Digestive System Overview

Digestive System

• Breakdown of food into smaller, simpler molecules.
• Two types of digestion - physical and chemical
• Physical digestion: Mechanical breakdown of food in the mouth, oesophagus, stomach, and small intestine.
  • Involves chewing, peristalsis, churning, and segmentation.
• Chemical digestion: Breakdown of food molecules with enzymes in the mouth, stomach, and small intestine.
  • Does not involve peristalsis.

Parts of the Digestive System

• Alimentary canal: The long, muscular tube from the mouth to the anus.
  • Includes the:
    • Mouth
    • Oesophagus
    • Stomach
    • Small intestine (duodenum, jejunum, ileum)
    • Large intestine (appendix, caecum, colon, rectum)
    • Anus
• Total length of alimentary canal: Approximately 9 meters
• Small intestine: Makes up two-thirds of the total length.
• Accessory organs: Liver, gallbladder, and pancreas.
  • Each organ plays a specialised role in digestion.

Digestion in the Mouth

• Mechanical breakdown of food: Chewing, increasing surface area for enzymes.
• Salivary glands release saliva.
  • Salivary amylase breaks down starch to maltose.
    • Starch + Water → Maltose
• Tongue forms bolus and pushes it into the oesophagus.
• Peristalsis pushes bolus down the oesophagus.

Digestion in the Stomach

• Sac-like muscular organ at the end of oesophagus.
• Stomach wall glands secrete gastric juice.
  • Hydrochloric acid: Kills bacteria, provides acidic environment for pepsin.
  • Mucus: Protects stomach lining from acid and enzymes.
  • Pepsin: Breaks down protein into polypeptides.
    • Protein + Water → Polypeptides
• Stomach stores food for 3-4 hours allowing mixes with juice.
• Chyme: Partly digested semi-liquid mass moved into small intestine.
• Sphincters: Ring-shaped muscles regulating food flow.
  • Cardiac sphincter: Controls food entry into stomach, prevents backflow.
  • Pyloric sphincter: Controls food flow from stomach to duodenum.

Digestion in the Small Intestine

• Consists of the duodenum, jejunum, and ileum.
• Receives:
  • Chyme from the stomach.
  • Bile from the liver - aids fat digestion.
  • Pancreatic juice from the pancreas - contains enzymes for carbohydrate, protein, and fat digestion.
• Villi: Finger-like projections in small intestine lining.
  • Increase surface area for nutrient absorption.
  • Contain microvilli, blood capillaries, and lacteals.
• Blood capillaries absorb glucose, amino acids, and water-soluble vitamins.
• Lacteals absorb fatty acids, glycerol, and fat-soluble vitamins.
• Nutrients travel through the bloodstream to the liver and then the body.

Defaecation

• Most water and digested food absorbed in the small intestine.
• Undigested food, dead cells, fiber, and water enter the large intestine.
• Water reabsorbed in the large intestine.
• Faeces: Remaining semi-solid waste.
• Peristalsis moves faeces to the rectum.
• Pressure in the rectum triggers the urge to defecate.
• Rectum contracts to expel faeces through the anus.
• Constipation: When faeces remain in the large intestine for a long time, leading to dry, hard stools.
  • Add more fiber to the diet to relieve constipation.

Gastroesophageal Reflux Disease (GERD)

• Stomach acid frequently flows back into the oesophagus.
• Symptoms: Heartburn, discomfort.
• Can cause inflammation and damage to oesophagus lining.
• Complications: Barrett's oesophagus, increased oesophageal cancer risk.
• Treatment: Lifestyle changes, medications, surgery.

Digestive Tract Cancers

• Cancers of the oesophagus, stomach, and intestines.
• Symptoms: Weight loss, abdominal pain, bowel habit changes.
• Early detection crucial for successful treatment.
• Risk factors: Age, genetics, smoking, diet.
• Screening tests: Colonoscopies.
• Treatment: Surgery, chemotherapy, radiation therapy.

Irritable Bowel Syndrome (IBS)

• Functional gastrointestinal disorder.
• Symptoms: Abdominal pain, bloating, bowel habit changes.
• Influenced by stress, diet.
• Treatment: Lifestyle changes (stress management, balanced meals, hydration, fiber), medications.

Lactose Intolerance

• Difficulty digesting lactose due to lactase deficiency.
• Symptoms: Bloating, diarrhoea, abdominal pain after consuming dairy.
• Treatment: Controlling lactose intake (lactose-free alternatives, supplements, gradual introduction).

Hiatal Hernia

• Stomach protrudes into the chest through the diaphragm.
• Symptoms: Acid reflux, chest pain, difficulty swallowing.
• Treatment: Lifestyle changes (diet, elevating head during sleep), surgery.

Stomach Ulcer

• Sore on the lining of the stomach.
• Causes: Helicobacter pylori infection, NSAID use.
• Symptoms: Burning stomach pain, bloating, indigestion.
• Treatment: Antibiotics, acid-suppressing medications, NSAID reduction, stress management, healthy diet.

Diarrhoea

• Loose or watery stools.
• Causes: Infections (bacteria, viruses, parasites), medications, health issues.
• Treatment: Antibiotics, antiparasitic medications, probiotics.

Constipation

• Infrequent bowel movements, difficulty passing stools.
• Causes: Low fibre diet, dehydration, medications, IBS, hypothyroidism.
• Treatment: Lifestyle changes (exercise, hydration, high-fibre diet), medications.

Appendicitis

• Inflammation of the appendix.
• Symptoms: Abdominal pain, nausea, fever.
• Treatment: Appendectomy (surgical removal).

Diabetes Mellitus

• Chronic metabolic disorder with high blood glucose.
• Cause: Insufficient insulin production or ineffective insulin utilization.
• Treatment: Managing blood sugar levels.