FINAL GI Flashcards
(116 cards)
Describe how layers of the GI tract are innervated. What is the name of the plexus that is dispersed throughout the walls of the GI tract?
A network of intrinsic nerves that controls mobility, secretion, sensation, and
blood flow is located solely within the GI tract and controlled by local and autonomic nervous system
stimuli through the enteric (aka INTRAMURAL) PLEXUS located in different layers of the GI walls
(see figure 35.2 in first edition text for a good image of this!)
Is salivation controlled by sympathetic or parasympathetic system?
Both.
Cholinergic parasympathetic fibres stimulate the salivary glands, and atropine (an anticholinergic agent)
inhibits salivation and makes the mouth dry. β-Adrenergic stimulation from sympathetic fibres also
increases salivary secretion.
Describe the esophagus in terms of portions that are voluntary and involuntarily controlled. How is each section innervated?
The pharynx and upper third of the esophagus contain striated muscle (voluntary) that is
directly innervated by skeletal motor neurons that control swallowing.
The lower two-thirds contain
smooth muscle (involuntary) that is innervated by preganglionic cholinergic fibres from the vagus nerve.
How is peristalsis stimulated in the esophagus?
Peristalsis is stimulated when afferent fibres distributed along the length of the esophagus sense
changes in wall tension caused by stretching as food passes.
The esophagus has both intrinsic and extrinsic innervation. Describe what this means
Extrinsic innervation = innervated by the vagus nerve
Intrinsic = also innervated by enteric nervous system, which is inside the walls of the esophagus. This is the same as the enteric/intramural plexus
**The enteric plexus serves as a type of secondary wave of peristalsis if the initial wave doesn’t get the food all the way to the stomach
When the swallowing reflex is initiated, afferent sensory information is sent to the swallowing center via 3 cranial nerves. Which 3 are they?
Efferent (motor) info is then sent back via 2 nerves…which are they?
Sensory:
Glossopharyngeal
Vagus
Trigeminal
Motor:
Vagus & glossopharangeal
What nerve is the primary control for tone of the lower esophageal sphincter?
Vagus! (basically, vagus for everything)
What are the two plexuses that constitute the enteric (intramural)
nervous system? (this is likely too detailed, but it does say that basically all of the GI tract has this intrinsic innervation)
myenteric plexus (Auerbach
plexus) and the submucosal plexus (Meissner plexus)
Sympathetic vs parasympathetic innervation of the stomach - what is responsible for each?
What nervous system
The vagus nerve provides parasympathetic innervation, and
branches of the celiac plexus innervate the stomach sympathetically.
the enteric (intramural)
nervous system within the stomach responds to local stimuli.
What is the function of bile?
Aids in intestinal digestion of fats. Bile salts aid in fat emulsification and absorption. Fats are broken down into fatty acids that are absorbed across the intestinal mucosa as micelles (water soluble fat products).
What is bile?
Yellow green alkaline fluid containing bile salts, cholesterol, bilirubin, electrolytes, and water. It is important in intestinal fat digestion and absorption.
Describe the production and flow of bile.
Bile is produced by the hepatocytes and moves through the liver via bile canaliculi to drain into bile ducts that eventually drain into the common bile duct. This leads to the ampulla of vater (where the bile duct and pancreatic duct meet), which empties into the duodenum called the major duodenal papilla (surrounded by the sphincter of oddi). If the spincter is closed (i.e., in periods between meals), bile backs up and is stored in the gall bladder.
What blood vessel returns bile salts absorbed in the terminal ileum to the liver?
Portal vein (enterohepatic circulation)
What stimulates the gallbladder to contract?
Food in the duodenum about 30min after eating. Contraction stimulated by the vagus nerve.
What stimulates the gallbladder to relax?
Sympathetic stimulation, vasoactive intestinal peptide, pancreatic polypeptide.
What is the function of the gallbladder?
Sac like organ on the inferior surface of the liver that stores and concentrates bile between meals. The mucosa of the gall bladder wall readily absorbs water and electrolytes, leaving a high concentration of bile salts, pigments, and cholesterol.
Define cholelithiasis
Formation of gallstones
Describe the epidemiology of cholelithiasis
More prevalent in developed countries and Indigenous populations
More common in women than men
Risk factors include obesity, middle age, pregnancy, use of oral contraception, rapid weight loss, genetic predisposition, and gallbladder, pancreatic, or ileal disease
True or false: gall stones are always symptomatic
False- can be asymptomatic for months to years. Symptoms result if gallstones become lodged in the cystic or common duct during contraction of the gallbladder.
What is the most common type of gallstone?
Cholesterol
What do all gallstones contain?
Cholesterol, unconjugated bilirubin, bilirubin calcium salts, fatty acids, calcium carbonate and phospates, and mucin glycoproteins
True or false: many gallstones can fill the entire gallbladder
True
When do gallstones become symptomatic?
When they become lodged in the cystic duct (or any part of bilirary tract), obstructing flow of bile out of the gallbladder, causing pain and inflammation
What are the two types of inflammatory bowel disease?
Crohn’s Disease and Ulcerative Colitis