Objectives - exam 2: med path

Gastrointestinal Physiology and Pathophysiology

Overview of Gastrointestinal System

  • The gastrointestinal (GI) system is a complex network of organs and tissues that performs essential functions to sustain life, including digestion and metabolism.

  • The GI tract is a hollow tube extending from the mouth to the anus and includes the following organs:

    • Mouth

    • Pharynx

    • Esophagus

    • Stomach

    • Small Intestine (duodenum, jejunum, ileum)

    • Colon

    • Rectum

    • Anus

  • Accessory organs include:

    • Liver: Produces bile for fat emulsification

    • Pancreas: Supplies digestive enzymes and bicarbonate (HCO3) for neutralizing stomach acid

    • Gallbladder: Stores and releases bile

GI System Functions

Wall Layers of the GI Tract

  • Mucosa: Innermost layer responsible for secretion and absorption.

    • Contains enterocytes for nutrient absorption and goblet cells that secrete mucus.

  • Submucosa: Contains dense connective tissue, blood vessels, and nerves. Includes Meissner's plexus, which regulates secretions.

  • Muscularis Externa: Composed of two main muscle layers (inner circular and outer longitudinal) responsible for peristalsis and segmentation.

  • Serosa: Outermost layer that provides a protective covering.

GI Functions and Processes

  • Digestion: The mechanical and chemical breakdown of food into absorbable molecules.

    • Mechanical digestion: Involves chewing in the mouth, churning in the stomach, and segmentation in the small intestine.

    • Chemical digestion: Involves enzymes such as salivary amylase (carbohydrate digestion), gastric acid (protein breakdown), and pancreatic enzymes (fats and proteins).

  • Absorption: Uptake of nutrients (carbohydrates, fats, proteins, vitamins, and minerals) into the bloodstream or lymphatic system.

    • Transporters: Specialized proteins in the epithelium facilitate nutrient absorption.

    • Microvilli (brush border): Increase surface area for absorption.

  • Motility: Muscular contractions to propel and mix contents through the tract.

  • Secretion: Release of substances (enzymes, acids, bile, mucus) that aid in digestion and protect the mucosal lining.

  • Excretion: Elimination of undigested material and waste products through defecation.

Liver Functions

  • Major Functions:

    • Bile production

    • Metabolism (detoxification, urea cycle, ammonia conversion to urea, bile acid synthesis)

    • Protein synthesis (albumin, clotting factors)

    • Phase I and II metabolic processes.

  • Blood Supply:

    • Receives blood from the portal vein and hepatic artery.

    • Outflow through the hepatic vein.

Pathophysiology of Liver Diseases

  • Hepatitis: Inflammatory condition leading to hepatocyte injury (detectable via ALT and AST levels).

    • Causes include viral strains (A, B, C, D, E), alcohol use, and autoimmune factors.

  • Cirrhosis: Chronic liver injury leading to fibrosis and nodular liver formation, resulting in complications like portal hypertension, varices, and splenomegaly.

  • Hepatic Encephalopathy: Accumulation of ammonia due to liver dysfunction, leading to changes in mental state.

Gastroesophageal Reflux Disease (GERD)

  • Characterized by lower esophageal sphincter (LES) hypotonia, causing acid reflux and mucosal injury in the esophagus.

  • Risk Factors:

    • Obesity, smoking, alcohol consumption, pregnancy, and hiatal hernia.

  • Management: Use of proton pump inhibitors (PPIs) to block acid secretion.

Inflammatory Bowel Disease (IBD) and Irritable Bowel Syndrome (IBS)

Pathogenesis of IBD

  • An autoimmune response to gut microbiota with a genetic predisposition.

  • Major types: Crohn's disease and ulcerative colitis affecting intestinal motility and structure.

  • Symptoms: RLQ pain, bloody diarrhea, malabsorption, urgency.

Gut Microbiome Impact

  • Functions include colonization resistance, nutrient production, and immune regulation.

  • Dysbiosis can lead to inflammatory conditions and nutrient deficiencies.

Renal Physiology

Kidney Structure and Function

  • The kidney is a retroperitoneal, paired organ responsible for filtering blood and forming urine.

  • Nephron: Functional unit consisting of:

    • Glomerulus: Site of filtration. Blood enters via the afferent arteriole.

    • Proximal Tubule: Major reabsorption area; reabsorbs 65-70% of filtered substances.

    • Loop of Henle: Creates osmotic gradient in the kidney medulla.

    • Distal Tubule: Final adjustments to electrolyte and pH balance.

    • Collecting Duct: Hormonal control of water reabsorption.

Mechanisms of Glomerular Filtration

  • Governed by Starling forces: Hydrostatic pressure in the glomerulus drives filtration, while oncotic pressure and capsular pressure oppose it.

  • Normal Glomerular Filtration Rate (GFR): Approximately 120 mL/min.

Regulation of Body Fluid and Electrolyte Balance

  • RAAS (Renin-Angiotensin-Aldosterone System):

    • Important for managing blood pressure and fluid balance.

    • Dehydration triggers renin release, leading to angiotensin formation which causes vasoconstriction and aldosterone release for sodium retention.

Acute and Chronic Kidney Disease (AKI and CKD)

  • AKI: Sudden loss of kidney function, potentially reversible.

  • CKD: Progressive decline in nephron function due to various causes (diabetes, hypertension).

    • May lead to end-stage renal disease (ESRD) where kidneys can no longer sustain bodily needs.

Nephrotic Syndrome vs Nephritic Syndrome

  • Nephrotic Syndrome:

    • Characterized by massive proteinuria (>3.5g/day), hypoalbuminemia, edema, and increased risk of thrombosis.

  • Nephritic Syndrome:

    • Presents with hematuria, proteinuria (less than 3.5g/day), hypertension, and possible fluid retention.

    • Common causes include post-streptococcal glomerulonephritis and IgA nephropathy.

Dialysis Physiology

  • Indications for dialysis include inability to maintain electrolyte balance, waste removal, and volume management due to kidney dysfunction.

  • Laboratory Testing in Renal Dysfunction:

    • Key labs include urinalysis indicating proteinuria, glucose, and specific gravity for kidney function assessment.

Electrolyte Imbalances in Renal Disease

  • Symptoms may include sodium retention, hypertension, and hypocalcemia leading to secondary hyperparathyroidism.

  • Anemia due to erythropoietin deficiency causing normocytic anemia.

  • Metabolic acidosis secondary to reduced acid secretion and buffer system failure.