Accessory Digestive Organs: Structure and Function

Salivary Glands

  • Accessory digestive organs that secrete substances into the digestive tract.
  • Located within the oral cavity but not part of the physical digestive tract.
  • Function:
    • Secrete fluids to lubricate food.
    • Secrete enzymes to break down carbohydrates and some lipids.
  • Three pairs of salivary glands:
    • Parotid Salivary Gland:
      • Large gland near the surface of the mandible (jaw).
      • Secretes a thick substance containing salivary amylase, which breaks down carbohydrates.
      • Drains through the parotid duct, emptying near the second upper molar.
    • Submandibular Salivary Glands:
      • Lies on the floor of the mouth in the mandibular groove.
      • Secretes a mixture of liquids to assist in lubrication.
    • Sublingual Salivary Glands:
      • Lies on the floor of the mouth.
      • Produces a watery mucus secretion that acts as a lubricant.
  • Saliva Production:
    • Approximately 1 to 1.5 liters per day.
    • Composition:
      • 99% water.
      • 1% containing buffers, electrolytes, glycoproteins, antibodies, enzymes, and waste.
      • Buffers: Maintain a neutral pH of around 7 in the mouth.
      • Antibodies: Remove foreign substances and oral bacteria.
  • Functions of Saliva:
    • Lubrication of the mouth.
    • Moistening and lubricating food.
    • Stimulating taste buds by dissolving chemicals in food.
    • Initial digestion of carbohydrates.

Liver

  • Largest organ in the abdominal cavity, located in the upper right-hand quadrant.
  • Two main lobes: left and right.
  • Roles:
    • Filtering blood to ensure appropriate nutrient composition.
    • Cleaning blood and removing abnormal cells, pathogens, and toxins.
  • Metabolic Functions:
    • Hematologic functions: Removing old and damaged red blood cells, removing pathogens, and synthesis of plasma proteins.
    • Synthesis and secretion of bile, important for breaking down lipids (fats).
  • Structure:
    • Connected to the hepatic artery and the portal vein.
    • Hepatic Artery: Carries oxygen-rich blood from the aorta.
    • Portal Vein: Carries blood rich in digested nutrients from the digestive tract, spleen, and pancreas.
    • Blood vessels subdivide into smaller capillaries called sinusoids, leading to lobules.
    • Lobules: Functional units of the liver made up of hepatocytes (basic metabolic cells).

Gallbladder

  • Stores and concentrates bile produced by the liver.
  • Removal does not prevent liver from producing bile. Bile is still produced and secreted by the liver even after gallbladder removal.
  • Plays a role storage and concentration of bile.
  • Bile's role in lipid (fat) breakdown, individuals without a gallbladder may struggle with fatty meals.

Bile

  • Produced at approximately 1 liter per day in the liver.
  • Role: Aids in the digestion of lipids through emulsification.
  • Emulsification: Process of increasing the surface area of lipids, allowing greater access for enzymes to break them down into smaller components for absorption.
  • Analogy: Bile acts like a detergent, breaking down clumps of lipids into smaller droplets.
  • Promotes the absorption of lipids; without emulsification, lipids would clump and not be absorbed, potentially leading to fat-soluble vitamin deficiencies.
  • Bile salts are reabsorbed in the ileum and recycled by the body.

Pancreas

  • Lies posterior to the stomach, extending from the duodenum to the spleen.
  • Lobular textured organ.
  • Roles:
    • Exocrine cells: Secrete buffers to raise the pH, neutralizing stomach acid in the duodenum.
      • Secrete digestive enzymes to break down carbohydrates, lipids, and proteins.
      • Gastric acid has a low pH and moves into the duodenum.
      • If the acid doesn't get neutralized by the pancreases the enzymes need to operate effectively therefore they secrete these buffers that increase the pH.
    • Endocrine cells: Secrete hormones (insulin and glucagon) from pancreatic islets.
      • Insulin and glucagon: Involved in glucose storage and metabolism.
      • People with diabetes have issues with these cells.
  • Exocrine Function:
    • Secretion of buffers and digestive enzymes for nutrient digestion and absorption.
  • Common Bile Duct:
    • The pancreas and liver secrete into the duodenum through the common bile duct.
    • The digested food mixes with bile and pancreatic buffers/enzymes in the initial portion of the small intestine for efficient breakdown and absorption.