The Digestive System Overview

The Digestive System

• The digestive system takes in food, breaks it down, and excretes waste
• It is made up of a digestive tract and accessory organs
• The digestive tract is a long tube with two openings: mouth and anus
• The digestive tract is composed of the mouth, esophagus, stomach, small intestine, large intestine, and rectum

The Digestive Tract

• Lined with epithelial tissue made up of different cell types
• Goblet cells secrete mucus
• Mucus protects against digestive enzymes, allowing smooth passage
• Includes layers of muscles and nerves

Accessory Organs

• Not part of the digestive tract but aid in digestion
• Include the liver, gallbladder, and pancreas

Mechanical vs. Chemical Digestion

• Mechanical digestion is the physical breakdown of food
• Chemical digestion breaks down food using enzymes

Mouth

• Begins the process of breaking down food
• Mechanical digestion uses teeth and tongue
• Chemical digestion involves enzymes in saliva breaking down food molecules

Mouth: Saliva

• Provides water and enzymes (amylase) to chemically break down and moisten food
• Produced by epithelial tissue lining the mouth and salivary glands

Esophagus

• Muscular tube connecting the mouth to the stomach
• Food moves through involuntarily via peristalsis
• Peristalsis is involuntary muscle contraction that moves food through the esophagus

Esophagus: Epiglottis

• Tiny flap-like structure that covers the trachea
• Prevents food from entering the respiratory system during swallowing

Stomach

• Holds food and churns it (physical breakdown) to continue digestion
• Stomach lining produces digestive enzymes and acid (for chemical breakdown), as well as mucus
• Mucus protects the stomach lining tissue from acid

Small Intestine

• 6 meters long and narrow
• Site of most digestion and absorption of nutrients
• Goblet cells in the lining release mucus
• Nutrients diffuse through the wall of the small intestine and enter the bloodstream
• Contains smooth muscles that contract and relax involuntarily to move broken-down food

Small Intestine: Villi

• Small intestines contain finger-like projections called villi
• Villi increase the surface area for more nutrient absorption

Large Intestine (Colon)

• Only 1.5 meters long and wider than the small intestine
• Absorbs water from indigestible food
• Contains bacteria that assist in producing vitamins
• Remaining solid waste is excreted as feces from the anus

Accessory Organ: Liver

• Produces bile
• Bile is a fluid that helps mechanically break down fats in food

Accessory Organ: Gallbladder

• Stores bile produced by the liver

Accessory Organ: Pancreas

• Releases enzymes into the small intestine aiding in digestion
• Produces insulin that helps regulate blood glucose levels

Digestive System Diagram - Parts

• Diagram includes mouth, salivary glands, epiglottis, esophagus, stomach, pancreas, small intestine, large intestine, rectum, anus, liver, and gallbladder.

Digestive System Problems

• Diabetes: A condition where the pancreas produces too much or too little insulin, regulating blood glucose levels.
• Colitis: Inflammation of the large intestine caused by viruses, bacteria, narrowed blood vessels or immune system failure. Diagnosed with an endoscope and microscopic tissue examination.

When the Digestion Goes Wrong

• Toxins, produced by bacteria or spoiled food (or too much alcohol) are recognized by the body. The digestive tract responds rapidly to remove toxins via vomiting or diarrhea.

Video: The Journey of the Digestive System

• [Video title provided by Amoeba Sisters]

Homework

• Read pages 80-82 in the textbook
• Answer questions 2-4 on page 82

Extra Help

• Digestive system review

Answers

• Q2: for digestion to occur molecules need to be broken down so they can diffuse through intestines into bloodstream
• Q3: Substances added to the food are saliva, stomach acid, enzymes, bile, and mucus
• Q4: Muscle tissue contracts to push food through the digestive system