UBC Med Preclinical GI Curriculum Flashcards
As food passes along the GI tract, it crosses 3 significant junctions in the histology of the mucosal epithelium.
What are these 3 junctions?
- Esophagogastric junction (AKA the Z line)
- Gastroduodenal junction
- Anorectal junction (AKA dentate line)
– Histological junctions may be sites of precancerous metaplasia, especially when the environment is very different on either side, as it is across the Z line.
What different epithelial cells are found lining the stomach and its gastric pits?
- Surface Mucous cells are found throughout the stomach.
- Gastric pits (AKA Oxyntic glands) are home to Parietal cells, Chief (AKA Peptic) cells, Mucous Neck cells and Paracrine cells.
- Pyloric glands are home to G cells, which have an endocrine function: producing gastrin.
Acute pain due to pathology in the upper GI tract is sometimes localised to the epigastric or retrosternal areas.
What are some non-GI causes that should be considered for a patient with acute pain in those areas?
- CV: MI, angina, pericarditis, aortic dissection, ruptured aortic aneurism
- Other: pneumonia, musculoskeletal. Pain during contraction of abdominal muscles, such as during a sit-up, is indicative of a muscle problem.
What are the myenteric and submucosal plexuses?
These two ganglionated plexuses make up the enteric nervous system, a component of the autonomic nervous system that regulates GI movement patterns, secretions, and sensations.
The myenteric (Auerbach’s) plexus lies between the outer longitudinal and inner circular muscle layers of the muscularis externa, and the submucosal (Meissner’s) plexus lies between the muscularis externa and the submucosa.
Interstitial Cells of Cajal act as ‘pacemakers’ for GI smooth muscle cells.
What pattern of action potential do ICC cause?
ICC set up ‘slow wave’ action potentials in smooth muscle (AKA Basic Electrical Rhythm). Slow wave action potentials determine the frequency of some types of intestinal motility patterns, such as peristalsis. Slow waves vary from their normal pattern or rate in some conditions, such as diarrhea.
There are 4 main types of motility patterns in the GI system. Which type is impaired in gastroesophageal reflux disease?
The 4 main types of motility patterns are:
- Tonic contraction (sphincters)
- Rhythmic segmentation (mixing)
- Oscillatory (Pendular) movements (mixing)
- Peristalsis (movement of lumen contents)
– In GERD, tonic contraction of the LES is impaired, usually by prolonged or more frequent TLESRs (transient lower esophageal sphincter relaxations.) Other etiologies, such as low basal LES tone in scleroderma, are possible.
Esophageal manometry (AKA tonometry) measures the pressure applied by esophageal muscles.
For what esophageal motor disorder does manometry provide a definitive diagnosis?
In achalasia, inflammatory degeneration of the esophageal myenteric plexus causes an increase in LES pressure, aperistalsis, and incomplete reflex relaxation of the LES during swallowing.
Describe the steps in primary peristalsis of the esophagus (ie. swallowing.)
- Conscious desire to swallow activates the “swallowing centre” in the brain.
- The “swallowing centre” coordinates the muscles of swallowing via the “nucleus ambiguous” (which innervates esophageal striated muscle) and the “dorsal motor nucleus of the vagus nerve” (which innervates smooth muscle). Both of these muscle coordination centres are in the brainstem.
- The nucleus ambiguous sequentially activates the striated muscle in the upper esophagus
- The dorsal motor nucleus continues the swallowing contractions by activating a peristaltic pattern in the esophageal myenteric plexus
- The wave of contractions (ie. swallowing) traverses the esophagus in 9-10 seconds.
How does primary peristalsis differ from secondary peristalsis, in the esophagus?
- One is consciously activated, the other is a reflex activated by distention of the esophagus.
- One can occur even if the sensory pathways are damaged, the other is initiated by sensation.
- One is a continuation of the oropharyngeal phase of swallowing, the other can occur by itself.
- One is for swallowing food, the other is for clearing food remnants and refluxed gastric juice.
When swallowing (AKA deglutition) is impaired, which is common in elderly Pts, swallowed substances can linger in a patient’s esophagus.
What are possible negative consequences of this prolonged contact with the esophageal mucosa?
Some substances, such as pharmaceuticals, can irritate or damage the esophageal mucosa. Bisphosphonates, a class of drug used in the treatment of osteoporosis, can cause life-threatening esophageal perforations.
Chronic alcohol abuse is a risk-factor for esophagogastric varices, among many other GI and non-GI conditions.
Name 5 physical exam signs that may indicate chronic alcohol abuse.
Most signs of alcoholism are actually signs of significant damage to the liver:
Asterixis, palmar erythema, bilateral gynecomastia, parotid enlargment, tremulousness, Dupuytren’s contractures, hepatomegaly or a nobbly hard liver, splenomegaly, ascites, caput medusa, jaundice, rhinophyma (bulbous ruddy nose), telangiectasias, peripheral neuropathy, finger clubbing.
However, the Px may be normal despite the presence of alcoholism.
Nausea and vomiting is a common complaint in hospital and outpatient settings.
