Gastrointestinal Physiology Flashcards
Migrating Myoelectric Complex (MMC)
A four phased, interdigestive state that usually runs between 1-2 hours. Functionally, it serves as a house keeping mechanism of the GI tract from the mid-stomach to the terminal ileum. Stage 3 is triggered by motilin secreted by M cells of the digestive track and is a 10 minute period of serial contractions.
Contrast primary and secondary propulsion involved in swallowing.
Primary: a voluntary contract contraction caused by swallowing centers in the medulla. Secondary: an involuntary contraction caused by autonomic and enteric innervation.
Myenteric plexus
Question?
Achalasia
Caused by the inability lower esophageal smooth muscles to relax causing pain with swallowing and dilation of the superior esophagus. You can treat this by cutting the lower esophageal sphincter; however, this also results in GERD.
Ileosis
Tumor that obstructs the ileum. This area of the tract needs to be resected.
Gastric accommodation
When food enters the stomach, the vagus nerve sends signals for the stomach to expand. Feelings of pressure will not occur until roughly a liter of food enters to fill the stomach.
What is the effect of a vagotomy on gastric accommodation?
Without the vagus, there is no gastric accommodation and people experience pain when eating small amounts of food.
Describe the order in which things leave the stomach?
Carbohydrates, proteins, and finally fats
What is the first pass effect?
When things are digested, they pass first through the liver before they reach systemic circulation.
Where are the three places in the GI tract that do not have smooth muscle?
esophagus, external anal sphincter, and mouth
What are the functions of the GI tract?
Remember: DEEP MASS Digestion Endocrine Elimination Protection Motility Absorption Secretion Storage
Describe the pH throughout the GI tract.
Stomach 1-2 Jejenum 5 enters 7 exists
Describe the enteric nervous system.
Myenteric (muscle movement) and submucosal (secretions)
Describe action potential in the GI tract.
The resting membrane potential is not a flatline, but rather resting membrane potential (RMP) that are slow waves. Once it reaches threshold at -40 mV, there are action potentials that can be reached called spike potentials (SP). The amount of SP that are reached correlates to the strength of the contraction.
How do calcium levels change contraction in smooth muscle?
Increased Calcium levels intracellularly leads to increased binding to calmodulin and more crossbridges increasing the strength of the contraction.
Contrast the rate of contractions in the stomach v. the jejunum.
In the stomach, the rate is 3 waves/min in order to promote mixing; whereas in the jejunum the rate is 12 waves/min to promote movement to the colon.
Facts that can help depolarization of smooth muscles
Stretch, acetylcholine, parasympathetics, gastrin, serotonin, substance P (tachykinin)
Factors that can help in hyperpolarization of smooth muscle
Sympathetics, VIP (vagoactive intestinal peptide), NO
What sets the timing for action potentials in the GI tract?
RMPs, slow waves
Describe motility in the small intestines.
Peristalsis - contraction of the circular muscle behind and relaxation of the circular muscle in front of the bolus. Cholinergic leads to contraction and VIP leads to relaxation. This is mainly under vagal/extrinsic control.
Segmentation - There is contraction behind and ahead of the bolus to promote mixing as well as motion down the GI tract. This is predominantly under enteric control/ intrinsic control.
Describe contractions in the gall bladder.
CCK or cholescystokinin causes contraction of the gallbladder that induces the release of bile. Vagal stimulation is also involved.
The sphincter of Oddi is opened by vagal relaxation.
Describe motion in the colon.
- Segementation caused by the contraction of tenai coli and is very slow.
- Mass movements: peristaltic contractions in the ascending and transverse colon under vagal control. Note that the distal colon is not under vagal control.
Gastrocolic reflex
When you eat, the fullness of the stomach causes vagal activation leading to mass movement in the colon leading often to the rectospincteric reflex in which you feel the need to defecate.
Valsalva maneuver
increase in abdominal pressure to move feces out of the colon
