Gastrointestinal Tract Overview

Gastrointestinal Tract

• Digestion and absorption of food is a complex process involving integrated activity of alimentary tract organs
• Carbohydrates are converted to monosaccharides from disaccharides
• Proteins are broken down by proteases (inactive precursors) and peptidases to oligopeptides and amino acids
• Fats require mechanical mixing, bile salts and enzyme action to emulsify triglycerides
• Enzymes, cofactors and substrates need optimal pH (H+) for activity
• Pancreatic lipase converts triglycerides to free fatty acids and monoglycerides

The Stomach

• Food mixes with acidic gastric juice in the stomach
• Gastrin is secreted by G cells in the stomach antrum to stimulate motility, acid secretion (HCl) from parietal cells, and mucosal/pepsinogen secretion from chief cells

Gastric Function & Investigation

• Biochemical tests are limited in diagnosing gastric disorders; endoscopy, contrast radiography and biopsies can provide more details
• Peptic ulceration, often linked to non-steroidal anti-inflammatory drugs or Helicobacter pylori colonization. Diagnosis includes serology, 13C urea breath test and stool antigen test.
• H. pylori infection diagnosis uses 13C or 14C urea (isotope) in the breath test to find ammonia/carbon dioxide from urea splitting by the bacteria
• Atypical peptic ulceration cases may be resistant to treatment or recur
• Zollinger-Ellison syndrome involves gastrinoma, causing hypergastrinaemia
  • Patients might have steatorrhoea due to inhibited pancreatic lipase from high gastric acid levels. Fasting plasma gastrin concentrations are tests for diagnosing this syndrome.

The Pancreas

• Essential endocrine organ for producing insulin, glucagon, pancreatic polypeptide and other hormones (details in Chapter 13)
• Pancreatic exocrine fluid is alkaline, bicarbonate rich, and contains various digestive enzymes like proenzymes (proteases), lipases, amylase, hydrolases for starches, cholesterol, phospholipids and nucleases
• Pancreatic enzyme secretion is mainly controlled by hormones (secretin and CCK) in the small intestine
  • Secretin stimulates alkaline fluid secretion
  • CCK stimulates pancreatic enzyme secretion and gallbladder contraction.
• Important pancreatic disorders include acute and chronic pancreatitis, pancreatic cancer and cystic fibrosis

Acute Pancreatitis

• Acute abdomen pain, shock and variable degrees of shock are symptoms occurring due to causes like excessive alcohol, gallstones, ERCP complications, and idiopathic conditions
• Diagnosis confirmed with a high plasma amylase or lipase activity (more than three times higher than upper reference limit) and CT scans
• Case history details include a 53-year-old man suffering from severe abdominal pain potentially linked to heavy ethanol intake. The case highlights the need for clinical history, inflammation signs and high enzyme levels to conclusively diagnose pancreatitis.

Chronic Pancreatitis

• Chronic abdominal pain and malabsorption are common in chronic pancreatitis
• Pancreatic elastase and chymotrypsin activity in faeces are reduced in pancreatic insufficiency, and often used to distinguish between pancreatic and non-pancreatic diarrhoea

Carcinoma of the Pancreas

• Plasma tumor markers (CEA, CA 19-9) are frequently elevated in pancreatic malignancy (cancer)
• Causes of increased plasma amylase activity range from perforated duodenal ulcers to acute pancreatitis, other abdominal disorders, kidney injury and even diabetic ketoacidosis

Pancreatitis Severity Assessment

• The modified Glasgow score assesses severity within 48 hours of symptom onset, using factors such as age, white blood cell count, and glucose levels, to determine the severity of pancreatitis

Case History (page 7)

• A patient with abdominal bloating, frequent/bulky bowel movements (malabsorption symptoms), a low faecal elastase activity and abdominal pain.
• The case shows hypocalcaemia, hypophosphataemia, high alkaline phosphatase, low vitamin D.
• The decreased faecal elastase activity strongly suggests pancreatic insufficiency
• Mildly elevated glucose values (if confirmed) point towards diabetes
• The diagnosis confirmation in this case supports the importance of clinical history, biochemical findings, and response to treatment for evaluating pancreatic disorders.