GI Motility and Regulation Flashcards
Describe the movement of segmentation.
Segmentation is mixing of the luminal contents.
Review the mechanism of smooth-muscle contraction.
Myosin light chain kinase is inside the cell, but is inactive.
Calcium enters the cell during an NMJ depolarization.
Calcium interacts with calmodulin, and the active form of calmodulin activates myosin light chain kinase (MLCK).
MLCK phosphorylates myosin, leading to the actin/myosin interaction and contraction.
Smooth muscle cells are held together via _______________ and communicate via ______________.
adherens junctions; gap junctions
Auerbach’s plexus is also called ______________.
the myenteric plexus
As you go further down the GI tract, the basic electrical rhythm _____________. Why?
increases in frequency; this is important because food material will empty faster than material enters
Describe the three phases of digestion in terms of molecular signalling.
(1) Cephalic phase: entirely controlled by the nervous system; occurs when we see/think about food.
(2) Gastric phase: neural and hormonal
(3) Intestinal phase: mostly hormonal
Capsaicin activates ___________ in the esophagus.
substance P-sensitive contraction (this is why spicy food stimulates digestion)
Failure of the lower esophageal sphincter to relax is called _____________; it can make swallowing difficult.
achalasia
The pyloric sphincter prevents passage of particles greater than _________.
2 mm in diameter
The stomach can store up to ______________.
4 liters of food
Hydrochloric acid in the stomach does what?
Denatures proteins
Kills bacteria
Gastric motility contractions begin in the _____________.
distal stomach (in the antrum) and proceed to the proximal stomach
Compare emptying rates for carbohydrates, fat, and protein.
Carbohydrates: fastest
Fat: slowest
Protein: intermediate
Describe the steps of vomiting.
(1) Increased salivation of bicarb-rich secretions
(2) Reverse peristalsis from small intestine to stomach
(3) Abdominal muscles contract
(4) Relaxation of the UES and LES
(5) Gastric emptying
Explain the gastroileal and gastrocolic reflexes.
Gastroileal: food arrival in the stomach stimulates movement through ileocecal sphincter
Gastrocolic: food arrival in the stomach stimulates movement through the colon
Both are mediated by the enteric nerve.
Explain the migrating motor complex phases.
Every 90-100 minutes, the stomach and small intestine contract to clean out the gut.
Phase I: quiescence
Phase II: irregular contractions mix up the food, but do not cause peristalsis
Phase III: pushes food to ileocecal valve
True or false: the large intestine also has regular contractions in the absence of feeding.
False. The MMC phases stop at the ileocecal valve.
The sections of large intestine are called ___________.
haustra
Haustrations serve to _________________.
compact food
The basal electric rhythm is ______ derived.
myogenically
Gastrin is induced by ____________ and stimulates increased ___________ and decreased _____________.
gastric distension; peristalsis; pyloric tone
Arrival of ____________ leads to secretion of cholecystokinin by the enteric endocrine cells.
fats in the duodenum
Transit of the intestine takes about ________ hours.
3-5
