The Digestive System

• The digestive system is crucial for providing cells with the chemical energy they need.
• It facilitates the transportation of necessary chemicals from the mouth to the cells throughout the body.

Components of the Digestive System

• The digestive system comprises the digestive tract (gastrointestinal tract) and accessory organs (pancreas, liver, gallbladder).
• Accessory organs aid in digestion, but food doesn't pass through them.

Digestive Pathway

• The digestive pathway includes: Mouth → Pharynx (Throat) → Esophagus → Stomach → Small Intestine → Large Intestine → Anus.

Overview of the Digestive System

• Digestive system facilitates the passage of nutrients to the circulatory system, which then delivers them to cells.
• The digestive tract is a continuous tube with an entry and an excretion site.
• Its main functions include mechanical and chemical digestion.

Processes of the Digestive System

• Ingestion: Taking in food.
• Digestion: Breaking down food into nutrients.
• Absorption: Absorbing the nutrients.
• Egestion: Eliminating wastes.

Mouth

• Initial stage of food breakdown occurs.
• Mechanical digestion: Teeth and tongue break down food.
• Chemical digestion: Enzymes break down food molecules.
• Teeth physically break down the food.
• Tongue rolls the food into a bolus.
• Saliva, secreted by epithelial tissue surrounding the mouth, contains water, mucus, and enzymes.
  • Saliva production averages ~1.5 liters per day.
  • Water moistens and softens food.
  • Mucus lubricates the food.
  • Enzymes chemically break down the food.
• Saliva mainly consists of amylase, an enzyme that breaks down starch.

Esophagus

• Muscular tube connecting the mouth to the stomach.
• Consists of smooth muscle tissue and nerve tissue.
• Smooth Muscle Tissue: Involuntary muscle contraction. Contracts and relaxes to push the bolus towards the stomach. The process is called peristalsis. There is no chemical digestion in esophagus.
• Nerve Tissue: Senses the presence of the bolus and moves it towards the stomach.

Stomach

• The inner lining is folded into rugae, increasing the surface area for gastric juice production.
• Sphincters (ring-shaped muscles) control what enters and leaves the stomach.
• Contents exit through the pyloric sphincter.

Stomach Digestion

• Mechanical digestion: Three layers of smooth muscle tissue contract in different directions to churn the food.
• Chemical Digestion: Epithelial tissue releases digestive enzymes and acid to break down food and kill bacteria. Gastric acid aids in digestion.
• Special cells release mucus to protect the stomach lining from acid.
• Nerve tissue signals feelings of hunger or fullness.
• The combination of the bolus and gastric juices is called chyme.

Small Intestine

• Located between the stomach and large intestine.
• Approximately 6 meters (19 ft 8 inches) long and narrow.
• Primary site of digestion.

Segments of Small Intestine

• Duodenum (chemical digestion): Receives digestive enzymes from the pancreas, liver, and gallbladder (accessory organs).
• Jejunum (absorption of nutrients).
• Ileum (absorption of nutrients).

Digestion in the Small Intestine

• Mechanical digestion: Peristalsis in smooth muscle tissue moves chyme towards the large intestine.
• Chemical digestion: Epithelial tissue produces enzymes for further food breakdown and mucus for lubrication.
• Nutrients diffuse through the walls of the small intestine (villi) and enter the bloodstream for distribution to body cells.

Small Intestine and Villi

• The inside lining of the small intestine is covered in villi to increase surface area for efficient absorption.
• Villi are bumps of epithelial tissue.
• Each villus contains a small blood vessel.
• 400-500 million villi in each person.
• Nutrients pass through the bloodstream.

Large Intestine (Colon)

• 1.5 meters long.
• Larger in diameter than the small intestine.
• The lining absorbs water from indigestible food.
• Remaining solid matter is excreted as feces through the anus.

Parts of the Large Intestine

• Cecum: A pouch where the small and large intestines meet; home to the appendix.
• Colon: Epithelial tissue absorbs water (osmosis) and vitamins B and K.
• Rectum: Storage of waste. Nerves detect the movement of feces, stimulating the urge for bowel movement.
• Anus: Transverse opening where feces is eliminated.
  • Anal sphincter: When relaxed, feces are eliminated.

Appendix

• Located at the cecum.
• Its function is not definitively known.
• Suspected to house beneficial gut flora and serve an immune function.
• People can survive without it.

Accessory Organs

• Liver: Produces bile, which helps break down fats and neutralize stomach acids. It also removes toxins from bloodstream.
• Pancreas: Produces insulin, which regulates glucose concentration in blood.
• Gallbladder: Stores and concentrates bile, releasing it into the small intestine.

Diseases of the Digestive System

• Celiac Disease: Gluten triggers the immune system to attack the small intestine, damaging the lining (villi) and preventing nutrient absorption.
• Diabetes: Insufficient insulin production or cells stop responding to insulin, resulting in too much glucose in the bloodstream.
  • Type 1: Pancreas does not produce enough insulin; typically shows up early in life.
  • Type 2: Body can't properly use insulin (insulin resistance); often lifestyle-related.
• Crohn's Disease/Ulcerative Colitis: Inflammatory bowel disease.
• Acid Reflux/Heartburn: Stomach acid flows back into the esophagus, causing a burning sensation. Reasons include obesity, diet, smoking, lying down after eating, or GERD.
• Gastric Ulcer: An open sore in the stomach lining due to the bacteria Helicobacter pylori.
• Appendicitis: Inflammation of the appendix, often caused by a blockage, which may lead to it bursting.

The digestive system provides cells with the chemical energy they need by transporting chemicals from the mouth to cells. It includes the digestive tract and accessory organs like the pancreas, liver, and gallbladder. The digestive pathway involves the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus.