1. The digestive system break down (digest) feed into a form that can be absorbed by the body which are the nutrients (sugars, amino acids and fatty acids), water, electrolytes and vitamins-organic molecules necessary for health to the body. 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. Digestive system

3. The alimentary canal is a muscular tube made up of 4 layers: * Mucosa * Submucosa * Muscularis externa * Serosa Histological Organization of the Digestive Tract

4. The Mucosa is formed from primarily of epithelium that is invested with goblet cells. This inner lining of this layer has many tiny folds on it in order to increase the overall absorptive surface area. This is the layer of the tract that actually absorbs and secretes (absorbs food, secretes digestive enzymes). HISTOLOGY OF THE ALIMENTARY CANAL * The Submucosa in made up primarily of loose connective tissue, blood vessels, glands, and nerves.

5. * Muscular Layer: this layer is made up of 2 layers of smooth muscle, and provides movement for the tube. 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. The serous layer secretes serous fluid.

6. Histological Structure of the Digestive Tract

7. Visceral smooth muscle tissue – digestive tract – a single smooth muscle cell: 5-10um in diameter and 30- 200um in length - muscle cells are nonstriated, involuntary muscle - contractions are as strong as skeletal or cardiac muscle - muscle cells are arranged in sheets - 1 cell contracts spreads like a wave throughout the tissue - contractions lead to 2 types of movement: peristalsis and segmentation

8. * Contractile filaments of smooth muscle cells are not rigidly organized - plasticity, tolerate extreme stretching, a stretched cell adapts to its new length and retains ability to contract on demand - pacemaker cells in the muscularis mucosae and muscularis externa undergo spontaneous depolarization - which trigger contractions leading to 2 types of movement: peristalsis and segmentation

9. Peristalsis * Muscularis externa via peristalsis propels materials from 1 region of the tract to another * Waves of contractions move a bolus of food – 1. circular muscles contract behind the digestive contents 2. followed by longitudinal muscle contraction that shorten adjacent segments 3. wave of contraction in circular muscle layer forces bolus forward

10. Segmentation * Contractions in most areas of the small intestine and some regions of the large intestine churn and fragment the digestive materials * The contents are mixed with intestinal secretions * No net movement is produced

12. * The Mouth is the first item in line in the alimentary canal. Mechanical digestion begins here with mastication (chewing). * The Tongue is an accessory organ of digestion. It functions to position food in the mouth. It is held to the floor of the mouth by the lingual frenulum. The top of it is covered with structures called papillae which help to handle food and provide the sense of taste. The tongue also helps in the formation of speech. THE ALIMENTARY CANAL

13. * The Palate forms the roof of the oral cavity. It consists of a hard (bony) anterior portion and a soft posterior portion. A cone shaped projection called the uvula hangs from the posterior most aspect of the palate. * The Teeth are the hardest structures in the body. They aid digestion by way of mastication. There are two sets of teeth in humans, deciduous and permanent. Children will typically have 20 teeth that are gradually replaced by the adult teeth. Adults typically have 32 teeth. THE ALIMENTARY CANAL

14. The Pharynx is divided into 3 separate regions: * Nasopharynx * Oropharynx * Laryngopharynx The pharynx is connects the mouth to the Esophagus. Neither of these organs digest food, but are important passage ways to the Stomach. THE ALIMENTARY CANAL

15. * The Esophagus is a straight, collapsible tube that leads from the pharynx through the thoracic cavity to the stomach. It penetrates the diaphragm through an opening called the Esophageal Hiatus. * The esophagus terminates at the Cardiac Sphincter just above the stomach. THE ALIMENTARY CANAL

16. The Stomach is a curved pouch-like organ that is located in the upper left quadrant of the abdomen. The inner lining is marked by thick folds called rugae. The stomach secretes Gastric Juice that has a very low pH and contains an enzyme called Pepsinogen that initiates the digestion of proteins. Where most of the organs of digestion have two layers of smooth muscle to help with peristalsis, the stomach has three layers. This helps the stomach to churn and mix food in the process of mechanical digestion. THE ALIMENTARY CANAL

17. * The stomach is divided into 4 regions. - The cardiac region is located lust inside the cardiac sphincter. - The fundus is the superior most portion located above the cardiac sphincter. - The body makes up the bulk of the organ in the middle. - The pyloric region is the inferior most area, just above the Pyloric Sphincter. The pyloric sphincter retains food in the stomach until it is released into the Small Intestines. THE ALIMENTARY CANAL

18. * The gastric glands contain 3 types of exocrine gland cells that secrete their products into the lumen of the stomach. * Mucous neck cells – secrete mucous. * Parietal cells – produce intrinsic factor. THE ALIMENTARY CANAL * Chief cells – secrete pepsinogen and gastric lipase. * These secretions are called gastric juice (approximately 2000 – 300 ml per day).