Midterm 2: Small Intestine Flashcards
Main absorptive organ of the GI tract. What does it absorb?
Small intestine
proteins, fats, carbohydrates, vitamins, electrolytes
Dimensions of the small intestine (length and diameter)
Variable length: 4-10 m with reported means of 6.5-7.0 m (longest component of GI tract)
Diameter: 3 cm
Sections of the small intestine from proximal to distal.
Duodenum
Jejunum
Ilium
What are the different parts of the duodenum from proximal to distal? Describe each section.
1) Duodenal cap/Superior portion (proximal):
- Attachment to stomach at pyloric sphincter
- Peritoneal
2) Descending portion:
- Circular/Kerckring folds (aka plica circulares) slow movement of chyme to allow ample time for digestion and absorption
- Receives secretions from liver, gallbladder and pancreas at major duodenal papilla/hepatopancreatic ampulla
- Secondary retroperitoneal
3) Horizontal portion:
- Secondary Retroperitoneal
4) Ascending part (distal):
- Terminates at junction with the peritoneal jejunum
- Secondary Retroperitoneal
What parts of the duodenum are secondary retroperitoneal?
Descending portion, horizontal portion, ascending portion. Everything but the cap.
What comes after the duodenum in the small intestine? How long is this section? Describe this part of the organ. What does it absorb?
- Jejunum
- 2-3 meters long
- Numerous and distinct circular folds
- Absorption of nutrients and continued digestion (sugars and amino acids)
- Peritoneal
What is the last section of the small intestine? Describe this section. What does it absorb?
-Ilium
-3-4 meters
-Fewer and less prominent circular folds compared to the jejunum as most nutrient absorption already completed
bile salts reabsorbed here
Peritoneal
What are the layers of the small intestine from most inner to outer?
1) Mucosa
2) Submucosa
3) Muscularis Externa
4) Serosa
What layer of the small intestine holds most of the blood vessels?
Submucosa
Where are Brunner’s glands located? What do they secrete? What do they protect?
Brunner’s glands located above the major duodenal papillae secrete alkaline-rich mucus to protect the intestinal wall from chyme passing into this region from the stomach
Where are Brunner’s glands located? What do they secrete? What do they protect?
Brunner’s glands located above the major duodenal papillae and in the submucosa layer secrete alkaline-rich mucus to protect the intestinal wall from chyme passing into this region from the stomach
Below the major duodenal papillae of the submucosa, what protects the mucosal lining? What is it secreted by? What is it triggered by?
Below the major duodenal papillae, the mucosal lining is protected by HCO3- secretion from the exocrine pancreas and is triggered by the hormone secretin secretion from intestinal enteroendocrine cells
Describe the muscularis external layer of the small intestine
Contains a 2 layer format consisting of circular and longitudinal layers of muscle
Describe the serosa/adventitia layer of the Small intestine
Serosa: Superior part of duodenum, jejunum (all are peritoneal)
Adventitia: Duodenum EXCEPT superior part, so descending, horizontal and ascending parts (secondary retroperitoneal)
True or false:
Villi are present in the mucosa of the SI
True
_______________ are intestinal glands containing specialized cells
Crypts of Lieberkühn
What are the 6 specialized cells found in the Crypts of Lieberkühn of the small intestine?
- Enterocytes
- Goblet cells
- Paneth cells
- Stem cells
- Enteroendocrine
- Peyer’s Patches and Microfold cells
Describe the enterocytes in the small intestine
- Main absorptive cell
- simple columnar cells with microvilli on apical surface
- found in/outside intestinal gland (i.e., crypts)
Where can goblet cells be found in SI?
Both in/outside intestinal gland
Paneth cell function
Immunological function
secrete lysozyme
______________ cells can differentiate into any other specialized cell in the intestinal mucosa
Multipotent stem
How are Enteroendocrine (neuroendocrine) cells important in the small intestine?
Their secretions contribute to digestion (CCK and secretin), insulin secretion from pancreas via GIP and the hunger response (gherlin)
gut-associated lymphatic tissue
Peyer’s patches
What do microfold cells do?
Assist in presenting antigen to immune cells within the Peyer’s patches
Underlying layer of loose connective tissue in the mucosa layer
Lamina propria
Describe the vessels and muscle in the mucosa layer
Rich in blood, lymph vessels, and smooth muscle cells
lacteals → absorb digested fats and directly transfer to arterial system as portal circulation is bypassed
