GI motility and regulation

Question 1

types of GI motility

Answer 1

Mixing – Segmentation. Propulsive Movements – Peristalsis

Question 2

the role of calcium in muscle contraction

Answer 2

Ca binds calmodulin > activates myosin light chain kinase > phosphorylates myosin > myosin binds actin > ATP hydrolysis > contraction

Question 3

How does the BER regulate the pace of contraction.

Answer 3

in stomach, 3 cycles per minute. In duodenum, 12 cycles per minute.

Question 4

describe communication btw cells in GI tract

Answer 4

Smooth muscle cells are of the single unit type, - Held together by adherens junctions and communicating via gap junctions. Pacemaker cells have spontaneous activity which produce basal electrical rhythm and muscle tone w/out tension

Question 5

What produces tension in GI tract

Answer 5

•neurotransmitters acting on muscle – Role of the ANS. Ach allows membrane threhold to be exceeded and contractions occur at the frequency of the basal electrical rhythm

Question 6

is Basal electrical rhythm neurogenic or myogenic

Answer 6

myogenic- intrinsic property of muscle cells

Question 7

Innervation of GI tract

Answer 7

parasympathetic: vagus innervates lower esophagus, stomach, small intestine, upper large intestine. Pelvic nerve innervates lower large intestine and rectum. SNS: celiac innervates esophagus, stomach and small intestine. Superior mesenteric innervates descending large intestine. Inferior mesenteric innervates descending colon and rectum

Question 8

2. Describe the three phases of digestion and what controls them

Answer 8

Cephalic Phase – Neural Control. Gastric Phase – Neural (early) & Hormonal . Intestinal – Mostly Hormonal but some Neural

Question 9

Steps of swallowing, and which are voluntary

Answer 9

Stage 1: Voluntary (oral cavity then bolus pushed by tongue to oropharynx). Stage 2: Involuntary pharyngeal (glottis covers trachea; UES relaxes). Stage 3: Involuntary esophageal (esophageal peristalsis)

Question 10

achalasia

Answer 10

Failure of lower esophageal sphincter to relax due to damage/loss of the enteric nerves of the LES wall. Makes swallowing difficult

Question 11

What causes acid reflux

Answer 11

inappropriate lower esophageal sphincter relaxation

Question 12

What nerve facilitates peristalsis in esophagus

Answer 12

vagus- but if injured, a local myenteric complex can maintain swallowing

Question 13

Where is intrinsic factor produced

Answer 13

stomach- facilitates Vit B12 absorption

Question 14

Factors that increase/ decrease rate of gastric emptying

Answer 14

distension (through vagal and myenteric reflexes) and gastric which both increase peristalsis. Arrival of bolus in duodenum causes reflex inhibition of gastric peristalsis and increased pyloric tone, decreasing gastric emptying

Question 15

compare rate of stomach emptying with diff food

Answer 15

Carbs: leave stomach in few hours. Proteins: slower. Fats: slowest b/c fats in the duodenum cause secretion of cholecystokinin which decreases gastric motility

Question 16

Steps of vomiting

Answer 16

Salivation (HCO3-) & sensation of nausea *Reverse peristalsis from upper small intestine to stomach *Abdominal muscles contract & UES and LES relax *Gastric contents are ejected

Question 17

hormones acting on small intestines

Answer 17

CCK, secretin and GIP

Question 18

types of motility in small intestine

Answer 18

peristaltic and segmentation

Question 19

What is segmentation

Answer 19

contraction is isolated and not coordinated with movement above and below. Contents are propelled in both directions causing mixing and ensures proper digestion and absorption

Question 20

What is peristalsis

Answer 20

contractions of adjacent segments are coordinated in a proximal to distal manner, resulting in net propulsion of contents. A bolus induces distention of intestine wall, leading to contraction just proximal to bolus which pushes the bolus distally. Receptive relaxation of intestines distal to bolus also occurs

Question 21

intestinal reflexes

Answer 21

gastroilieal: - stomach activity stimulates movement of chyme through the ileocecal sphincter. Gastrocolic reflex – food in stomach stimulates mass movement in colon

Question 22

phases of migrating motor complex

Answer 22

phase 1: quiescence for most of the 90 minutes duration. Phase II: motility increases, irregular contraction, no propulsion of luminal content. Lasts 20-30% of MMC duration. Phase III: 5-10 minutes of intense contractions from From body of stomach to pylorus to duodenum to ileocecal valve. Pylorus fully opens

Question 23

How does the ileocecal valve open and close

Answer 23

Opened by distension of end of ileum (local reflex) . Closed by distension of proximal colon (local reflex)

Question 24

Which colon sphincters are voluntary vs involuntary

Answer 24

Internal is involuntary. External is voluntary

Question 25

Types of colon motility

Answer 25

haustration and mass movement. NO MMC

Question 26

Describe haustration and mass movements

Answer 26

Haustration: Muscles of the colon wall are contracted intermittently to divide the colon into functional segments known as “haustra.” segmentation contractions mix and dry chyme. Mass movements: strong peristaltic waves 1-3 X/day, following meals. Slow process which strips and are of colon clear of contents. Haustration is lost during mass movements.

Question 27

Rectoanal inhibitory reflex

Answer 27

Filling of the rectum causes relaxation of the internal anal sphincter via release of VIP and NO from intrinsic nerves. At same time, the external anal sphincter contracts

Question 28

Which nerve facilitates defecation reflex

Answer 28

pelvic nerves- reflex relaxation of the internal anal sphincter followed by voluntary relaxation of the external anal sphincter and defecation