Digestion and Absorption Flashcards

Secretions from the GI Tract

Mouth

• Saliva production by salivary glands.
  • Lysozyme: Kills microbes.
  • Salivary amylase: Digests starch (carbohydrate).
  • Lingual lipase: Digests lipids (fats).

Stomach

• Gastric lipase: Digests lipids (fats).
• Hydrochloric acid (HCl):
  • Keeps pH low, killing microbes.
  • Converts pepsinogen to pepsin (active form).
• Pepsin: Digests protein.
  • Released as pepsinogen (inactive form).
  • Activated by hydrochloric acid.

Small Intestine

• Enterocytes produce brush border enzymes.
  • Finalize digestion of macronutrients.

Accessory Organs

Liver

• Produces bile.

Gallbladder

• Stores and concentrates bile.
• Bile emulsifies fat globules, increasing surface area for enzymatic action.
  • Note: Bile is NOT an enzyme; it does not break bonds.

Pancreas

• Secretes bicarbonate.
  • Neutralizes acid from the stomach.
• Produces and secretes enzymes:
  • Amylases: Digest starch.
  • Lipases: Digest fats.
  • Proteases: Digest proteins.

GI Hormones

• Hormones are secreted into the bloodstream, not the GI tract.

• Released by tissues and act on other or nearby tissues.

• Refer to table 4-4 in the textbook for details.

• Examples:

  • Cholecystokinin (CCK): Released by intestinal cells, promotes bile release from the gallbladder.

Purpose of Digestion

• Break down food into component parts for absorption.
• Macronutrients must be broken down into their smallest absorbable forms:
  • Proteins to amino acids.
  • Carbohydrates to monosaccharides.
  • Fats (triglycerides) to free fatty acids and monoglycerides.

Absorption of Nutrients

• Protein: Absorbed as amino acids, dipeptides, and tripeptides.
• Carbohydrates: Absorbed as monosaccharides.
• Fats: Triglycerides broken down into free fatty acids and monoglycerides.

Location of Absorption

• Small intestine: Most carbohydrate, protein (amino acids), and fat absorption; most minerals and vitamins.
• Alcohol: Can be absorbed throughout the GI tract.
• Water: Absorbed throughout the GI tract.
• Large intestine:
  • Electrolytes (sodium, potassium).
  • Fatty acids (short-chain fatty acids produced by microbes, providing energy for colonocytes).
  • Vitamin K and biotin (synthesized by microbes).
  • Bile acids: Reabsorbed in the ileum.

Circulation

• Nutrients absorbed in the small intestine enter the bloodstream or lymphatic system.
• Blood from the intestine flows directly to the liver via the portal vein.
• The liver processes, repackages, and stores nutrients before releasing them into the bloodstream.
• Fat-soluble nutrients and long-chain fatty acids are absorbed into lacteals, which drain into the lymphatic system.

Transport of Absorbed Nutrients

• Amino acids and monosaccharides:
  • Absorbed into the blood.
  • Carried to the liver via the portal vein.
• Fatty acids and monoglycerides:
  • Resynthesized into triglycerides.
  • Packaged into chylomicrons.
  • Enter the lymphatic system.
• Long-chain fatty acids:
  • Transported via chylomicrons through the lymphatic system.
• Fat-soluble vitamins:
  • Also packaged into chylomicrons.
• Short-chain and medium-chain fatty acids:
  • Absorbed directly into the bloodstream.

Common GI Issues

Gastroesophageal Reflux Disease (GERD)

• Chronic condition similar to heartburn.
• Lower esophageal sphincter relaxes, allowing stomach acid to enter the esophagus.
• Causes:
  • Alcohol intake.
  • Smoking.
  • Certain foods (caffeine, chocolate).
  • Large, fatty meals.
  • Tight clothing.
• Lowers the pH of the esphogus
• Symptoms:
  • Pain and burning.
  • Can lead to esophageal sores and, if untreated, cancer.
• Risk factors:
  • Smoking.
  • Heavy alcohol consumption.
  • Diet (citrus, spicy foods, tomato products).
• Treatments:
  • Dietary modifications.
  • Medications to decrease acid production.
  • Medications to tighten the sphincter.
• Factors contributing to GERD:
  • Large meals.
  • Fatty meals.
  • Nasogastric tube: Keeps the sphincter open.
  • Gastroparesis: Delayed gastric emptying increases pressure.
  • Pregnancy: Compression of the stomach increases pressure.

Inflammatory Bowel Disease (IBD)

• Umbrella term for conditions including Crohn's disease and ulcerative colitis.
• Different from Irritable Bowel Syndrome (IBS).
• Cause is not exactly known; Involves environmental factors and immune system response.

Crohn's Disease

• Inflammation and ulceration in all layers of the GI tract.
• Can occur from mouth to anus, but typically found in the ascending colon and ileum.

Ulcerative Colitis

• Inflammation and ulceration of the large intestine (colon) only.
• Limited to the mucosa layer.

Consequences of both

• Ulceration leads to scar tissue and narrowing of the GI tract (stricture).
• Fistulas (abnormal connections between GI tract parts) can form.
• Inflammation and ulceration impairs digestion and absorption. Swelling impacts digestion and absorption.
• Malabsorption occcurs

Symptoms

• Rectal bleeding.
• Diarrhea.
• Abdominal pain.
• Weight loss.
• Fever.

Nutrition issues

• Malabsorption.
• Decreased appetite.
• Anemia (low red blood cell count).
• Malnutrition.
• Increased nutrient requirements.

Treatment

• Manage symptoms and ensure adequate nutrition.
  • Address calorie, protein, macro, and micronutrient needs.
• Medical treatment:
  • Medications to suppress the immune system.
  • Antibiotics to treat infections.
• Surgery:
  • Resection (removal) of damaged tissue.
• Colectomy:
  • Total colectomy: Removal of the entire colon.
  • Partial colectomy: Removal of parts of the colon.
• Ileostomy:
  • The end of the ileum is brought to the surface of the abdomen, creating an opening for waste removal into a bag.