Week 2 - Oesophagus, Stomach, Small Intestine and Associated Disorders Flashcards
Define the term enteric nervous system. Which plexuses make up this division of the nervous system?
ENS provides intrinsic nervous supply to the GIT with two major plexuses:
Submucosa nervous plexus (located within the submucosal layer)
Myenteric nervous plexus (located between circular and longitudinal layers of the muscularis)
List the cell types found in the gastric glands and describe their function.
Mucous neck cells - produce mucous
Parietal cells - secrete HCl and produces intrinsic factor for the absorption of Vitamin B12 in terminal ileum
Chief cells - produce pepsinogen (low pH required for conversion to pepsin) and gastric lipase (breaks down lipids)
Entero-endocrine cells - secretes hormones and chemical mediators; gastrin from G cells controls secretory activity of stomach; histamine (secretion) and serotonin (contractility) is also released
List the cell types found in villus and intestinal crypt structures and describe their function.
Enterocytes
- absorptive cells endowed with microvilli
- crypt enterocytes secrete intestinal juice
Goblet cells
- produce alkaline mucus (relies on prostaglandin presence)
Enteroendocrine cells
- secrete hormones (e.g. CCK, secretin)
Paneth cells
- release antimicrobial agents (e.g. lysozymes)
Stem cells
- renew the epithelium every 3-5 days
Describe the lower oesophageal sphincter (i.e. other names, why is it not a truly anatomical sphincter, what reinforces it)
Fourth constriction point in the oesophagus
Also known as the gastroesophageal or cardiac sphincter
It is a function sphincter as the slight thickening of the circulation muscle creates this point of slight narrowing
Reinforced extrinsically by the diaphragm
Describe the potential outcomes of GORD.
Potential outcomes include: -
- healing with no residual effects
- healing with fibrosis
- slow blood loss leading to iron deficiency anaemia
- oesophageal ulceration
- Barrett’s mucosa (metaplasia)
Summarise the risk factors for GORD.
Decreased tone of LOS (caffeine, fatty foods, hiatal hernia)
Impaired mucosal defences (smoking, alcohol)
Increased intra-abdominal pressure (pregnancy, obesity, ascites, lifting and bending)
What type of anaemia is associated with autoimmune gastritis? How might it present clinically?
Pernicious anaemia (autoimmune gastritis), where antibodies are produced against parietal cells and intrinsic factor (leading to vitamin B12 deficiency - inability to absorb in the ileum) and megaloblastic anaemia) Present with usual SSx of anaemia (SOB, pale conjunctiva, fatigue); also, neurological deficits (due to demyelinating lesions = loss of vibration/tactile sensation)
List the four general mechanisms by which antibiotics act
- inhibition of cell wall synthesis
- disruption of the cell membrane
- inhibition of protein synthesis
- inference with metabolic synthesis
Compare the aetiologies of acute and chronic gastritis
Acute gastritis - infective agents (salmonella, e. coli), direct damage (alcohol, NSAIDS) or inhibition of mucosal replacement (chemotherapy, radiotherapy)
Chronic gastritis - Helicobacter pylori infection (80% of cases); autoimmune gastritis
How does GORD commonly present? Are there any important differential diagnoses that you must not overlook in a patient with GORD-like symptoms?
Clinical features:
- heartburn (epigastric and/or retrosternal pain)
- dyspepsia (general feeling of discomfort)
- dysphagia (difficulty swallowing)
- odynophagia (pain with swallowing)
Consider cardiac, respiratory or musculoskeletal DDx
Identify the most common type of gastric carcinoma and its usual site in the stomach.
95% of gastric cancers are adenocarcinomas
50% occur in the pylorus or antrum
What is located between the two layers of muscle in the muscularis
Meissner’s plexus/Myenteric nervous plexus
What is the neurovascular supply of the stomach?
Nerve supply
- intrinsic: ENS
- extrinsic: PNS (CNX); SNS (greater splanchnic nerve T6-T9); Visceral afferents
Arterial supply
- rich supply from branches of the celiac trunk
- anastomose along lesser curvature (left and right gastric artery)
- anastomose along greater curvature (left and right gastro-omental arteries)
- 4-5 short gastric arteries supply fundus
Venous drainage
- R and L gastric veins (drains into portal vein)
- short gastric vein and L gastro-omental vein (drain into splenic vein)
- right gastro-omental vein (drains into SMV)
- SMV and splenic vein unit to form portal vein
List the basic layers of the wall of the GIT
From innermost to outermost:
Mucosa (epithelium, lamina propria and thin muscularis mucosa)
Submucosa (contains lymphatic, neural tissue and glands)
Muscularis (longitudinal and circular muscle layer)
Serosa or Adventitia (if covered by peritoneum = serosa; if retro-peritoneal = adventitia) an organ can have both e.g. liver
What clinical features might make you suspicious that your patient may be suffering from something more sinister than a gastric ulcer?
More dramatic clinical features:
- haematemesis (vomiting blood)
- melena (dark blood in faeces)
- symptoms of pyloric obstruction
Compare the factors that stimulate gastric secretion/emptying to those that inhibit gastric secretion/emptying
Stimulatory events for gastric secretion/emptying:
cephalic phase -
1. sight and thought of food
2. stimulation of taste and smell receptors
gastric phase -
- stomach distension activates stretch receptors
- food chemicals (especially peptides and caffeine) and rising pH active chemoreceptors
intestinal phase -
1. presence of partially digested foods in the duodenum or distension of the duodenum when stomach begins emptying
inhibitory events:
cephalic phase -
1. loss of appetite, depression
gastric phase:
- excessive acidity (pH < 2) in stomach
- emotional stress
intestinal phase -
- distension of duodenum; presence of fatty, acidic or hypertonic chyme; and/or irritants in the duodenum
- distension; presence of fatty, acidic, partially digested food in the duodenum
What other risk factors have been associated with peptic ulceration?
NSAIDS (reduce PGE2 content = reduced mucosal secretion; aspirin can directly damage cell membranes)
Smoking (generation of ROS = mucosal damage; reduces healing rate once an ulcer has formed)
Familial factors (determine susceptibility to ulcers and site of formation = increased risk if 1st degree relative has an ulcer)
Identify the type and function of the epithelium that lines the mucosa of the stomach.
Simple columnar epithelium - these contain mucous cells that secrete a protective alkaline mucous
Differentiate a short digestive reflex from a long digestive reflex. Can you provide an example of each?
Short reflexes - mediated entirely by the ENS in response to stimuli in the GIT (e.g. peristalsis)
Long reflexes - involves integration with the CNS and extrinsic autonomic nerves (PNS/SNS) (e.g. defecation)