L7 Small Intestinal Secretions and GI Motiloty

Question 1

Surfaces Adaptations of the Small Intestine to Aid in Digestion?

• _________: Large, Ridge-like folds out into Lumen
• _________: Hair like structures on the Ridge-like folds of the Plicae Circularis
• __________: Hair top of intestinal Villi (Need EM to see)

Answer 1

Plicae Circularis: Large, Ridge-like folds out into Lumen

Villi: Hair like structures on the Ridge-like folds of the Plicae Circularis

Microvilli (aka. Brush Border): Hair top of intestinal Villi (Need EM to see)

Question 2

Absorptive cells of small intestine (_______ in colon)

Answer 2

Enterocytes

Question 3

Secretory, mucosa-producing cells => protection from acid in chyme

Answer 3

Goblet Cells

Question 4

Host defense cells Located in Glands (Crypts of Lieberkühn)

Answer 4

Paneth Cells

Question 5

Hormonal cells located in Glands (Crypts of Lieberkühn)

Answer 5

Enteroendocrine Cells

Question 6

Amount of secretions from the Small Intestine daily?

Answer 6

1.5 liters of secretion daily

Question 7

Duodenum Mucous/Enzyme Secretions?

• Mucous from _________ and ___________ cells
• _______________________ at brush border (converts trypsinogen into its active form trypsin, resulting in the subsequent activation of pancreatic digestive enzymes)
• ______________________ (starch into sugars)

Answer 7

Duodenum Mucous/Enzyme Secretion

• Mucous from Brunner’s Glands and Goblet cells
• Enterokinase mucosal cells at brush border (converts trypsinogen into its active form trypsin, resulting in the subsequent activation of pancreatic digestive enzymes)
• Amylase from the pancreatic duct (starch into sugars)

Question 8

Cholecystokinin (CCK) Source/Trigger/Action?

Answer 8

Source: I cells of Villus

Trigger: Fatty Acids/Amino Acids in small intestine

Action:

• DECREASES gastric emptying rate
• INCREASES Pancreatic/Gallbladder Secretions
• Induction of Satiety

Question 9

Motilin Source/Action?

Answer 9

Source: M cells of Crypts

Action: Stimulates gastric/small intestine motility (Migrating motor (myoelectrical) complex)

Question 10

Neurotensin Source/Action?

Answer 10

Source: N cells of Villus

Action: facilitates fatty acid uptake in the duodenum and induces histamine release from mast cells

Question 11

Secretin Source/Trigger/Action?

Answer 11

Source: S cells of Villus

Trigger: S- cells perceive decreased pH as chyme enters duodenum

Action: Inhibits gastric motility and Promotes Pancreatic secretion of Aqueous component w/ bicarbonate

Question 12

Serotonin Source/Action?

Answer 12

Source: Enterochromaffin Cells

Action: Promotion of gut motility

Question 13

Somatostatin Source/Action?

Answer 13

Source: D Cells of Villus

Action: Inhibits G cell secretion of gastrin (Reducing acid production)

Question 14

Isotonic Fluid (Cl-) Source/Significance?

Answer 14

Crypts

Greatest volume of Small Intestine secretion is a Cl- rich isotonic fluid!!!

Question 15

What cells are definitive of the Duodenum?

Answer 15

Brunner’s Glands (Secretes Mucous)

Question 16

Section of small intestine that is a Catalytic Site for Digestion/Absorption characterized by MORE Plicae (circular folds)?

Answer 16

Jejunum

Question 17

Section of the small intestine with FEWER plicae and MORE lymphoid tissue (Peyer’s Patches) and goblet cells?

Answer 17

Ileum

Question 18

Arterial supply of the Small Intestine?

Answer 18

Superior Mesenteric Artery

Question 19

Function of Segmentation (Mixing Contractions) in the Small Intestine?

What mediates these contractions?

Answer 19

Most common contractions after feeding

Chyme is displaced in both directions by stationary contractions=> Functions to mix luminal contents

DO NOT undergo peristalsis: Stationary, irregular contractions mix the chyme

Mediated by: Enteric/Para/Sympathetic Nervous systems

Question 20

Function of Peristalsis in the Small Intestine?

What mediates these contractions?

Answer 20

Occurs in response to luminal distension

Sequence of adjacent contractions => aboral (away from mouth) movement of chyme

Peristaltic reflex involves the coordination of both longitudinal and circular smooth muscle

Mediated by: Enteric nervous system (ACh) + Nitric Oxide

Question 21

Function of Migrating Motor Complex in the Small Intestine?

What stimulates these contractions?

Phases?

Answer 21

‘House-keeping’ contractions - Sweeps from stomach to large intestine=> Slow migration of undigested food

Stimulated by the hormone Motilin (M cells of Crypts)

Question 22

The contribution of the vagus nerve to GIT motility ___________ as you descend down the GI

Answer 22

The contribution of the vagus nerve to GIT motility DECREASES as you descend down the GI

Question 23

__________________ set basal contraction rate which differs in each part of intestine => Pressure gradient from the small intestine to large

Answer 23

Interstitial cells of Cajal set basal contraction rate which differs in each part of intestine => Pressure gradient from the small intestine to large

Question 24

__________ stimulates the Migrating Motor Complex

Answer 24

Motilin stimulates the Migrating Motor Complex

Question 25

___________ stimulates Ileum (Gasto-Ileal Reflex)

Answer 25

Gastrin stimulates Ileum (Gasto-Ileal Reflex)