Alterations of Digestive Function: Clinical Physiology of the Liver and Pancreas

Alterations of Digestive Function - NURS 3110

Concept Overview: Liver and Pancreas Clinical Physiology

Clinical Liver Physiology
General Functions of the Liver

  • The liver plays a crucial role in various metabolic and physiological functions, including:

    • Conversion of Unconjugated Bilirubin to Conjugated Bilirubin

    • Red blood cell hemoglobin breakdown products include heme and globin.

    • Unconjugated Bilirubin is converted to Conjugated Bilirubin in the liver, which is secreted into bile.

    Process of Bilirubin Conversion

    • Production of Albumin

    • The liver synthesizes 90% of plasma proteins, including albumin.

    • Albumin maintains plasma oncotic pressure, helping to retain water in the plasma, preventing excessive water from escaping into tissues.

      • Plasma oncotic pressure can be influenced by the levels of albumin in the blood (H2O and albumin levels interact).

    • Production of Clotting Factors

    • The liver produces all clotting proteins (factors) crucial for coagulation, specifically fibrin.

    • Production of Inflammatory Proteins

    • The liver synthesizes Complement proteins, which opsonize bacteria for phagocytosis and contribute to the lysis of foreign organisms.

    • Conversion of Ammonia to Urea

    • During protein breakdown, ammonia is released, which is toxic; the liver converts ammonia into urea to prevent cell injury.

      • The reaction involved is:
        2NH3 + 3CO2 → H2N - C(=O) - NH2 + H_2O

    • Glucose Storage and Metabolism

    • The liver stores glucose as glycogen and plays a role in gluconeogenesis, ensuring glucose homeostasis through various pathways:

      • Glycogenolysis allows the conversion of glycogen back to glucose when needed.

      • Glucose can also be derived from lactate, amino acids, and glycerol for ATP production.

Hepatic Portal System

  • Hepatic Portal System: All venous blood from the digestive organs passes through the liver via the hepatic portal vein before reaching the heart.

    • This system includes veins from various digestive organs such as the liver, stomach, duodenum, pancreas, and spleen, which drain into the hepatic portal vein.

Portal Hypertension

  • Portal Hypertension occurs when the blood flow through the liver is obstructed, leading to elevated pressures in the hepatic portal system:

    • Blood enters the liver through the Hepatic Portal Vein and flows through hepatic sinusoids (capillaries).

    • After passing through the liver, blood exits via the hepatic vein into the inferior vena cava (IVC).

Clinical Measures of Liver Function

  • Alterations in Liver Enzymes:

    • Alanine Transferase (ALT), Aspartate Aminotransferase (AST), and Alkaline Phosphatase (ALP) are liver-specific enzymes released during hepatocyte injury or death.

    • Unconjugated Bilirubin levels may indicate liver dysfunction, as elevated levels occur when bilirubin conversion is impaired.

    • Albumin and total protein levels reflect liver function; decreased levels suggest dysfunction.

    • Lactate Dehydrogenase (LDH) is released during hepatocyte injury but is not specific to liver dysfunction.

    • Prothrombin Time (PT) measures blood clotting time and can be elevated in liver dysfunction due to a decrease in clotting protein production.

Clinical Anatomy & Physiology of the Pancreas

  • The pancreas is located in the retroperitoneal space behind the stomach and plays a dual role as both an endocrine and exocrine organ:

    • Secretory Functions:

    • Exocrine pancreas: secretes digestive enzymes (proteases, amylases, lipases) into the pancreatic duct, which joins the common bile duct at the sphincter of Oddi.

      • Pancreatic lipase is the primary digestive lipase.

      • Proteases are secreted as proenzymes or inactive enzymes to ensure they do not digest pancreatic tissue.

    • Endocrine pancreas: secretes hormones such as insulin and glucagon to regulate blood glucose levels.

Clinical Measures of Pancreatic Function

  • Elevated levels of plasma amylase and lipase suggest pancreatic inflammation or damage, commonly used in diagnosing pancreatitis.

Disorders of the Esophagus, Stomach & Intestines; Liver and Pancreas Disorders
Constipation

  • Overview: Constipation involves difficulty or infrequent defecation, often due to excessive water removal from intestinal contents, leading to hard stools.

