common is celiac disease?
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The most common genetic disease in europe!
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What happens in celiac disease?
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The immune cells destroy villi so nutrients can't be absorbed.
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What is the treatment for celiac disease?
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Adopt a gluten-free diet
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