GI Topic 2 - Upper GI tract Flashcards
Describe the intestinal phase of gastric function
- Proteins in duodenum - gastrin release (excitatory)
- Duodenum distention/presence of acidic chyme - enterogastric reflex (inhibitory)
- Secretin released by S cells in response to acid, inhibit gastrin release (reduces affinity of parietal cells to gastrin)
- CCK, GIP and peptide YY released in presence of lipids - inhibits gastrin release
What is the function of the mucous neck cells of the stomach?
Secrete mucous - protection of stomach walls from acidic contents and digestive enzymes
List the cell types of the stomach mucosa
- Columnar epithelial cells
- Mucous neck cells
- Parietal cells
- Chief cells
- G cells
- Stem cells
List the post-prandial phases of stomach function
- Cephalic
- Gastric
- Intestinal
Describe the gastric transit time of liquids compared with solids
Liquids leave the stomach 20 minutes after ingestion, solids take 3-4 hours
Describe the potential complications of a peptic ulcer
- Bleeding
- Gastric/duodenal perforation leading to acute peritonitis (indicated by extreme stabbing pain)
What causes increased gastric emptying?
Increased food volume (stretching of stomach walls)
Presence of digestive products of proteins - causes Gastrin secretion
How are peptic ulcers prevented?
- Proton-pump inhibitor prescribed to those on long-term NSAIDs
- Switch non-selective COX inhibitors for COX-2 NSAIDs
Describe the motility of the stomach in the interprandial period
- Migrating motor complex, every 90-120 minutes
- Regulated by motilin - produced by M cells in the small intestine
- Stimulates fundus contraction, increases emptying of the stomach - cleanses the stomach
Describe the organisation of the muscularis propria of the stomach
Inner oblique, middle circular and outer longitudinal smooth muscle layers
Describe the secretions of:
- G cells
- D cells
- K cells
- S cells
- I cells
- Gastrin
- Somatostatin
- Gastric inhibitory peptide (GIP)
- Secretin
- Cholecystokinin (CCK)
What produces the basal motor activity of the stomach?
Interstitial cells of Cajal produces the basal electrical rhythm of the stomach
Describe the extrinsic reflexes which cause increased pyloric sphincter contraction
Signals travel from the stomach/duodenum to the prevertebral sympathetic ganglia which stimulates inhibitory sympathetic fibres
Describe the location of the lesser sac
- Also known as omental bursa
- Cavity in the abdomen formed by the greater and lesser omentum
- Connected to the greater sac via the epiploic foramen
What is the function of pepsin in gastric secretions?
Endopeptidase - breaks down proteins to peptides
Describe the serosa of the stomach
Continuous with the greater and lesser omentum
What is the function of intrinsic factor in gastric secretions?
Needed for B12 absorption
Describe the cephalic phase of stomach function
- Secretory phase - sight, smell or taste of food stimulates dorsal motor neurons of the vagus nerve
- Vagal postganglionic muscarinic receptors in stomach body release acetyl choline, parietal cells secrete hydrogen ions
- Release of gastrin from G cells stimulates HCl and pepsinogen release
- Vagal action and gastrin stimulate histamine release from mast cells and enterochromaffin-like cells
- Histamine acts on H2 receptors on parietal cells - causes more hydrogen ion secretion
Describe the pharmacological treatments for gastroparesis
- SHT4 agonists - cisapride
- D2 antagonist - metoclopramide, domperidone
- Motilin agonist - erythromycin
List the contents of saliva
- Mucous - lubrication
- Amylase - digests starch
- Bicarbonate - neutralises acid
- Thiocyanate, lysozyme - bacteriocidal
Describe the innervation of the stomach
- Autonomic - parasympathetic and sympathetic
- Parasympathetic from vagus nerve branches
- Sympathetic - T6-9 spinal nerves via the greater splanchnic nerve to form the coeliac plexus
- Also has afferent pain transmitting fibres
How does pyloric sphincter function at normal tone?
Allows fluid chyme to empty, prevents passage of solid food
Describe the arterial supply of the oesophagus
- Superior and inferior thyroid artery
- Branches of the bronchial, intercostal, descending aorta, left gastric, left inferior phrenic and splenic arteries
- Dense anastomoses in submucosa - infarction is rare
What is diffuse oesophageal spasm?
