Lecture 22 small intestine Flashcards
what are the 3 main regions where the small intestine is located?
- Duodenum: ~25cm
- Jejunum: ~2.5m
- Ileum: ~3.6m
Total length = ~6m
whats the Initial segment of duodenum?
retroperitoneal
how is the small intestine held in place?
by mesentery
what does the mesentery do for the small intestine?
holds SI in place
Allows movement, but prevents SI from getting tangled
what does the mesentery of SI contain?
arteries,
veins,
nerves,
lymphatics
What’s delivered to the Small Intestine?
Chyme = acidic
how does the small intestine protect its epithelium?
Mucous secreting cells
Glands in submucosa (specifically in duodenum)
how does the SI neutralize pH?
Bicarbonate (HCO3-from pancreas
what does the SI still need to carry out and how?
further digestion, and then absorption
Need a large SA
what are Plicae Circulares (Circular Folds)?
Permanent large folds of SI
Core of submucosa (with overlying mucosa)
wheres villi found in SI?
surface of the plicae circulares
what does the Muscularis mucosae of SI allow?
villi to wiggle back and forth
whats is the Core of each villi is made of?
FCT (lamina propria)
what vessels are contained in villi?
- Lymph lacteal (products of fat digestion)
* Capillary network (products of protein and carbohydrate digestion)
whats lymph lacteal?
products of fat digestion
whats Capillary network?
products of protein and carbohydrate digestion
what enters the mesenteric veins?
Nutrient rich, deoxygenated blood absorbed in the small intestine
what do mesenteric veins drain into?
hepatic portal vein
what do lymph lacteals drain into?
drain into the cisterna chyli, thoracic duct and then left subclavian vein
how does SI increase surface area?
1: Long (~6m in length!)
2: Fold the submucosa – permanent folds = plicae circulares
3: Fold the mucosa (not the muscularis mucosa) = villi
4. Fold the apical plasma membrane of the epithelium = microvilli
what epithelium is in SI?
simple columnar
Microvilli on apical surface – Increase surface area further
whats on the epithelium of the SI?
Microvilli brush border
Gycocalyx:
- Glycoproteins – branched filaments
- Tether enzymes
Contact digestion: involves
brush border enzymes
whats gycocalyx?
- Glycoproteins – branched filaments
- Tether enzymes
whats does contact digestion involve?
brush border enzymes
what are the Junctions Between Epithelial Cells?
Tight junctions:
• Very tight
• Small molecules may diffuse through
whats the plasma membrane?
a barrier:
• Selectively permeable
• Has proteins – channels, transporters
whats included on the epithelium of the SI?
Enterocytes - Absorptive cells
Goblet cells - Secrete mucous for protection
Stem cells - Make all cell types
Paneth cells - granules, antibacterial enzymes
Endocrine cells - secrete hormones
what are Enterocytes?
Absorptive cells
what are Goblet cells?
Secrete mucous for protection
what are stem cells?
Make all cell type
what are paneth cells?
granules, antibacterial enzymes
what are endocrine cells?
secrete hormones
Which are permanent folds of the small intestine with a core of submucosa?
Plicae Circulares
