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Saliva
Fluid secreted by the salivary and mucous glands of the mouth that moistens food and begins the process of digestion.
Salmonella
A bacterium that may cause intestinal infection and diarrhea.
Sarcoidosis
A condition that causes small, fleshy swellings in the liver, lungs, and spleen.
Secretin
A hormone made in duodenum. Causes the stomach to make pepsin, the liver to make bile, and the pancreas to make a digestive juice.
Segmentation
The process by which muscles in the intestines move food and wastes through the body.
Serotonin
an agent that acts to constrict blood vessels and also inhibits gastric secretion
Shigellosis
Infection with the bacterium Shigella. Usually causes a high fever, acute diarrhea, and dehydration. 
Shwachman's Syndrome
A digestive and respiratory disorder of children. Certain digestive enzymes are missing and white blood cells are few. Symptoms may include diarrhea and short stature.
Side effect
See adverse reaction.
Sigmoid Colon
The lower part of the colon that empties into the rectum.
Sigmoidoscopy
Looking into the sigmoid colon and rectum with a flexible or rigid tube.
Sitz Bath
A person sits in a few inches of warm water to help relieve discomfort of hemorrhoids or anal fissure.
Small Bowel Enema
X-rays of the small intestine taken as barium liquid passes through the organ.
Small Intestine
It measures about 20 feet. Organ where most digestion occurs. 
Splanchnic
pertaining to the internal organs
Spasms
Muscle movements  that cause pain, cramps, and diarrhea.
Spastic Colon
See Irritable Bowel Syndrome  (IBS).
Sphincter
A ring-like band of muscle that opens and closes an opening in the body. 
Spleen
The organ that cleans blood and produces white blood cells. 
Splenic Flexure Syndrome
A condition that occurs when air or gas collects in the upper parts of the colon. Causes pain in the upper left abdomen. The pain often moves to the left chest and may be confused with heart problems.
Steatorrhea  
A condition in which the body cannot absorb fat. Causes a buildup of fat in the stool and loose, greasy, and foul bowel movements.
Stenosis
Narrowing of a duct or canal.
Stomach  
The organ between the esophagus and the small intestine. The stomach is where digestion of protein begins.
Stomach Ulcer
An open sore in the lining of the stomach. Also called gastric ulcer.
Stress Ulcer
An upper GI ulcer from physical injury such as surgery, major burns, or critical head injury.
Stricture  
The abnormal narrowing of a body opening. Also called stenosis.
Stroke
Disease caused by damage to blood vessels in the brain.  Usually only one side of the body is affected.
Subcutaneous Injection
Putting a fluid into the tissue under the skin with a needle and syringe.
Sugar
A class of carbohydrates that taste sweet. Sugar is a quick and easy fuel for the body to use. Types of sugar are lactose, glucose, fructose, and sucrose.
Sulfonylureas
Pills or capsules that people take to lower the level of glucose (sugar) in the blood. See also: Oral hypoglycemic agents.
Syndrome
A set of signs or a series of events occurring together that make up a disease or health problem.
Synovial
relating to the lubricating fluid in joints
Synovial fluid
Fluid released into movable joints by surrounding membranes. This fluid lubricates the joint and reduces friction.
Synovitis
inflammation of the joints; arthritis
Systemic
A word used to describe conditions that affect the entire body. Diabetes is a systemic disease because it involves many parts of the body such as the pancreas, eyes, kidneys, heart, and nerves.
Systemic lupus erythematosus
Lupus is an autoimmune disease, which causes the body to harm its own healthy cells and tissues. This leads to inflammation and damage of various body tissues.