- Rare
- Rapid peristaltic contraction
- Causes chest pain, can impair swallowing function
How does H. Pylori infection affect gastric acid production?
- Lies in gastric glands, next to D cells
- D cells function to sense acidity and produce somatostatin to inhibit gastrin production and decrease gastric acid production
- H. Pylori increased the pH of gastric glands due to alkaline secretions, D cells do not sense acidity and somatostatin is not released
- Increased gastrin production, increased gastric acid secretion
How does NSAID use contribute to peptic ulcer formation?
- NSAIDs inhibit COX - catalyses prostaglandin synthesis
- Prostaglandins stimulate neck and isthmic gastric/duodenal cells to secrete buffer layer of bicarbonate, underneath mucin blanket
- Blockage of pathway - epithelium susceptible to damage (especially where already thinned e.g. due to H. Pylori infection)
Describe the branches of the common hepatic artery
- Gastroduodenal artery
- R gastric artery
- Bifurcates into left and right hepatic arteries
- Right artery gives off cystic artery
Describe the location of the greater sac
- Cavity in the abdomen inside the peritoneum but outside the lesser sac
- Connected to lesser sac by the epiploic foramen
What is achalsia?
- No peristalsis therefore no movement of the food bolus
- Lower oesophageal sphincter doesn’t relax - constant high pressure, functional outlet obstruction at bottom of oesophagus
- Causes regurgitation of food, weight loss
Describe the path of ingested food as it passes through the stomach
- Abdominal oesophagus
- Lower oesophageal (cardiac) sphincter
- Cardia
- Body
- Pyloric antrum
- Pyloric orifice
- Duodenum
What is the main side effect of proton pump inhibitors?
Increased risk of enteric infection e.g. C. Diff
Describe the process of swallowing and how it is controlled
- Voluntary then involuntary
- Opening of upper oesophageal sphincter - initially voluntary but once started involuntary
- Controlled by ‘swallowing centre’ in the reticular formation of the brainstem
What is the function of the circular muscle layer of the GI tract?
Constriction
What is the function of the parietal cells of the stomach?
Secrete HCl and intrinsic factor (needed for B12 absorption)
What causes disorders of accelerated gastric emptying?
- Usually history of previous gastric surgery e.g. Bilroth 1 or 2
- Bilroth 1 - removal of pylorus
- Bilroth 2 - removal of of part of small intestines
Describe the structure and location of the greater and lesser omentum
- Double layers of peritoneum
- Greater - attaches to the greater curvature of the stomach, hangs over the transverse colon
- Lesser - attaches from the lesser curvature of the stomach to the liver
Why is the greater omentum called the policeman of the abdomen?
- Immune function - contains collections of macrophages
- Infection and wound isolation - prevents spread of infection by wrapping around infected area to isolate it
What type of cells are the chief cells of the stomach?
Cuboidal epithelial cells
Define a hiatus hernia
Weaknening of oesophageal ligament, stomach migrates forwards into chest, separation of sphincter and diaphragm
What common drug affects MMCs and therefore stomach motility?
Erythromycin is a motilin agonist - accelerates MMCs
Describe the contents of the submucosa of the GI tract
Meissner’s submucosal plexus
Describe the structure of the oesophagus
- Upper oesophageal sphincter to lower oesophageal sphincter
- Upper 1/3 is voluntary striated (skeletal) muscle
- Lower 2/3 is involuntary smooth muscle
How is Gastric electrical stimulation used in the management of gastroparesis?
- 2 electrodes, 1cm apart, 9cm from pylorus in greater curvature of the stomach
- Stimulates high frequency low amplitude contractions
- Does not increase gastric emptying, improves nausea/vomiting
- Effective for diabetics
Describe the external anatomy of the stomach
- Greater curvature around left side of the body
- Lesser curvature around right side of the body
- Cardial notch between the oesophagus and the fundus
- Angular incisure between the lesser curvature and the beginning of the duodenum
How much saliva is produced per day?
0.5L/day