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)
What is the arterial supply of the different components of the small intestine?
Duodenum - gastroduodenal artery and superior pancreaticoduodenal artery (common hepatic artery, off celiac trunk); inferior pancreaticoduodenal artery (SMA)
Jejunum and Ileum - SMA provides 15-18 branches (run between layers of mesentery)
Describe the role of the oesophagus in propulsion (deglutition & peristalsis)
Propulsion conveys food to the stomach. It involves two phases:
Deglutition:
- Buccal phase (voluntary)
- Pharyngeal-oesophageal phase (involuntary)
Pharyngeal-oesophageal phase
- food moves from pharynx into oesophagus
- this requires blocking of trachea (epiglottis) and relaxation of upper oesophageal sphincter
- peristaltic waves propel food distally (adjacent segments of the oesophageal wall alternately contract and relax)
- relaxation of the lower oesophageal sphincter allows food to enter the stomach
Describe the “classic triad” of clinical features associated with oesophageal cancer
- dysphagia
- odynophagia
- weight loss
What structures are located in D2?
Hepatopancreatic ampulla/duct enter via D2 at the major duodenal papilla
Accessory pancreatic duct enters via the minor duodenal papilla
How would you introduce the stomach (structure, function and location) in the setting of a lab exam?
Structure - the stomach is generally the shape of the letter J. From a histological perspective, it is composed of simple columnar epithelium
Location - it is the expanded part of the digestive system, between the oesophagus and small intestine
Function -
- food blender and reservoir
- secretes gastric juice (converts food to chyme)
- secretes intrinsic factor (allows absorption of vitamin B12)
Discuss the factors that are implicated in the development of gastric cancer, as well as those associated with risk reduction.
Increased risk:
- H. pylori infection (chronic gastritis - proliferation of immune cells and pro-inflammatory cytokines = increased turnover of epithelia cells and cellular transformation)
- Diets high in salt
- Autoimmune gastritis
Reduced risk:
- Diets high in Vit C and carotenoids
Describe two properties of parietal cells that are important for the process of HCl secretion
Parietal cells contain receptors for gastrin, histamine and acetylcholine (helps activate second messenger systems to drive membrane-bound pumps)
They also contain membrane bound pumps (H+/K+ ATPase) (HCO3-/Cl-) to maintain cell balance
List the six digestive system processes and provide a brief description of each
I Might Park Down Alexandra Drive
Ingestion - putting food in mouth
Mechanical breakdown - chewing, churning, segmentation of food
Propulsion - deglutition (swallowing) and peristalsis (propel food down to stomach)
Digestion - enzymatic breakdown
Absorption - passage of nutrients through GIT mucosal cells into blood or lymph
Defecation - excretion of substances unable to be absorbed by the body
Summarise the pathological bowel changes that occur in Coeliac disease. Which aspect of the bowel is most affected?
- type 4 (cell-mediated) hypersensitivity reaction
- immune cells infiltrate lamina propria
- t-lymphocytes release inflammatory cytokines
- plasma cells produce IgA antibodies
- damage to mucosa and atrophy of villi
- impaired intercellular metabolism
- elimination of gluten, where epithelium returns to normal
Proximal bowel most affected, especially the duodenal-jejunal flexure
How is carbonic acid formed in parietal cells? What does this acid readily dissociate into?
Carbonic acid is formed from H2O (water) and CO2 (carbon dioxide) (this requires carbonic anhydrase to occur)
It then readily dissociates into H+ (hydrogen) and HCO3 (bicarbonate)
Describe three unique adaptations of the small intestine that assist in digestion and/or absorption
- Circular folds (mucosa and submucosa arranged in permanent folds; force chyme to spiral through lumen)
- Villi (finger-like projections of the mucosa; in the core of each villus, there is a dense capillary bed and a lymphatic capillary - relate closes to tubular glands containing substance-secreting cells)
- Microvilli (cytoplasmic extensions of mucosal absorptive cells; brush border enzymes perform final digestion of food)
List some risk factors for oesophageal cancer
- smoking
- excessive alcohol consumption
- Barrett’s mucosa (metaplasia)
Describe the role that H. pylori plays in the development of peptic ulceration (i.e. what pathogenic properties does it possess?)
Pathogenic properties of H. pylori:
- produces urease which allows survival in low pH = breaks down urea of stomach
- helical structures and flagella provide burrowing capacity
- release of bacterial toxins and reactive oxygen species causes direct damage to mucosa
- recruitment of neutrophils, mast cells and macrophages results in release of inflammatory cytokines (further injury)
What is the venous drainage of the different components of small intestine?
Duodenum
- duodenal vein follows related artery and drains into the portal vein
Jejunum and Ileum
- SMV (unites with splenic vein to form portal vein)
What is the neurovascular supply of the oesophagus?
