Do Now What do you already know about the digestive system? List 3 things! What would happen if you were tied upside down, would you still be able to eat? Explain. List the components of the alimentary canal.

The Digestive System! Chapter 15

Objectives To compare and contrast chemical vs. mechanical digestion. To explain the general characteristics of the alimentary canal. To explain the process of swallowing and peristalsis. To identify the structures of the mouth and explain their function. To understand the necessity of salivary glands and name each type.

Digestion Chemical digestion- complex molecules are broken down into smaller molecules Mechanical digestion- physical movement of food that breaks it down into smaller pieces Ex. Chewing, grinding, mashing Chewing is called “mastication”

Components of Digestive System Alimentary Canal “digestive tract” Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum and anus Accessory Structures: Salivary glands, liver, gallbladder, & pancreas

Alimentary Canal Muscular tube that passes through the body’s ventral cavity About 9 meters long Contains 4 layers

Alimentary Canal 1) Mucosa (innermost): 2) Submucosa: Protects the tissues beneath it & carries out secretion and absorption Consists of epithelium, underlying CT, and a little bit of smooth muscle 2) Submucosa: Nourishes surrounding tissue and carries away absorbed materials Consists of loose connective tissue, blood vessels, glands.

Alimentary Canal 3) Muscular Layer: 4) Serosa: Layer which moves the tube Contains two coats of smooth muscle tissue & nerves (plexus) Fibers of the inner coat (circular) surround the tube When they contract the tube’s diameter decreases Fibers on the outer muscular coat (longitudinal) run lengthwise When they contract the tube shortens 4) Serosa: Protects underlying tissues and secrete serous fluid

Alimentary Canal

Movements of the Alimentary Canal Mixing Movement Occurs when smooth muscle in small units of the tube contract rhythmically Mixes food with digestive juices secreted by the mucosa Propelling Movement Known as peristalsis

Do Now -Which layer of the alimentary canal is responsible for moving the tube? What type of tissue is this layer? - List the 3 macromolecules found in your food and what they’re broken down into. P.3

Alimentary Canal Length

Organs of the Digestive System The Mouth Receives food and begins digestion mechanically Reduces the size of solid particles and mixes them with saliva Oral cavity - Lips, cheeks, tongue & palate Vestibule - Narrow space between teeth, cheeks, & lips

Salivary Glands Secrete saliva Contain 2 types of secretory cells: Serous cells: produce salivary amylase (breaks down carbs) Mucous cells: produce mucus to bind to food and lubricate during swallowing *Major glands: Parotid Submandibular Sublingual

Pharynx Connects nasal and oral cavities with larynx and esophagus Contains 3 parts: Nasopharynx Oropharynx Laryngopharynx

Swallowing Mechanism 1. Food is chewed and mixed with saliva,tongue rolls this into a mass or bolus and forces it into the pharynx 2. Food stimulates sensory receptors around the pharyngeal opening, triggering the swallowing reflex 3. Momentarily inhibits breathing, peristalsis transports food into the esophagus and to the stomach

Esophagus Connects pharynx to the stomach Separated from the stomach by the cardiac sphincter Contracts and closes the sphincter to prevent regurgitation

Stomach J shaped with about a 1 liter capacity Contains rugae, which allow it to expand Divided into 4 regions Cardiac Fundic Body Pyloric Contains cardiac and pyloric sphincters

Stomach Juices “Gastric Juice” consists of: HCl Mucus Viscous alkaline secretion that coats the stomach Enzymes: Proteases such as Pepsin- digests protein (starts as pepsinogen and when mixed with HCl makes pepsin) P.6

Stomach Juices The mixture of gastric juice and the bolus gives us chyme Chyme pushed into the small intestine Type of food can affect rate of emptying: Fatty food 3-6 hrs. in stomach Proteins move more quickly Carbs go through the fastest!

Gastric Absorbtion The stomach mostly breaks things down Can absorb only small amounts of water, certain salts, alcohol, and some lipid- soluble drugs. EX: Aspirin

Pancreas Secretes pancreatic juice into the duodenum Pancreatic enzymes: Pancreatic amylase Digests carbs Pancreatic lipase Digests fats Nucleases Digests nucleic acids Proteases: Digest protein

Liver Effects carbohydrate, lipid, and protein metabolism Produces bile: Contains bile salts, bile pigments (bilirubin and biliverdin) **bile salts emulsify fats and also increase absorption of fat-soluble vitamins (A,D,E, & K)

Liver Also involved in… Blood sugar regulation Storage of iron, vitamins A, D, B12 Detoxifies blood (ex: removes alcohol, H202)

Small Intestine 3 sections: Duodenum, Jejunum, Ileum Receives secretions from pancreas and liver Contain intestinal “villi”- increase surface area for absorption *Most of the absorption occurs here!

Large Intestine Contains cecum (appendix attached), colon, rectum, anal canal Main function is to absorb water and electrolytes from remaining chyme, and forms and stores feces.

Feces Contains materials not digested or absorbed Water Electrolytes Mucus Shed intestinal cells Bacteria (makes it smell!)

Review What is the process that occurs after swallowing? What is the scientific name for the digestive tract? How many layers is this tract? What are the 3 parts of the pharynx? What is absorbed in the stomach? What does the pancreas do? Why are bile salts important?