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89 Cards in this Set

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