Digestive System

Alimentary Canal Mouth Pharynx Esophagus Stomach Small Intestine Large Intestine Rectum Anus

The Oral Cavity Accessory organs –Tongue –Teeth –Salivary glands

Salivary Glands 1.Parotid 2.Submandibular 3.Sublingual Saliva is comprised of water (99.4%) with an assortment of ions, buffer, metabolites, and enzymes. Collectively, the salivary glands produce L/day

2.Esophagus peristalsis pushes food to stomach. Peristalsis wavelike motion that propels food. 3.Stomach secretes acid and enzymes. Mixes food with secretions to begin enzymatic digestion of proteins.

Digestive System Structures Digestive tract Accessory organs Teeth Tongue Salivary glands Liver Gall bladder pancreas Oral cavity Pharynx Esophagus Stomach Small intestine Large intestine

4.Small Intestine mixes food with bile and pancreatic juice. Final enzymatic breakdown of food molecules: main site of nutrient absorption.  Liver produces bile, which emulsifies fat.  Gallbladder stores bile and introduces it into small intestine.  Pancreas produces and secretes pancreatic juice, containing digestive enzymes and bicarbonate ions, into sm. Intestine.  Accessory organs are organs that are not a direct route of the digestive system.

5.Large intestine absorbs water and electrolytes to form feces. 6.Rectum regulates elimination of feces. 7.Anus eliminates feces.  The digestive system is a tube, open at both ends, that has a surface area of 186 square meters.  The main function is to supply body with nutrients.

Alimentary Canal 1.Mucosa or mucous membrane the inner most layer. Contains glands that secrete mucus and digestive enzymes. Carries on secretion and absorption. Also, has projections that increase the surface area. Lumen=passageway. 2.Submucosa contains loose connective tissue, glands, blood vessels, lymphatic vessels, and nerves. Carry away absorbed materials.

3.Muscular layer produces the movements. 4.Serosa or serous layer the outer covering of the digestive tube. Secretes fluid that lubricates the tube’s outer surface so organs slide freely against one another.

The Pharynx The pharynx is a muscular structure with as epithelial lining that functions in both respiration and digestion. Pharyngeal muscles cooperate with the oral cavity and esophagus to initiate the swallowing process 3 Divisions: Nasopharynx Oropharynx Laryngopharynx

Three Phases of Swallowing 1.Buccal (Oral)Phase 2.Pharyngeal Phase 3.Esophageal phase

During swallowing, muscles draw the soft palate and uvula upward to separate the oral and nasal cavities. Salvia cleanse the mouth and teeth, dissolve chemicals necessary to tasting food, and help in the formation of food bolus.

Tonsils Palatine are lymphatic tissue in the back of the mouth, on either side of the tongue and closely associated with the palate. Help to fight infection. Pharyngeal or adenoids are on the posterior wall of the pharynx. They can be removed. Tonsillectomy tonsil are surgically removed.

Teeth 4 types of teeth 1.Incisors (Front 4 teeth) bite off pieces of food. 2.Cuspid grasp and tear food. 3.Bicuspids or premolars grind food. 4.Molars grind food.

The Stomach Landmarks: –Lesser curvature –Greater curvature Functions: –Bulk storage of ingested food –Mechanical breakdown of ingested food –Chemical digestion of ingested food via the disruption of chemical bonds by acids and enzymes *The mixing of ingested substances with the gastric juices (secreted by gastric glands) produces chyme.

Stomach The stomach is divided into four regions. 1.Cardiac 2.Fundic is the area that acts as a temporary storage area for ingested food. 3.Body 4.Pyloric  Fatty food stay in the stomach the longest.

Gastric Gland Secretions –Mucous cells –Parietal cells –chief cells –Enteroendocrine cells (G cells)

Gastric Secretions Gastric juice 1.Hydrochloric acid 2.Pepsin begins to digest protein  Chyme is a semifluid paste of food particles and gastric juice.

Time Spent in organs Mouth a few minutes Esophagus a few minutes Stomach 4 hours Small Intestine 12 hours Large Intestine 5 hours Total time in digestive system 21 hours.

The Small Intestine Duodenum – “mixing bowl” receives chyme from stomach and digestive enzymes from pancreas and liver Jejunum – bulk of chemical and nutrient absorption Ileum– controls flow of material into the large intestine via Pyloric Sphincter

Absorptive structures Villi –These structures function to increase the surface area of the inner intestinal wall thereby facilitating absorption.

The Large Intestine Divisions: –Cecum –Colon –Rectum Functions: –Re-absorption of water and electrolytes –Compaction of intestinal contents into feces –The absorption of vitamins

Rectum and Anus Internal anal sphincter – involuntary smooth muscle. External anal sphincter – voluntary skeletal muscle whose relaxation allows for defecation

Gall Bladder The gallbladder is a sac located under the liver. It stores and concentrates the bile produced in the liver. Bile is released from the gallbladder in response to food, especially fats, in the upper small intestine.

15.7 Pancreas The pancreas make three different enzymes. One enzyme break down fats (pancreatic lipase), one enzyme break down protein (proteolytic), and the third enzymes break down carbohydrates.

15.8 Liver The liver is the largest organ in the body it is the heaviest organ in the body at around 3 pounds. It makes the chemical bile. Bile is a green liquid that breaks large fat droplets into small fat droplets. Gallbladder is a small, baglike part located under the liver. It stores bile until it is needed by the small intestine.

Hepatitis Hepatitis is an inflammation of the liver. Types of Hepatitis 1.Hepatitis A spreads by contact with food or objects contaminated with virus- containing feces. 2.Hepatitis B spreads by contact with virus- containing body fluids, such as blood, saliva, or semen.

Digestive enzymes Salivary glands make chemicals that digest only carbohydrates. Pancreas makes chemicals that digest fat, protein, and carbohydrates. Liver makes chemicals that digest only fat. Stomach makes chemicals that digest only protein. Small intestine makes chemicals that digest protein and carbohydrates. Large intestine makes no chemicals to digest food.

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