Lecture 22 small intestine

Question 1

what are the 3 main regions where the small intestine is located?

Answer 1

1. Duodenum: ~25cm
2. Jejunum: ~2.5m
3. Ileum: ~3.6m

Total length = ~6m

Question 2

whats the Initial segment of duodenum?

Answer 2

retroperitoneal

Question 3

how is the small intestine held in place?

Answer 3

by mesentery

Question 4

what does the mesentery do for the small intestine?

Answer 4

holds SI in place

Allows movement, but prevents SI from getting tangled

Question 5

what does the mesentery of SI contain?

Answer 5

arteries,
veins,
nerves,
lymphatics

Question 6

What’s delivered to the Small Intestine?

Answer 6

Chyme = acidic

Question 7

how does the small intestine protect its epithelium?

Answer 7

Mucous secreting cells

Glands in submucosa (specifically in duodenum)

Question 8

how does the SI neutralize pH?

Answer 8

Bicarbonate (HCO3-from pancreas

Question 9

what does the SI still need to carry out and how?

Answer 9

further digestion, and then absorption

Need a large SA

Question 10

what are Plicae Circulares (Circular Folds)?

Answer 10

Permanent large folds of SI

Core of submucosa (with overlying mucosa)

Question 11

wheres villi found in SI?

Answer 11

surface of the plicae circulares

Question 12

what does the Muscularis mucosae of SI allow?

Answer 12

villi to wiggle back and forth

Question 13

whats is the Core of each villi is made of?

Answer 13

FCT (lamina propria)

Question 14

what vessels are contained in villi?

Answer 14

• Lymph lacteal (products of fat digestion)

* Capillary network (products of protein and carbohydrate digestion)

Question 15

whats lymph lacteal?

Answer 15

products of fat digestion

Question 16

whats Capillary network?

Answer 16

products of protein and carbohydrate digestion

Question 17

what enters the mesenteric veins?

Answer 17

Nutrient rich, deoxygenated blood absorbed in the small intestine

Question 18

what do mesenteric veins drain into?

Answer 18

hepatic portal vein

Question 19

what do lymph lacteals drain into?

Answer 19

drain into the cisterna chyli, thoracic duct and then left subclavian vein

Question 20

how does SI increase surface area?

Answer 20

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

Question 21

what epithelium is in SI?

Answer 21

simple columnar

Microvilli on apical surface – Increase surface area further

Question 22

whats on the epithelium of the SI?

Answer 22

Microvilli brush border

Gycocalyx:

• Glycoproteins – branched filaments
• Tether enzymes

Contact digestion: involves
brush border enzymes

Question 23

whats gycocalyx?

Answer 23

• Glycoproteins – branched filaments

- Tether enzymes

Question 24

whats does contact digestion involve?

Answer 24

brush border enzymes

Question 25

what are the Junctions Between Epithelial Cells?

Answer 25

Tight junctions:
• Very tight
• Small molecules may diffuse through

Question 26

whats the plasma membrane?

Answer 26

a barrier:
• Selectively permeable
• Has proteins – channels, transporters

Question 27

whats included on the epithelium of the SI?

Answer 27

Enterocytes - Absorptive cells
Goblet cells - Secrete mucous for protection
Stem cells - Make all cell types
Paneth cells - granules, antibacterial enzymes
Endocrine cells - secrete hormones

Question 28

what are Enterocytes?

Answer 28

Absorptive cells

Question 29

what are Goblet cells?

Answer 29

Secrete mucous for protection

Question 30

what are stem cells?

Answer 30

Make all cell type

Question 31

what are paneth cells?

Answer 31

granules, antibacterial enzymes

Question 32

what are endocrine cells?

Answer 32

secrete hormones

Question 33

Which are permanent folds of the small intestine with a core of submucosa?

Answer 33

Plicae Circulares