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Digestive System
1. Digestive organs
Alimentary canal: mouth, esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (cecum, colon, rectum), anus
Digestive gland: salivary gland, liver, pancreas, and peptic gland and other digestive glands
2. Teeth
-breaks down food into smaller pieces for digestion
-composed of dentin, enamel, cementum, pulp
-types: incisor, molar, and canine
-adult had 32 permanent teeth
-child has 20 baby teeth
3. Function of tongue: sense of taste, mastication (chewing), swallowing, speech
4. Oral gland: serous and mucous
5. Saliva:
-healthy person produces about 1.5 L per day
-moistens food for easy swallowing
-contains enzymes (amylase, ptyalin) that breaks down carbohydrates
6. Esophagus:
-about 25 cm long (10 inches)
-extends from the hypopharynx to the stomach
-carries food from mouth to stomach (swallowing)
7. Stomach:
-an organ in the gastrointestinal tract used to digest food
-lies between the esophagus and the first part of the small intestine (the duodenum)
-divided into five sections, each of which has different cells and functions
-stomach walls made of a number of layers
-able to hold 1200 -1400 ml
Stomach (gastric) Acid:
-produced by parietal cells (also known as oxyntic cells) in the stomach
-pH 1.0 - 1.5, very acidic
-about 2000 - 3000 ml secreted daily
-maintain a sterile environment
-initiate the conversion of pepsinogen to pepsin
-mixes thoroughly with food and other digestive enzymes with digestive fluid to further decompose foods chemically for a few hours (for further digestion)
8. Small Intestine
-6-7 meters in lenght
-duodenum, jejunum, ileum
-part of the gastrointestinal tract between the stomach and the large intestine (colon)
-site where most of the nutrients from ingested food are absorbed
Duodenum:
-about 25 cm long, C shaped organ
- hollow jointed tube connecting the stomach to the jejunum
-the first and shortest part of the small intestine
-largely responsible for the breakdown of food in the small intestine
Jejunum:
-central of the three divisions of the small intestine and lies between the duodenum and the ileum
-usually between 2-8m (06'''' 07"-26'''' 03") long
-the pH is usually between 7 and 8 (neutral or slightly alkaline)
-inner surface, mucous membrane, is covered in projections called villi, which increase the surface area of tissue available to absorb nutrients from the intestinal contents
Ileum:
-the final section of the small intestine, about 4m long
-absorb vitamin B12 and bile salts
-has an extremely large surface area both for the adsorption (attachment) of enzyme molecules and for the absorption of products of digestion
9. Large Intestine
-extends from the ileocecal junction to the anus and is about 1.5m long
-divided into 6 parts: cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum
-responsible for absorption of water and electrolyte, and excretion of solid waste material
10. Liver
-normally weighs between 1.0 - 2.5 kilograms
-a soft, pinkish-brown "boomerang shaped" organ, located immediately under the diaphragm on the right side of the upper abdomen.
-second largest organ in body (next to skin)
-Functions:
1) produces and excretes bile required for food digestion
2) performs several roles in carbohydrate metabolism (glyconeogenesis, glycogenolysis, glycogenisis)
3) takes important role in lipid metabolism (produces coagulation factor and other enzymes, cholesterol synthesis and etc.)
4) breaks down hemoglobin, and other toxic substances (filters out toxins)
5) stores various substances (glycogen, Vit B 12, iron, copper)
6) converts ammonia to urea
11. Pancreas
-located posterior to the stomach and in close association with the duodenum
-small elongated organ with hear, body, and tail
-Function: produces enzymes that break down all categories of digestive foods and excretes hormones for carbohydrate metabolism
1) exocrine: produces pancreatic juice containing digestive enzymes
2) endocrine: produces several important hormones, (Islets of Langerhans produces insulin and glucagon)
12. Gall Bladder
-pear-shaped organ that is connected to the liver and the duodenum by the biliary tract.
-about 7 - 10 cm on length, dark green in color
-stores about 50 ml of bile until needed for digestion
-Function: stores bile, which is released when food containing fat enters the digestive tract
Bile:
-bitter, greenish-yellow alkaline fluid secreted by the liver
-500 - 1000ml of bile produced by liver daily
-The components of Bile:
Water
Cholesterol
Lecithin (a phospholipid)
Bile pigments (Biliruben & Biliverden)
Bile salts (sodium glycocholate & sodium taurocholate)
-needed for digestion of fats/lipids