Midterm 2: Small Intestine

Question 1

Main absorptive organ of the GI tract. What does it absorb?

Answer 1

Small intestine

proteins, fats, carbohydrates, vitamins, electrolytes

Question 2

Dimensions of the small intestine (length and diameter)

Answer 2

Variable length: 4-10 m with reported means of 6.5-7.0 m (longest component of GI tract)

Diameter: 3 cm

Question 3

Sections of the small intestine from proximal to distal.

Answer 3

Duodenum
Jejunum
Ilium

Question 4

What are the different parts of the duodenum from proximal to distal? Describe each section.

Answer 4

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

Question 5

What parts of the duodenum are secondary retroperitoneal?

Answer 5

Descending portion, horizontal portion, ascending portion. Everything but the cap.

Question 6

What comes after the duodenum in the small intestine? How long is this section? Describe this part of the organ. What does it absorb?

Answer 6

• Jejunum
• 2-3 meters long
• Numerous and distinct circular folds
• Absorption of nutrients and continued digestion (sugars and amino acids)
• Peritoneal

Question 7

What is the last section of the small intestine? Describe this section. What does it absorb?

Answer 7

-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

Question 8

What are the layers of the small intestine from most inner to outer?

Answer 8

1) Mucosa
2) Submucosa
3) Muscularis Externa
4) Serosa

Question 9

What layer of the small intestine holds most of the blood vessels?

Answer 9

Submucosa

Question 10

Where are Brunner’s glands located? What do they secrete? What do they protect?

Answer 10

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

Question 11

Where are Brunner’s glands located? What do they secrete? What do they protect?

Answer 11

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

Question 12

Below the major duodenal papillae of the submucosa, what protects the mucosal lining? What is it secreted by? What is it triggered by?

Answer 12

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

Question 13

Describe the muscularis external layer of the small intestine

Answer 13

Contains a 2 layer format consisting of circular and longitudinal layers of muscle

Question 14

Describe the serosa/adventitia layer of the Small intestine

Answer 14

Serosa: Superior part of duodenum, jejunum (all are peritoneal)
Adventitia: Duodenum EXCEPT superior part, so descending, horizontal and ascending parts (secondary retroperitoneal)

Question 15

True or false:

Villi are present in the mucosa of the SI

Answer 15

True

Question 16

_______________ are intestinal glands containing specialized cells

Answer 16

Crypts of Lieberkühn

Question 17

What are the 6 specialized cells found in the Crypts of Lieberkühn of the small intestine?

Answer 17

• Enterocytes
• Goblet cells
• Paneth cells
• Stem cells
• Enteroendocrine
• Peyer’s Patches and Microfold cells

Question 18

Describe the enterocytes in the small intestine

Answer 18

• Main absorptive cell
• simple columnar cells with microvilli on apical surface
• found in/outside intestinal gland (i.e., crypts)

Question 19

Where can goblet cells be found in SI?

Answer 19

Both in/outside intestinal gland

Question 20

Paneth cell function

Answer 20

Immunological function

secrete lysozyme

Question 21

______________ cells can differentiate into any other specialized cell in the intestinal mucosa

Answer 21

Multipotent stem

Question 22

How are Enteroendocrine (neuroendocrine) cells important in the small intestine?

Answer 22

Their secretions contribute to digestion (CCK and secretin), insulin secretion from pancreas via GIP and the hunger response (gherlin)

Question 23

gut-associated lymphatic tissue

Answer 23

Peyer’s patches

Question 24

What do microfold cells do?

Answer 24

Assist in presenting antigen to immune cells within the Peyer’s patches

Question 25

Underlying layer of loose connective tissue in the mucosa layer

Answer 25

Lamina propria

Question 26

Describe the vessels and muscle in the mucosa layer

Answer 26

Rich in blood, lymph vessels, and smooth muscle cells

lacteals → absorb digested fats and directly transfer to arterial system as portal circulation is bypassed