Digestive System

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Accessory Organs

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A term often used to refer to the pancreas, liver and gall bladder because their role in the process of digestion is vital, but they are not physically a part of a digestive tract.

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Salivary Amylase

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An enzyme in the saliva that breaks down starch into simpler sugars and catalyses the hydrolysis of carbohydrates.

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Catalyst

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A chemical that speeds up a chemical reaction but is not used up in the reaction.

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Hydrolysis

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A chemical reaction in which the addition of a water molecule splits a macromolecule into subunits.

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Chyme

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Thick liquid formed by mixing food with gastric juice in the stomach.

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Digestive Tract

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In animals, a long tube that extends from the mouth to the anus, through which food moves and is broken down into simpler compounds that are used for energy, growth and cell repair.

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Bolus

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Smooth, lump-like mass of food rolled by the tongue to aid in swallowing.

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Macromolecule

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A large, complex assembly or organic molecules; four categories include: carbohydrates, proteins, lipids and nucleic acids.

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Disaccharide

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Sugar that can be hydrolysized into two monosaccharide subunits; examples include sucrose and maltose.

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Monosaccharide

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Simple sugars that cannot be hydrolyzed into simpler sugars; examples include glucose, galactose and fructose.

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Dehydration Synthesis

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A chemical reaction that results in the formation of a covalent bond between two subunit molecules by the removal of a water molecule.

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Gall Bladder

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An organ that stores bile produced by the liver.

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Homeostasis

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The tendency of the body to maintain a relatively constant internal environment.

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Bioavailability

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The amount of a nutrient that a person absorbs from a source, rather than the total amount actually in the source.

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Pancreas

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A small gland in the abdomen that secretes digestive enzymes into the small intestine, as well as bicarbonate to neutralize hydrochloric acid from the stomach; also secretes insulin.

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Inhibitor

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A molecule that attaches to an enzyme and reduces its ability to bind substrate; two classes include: competitive and non-competitive.

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Peristalsis

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A wave-like series of muscular contractions and relaxations of the circular and longitudinal muscles that surround the various parts of the digestive tract; aids movement of food.

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Polysaccharide

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A complex carbohydrate consisting of many simple sugars linked together; examples include starch, cellulose and glycogen.

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Triglyceride

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A high energy organic molecule composed of one glycerol molecule and three fatty acid molecules; main component of fats and oils.

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Villus (villi)

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A finger-like projection along the ridges of the small intestine; increases surface area to aid in the absorption of nutrients.

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Essential Amino Acids

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Refers to any of the nine of twenty amino acids that must come from the diet because the human body cannot synthesize them.

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Nucleic Acid

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A macromolecule formed from a long chain of nucleotide subunits, each consisting of a five-carbon simple sugar, a nitrogen-containing base, and a phosphate group. Two types include: RNA and DNA.

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Protein

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An organic macromolecule assembled from subunits of amino acids.

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Segmentation

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A process by which some physical digestion occurs in the small intestine; chyme sloshes back and forth between segments of the small intestine that form when bands of circular muscle briefly contract.

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Liver

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An organ found in the abdomen that performs hundreds of functions as an accessory organ of the digestive system, including the secretion of bile to digest fats; other functions include plasma protein production, blood detoxification, and glycogen storage.

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Esophageal Sphincter

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A muscular ring between the esophagus and the stomach that controls the movement of food into and out of the stomach.

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Gastrin

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A stomach hormone that stimulates the secretion of hydrochloric acid and the inactive precursor molecule of pepsin from glands in the stomach.

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Lipase

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An enzyme that catalyzes the hydrolysis of triglycerides into glycerol and fatty acids.

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Pepsin

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A protein-digesting enzyme secreted in the stomach; remains inactive until hydrochloric acid is present.

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Protease

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An enzyme that hydrolyzes the peptide bonds that link amino acids in proteins and peptides.

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Substrate

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A substance upon which an enzyme acts.

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Peptide Bond

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A bond between the amino group of one amino acid and the carboxyl group of another in a protein.

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Pyloric Sphincter

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A muscular ring that acts as a valve between the stomach and the first part of the small intestine (duodenum), controlling the passage of food out of the stomach.

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Small Intestine

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The length of the digestive tract comprised of the duodenum, jejunum, and ileum; main function is to complete the digestion of macromolecules and to absorb their component subunits.

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Large Intestine

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The portion of the digestive system comprised of the caecum, colon, rectum, and anal canal; main function is to concentrate and eliminate waste materials.

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Duodenum

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The first 25 cm of the small intestine; important site of chemical digestion of chyme from the stomach.

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Microvilli

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Microscopic projection found along exposed cell surfaces that greatly increases the surface area of the cell; found on the villi of the small intestine and on the membranes of certain cells.

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Nuclease

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An enzyme that hydrolyses the bonds between nucleotides in nucleic acids.

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Secretin

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One of three enzymes secreted into the bloodstream by the duodenum, causing inhibition of stomach movement and secretions, and enabling fatty meals to remain in the stomach longer than non-fatty meals; also stimulates the pancreas to release more bicarbonate to neutralize acidic chime.

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CCK

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Same actions as secretin; also stimulates increased pancreatic secretions of digestive enzymes and gall bladder contractions.

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GIP

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Same as secretin.