Overview
This lecture explains the structure and function of the human digestive system, detailing each stage as food transforms into energy and nutrients.
Structure of the Digestive System
- The digestive system processes between 1-2.7 kg of food per person daily.
- It comprises ten organs, nine meters in length, and over 20 specialized cell types.
- Four main components: gastrointestinal (GI) tract, accessory organs (pancreas, gallbladder, liver), regulatory systems (enzymes, hormones, nerves, blood), and the mesentery tissue.
- The GI tract has an internal surface area of 30–40 m².
Stages of Digestion
- Digestion begins with saliva production in anticipation of food, creating about 1.5 liters daily.
- Chewing and saliva turn food into a bolus and begin starch breakdown via enzymes.
- The bolus travels down the esophagus via peristalsis (muscular contractions).
- In the stomach, acids and enzymes break down proteins, and hormones stimulate accessory organs.
- After roughly 3 hours, the bolus becomes chyme and moves into the small intestine.
Small Intestine Function
- Bile from the liver and gallbladder digests fats in the duodenum.
- Pancreatic and intestinal juices further break down fats, proteins, and carbohydrates.
- Villi in the jejunum and ileum increase absorption surface for nutrients to enter the bloodstream.
Large Intestine and Waste Removal
- Fiber, water, and dead cells enter the colon (large intestine).
- The colon absorbs remaining water, forming stool.
- Stool is stored in the rectum until expelled through the anus.
- The full digestive process takes about 30–40 hours.
Key Terms & Definitions
- Bolus — moist lump of chewed food ready to be swallowed.
- Peristalsis — series of muscular contractions moving food through the GI tract.
- Chyme — frothy liquid form of food after stomach processing.
- Bile — digestive fluid from the liver/gallbladder that breaks down fats.
- Villi — small projections lining the small intestine to aid nutrient absorption.
- Stool — waste mass formed in the colon, expelled from the body.
Action Items / Next Steps
- Review the stages of digestion and key organ functions for better understanding.
- Prepare any questions about the digestive process for discussion.