Arterial supply
- branches from inferior thyroid artery
- oesophageal artery (aorta)
- left gastric artery (branch of celiac trunk)
- left inferior phrenic artery (aorta)
Venous drainage
- inferior thyroid vein
- oesophageal vein drain into azygous vein
- left gastric vein drains into portal vein
Lymphatic drainage
- paratracheal nodes
- inferior deep cervical nodes - posterior mediastinal nodes
- left gastric nodes
Nerve supply
- upper 1/2 of cervical part (under somatic control) = recurrent laryngeal nerve (CNX branch)
- rest of oesophagus = intrinsic (ENS); extrinsic (PNS - CNX) (SNS - cervical sympathetic ganglia, cardiopulmonary splanchnic nerves, abdominopelvic splanchnic nerves); visceral afferents
How might a patient with GORD be able to reduce his/her symptoms?
- Medication (GP or over the counter) (e.g. PPI - first line therapy, H2RA, antacids)
- Patient advice: (elevate head in bed, lose weight if obese, consume less caffeine/alcohol/fatty foods)
Define the term gastroesophageal reflux disease. What is another term for this condition?
Refers to the symptomatic passage of gastric contents to lower oesophagus. This is also referred to reflux oesophagitis
Define the term peptic ulceration. What are the most common sites for this disease?
Peptic ulceration refers to ulceration in any part of the GIT that is exposed to gastric secretions.
Common sites - duodenum (D1 due to proximity to acidity of stomach) and stomach (lesser curvature)
What is the nerve supply of the small intestine?
Nerve supply Intrinsic - ENS Extrinsic - - SNS - greater and lesser splanchnic nerve (T5-T9) via the celiac and superior mesenteric plexuses - PNS - vagus nerve - visceral afferents
Which substances stimulate the process of HCl secretion? How do they achieve this?
Gastrin (from G cells)
Histamine (from entero-endocrine cells)
Acetylcholine
Histamine H2-receptor antagonists and proton pump inhibitors are commonly used in the management of GORD. What is the action of these medications?
Histamine H2 receptor antagonists prevent the binding of histamine to receptors on the parietal cells walls. This therefore stops the stimulation of secondary messenger cells, that assist in the stimulation of membrane-bound pumps.
Proton pump inhibitors inhibit the H+/K+ ATPase membrane bound pump irreversibly. This stops hydrogen from exiting the cell (one half of HCl)
Define the term hiatal hernia. What is the difference between a sliding and rolling hiatal hernia?
Hiatal hernia refers to when the upper part of the stomach pushes through the oesophageal hiatus. It is often asymptomatic.
Sliding hiatal hernia - LOS is above the oesophageal hiatus
Rolling hiatal hernia - LOS is stationary and more stomach is located above oesophageal hiatus
Outline the potential clinical features and complications of Coeliac disease
Adult onset:
- can vary from silent, mild to florid disease
- weight loss, diarrhoea
- abdominal discomfort, excessive flatus
- fatigue
- amenorrhea - malabsorption of nutrients, resulting in irregularity of cycle (women of a reproductive age)
Childhood onset:
- usually occurs several months after weaning
- irritability, failure to thrive, abdominal distension
- voluminous, pale stool (lack of fat absorption)
How would you introduce the oesophagus (structure, function and location) in the setting of a lab exam?
Structure - muscular tube ~25cm long and ~2cm in diameter with food; composed of a cervical, thoracic and abdominal portion
Location - located between the pharynx and stomach, in the midline of the body
Function - provides a passageway for food bolus and assists in food propulsion to the stomach
What are the different components of the stomach?
Cardia - between the abdominal oesophagus and stomach
Fundus - relates to the left dome diaphragm; the dilated superior region
Body - region between fundus and pyloric atrium
Pyloric part - funnel part of the stomach (antrum and canal)
Lesser curvature - shorter concave border of the stomach
Greater curvature - longer, convex border
Define Barrett’s mucosa
Metaplasia of oesophageal epithelium - stratified squamous epithelium is replaced by simple columnar epithelium
It is considered a pre-malignant transformation
What substance is required for the secretion of gastric mucous? Provide an example of a medication that can impair this process.
Mucous secretion is stimulated by prostaglandins
NSAIDs can interfere with the process, which inhibit prostaglandin production; this may then impair protection against stomach pH
Summarise the clinical features of peptic ulceration
Epigastric pain (periodicity of several weeks; relationship to food) Anorexia Dyspepsia Nausea Vomiting Can be asymptomatic in the elderly
Complications:
- healing with fibrosis can cause pyloric stenosis
- blood vessel erosion can lead to iron deficiency anaemia, melena and haematemesis)
Identify the types of epithelia found in the oesophagus
Mostly: stratified squamous epithelium
At the gastroesophageal junction: simple columnar epithelium (mucous-secreting potential)
Define Coeliac disease
A genetically-determined, abnormal, hypersensitivity reaction to gluten or its peptide derivative, gliadin
