The Digestive System

1. The Digestive System SBI 3U January 10th, 2013

2. From a Cell to a System • Cells with similar functions come together to form tissues • Ex: stomach includes muscle tissue • 4 types of tissue: connective tissue, epithelial tissue, nervous tissue and muscle tissue • Several types of tissues that come together to perform one overall function  organs

3. Building a Digestive System • Organ system  several organs working together to perform an important function • Maintenance of homeostasis • All cell require nutrients and oxygen  respiratory and digestive systems provide these and the circulatory system ensures that all cells get these essentials

4. Structures, Functions, and Processes of the Digestive System • Digestive tract = Gastrointestinal tract = Alimentary canal • Digestive tract  series of hollow organs joined in a long, twisted tube from mouth to exit of body • Structure allows for food to enter through mouth, nutrients to be absorbed and wastes to be excreted

5. Organs in Digestive Tract • Major organs: mouth, pharynx, esophagus, stomach, small intestine, large intestine (colon), and anus • Accessory organs: salivary glands, pancreas, liver, and galbladder

7. Structure of the Wall of the Digestive Tract • Lumen: central space • 5 layers of tissue surrounding lumen • Mucosa • Submucosa • A circular layer of smooth muscle • Longitudinal layer of smooth muscle • Serosa

8. Structure of the Wall of the Digestive Tract - Mucosa • Depending upon the section of the digestive tract: -mucosa protects digestive tract wall -secretes substances and; -absorbs the end products of digestion

9. Structure of the Wall of the Digestive Tract - Submucosa • Lies outside the mucosa • Connective tissue consisting of blood vessels, lymphatic vessels, and nerve fibers

10. Structure of the Wall of the Digestive Tract – Circular Smooth Muscle • Layer of muscle • Mouth and pharynx: consists of skeletal muscle • Rest of the digestive tract: consists of smooth muscle and nerve fibers

11. Structure of the Wall of the Digestive Tract – Serosa • Composed of connective tissue • Forms the covering of the digestive tract

12. Steps in Digestion • Function of digestive system: change the foods you eat into chemical forms your body can use • Ingestion: food is acquired • Food useful once it has been converted into diffusible substances • Prep of food for absorption is termed digestion

13. Steps in Digestion • Carbs monosaccharides • Proteins  amino acids • Fats  fatty acids and glycerol • 2 types of digestion: mechanical digestion & chemical digestion

14. Mechanical vs. Chemical Digestion • Mechanical: in mouth and stomach • Chemical: the breakdown of food into smaller and simpler compounds

15. Mechanical Digestion • Shredding, tearing and grinding food  teeth  incisors, canines and pre-molars/molars • Herbivore teeth vs. Carnivore • Human teeth resemble both herbivore and carnivore

16. Chemical Digestion • Can occur once food has been broken down • Food mixed with various juices from digestive glands • Enzymes act upon broken-down food • Absorption: primarily in small intestine. Large intestine only for water and some vitamins • Elimination: occurs through rectum and anus

17. Steps through the Digestive Tract • Begins at the oral cavity  where food is manipulated by the mouth • Lips, tongue, teeth and jaw muscles used • Incisors, canines, molars • Salivary amylase  beginning of chemical digestion • Bolus created

18. Steps through the Digestive Tract • Bolus passes through pharynx • Epiglottis and trachea • Bolus drops into esophagus