GI motility and regulation Flashcards
types of GI motility
Mixing – Segmentation. Propulsive Movements – Peristalsis
the role of calcium in muscle contraction
Ca binds calmodulin > activates myosin light chain kinase > phosphorylates myosin > myosin binds actin > ATP hydrolysis > contraction
How does the BER regulate the pace of contraction.
in stomach, 3 cycles per minute. In duodenum, 12 cycles per minute.
describe communication btw cells in GI tract
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
What produces tension in GI tract
•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
is Basal electrical rhythm neurogenic or myogenic
myogenic- intrinsic property of muscle cells
Innervation of GI tract
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
- Describe the three phases of digestion and what controls them
Cephalic Phase – Neural Control. Gastric Phase – Neural (early) & Hormonal . Intestinal – Mostly Hormonal but some Neural
Steps of swallowing, and which are voluntary
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)
achalasia
Failure of lower esophageal sphincter to relax due to damage/loss of the enteric nerves of the LES wall. Makes swallowing difficult
What causes acid reflux
inappropriate lower esophageal sphincter relaxation
What nerve facilitates peristalsis in esophagus
vagus- but if injured, a local myenteric complex can maintain swallowing
Where is intrinsic factor produced
stomach- facilitates Vit B12 absorption
Factors that increase/ decrease rate of gastric emptying
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
compare rate of stomach emptying with diff food
Carbs: leave stomach in few hours. Proteins: slower. Fats: slowest b/c fats in the duodenum cause secretion of cholecystokinin which decreases gastric motility
Steps of vomiting
Salivation (HCO3-) & sensation of nausea *Reverse peristalsis from upper small intestine to stomach *Abdominal muscles contract & UES and LES relax *Gastric contents are ejected
hormones acting on small intestines
CCK, secretin and GIP
types of motility in small intestine
peristaltic and segmentation
What is segmentation
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
What is peristalsis
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
intestinal reflexes
gastroilieal: - stomach activity stimulates movement of chyme through the ileocecal sphincter. Gastrocolic reflex – food in stomach stimulates mass movement in colon
phases of migrating motor complex
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
How does the ileocecal valve open and close
Opened by distension of end of ileum (local reflex) . Closed by distension of proximal colon (local reflex)
Which colon sphincters are voluntary vs involuntary
Internal is involuntary. External is voluntary
Types of colon motility
haustration and mass movement. NO MMC
Describe haustration and mass movements
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.
Rectoanal inhibitory reflex
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
Which nerve facilitates defecation reflex
pelvic nerves- reflex relaxation of the internal anal sphincter followed by voluntary relaxation of the external anal sphincter and defecation
