Human Digestive System Overview

The Human Digestive System

• The digestive system breaks down food into smaller parts, allowing the body to absorb and use it for energy, growth, and repair.

Digestive System Organs

• The digestive system includes a tube-like structure (the gastrointestinal tract) with organs that work together.
• These structures include: mouth, pharynx, esophagus, stomach, small intestine, large intestine, and rectum.
• Accessory organs such as the liver, gallbladder and pancreas assist in the digestive process.

Functions of the Digestive System

• Digestion: the breakdown of large, insoluble food molecules into small, water-soluble molecules that can be absorbed into the bloodstream.
• Mechanical Digestion: physical breakdown of food (e.g., chewing, churning in the stomach, segmentation in the small intestine).
• Chemical Digestion: enzymes breaking the chemical bonds holding food particles together, allowing food to be broken down into digestible parts.

Major Processes of Digestion

• Ingestion: Entry of food into the alimentary canal through the mouth; chewing and mixing food with saliva (which contains enzymes) to start breaking down carbohydrates and some lipids aids in creating a bolus.
• Absorption: Movement of nutrients, water, and electrolytes from the lumen of the small intestine into the bloodstream. Small, soluble substances can pass through the walls of the small intestine; large, insoluble substances cannot.
• Assimilation: The process of absorbing nutrients during digestion and distributing them to the body for growth and repair.
• Elimination: Food molecules that cannot be digested or absorbed are stored in the rectum of the large intestine until ready to be expelled as feces through the anus.

Bacteria in the Digestive System

• Bacteria play a crucial role, digesting substances not digestible by humans, reducing harmful bacteria, and producing vital vitamins (like B and K).

Parts and Functions of Digestive Organs

• Mouth: Teeth break down food; tongue mixes food with saliva, which digests starch. Epiglottis prevents food from entering the trachea.
• Esophagus: Approximately 10 inches long, secretes mucus and moves food to the stomach via peristalsis. Acid reflux from the stomach can cause heartburn.
• Stomach: J-shaped muscular bag storing food, breaking it down into smaller pieces by mixing with digestive juices containing enzymes to break down proteins and lipids, and killing bacteria by producing acid. Chyme is churned food. Holds 1-1.5 liters of food.
• Small Intestine: About 7 meters long, lining has finger-like projections (villi) and tiny hair-like projections (microvilli) to increase surface area, assisting with absorption (80% of ingested water, vitamins, minerals, carbohydrates, proteins, lipids). Enzymes are secreted to aid in the process. Duodenum starts the digestive process, Jejunum and Ileum absorb nutrients.
• Large Intestine: About 5 feet long; absorbs more water, concentrates wastes, facilitates bacteria digestion, ferments carbohydrates, and completes protein breakdown. Rectum holds feces temporarily before elimination.

Accessory Organs

• Liver: Produces bile to aid in fat digestion, and filters out toxins, drugs, and alcohol.
• Gall Bladder: Stores bile produced by the liver and releases it into the small intestine. Gallstones can form in the gallbladder due to fatty diets.
• Pancreas: Produces enzymes to digest fats, carbohydrates, and proteins, and regulates blood sugar by producing insulin.