生理学笔记book note 4.docx

Chapter 21 the digestive system
overview of the digestive system
1. the digestive system consists of the gastrointestinal tract and the accessory ans
Digestive system
Description
Organs
Gastrointestinal (GI) tract/
alimentary canal
A continuous tube that extends from the mouth to the anus
Mouth, pharynx, esophagus, stomach, small intestine, large intestine
Accessory ans
Teeth, tongue, salivary glands, pancreas, liver, gallbladder胆囊
2. there are six basic digestive processes
Ingestion: taking foods and liquids into the mouth(eating)
Secretion: water, acid, buffers, enzymes are secreted into the lumen of the tract
Motility: the capability of the GI tract to mix and move material along its length
Digestion: mechanical [teeth grind& smooth muscle churn搅拌] and chemical [hydrolysis by digestive enzymes] process break down ingested food into small molecules.
Absorption: the movement of the products of digestion from the lumen of the GI tract into blood or lymph [a few substances can be absorbed without digestion: vitamins, ions, cholesterol, water]
Defecation: feces
3. the wall of the GI tract prised of four functional layers
From inside to outside: mucosa, submucosa粘膜下层, muscularis externa外肌层, serosa浆膜
Mucosa
Epithelium: tight junctions firmly seal neighboring epithelial cells to restrict leakage between the cells. The rate of renewal of GI tract epithelial cells is rapid.
①Exocrine cells: secrete fluids and other substances into the lumen of the GI tract
②Endocrine cells (enteroendocrine cells): secrete hormones into the bloodstream.
③Absorptive cells: transport nutrients form the lumen of the GI tract into the blood of lymph.
Lamina propria固有层: a layer of connective tissue. Contains ①small blood and lymphatic vessels, which are the sites where absorbed nutrients enter blood or lymph. ②Gut-associated lymphoid tissue (GALT). GALT is present all along the GI tract, especially in the small intestine, appendix, and large intestine.
Muscularis