Lecture 22: The small intestine Flashcards
What are the three main regions of the small intestine?
1st section = Duodenum ~ 25cm
2nd section = Jejunum ~ 2.5m
3rd section = Ileum ~ 3.5m
What is the role of the duodenum?
- receives acidic chyme from stomach
- where enzymes & bicarbonate get added from pancreas
- where bile from liver gets added
What is the main role of the Jejunum and Ileum?
Digestion and absorption
Where is each section of the small intestine and what holds it in place?
- Initial segment of small intestine (duodenum) is
retroperitoneal - Rest of small intestine is in the lower abdominal cavity below the stomach, held in place by mesentery - Allows movement, but prevents tangling
What structures does the mesentery contain?
Mesentery contains arteries, veins, nerves and lymphatics
What is the drainage pathway for blood from the small intestine and where does lymph travel?
- Nutrient rich, deoxygenated blood from small intestine
enters mesenteric veins - These drain to the hepatic portal vein
- Lymph lacteals ultimately drain into cisterna chyli,
thoracic duct, then left subclavian vein (see CVS)
How does the small intestine achieve high SA to allow for optimal absorption?
Achieved in 4 key ways:
1. Length
2. Folding of intestinal wall (plicae circulares)
3. Extensions of mucosa (villi)
4. Extensions of epithelial cells (microvilli)
What are plicae circulares?
- Permanent large folds of of small intestine
- makes up the core of submucosa with overlying mucosa
What allows movement of villi?
Muscularis mucosae allows villi movement
Where are villi found and what layer of the gut tube are they apart of?
- Numerous villi, found on the surface of the plicae circulares
- Part of mucosa
What is the core of the villi made of and what do they contain?
Core of each villus is made of lamina propria
Contains:
* Lymph lacteal (absorbs products of fat digestion)
- Capillary network (absorbs products of protein and carbohydrate digestion)
What epithelium does the small intestine have and what do they have on the surface of the cells?
- Epithelium of the small intestine is simple columnar
- The absorptive cells (enterocytes) have microvilli on apical surface (faces the lumen)
What is the role of glycocalyx in the small intestine?
- Glycoproteins – branched filaments
- Tether enzymes
What is the role of the microvilli brush border?
Contact digestion:
involves enzymes - attached to brush border
Describe the plasma membrane of the small intestine epithelial cells:
The plasma membrane is a barrier:
* Selectively permeable
* Has proteins
* channels
* transporters