Chapter 14: The Digestive System & Nutriti
Digestive system function: to bring nutrients to the body
The digestive system includes
Gastrointestinal (GI) tract (hollow tube)
--Lumen: space within this tube
--Includes mouth, pharynx, esophagus, stomach, small intestine, large intestine, rec
Accessory Organs
--Salivary glands, liver, gallbladder, pancreas
Walls of the GI Tract
Composed of 4 layers:
--Mucosa: innermost layer mucous membrane in contact with the lumen
--Submucosa: layer of connective tissue containing blood vessels, lymph vessels, n
--Muscularis: 2 or 3 layers of smooth muscle, responsible for movement, motility
--Serosa: outermost layer
Sphincters: thick muscular rings that separate some of the organs
5 Basic processes of the digestive system:
Mechanical processing and movement
--chewing and mixing
Secretion
--Fluid
--Digestive enzymes and hormones
--Bile, acid, alkali, mucus
Digestion
--Breaking down food to smallest absorbable unites
--Chemical and mechanical breakdown
Absorption
--Through mucosa
--Into blood or lymph vessels
Elimination
--Undigested material eliminated
Motility
Function: enabled by smooth muscle in the muscularis layer
, Small Intestine
Function: digests food and absorbs nutrients and water
o Digestion
--Neutralizes acid from stomach
--Adds digestive enzymes and bile
--Breaks down proteins, carbohydrates, and lipids to absorbable materials
o Absorption
--90% of food absorbed is in small intestine
Small intestine
…has large surface area for absorption
Regions
--Duodenum: most digestion occurs here
--Jejunum: absorption
--Ileum: absorption
Mucosa adaptions increase surface area to facilitate absorption
--Large folds
--Villi: microscopic projections containing blood and lacteal capillaries
--Microvilli: cytoplasmic projections of epithelial cells of the villi
Accessory Organs Function: aid digestion and absorption
Pancreas
--Exocrine functions
--Secretes digestive enzymes and sodium bicarbonate
--Digestive enzymes include:
-Proteases: trypsin, chymotrypsin, carboxpeptidase
-Pancreatic amylase
-Lipase
Liver
--Produces bile, which emulsifies lipids
--Hepatic portal system
-drains blood from the digestive tract to the liver
--Metabolic functions
-storage, synthesis, and chemical processing
Gallbladder
--Concentrates and stores bile
Large Intestine
2 Functions:
o Absorbs nutrients and water
o Temporarily stores and eliminates waste
Structure of large intestine
Cecum, appendix
Colon
--Ascending, transverse, descending, sigmoid
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