What are some associated symptoms that can help determine the cause of N/V?
- Abdominal pain points to a GI cause, although a MI is also a possibility.
- Pain relief by vomiting indicates a GI obstruction or GERD, while pain that is not relieved can indicate an MI, pancreatitis, hepatitis, gallbladder Dz, or infectious gastroenteritis.
- Associated Sx such as headache or dizzyness indicates a central nervous system disorder, such as increased intracranial pressure, migraine, or a vestibular problem.
- Painless N/V can be due to a wide variety of causes, such as drugs and toxins, pregnancy, gastroparesis, and various metabolic disorders (eg. acidosis, hyperkalemia, hypercalcemia, uremia)
Polyhydramnios can occur in a fetus that is unable to swallow and then absorb amniotic fluid.
Name 3 congenital malformations of the upper GI tract that may present with polyhydramnios due to impaired GI absorption.
- Atresia of the esophagus
- Hypertrophic pyloric stenosis
- Duodenal atresia
– If you suspect these conditions in a neonate who isn’t feeding properly, the details of how the neonate is vomiting may allow differentiation, eg. by the force of the vomiting (‘projectile vomiting’) or the presence of bile in the vomitus.
The pancreas forms from a ventral bud and a dorsal bud, which fuse together.
Which pancreatic duct corresponds with each pancreatic bud?
The ventral bud, which forms in conjunction with the bile duct, forms the main pancreatic duct.
The dorsal bud, which makes up most of the pancreas, forms the accesory duct.
As organs form and rotate in the dorsal & ventral mesogastrium of an embryo, they partition the mesogastrium into a variety of ligaments and peritoneal structures.
Name the ligament derivatives of the ventral mesogastrium.
- The falciform ligament connects the liver to the anterior wall.
- Together, the hepatogastric ligament and hepatoduodenal ligament form the lesser omentum, connecting the liver to the stomach and first part of the duodenum.
- The free border of the lesser omentum marks the epiploic foramen (AKA the foramen of Winslow,) which connects the lesser sac behind the stomach to the rest of the peritoneal cavity (AKA the greater sac.)
What are the 5 regions of the stomach?
- Cardia: the portion adjoining the esophagus; involved in hiatus hernia
- Fundus: the domeshaped upper portion, to the left of the cardia
- Body (Corpus): the largest region of the stomach
- Antrum: the distal narrowing; has a thicker circular layer of muscularis
- Pylorus: thick circular muscularis forms the pyloric sphincter at the gastroduodenal junction
What are the different parts of the duodenum?
- 1st (superior) part: pyloric orifice to neck of the gallbladder; intraperitoneal; location for most duodenal ulcers.
- 2nd (descending) part: superior duodenal flexure to the inferior flexure; contains the major (and minor) duodenal ampulla, the transition to the midgut.
- 3rd (horizontal or inferior) part: the longest section, crossing several structures such as the aorta, IVC, and vertebral column.
- 4th (ascending) part: suspended by the musculofibrous ligament of Treitz, the duodenojejunal flexure marks the end of the duodenum.
What is the main blood supply of the foregut?
The celiac trunk arises from the aorta and branches into:
- L. gastric a.: Supplies the lesser curvature and lower esophagus.
- Common hepatic a.: Supplies the liver, gallbladder, pylorus, duodenum, and head of the pancreas via its branches → the hepatic a. proper and the gastroduodenal a.
- Splenic a.: Supplies the spleen, greater curvature, and tail of the pancreas.
What is the autonomic innervation of the upper GI tract?
- Sym. N.S.: T5-9 via the greater splanchnic nerve.
- Para. N.S.: via the vagus nerve (cranial n. X.)
A vagotomy (resection of the vagus n.) is an option in surgical treatment of intractable peptic ulcer Dz.
What is McBurney’s point?
McBurney’s point, one third of the way from the ASIS to the umbilicus, is a landmark for the typical location of the appendix.
What are Virchow’s node and Sister Mary Joseph’s nodule?
Virchow’s node is a palpable medial-left supraclavicular node, suggesting cancer spreading via the thoracic duct.
Sister Mary Joseph nodules are are palpable periumbilical nodules.
Either may indicate metastatic GI cancer. Rarely, cancer of the stomach can metastasise to the left axillary node (Irish’s node.)
What are 6 exocrine secretions of the stomach?
- HCl
- Pepsinogen
- Gastric lipase
- Intrinsic factor (important for absorbing Vit B12)
- Mucus
- Bicarbonate (sets up a protective pH gradient in the mucus layer)
What are the functions of gastric acid?
- Acts as a bacteriostatic agent
- Transforms pepsinogen into active pepsin
- Denatures proteins
- Facilitates absorption of iron, calcium, and vitamin B12
NSAIDs inhibit the formation of prostaglandins by cyclooxygenase, causing gastric side effects.
Name at least 3 protective effects of PGs on the gastric mucosal barrier.
- Inhibit acid secretion
- Stimulate mucus and bicarb secretion
- Enhance synthesis of surface-active phospholipids
- Prevent surface epithelial cell exfoliation
- Increase mucosal blood flow