Overview
This lecture covers the roles and organs of the digestive system, focusing on digestion, absorption, and the journey of food through the body.
Roles of the Digestive System
- The digestive system has two main roles: digestion and absorption.
- Digestion breaks down large food molecules into smaller molecules (e.g., starch to glucose, proteins to amino acids, fats to glycerol and fatty acids).
- Absorption moves these small molecules, along with vitamins, minerals, and water, from the digestive tract into the bloodstream for use by the body.
Organs and Their Functions
- The mouth contains teeth (physical breakdown of food) and salivary glands (release saliva containing the enzyme amylase to digest starch).
- The esophagus (gullet) is a muscular tube that transports food to the stomach.
- The stomach mixes food, produces pepsin (protease to break down proteins), and secretes hydrochloric acid (kills bacteria and provides optimal pH for pepsin).
- The pancreas releases digestive enzymes (carbohydrases, proteases, lipases) into the small intestine.
- The gall bladder stores and releases bile, which is made in the liver; bile neutralizes stomach acid and emulsifies lipids for digestion.
- The small intestine is where most digestion and nutrient absorption occurs, with digestive enzymes supplied by itself and the pancreas.
- The surface of the small intestine is covered in finger-like villi, increasing surface area and maximizing absorption.
- The large intestine absorbs excess water, leaving behind feces that are stored in the rectum and excreted through the anus.
Special Features for Absorption
- Villi in the small intestine provide a large surface area for nutrient diffusion.
- Villi have a single layer of surface cells for a short diffusion distance.
- A rich blood supply in villi maintains concentration gradients for absorption.
- Microvilli on villi cells further increase surface area.
Key Terms & Definitions
- Digestion — Breaking down large food molecules into smaller, absorbable molecules.
- Absorption — Uptake of small molecules, vitamins, minerals, and water into the bloodstream.
- Enzyme — A biological catalyst that speeds up chemical reactions, like breaking down food.
- Villus (Villi) — Small, finger-like projections lining the small intestine, increasing surface area for absorption.
- Bile — Alkaline fluid made in the liver, stored in the gall bladder, emulsifies fats and neutralizes stomach acid.
Action Items / Next Steps
- Review the functions of each digestive organ.
- Study the process of nutrient absorption in the small intestine.
- Understand the roles of digestive enzymes and bile.