Lecture 16 - Small Intestinal motility (Sanchez)

Question 1

characteristics of longitudinal muscle

Answer 1

• thin muscle coat
• contraction shortens length, expands radius
• few gap junctions
• external Ca++ infux important in excitation contraction coupling
• innervated and activated by motorneurons

Question 2

circular muscle

Answer 2

• thick muscle coat
• contraction increases length, shortens radius
• innervated by excitatory and inhibitory motorneruons
• activated by intersitial cells of Cajal
• many gap junctions
• intrcellular Ca++ release important for excitation contraction coupling

Question 3

slow waves =

Answer 3

basic electrical activity of small intestine

- rate decreases along SI

Question 4

what is the migrating motility complex (MMC)

Answer 4

the basic myoelectrical unit of the SI made up of 3 components:

1. Phase 1 = comprised of only SW, no action potential. thus no contractions evident
2. Phase 2 = intermittent AP with a variable pattern
3. Phase 3 = AP occurs with every SW thus this phase has intense sustained contraction

Question 5

segmentation

Answer 5

isolated contractions that result in mixing of contents

Question 6

peristalsis

Answer 6

consists of aborally propagating rings of contraction that move contents some distance down the tract

Question 7

species differences in feeding patterns (essentially a prolonged phase II)
dog
pig
horse 
ruminants

Answer 7

dog - very affected
pig - variable
horse - kind of effected
rumiants - no feeding pattern

Question 8

what is the default muscular state of the small intestine?

Answer 8

muscular relaxation is the default state as the circulatory smooth muscle is under active control of the inhibitory motor neruons. this condition is called “physiological ileus”

Question 9

what is the most prominent nsympathetic (adrenergic) neurotransmitter?

Answer 9

NE - the effect is inhibitory

Question 10

where do parasympathetic efferents synapse? what transmitter do they use?

Answer 10

eneteric nervous system; Ach

Question 11

characteristics of alpha 2 adrenoreceptors

Answer 11

INHIBITS release of Ach from cholinergic neurons within myeneteric plexus

• alpha 2 agonist: (decreases motility)
• alpha 2 antagonist: (increases motility)

Question 12

prokinetics

Answer 12

increase motility

Question 13

what agents inherently decrease motility and are commonly used as sedatives and anaglesic agents?

Answer 13

alpha 2-adrenoreceptor AGONISTS and opoids