Digestive System: Mouth, Pharynx, and Esophagus

• The digestive system comprises the gastrointestinal tract, liver, pancreas, and gallbladder
• It is primarily responsible for digesting and absorbing food

Mouth

• Entry point for food, where both mechanical and chemical digestion begin
• Teeth break down food into smaller pieces
• The tongue mixes saliva with food
• Saliva contains ptyalin, or salivary amylase, which digests starch into maltose and dextrin

Pharynx

• Also known as the "throat"
• Serves as a passageway for both food and air
• Connects the mouth to the esophagus and the windpipe to the lungs
• Food that is chewed and pushed to the pharynx is called a bolus
• The epiglottis closes the windpipe when swallowing food

Esophagus

• A muscular tube that connects the mouth to the stomach
• Food (bolus) moves through the esophagus via peristalsis, an involuntary wave-like muscular contraction
• Peristalsis continues through the stomach, small intestine, and large intestine
• The lower esophageal sphincter (LES) opens to allow food into the stomach and closes to prevent backflow

Stomach

• A muscular sac that stores and digests food
• Contains glands that secrete acid and enzymes for digestion
• Gastric juice includes hydrochloric acid (HCl) and pepsin
• Both mechanical and chemical digestion occur in the stomach
• Bolus transforms into a thick, semi-liquid mass called chyme

Small Intestine

• About 6-7 meters long and 2-4 cm wide
• Nutrients and minerals are absorbed here
• Composed of the duodenum, jejunum, and ileum
• Duodenum: digests and neutralizes chyme's activity
• Jejunum: absorbs sugars, amino acids, and fatty acids
• Ileum: absorbs vitamin B12, bile salts, and other nutrients not absorbed by the jejunum

Accessory Organs

• Liver: secretes bile to emulsify fats in the small intestine
• Gallbladder: stores bile
• Pancreas: secretes pancreatic juice to break down proteins, fats, and carbohydrates

Large Intestine

• Also called the "colon"
• Reabsorbs water and mineral salts

Appendix

• A small, thin tube attached to the large intestine in the lower right abdomen
• Its exact function is unknown; one theory suggests it stores good bacteria

Rectum

• Temporarily stores undigested food from the colon, which becomes stool or feces

Anus

• The opening of the rectum to the outside of the body
• The end of the gastrointestinal tract

Digestive Processes

• Ingestion: Food enters the mouth, beginning with mastication (chewing)
• Digestion: Breakdown of food into simpler forms for absorption and assimilation
  • Mechanical: Chewing, grinding, churning, mixing
  • Chemical: Actions of digestive enzymes, bile, gastric juices
• Absorption: Release of digested food into the bloodstream
  • Begins in the stomach; mostly occurs in the jejunum and ileum of the small intestine
• Assimilation: Nutrients are taken from the blood into the cells
• Elimination/Excretion: Removal of metabolic waste products from the body as stool or urine

Macro and Micro Nutrients

• Macronutrients: Needed in large amounts regularly
  • Carbohydrates: Source of energy (at least 50 grams needed)
    • Monosaccharides (simple sugar): fruits, honey, candy
    • Disaccharides (2 monosaccharides): milk, cheese, ice cream, milkshake
    • Polysaccharides (10+ monosaccharides): starch, glycogen, fibers
  • Proteins: Build and repair body tissues; can be used for energy
    • Made up of amino acids; sources include nuts, eggs, milk, meat, fish
  • Fats and oils: Provide energy; synthesize hormones
    • Saturated (unhealthy, solid at room temp)
    • Unsaturated (healthier, liquid at room temp)
  • Water: Helps flush out toxins and keeps the body hydrated
• Micronutrients: Needed in small amounts only
  • Vitamins: Organic molecules found in small amounts (e.g., fruits and vegetables)
  • Minerals: Inorganic substances (e.g., calcium, sodium, potassium, chlorine, phosphorus)

Diseases

• Gastroesophageal Reflux Disease (GERD): Stomach acid repeatedly flows back into the esophagus
  • Causes: Frequent acid reflux or reflux of non-acidic content; sphincter not relaxing properly or weakening
  • Symptoms: Heartburn, regurgitation, upper abdominal or chest pain, trouble swallowing, lump sensation in the throat
  • Treatments: Antacids, H2 blockers, proton pump inhibitors (PPI)
• Gallstones: Hard materials formed in the gallbladder
  • Causes: Too much cholesterol or improper gallbladder emptying
  • Symptoms: Pain in the upper right or center of the abdomen, back pain, right shoulder pain, nausea, vomiting; in severe cases, high fever, chills, jaundice
  • Treatments: Cholecystectomy (gallbladder removal)
• Stomach Ulcer: Painful sore in the stomach lining
  • Causes: Helicobacter pylori (H. pylori) infection, long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs) like Advil, ibuprofen, and aspirin
  • Symptoms: Painful sore in the stomach, fullness, bloating, belching, heartburn, nausea
  • Treatments: Antibiotics to kill H. pylori, PPI medication, antacids
• Irritable Bowel Syndrome (IBS): Digestive problem affecting the colon or large intestine
  • Causes: Abnormalities in digestive system nerves, stronger/longer muscle contractions, inflammation, severe infection, changes in microflora
  • Symptoms: Weight loss, rectal bleeding, iron deficiency anemia, nighttime diarrhea, unexplained vomiting, difficulty swallowing
  • Treatments: Progressive relaxation exercises, mindfulness training
• Appendicitis: Inflammation of the appendix
  • Causes: Obstruction, hardened stool buildup, tumor, traumatic injury
  • Symptoms: Pain in the lower right abdomen, nausea, vomiting, loss of appetite, constipation or diarrhea
  • Treatments: Appendectomy, antibiotics
• Indigestion/Dyspepsia: Discomfort or pain in the upper abdomen
  • Causes: Excessive alcohol, smoking, stress, fatigue, overeating, eating too fast, not chewing properly
  • Symptoms: Abdominal pain, bloating, belching and gas, nausea and vomiting, acidic taste, growling stomach, heartburn
  • Treatments: Aspirin and painkillers, proper medication with a doctor
• Constipation: Difficulty in moving bowels regularly
  • Causes: Inadequate fiber or water intake, lack of exercise, stress, overuse of laxatives, strong medication (antidepressants, iron pills, antacids), pregnancy, colon cancer
  • Symptoms: Bloated, hard, small, and difficult-to-excrete stools
  • Treatments: Increase fruits and vegetables, drink more water, eat prunes and bran cereals, drink warm liquids, exercise, avoid resisting the urge to poop
• Colorectal Cancer: Cancer starting in the colon or rectum
  • Causes: Often undetermined, but risk factors include old age, genetics, inflammatory intestinal conditions, low-fiber diet, high-fat diet, diabetes, smoking, alcohol, and radiation therapy
  • Symptoms: Rectal bleeding or blood in stool, persistent abdominal discomfort, weakness or fatigue, unexplained weight loss, persistent change in bowel habits
  • Treatments: Surgery, radiation therapy, chemotherapy, targeted therapy, immunotherapy