M19: Small Intestine

Question 1

3 regions of small intestine

Answer 1

1. DUODENUM (25cm)
   - retroperitoneal
   - c-shaped
2. JEJUNUM (1m)
3. ILEUM (2m)
   - connects to large intestine at ileocecal sphincter

Question 2

small intestine - circular folds

Answer 2

aka PLICAE CIRCULARIS
- created by ridges in submucosa
- submucosa makes fingerlike projections
- increase surface area in SI
- spiral pattern - allows all chyme to come in contact with SI walls for nutrient absorption

Question 3

in the SI, microvilli are extensions of ____ while vili are extensions of _____

Answer 3

microvilli: epithelia
villi: lamina propria

Question 4

structures in SI villi

Answer 4

• large vascular network
• LACTEALS: lymphatic system extension. Take things too large to enter into capillaries

Question 5

specialized epithelial cells on villi

Answer 5

top to bottom on villi
- ABSORPTIVE CELLS (absorb nutrients via microvilli)
in pit (intestinal gland)
- GOBLET CELLS (interspersed between absorptive cells)
- PANETH CELLS (secrete lysozymes that break down foreign materials, capable of phagocytosis)
- ENTEROENDOCRINE CELLS (secrete hormones secretin and cholecystokinin)

Question 6

name of pits between SI villi

Answer 6

intestinal gland

Question 7

hormones secreted by enteroendocrine cells in SI

Answer 7

secretin and cholecystokinin

Question 8

functions of paneth cells in SI

Answer 8

• secretes lysozyme
• capable of phagocytosis
• mantains SI microbiome

Question 9

order of structures, smallest to largest, that help increase surface area in small intestine

Answer 9

microvilli
villi
circular folds

Question 10

paneth cells

Answer 10

• secrete lysozymes that break down foreign materials
• capable of phagocytosis

Question 11

absorptive cells

Answer 11

• epithelial cells on villi
• absorb nutrients via microvilli

Question 12

enteroendocrine cells

Answer 12

secrete hormones secretin and cholecystokinin

Question 13

qualities of intestinal juice

Answer 13

• body produces 1-2L per day
• pH 7.6
• made of water, mucous, bicarbonate ions

Question 14

brush border enzyme

Answer 14

• Digestive enzymes embedded into intestinal wall (SI designed to move chyme via circular folds to come in contact with them)
• Different enzymes to digest carbohydrates, proteins and nucleotides

Question 15

brush border enzymes that digest carbohydrates

Answer 15

α-dextrinase
maltase
sucrase

Question 16

brush border enzymes that digest proteins

Answer 16

aminopeptidase
dipeptidase

Question 17

brush border enzymes that digest nucleotides

Answer 17

nucleosidases
phosphatases

Question 18

2 main types of movement in the small intestine

Answer 18

1. SEGMENTATION: local mixing of chyme with intestinal juices
   - circular muscles contracting (creates pouches of chyme to mix)
   - stops when enough fluid and nutrients are absorbed (~90%), triggers migrating motility complex
2. MIGRATING MOTILITY COMPLEX
   - circular muscles squeeze leftover chyme to ileum
   - may cause “tummy rumbling” sounds

Question 19

basics of chemical digestion in mouth

Answer 19

CARBS: salivary amylase breaks down starch, stays active until it hits stomach acids
LIPIDS: lingual lipase released, not active
PROTEINS: n/a

Question 20

basics of chemical digestion in stomach

Answer 20

CARBS: n/a
LIPIDS: lingual lipase, gastric lipase not very active
PROTEINS:
HCL -> denatures proteins
Pepsin -> proteins to peptides

Question 21

chemical digestion of carbohydrates in small intestine

Answer 21

PANCREATIC AMYLASE: digests any polysaccharides not digested by salivary amylase
BRUSH BORDER ENZYMES: α-dextrinase, lactase and maltase -> monosaccharides

Question 22

what does α-dextrinase break down?

Answer 22

Specifically, a carbohydrate called dexterin

Question 23

chemical digestion of proteins in small intestine

Answer 23

PANCREATIC JUICE
- digestive enzymes: typsin, chymitrypsin, carboxypeptidase, elastase -> split peptide bonds between different amino acids

BRUSH BORDER ENZYMES (final breakdown into amino acids)
- aminopeptidase, dipeptidase -> split off amino acid at amino end of molecule

Question 24

chemical digestion of lipids in small intestine

Answer 24

BILE
- emulsification
PANCREATIC LIPASE
- cleaves fatty acids from glycerol -> splits into fatty acids and monoglycerides
NO ENZYMES IN BRUSH BORDER

Question 25

Can lipids be digested by brush border enzymes?

Answer 25

no

Question 26

Where are most fats digested?

Answer 26

small intestine

Question 27

chemical digestion of nucleic acids in small intestine

Answer 27

Pancreatic juice - 2 nucleases
- RIBONUCELASE - RNA
- DEOXYRIBONUCLEASE - DNA

Nucelotides further digested by brush border enzymes (NUCELOSIDASE and PHOSPHATASE)

Question 28

Absorbable molecules for cho, pr- and lipids

Answer 28

CHO
- monosaccharides (glucose, fructose, galactose)

PRO
- single amino acids, dipeptides, tripeptides

LIPIDS
- free fatty acids, glycerol, monoglycerides

Question 29

% of digestion that occurs in stomach vs small intestine

Answer 29

90% SI
10% stomach

Question 30

types of muscle in muscularis, superficial to deep

Answer 30

longitudinal
circular

Question 31

what layer of GI contain the vili?

Answer 31

mucosa

Question 32

what layer of GI creates the circular folds?

Answer 32

submucosa