Intestinal Motility (#1)

Question 1

What type of innervation stimulates motility? Neurotransmitter? Which nerves?

Answer 1

Parasympathetic; Ach; Vagus and pelvic nerves

Question 2

What type of innervation inhibits motility? Neurotransmitter? Which nerves?

Answer 2

Sympathetic; NE; Postganglionic nerves in celiac/superior and inferior mesenteric ganglia

Question 3

Where are the sensory nerves?

Answer 3

Cell bodies in the nodose ganglia and DRG. They are chemoreceptors, nociceptors and mechanoreceptors.

Question 4

Where are the cell bodies of the myenteric plexus? Exictatory and Inhibitory transmitters?

Answer 4

Between the longitudinal and circular muscle layers; Ach excites, VIP and NO relaxes

Question 5

What does Ach do in the myenteric plexus?

Answer 5

Increases calcium in smooth muscle cells, causing contraction.

Question 6

What does VIP and NO do in the myenteric plexus?

Answer 6

VIP increases smooth muscle cAMP while NO increases cGMP. Both will cause hyperpolyerization of GI smooth muscle.

Question 7

Where are the intrinsic sensory nerves in the myenteric plexus? What excites them?

Answer 7

They are bipolar nerves. One pole terminates in the mucousal villi, the other relays to CNS. They are excited by mechanical and chemical stimuli.

Question 8

What is the role of the Enteroendocrine cells?

Answer 8

They release 5-HT (paracrine) which acts on 5-HT3 receptors on sensory nerves causing excitation. Also release Motilin for MMC.

Question 9

Can extrinsic nerves affect enteric nerves?

Answer 9

YES

Question 10

Describe the Antroduodenal reflex.

Answer 10

1. Content in the antrum increases pressure which causes its contraction and pyloric relaxation.
2. Reflex contraction is mediated by Ach and pyloric relaxation via NO.

Question 11

Why do diabetic patients experience delayed gastric emptying?

Answer 11

They have deficits in NO containing nerves in the stomach.

Question 12

Differentiate Segmenting, perstaltic, and tonic concentrations.

Answer 12

Segmentation: Contractions that expose intestinal content to digestive enzymes to the microvilli

Peristalsis: Propulsive contractions that propel intestinal content towards the anus.

Tonic: Sustained contractions that separate boluses of intestinal content.

Question 13

Differentiate the 3 phases of MMC

Answer 13

Phase 1: Little to no contractile activity
Phase 2: intermittent and irregular activity
Phase 3: Strong, propagating contractions from the antrum to terminal ileum. Preceded by motilin

Question 14

What is the danger of intestinal bacterial overgrowth?

Answer 14

Impaired interdigestive motility

Question 15

What is the purpose of the ileocecal reflex?

Answer 15

Controls movement of content from SI into the colon. Prevents reflux

Question 16

What is the purpose of the recto-sphincteric reflex?

Answer 16

Movement of content into rectum initiates contractions and relaxation of internal sphincter.