Ch. 22_The Digestive System Notes.docx - The Digestive System Chapter 22 Overview of the Digestive System Introduction Digestive system \u2013 set of

Ch. 22_The Digestive System Notes.docx - The Digestive...

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The Digestive System Chapter 22 Overview of the Digestive System Introduction Digestive system – set of organs that breaks down food items into nutrients that can be delivered by bloodstream to cells in body; organs are located from head to abdominopelvic cavity Digestive system consists of two types of organs: organs of alimentary canal , also known as gastrointestinal ( GI ) tract or digestive tract , and accessory organs Alimentary canal – continuous tube through which food passes directly; consists of oral cavity (mouth), pharynx , esophagus , stomach , small intestine , and large intestine Accessory organs – not part of alimentary canal but assist in digestion in some way; located around alimentary canal and include teeth , tongue , salivary glands , liver , gallbladder , and pancreas Food generally does not come into direct contact with accessory organs, although teeth and tongue are exceptions Basic Digestive Functions and Processes Most fundamental function of digestive system is to take food into body and break it down into its component nutrients so that they can be used by body cells; other functions include: Playing a critical role in fluid , electrolyte , and acid-base homeostasis by taking in water and electrolytes via diet and delivering them to blood Ingesting vitamins and minerals , producing hormones , and excreting metabolic wastes Digestive system must perform following basic processes to carry out these functions: o Food and water are brought into digestive system by ingestion ; occurs via mouth under normal conditions o Secretion – digestive organs contain both endocrine and exocrine glands that secrete a variety of substances—such as mucus, enzymes, acid, and hormones—to aid other digestive processes o Ingested food and liquids pass from one digestive organ to next by process of propulsion o Propulsion is accomplished largely by rhythmic contractions of smooth muscle of alimentary canal called peristalsis ; aided by mucus secreted by multiple organs Food breakdown occurs by process of digestion : o Mechanical digestion – digestive organs physically break food down into smaller pieces via processes such as chewing and mixing food by muscular movements of alimentary canal o Chemical digestion – enzymes secreted by digestive organs catalyze reactions that break chemical bonds within food particles until only small molecules remain Once food particles are digested, they move through wall of alimentary canal into blood or lymphatic vessels by a process called absorption o Water, electrolytes, and vitamins are also absorbed into blood in same manner 1
o Certain ingested materials are not digestible or usable by body; such materials continue their transit through alimentary canal until they exit body as feces through defecation o Defecation also provides body with a way to eliminate certain metabolic wastes; note that defecation is simply a specialized form of propulsion Regulation of Motility by the Nervous and Endocrine Systems Motility

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