1. What is the function of the digestive system? Digestive system When food is eaten, it is not in a form the body can use. It must be changed for the body to absorb it into the blood and carry it to cells. Functions: Provide the body with nutrients, water and electrolytes. 1

2. Digestive system The digestive system organs are separated into two major groups: The alimentary canal or gastrointestinal tract: a hollow tube extending from the mouth to the anus. It consists of the mouth, pharynx, esophagus, stomach, and small and large intestines. The accessory digestive organs: include the teeth, salivary glands, gallbladder, liver, and pancreas. 2

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4. Histological structure of the digestive tract The digestive tract wall is made up of 4 layers: The Mucosa: This is the inner layer of the tract that actually absorbs food and secretes digestive enzymes. The Submucosa in made up primarily of loose connective tissue, blood vessels, glands, and nerves. The Muscular Layer: this layer is made up of 2 layers of smooth muscle, the inner layer of muscle is circular while the outer layer is longitudinal. The Serosa is the outer most layer of the tube and is primarily composed of serous epithelium and some connective tissue. 4

5. Movement of Digestive Materials How does materials move along the digestive tract? The muscular layers of digestive tract have rhythmic cycles of activities (PERISTALSIS) consisting of waves of muscular contractions. It moves the bolus along the length of the tract. 5

6. Food ingestion: taking in food Digestion: breaking down food into nutrients Absorption: taking in nutrients by cells Elimination (Defecation): removing any leftover wastes There are four (4) stages to food processing: 6

7. Digestion of carbohydrates: Breakdown polysaccharides (polymers) to monosaccharaides (maltase, sucrase, lactase) Break off disaccharides into 2 monosaccharaides (mostly glucose) 7

8. Digestion of proteins: The endopeptidases digests internal peptide bonds to free smaller peptides. Peptidases (or dipeptidases) break off the bond between dipeptides to free 2 amino acids. 8

9. Digestion of fat: Triglycerides digested into monoglycerides and free fatty acids Intestinal lipase breaks off diglycerides into monoglycerides and fatty acids. 9

10. Functions of the oral cavity Ingestion: Begins when food enters the mouth. Sensory analysis The top of the tongue is covered with structures called papillae which help to handle food and provide the sense of taste of food before swallowing. Lubrication Mixing food with mucus and salivary gland secretions. 10

11. These glands lie beyond the oral mucosa and empty their secretions into ducts that lead to the oral cavity. The major salivary glands are: Parotid glands and parotid duct. Submandibular glands and submandibular ducts. Sublingual glands and lesser sublingual ducts. The oral cavity 11

12. The Salivary Glands secrete the fluid Saliva which helps to moisten food and begin the chemical break down of some nutrients. Saliva helps to cleanse the mouth and teeth, and helps to enhance taste. The pH of saliva is between 6.5 and 7.5. Saliva also contains a digestive enzyme called Salivary Amylase, which is responsible for beginning the break down of starchy foods. The major salivary glands are the Submandibular, the Sublingual, and the Parotid. The oral cavity 12

13. T he oral cavity Digestion in the mouth: Mechanical processing Mechanical digestion begins here with mastication (chewing) through actions of teeth, tongue, and palatal surfaces Chemical digestion - amylase, an enzyme in saliva that breaks down carbohydrates - Some lipase an enzyme in saliva that breaks down lipids. 13

14. The oesophagus A hollow muscular tube, about 25 cm long and 2 cm wide. Conveys solid food and liquids from the mouth to the stomach Begins from the pharynx through the thoracic cavity to the stomach. 14