  • Bristol Stool Chart Types:

    • Type 1: Separate hard lumps (Severe constipation)

    • Type 2: Lumpy and sausage-like (Mild constipation)

    • Type 3: Sausage shape with cracks (Normal)

    • Type 4: Smooth, soft sausage or snake (Normal)

    • Type 5: Soft blobs with clear-cut edges (Lacking fiber)

    • Type 6: Mushy consistency with ragged edges (Mild diarrhea)

    • Type 7: Liquid consistency with no solid pieces (Severe diarrhea)

  • Types of Constipation:

    • Normal Transit Constipation: Normal rate of stool passage but difficulty in evacuation, often due to lifestyle factors (sedentary lifestyle, low fiber diet).

    • Slow Transit Constipation: Slow passage due to impaired peristalsis, often related to aging or neurogenic disorders.

    • Outlet Obstruction: Difficulty expelling stool due to rectal issues (e.g., hemorrhoids, strictures).

Clinical Consequences of Constipation

  • Symptoms include difficulty passing stool, abdominal cramping/pain, and complications like fecal impaction or anal fissures.

Diarrhea

  • Overview: Diarrhea is characterized by the presence of loose or watery stools.

    • Bristol Stool Chart Types (Similar structure as constipation)

    • Types of Diarrhea:

    • Osmotic Diarrhea: Water is drawn into the large intestine due to substances present (e.g., lactose intolerance).

    • Secretory Diarrhea: Intestinal epithelium secretes large volumes of fluid (e.g., due to infections like E. coli).

    • Motility Diarrhea: Insufficient absorption due to rapid transit or bowel obstructions.

    • Special Case - Steatorrhea: The presence of fat in stools, often due to pancreatic enzyme insufficiency.

Clinical Consequences of Diarrhea

  • Loss of fluids can lead to dehydration, electrolyte imbalances such as hypokalemia and hyponatremia, especially in infants and children.

Gastroesophageal Reflux Disease (GERD)

  • Overview: Characterized by the reflux of gastric contents through the lower esophageal sphincter (LES), causing symptoms like heartburn.

  • Risk Factors:

    • Hiatal Hernia: Weakening of connections affecting LES stability.

    • Foods: Items such as coffee and alcohol that relax the LES.

    • Pregnancy: Increased intra-abdominal pressure impacting LES function.

Pathophysiology of GERD

  • Results in tissue erosion and ulceration in the esophagus due to acidic exposure from refluxed content.

Clinical Manifestations of GERD

  • Common symptoms include heartburn, regurgitation, and cough, with complications such as esophageal strictures and Barrett's esophagitis.

Peptic Ulcer Disease

  • Overview: A condition causing ulcerations in the stomach or duodenal linings, with H. Pylori infection being a significant cause (75% of cases).

Pathophysiology of H. Pylori Infection

  • Bacteria create tunnels in the mucus layer leading to epithelial damage from hydrochloric acid and digestive enzymes.

Other Causes of Peptic Ulcer Disease

  • Include NSAID use, psychological stress, alcohol, and smoking, contributing to gastric injury and ulcer development.

Clinical Consequences of Peptic Ulcer Disease

  • Symptoms range from abdominal pain and discomfort to upper GI bleeding and potential for anemia.

Inflammatory Bowel Diseases: Ulcerative Colitis and Crohn's Disease

  • Ulcerative Colitis: Autoimmune disease with chronic inflammation predominantly affecting the colon's mucosa; involves periods of exacerbation.

  • Crohn's Disease: Another autoimmune condition affecting any part of the digestive tract, characterized by skip lesions and transmural inflammation.

Comparison of UC & CD

  • Ulcerative Colitis: Superficial ulceration, continuous involvement beginning in the rectum.

  • Crohn's Disease: Transmural inflammation with potential for strictures and fistulas, often affecting younger populations.

Alcoholic Cirrhosis

  • Overview: Diffuse liver disease caused by excessive alcohol consumption; can also arise from other factors such as hepatitis and autoimmune disorders.

Pathophysiology of Alcoholic Cirrhosis

  • Involves the conversion of alcohol to acetaldehyde, leading to hepatocyte injury, inflammation, and eventual fibrosis.

Clinical Measures Related to Liver Function

  • Include levels of liver enzymes, bilirubin, albumin, and prothrombin time to assess liver health and function.

Pancreatitis

  • Overview: Inflammation of the pancreas can be acute or chronic; most common causes include obstruction of the pancreatic duct by gallstones or alcohol use.

Pathophysiology of Pancreatitis

  • Premature activation of digestive enzymes leads to autodigestion of pancreatic tissue, resulting in a range of clinical symptoms including epigastric pain and potential malnutrition from enzyme insufficiency.

Clinical Manifestations of Pancreatitis

  • Symptoms include severe epigastric pain radiating to the back, nausea, and possible malnutrition in chronic cases.