Gastroenteritis is a general term for inflammation* of the gastrointestinal (gas-tro-in-TES-ti-nal) tract, the part of the digestive system consisting of the stomach, small intestine, and large intestine. Loss of appetite, vomiting, cramps, nausea*, and diarrhea* are the most common symptoms of gastroenteritis.

Genetic Diseases

Every person develops under the influence of a mix of genes inherited from his or her mother and father. These genes, or small parts of chromosomes, determine the architecture and activity of the entire body.

Genital Warts

Genital warts may be dome shaped or nearly flat, but most commonly they grow on stalks in clumps that look like small heads of cauliflower. Warts of this shape are called condylomata acuminata (kon-dil-o-MAT-a a-koo-min-NAT-a).

German Measles (Rubella)

Rubella is not considered a serious illness, except when a pregnant woman gets the infection. It is spread through the air from an infected person to another person.


Giardiasis (je-ar-DY-a-sis) is a common infection caused by the Giardia lamhlia (je-AR-de-a LAM-bli-a) protozoan, which is a one-celled organism that lives as a parasite*. Giardia contamination can occur in any water source, from clear mountain streams to poorly filtered city water supplies.


If a balloon is slowly filled with water, eventually it will burst. But if the same balloon has several pin-sized holes at one end, then it becomes possible to continue adding water to the balloon to maintain its round shape, without breaking the balloon, as long as the amount of water being added is equal to the amount escaping through the pinholes.


Gonorrhea is an infection caused by Neisseria gonorrhoeae (ni-SEE-ree-a gon-o-REE-i) bacteria, which grow rapidly in the warm, moist tissues of the body's genital areas. Gonorrhea infection may cause pain during urination and a pus-like discharge from the genitals.


Uric (YUR-ik) acid is a waste product made by normal chemical processes in the body, as well as by the breakdown of certain foods, and it is usually eliminated in urine. Sometimes uric acid builds up and forms crystals, like sugar crystals, that collect in joints such as those of the big toe.

Growth Disorders

When Jeremy turned eight, he looked like he was trapped inside the body of a four-year-old. "My friends teased me and called me 'Shorty,'" he said.

Gum Disease

Like getting gray hair and wrinkles, losing teeth once seemed to be an inevitable part of growing old. The number one cause of tooth loss in adults is still gum disease, also known as periodontal (per-ee-o-DON-tel) disease.

Hair Loss

Hair is said to be a person's crowning glory. Most of the hair on a person's head is growing constantly.


Halitosis is the medical name for bad breath. Often people with halitosis do not know that they have it.


Hantavirus pulmonary syndrome (HAN-ta-vi-rus PUL-mo-nar-ee SIN-drome), or HPS for short, is an uncommon but deadly lung disease. It is caused by a type of virus known as hantavirus, which is carried by rodents*, especially deer mice.


Headaches are so common that it is hard to imagine someone who has not had a headache, unless perhaps it is a newborn baby. Although there are dozens of causes of headaches, most headaches are due to tension or stress.

Heart Disease

Max, who had just turned 14, and his grandfather Harry often shared a Saturday morning ritual: breakfast at their favorite diner, followed by a brisk game of tennis. On this occasion, they both ordered the special: two fried eggs, four strips of bacon, hotcakes, and a side of hash browns.

Heart Murmur

Jill's baby wiggled as the doctor placed a stethoscope on his chest to listen to the heartbeat. Jill smiled, because she knew how cold the device could feel on bare skin.

Heartburn (Dyspepsia)

Sarah's grandfather always comes to her house for Sunday dinner. For several weeks in a row, he seemed uncomfortable after eating and did not lie down for his usual nap.

Heat-Related Injuries

Texas was in the grip of a severe heat wave in August just as students were heading back to school after summer break. The extreme heat forced schools around the state to take action.


Most people take certain bodily functions for granted: breathing, digestion, healing. We do not have to think about them; they just happen.


Hemorrhage is any profuse internal or external bleeding from the blood vessels. The most obvious cause of hemorrhage is trauma or injury to a blood vessel.


Hemorrhoids occur in two places. When they are located in the upper part of the rectum, the hemorrhoids are called internal hemorrhoids.


The liver, a red-brown, wedge-shaped organ in the upper abdomen, is the largest internal organ in the body and performs the widest range of jobs. It gets rid of harmful substances in food, disposes of old blood cells, helps digest fat, produces chemicals to make the blood clot, and makes sure the blood carries the right balance of fat, sugar, and amino (a-ME-no) acids (the building blocks of proteins) to all the cells of the body.