GI Motility II

Question 1

What are the regions of the stomach?

Answer 1

Fundus- Resovoir
Body/(GC)- w/oxyntic glandular mucosa, PM cell
Antrum
Pylorus

Question 2

Gastric slow waves are ________, lasting about _____ seconds, and have a membrane threshold of ________. At threshold ______ is generated.

Answer 2

1) Trimeric (rapid upstroke, plateau, re-polarize)
2) 4+ Seconds
3) -40 mV
4) Contractile Force

Question 3

While slow waves are generated by ______, they can be modulated by ________, increasing/decreasing ________

Answer 3

1) pacemaker cells
2) Autonomic NS (Ach, NE)
3) Contractile Force

Question 4

Name the (4) gastric functions

Answer 4

1) Fillings
2) Storage
3) Mixing
4) Emptying

Question 5

Explain (2) mechanisms that allows for gastric filling?

Answer 5

Plasticity - SM cells in the Fundus region are elastic

Receptive Relaxation: mechanoreceptors sense distension, reflex is initiated by vagus nerve (NO, VIP, released) - Inhibitory NT (keep intra-luminal pressure constant)

Question 6

Explain how retropulsion facilitates mixing?

Answer 6

1) bolus is pushed towards closed pylorus
2) atrum churns material/opens sphincter
3) pylorus closing pushes food back to stomach

Question 7

Gastric Emptying (3) Regulation Factors

Driving Force & Regulation

Answer 7

1) Antral Peristaltic Contractions
2) Pylorus Valve reg emptying
3) Gastric Factors
4) Duodenal/Jejunal Factors

Question 8

What control Pylorus Valve?

Answer 8

Relaxation via vagal inhibitory fibers (VIP, NO)

Constriction - Excitatory Cholinergic vagal fibers Sympathetic Fibers, (4 hormones)

Question 9

Gastric Factors: Emptying

Answer 9

Volume: Distention
Fluidity: (fluid meal) Fast Emptying

Question 10

Explain Importance of SIF causing decreased gastric emptying? Acid, Fat, Other

Answer 10

Fat: Time for emulsification
Acid: Time for Neutralization
Other: Time for chyme processing

Question 11

Why do we vomit?
Explain Vomiting Reflex
What is and Emetic?

Answer 11

• Protects over-distention/ irritation
• Sensory input activates medulla oblongata (Vomiting Center)
• Emetics - chemical vomit trigger

Question 12

How does dumping syndrome lead to CV problems?

Pyloric Stenosis ?

Answer 12

Uncontrolled sphincter leads to rapid chyme dumping into SI, water enters luminal content leading to CB problems

PS: Hypertrophy causing blocking

Question 13

Name the Types of Motility in the SI

Answer 13

Segmentation - Mixing
Peristalsis - Moving
Migrating Myoeletic Complex - house keeping

Question 14

______ give rise to contractions, and can be accompanied by ___ leading stronger contractions. _____ innervation can only modulate rate/strength of contractoin

Answer 14

Pacemaker cells/ slow waves
Action Potentials
Extrinsic Innervation (PS, S) - Long Range Reflexes

Question 15

Migrating Myoeletic Complex - What is this? what is its house keeping function

Answer 15

Occurs in-between meals - long lasting wave that sweeps intestines, and prevents bacterial invasion at ileocecal valve.

Question 16

Where is the Muscularis Mucosae located?

Its contraction facilitated what functions?

Answer 16

In-between Mucosa and SM
- facilitate absorption
⁃ Incr emptying/flow of lymph vessels - (fat absorption)

Question 17

What are the long and short range reflexes of the small intestines?

Answer 17

S: Law of intestines
L: Intertino-intestinal reflex, Ileo-gastric reflex, gastro-ileal reflex

Question 18

Intertino-intestinal reflex
Ileo-gastric reflex
Gastro-ileal reflex

Answer 18

II: overextension causes relax (tm)
IG: ileum stretch –> dec. gastic motility
GI: stomach activity –> ileum motility

Question 19

Anal Sphincters

Answer 19

Internal: Thickened circular smooth muscle

External: Striated Muscle w/ somatic innervation

Question 20

Motility Types of Colon

Answer 20

Segmentation (Haustrations): mix
Propulsive peristalsis
Antipropulsion: more absorption
Mass Movement: Large/Longer Peristaltic Wave; empty proximal colon

Question 21

Large Intestine Innervation

Answer 21

PS: Vagal until 1/2 T- Colon: Segmental Contractions; Pelvic Nerves for rest of LI

S: Inhibitory
Somatic: Pudenal n. - E- Sphincter

Question 22

Colonic Reflexes (Long Range)

Colono-colonic Reflex
Gastro-colic Reflex

Answer 22

no short range reflexes:
CC: overextension causes relax (tm)

GC: stomach activity –> colon motility (mass movements)

Question 23

Explain the urge to defecate (Defecation Reflex)

Answer 23

Anal Canal filling causes reflexive relaxation of internal (DFR) anal sphincter and constriction of external anal sphincter (Urge to defecate)