Chapter 63 General Principles Of GI Flashcards
How do the muscle fibers in the GI work as a syncytium?
The muscle fibers, while separated into branches, are connected to each other via areas of fusion. When one fiber/bundle excites, this action potential carries to the surrounding.
How are the slow waves and spike potentials involved in making smooth muscles work along the GI tract?
Slow waves are caused by interactions between the interstitial cells of Cajal, as these are the electrical pacemakers. Slow waves excited spike potentials, and do not actually cause contractions.
Spike potentials occur at peaks of slow waves, when influx of calcium ions is great and resting membrane potential increases, allowing excitation of of the membrane.
List factors that depolarize and hyperpolarize the resting membrane potential in the GI tract.
Depolarize - less negative; stimulated by 1) stretching of the muscle 2) parasympathetic nerves releasing ACh 3) gastrointestinal hormones
Hyperpolarize - more negative; stimulated by 1) sympathetic neurotransmitters such as norepi or epi 2) stimulation of sympathetic nerves that release norepi
There are two different enteric nervous-system plexuses in the GI tract. What are they and their roles?
Myenteric - this is located between longitudinal and circular muscle layers; responsible for movement along the entire length of the tract; inhibitory actions include in intestinal sphincter muscles (pyloric and ileocecal valve)
Submucosal - this is located in submucosa; responsible for controlling local intestinal secretion, local absorption and contraction of submucosal muscles
There are 3 types of gastrointestinal reflexes. Describe them and give some examples.
- Reflexes entirely within enteric nervous system
- control GI secretion, peristalsis, mixing contractions, local inhibitory effects, etc - Reflexes originating from gut to prevertebral sympathetic ganglia and back to gut
- gastrocolic, enterogastric, colonoileal - Reflexes originating from gut to spinal cord or brain stem and back to GI tract
- controlling gastric motor and secretory activity; pain inhibition of entire GI tract; defecation reflex
What hormone is secreted by the "G" cells of the antrum of the stomach and acts to stimulate gastric acid secretion and stimulates growth of the gastric mucosa? A) Gastric inhibitory peptide B) Cholecystokinin C) Gastrin D) Secretin
C) Gastrin - this is stimulated by ingestion of a meal, distention of the stomach, proteins and gastrin-releasing peptide
This hormone is secreted by the "I" cells of the duodenum, jejunum and ileum, in response to fat, fatty acids and monoglycerides. Main responsibility is contraction of gallbladder, and slowing of stomach emptying. This also inhibits appetite to prevent overeating. A) Gastrin B) Cholecystokinin C) Secretin D) Motilin
B) Cholecystokinin - once the gallbladder contracts, this emulsifies contents in the small intestine and allows for digestion and absorption, while the contents in the stomach are held back; appetite inhibition occurs when sensory afferent nerve is stimulated, then vagus nerve inhibits feeding centers in the brain
What hormone helps promote pancreatic secretions of bicarbonate and is itself secreted in response to acidic gastric juice emptying into the duodenum? A) Gastrin B) Cholecystokinin C) Secretin D) Motilin
C) Secretin - this is secreted by the “S” cells in the mucosa of the duodenum; also has a mild effect on motility of GI tract
What hormone slows emptying of gastric contents into the duodenum when the SI is already overloaded? A) Motilin B) Gastric inhibitory peptide C) Secretin D) Gholecystokinin
B) GIP - this is secreted by muocosa of upper SI, in response to fatty acids and AA; it also stimulates insulin secretion
What hormone is secreted by fasting to increase GI motility and stimulate interdigestive myoelectric complexes? A) Cholecystokinin B) Gastrin C) Motilin D) Gastric inhibitory peptide
C) Motilin - this is secreted by stomach and upper duodenum
Describe the splanchnic circulation. What occurs in the reticuloendothelial cells?
Blood courses through gut, spleen and pancreas –> heads to liver through portal vein –> millions of liver sinusoids –> hepatic veins –> reticuloendothelial cells –> vena cava
The reticuloendothelial cells line the liver sinusoids and remove bacteria from the GI tract before entering the blood.
