Molecular model of quinine, an antimalarial drug, showing carbon (blue), hydrogen (gray), oxygen (red), and nitrogen (violet).

Molecular model of quinine, an antimalarial drug, showing carbon (blue), hydrogen (clear), oxygen (red), and nitrogen (violet).

Arthritis montage. An x-ray of osteoarthritic changes in the shoulder joint of an elderly male has superimposed over it three-dimensional molecular models of glucosamine and chondroitin sulfate, popular over-the-counter dietary supplements used to treat arthritis. Also shown is an illustration of a man hunched over with arthritic back pain.

Illustration of glucose control for diabetes. The collage shows a finger prick for blood glucose testing with a glucometer, a molecular model of glucose, and a glucose concentration graph in the background.

Illustration of eardrum perforation. The collage of images shows a normal eardrum (upper left); an eardrum perforation (upper right); and the eardrum repaired with a fibrin tissue seal (lower left). The components of the inner ear are also shown, including the cochlea, stapes, incus, and malleus.

Illustration of tonsillitis and pharyngitis. A human head in cross section shows inflamed tonsils and pharyngitis; the nasal cavity, tongue, and epiglottis are also shown.

Illustration of gastroesophageal reflux disease (GERD). GERD is a condition in which acidic stomach contents move back up (reflux) into the esophagus, irritating and inflaming the tissue, causing heartburn and pain.

3D illustration of urolithiasis, the disease associated with the formation or presence of a calculus, or stone, in the urinary tract, here a kidney stone. The stone is shown in the ureter, inset.

Illustration of hepatitis, shown in anterior views comparing a normal liver (top) to a liver swollen and inflamed secondary to hepatitis (bottom right). The position of the liver is shown with a silhouette view of a male torso.

Illustration of an enlarged liver (hepatomegaly) compared to a normal liver. Hepatomegaly is a presenting condition that may be due to many causes including infection, drugs or toxins, alcoholism, hepatic tumors, and metabolic disorders.

Illustration of liver cirrhosis. Chronic liver injury first leads to fibrosis and, over time, to cirrhosis, shown here by the increase in development of excess fibrous connective tissue.

Illustration comparing normal liver anatomy to stage four cirrhosis, showing the internal and external symptoms of cirrhosis.

Illustration of liver cirrhosis compared to normal liver anatomy, shown here by the increase in development of excess fibrous connective tissue. The position of the liver is shown with a silhouette view of a male torso.

Illustration showing the progression of fatal bacterial meningitis in an infant. Bacterial meningitis is the most deadly type of meningitis, particularly among infants.

Illustration of fatal meningitis, showing the spread of a systemic infection in an infant (left to right): the infection starts in the lungs and circulates through the blood vessels; next, it enters the meninges (membranes) that surround the spinal cord; finally, it attacks the meninges around brain and becomes fatal.

Illustration of bacterial meningitis in a child: normal brain, meninges, and spinal cord (left); infected and inflamed brain, meninges, and spinal cord due to bacterial meningitis (right).

Progression of meningococcal disease (bacterial meningitis) in a child. 1) Initial Bacteremia: bacteria enter the bloodstream and circulate throughout the body. 2) Subsequent Vasculitis: bacteria propagate leading to vasculitis, which causes leg pain and petechia. 3) Meningitis: bacteria infect and inflame the meninges that cover the brain.

Illustration of bacterial meningitis in an adult: normal brain, meninges, and spinal cord (left); infected and inflamed brain, meninges, and spinal cord due to bacterial meningitis (right).

Illustration of spinal meningitis: anatomical orientation of a normal spinal cord at the base of the brain (left); the meninges that cover spinal cord (top detail); an infected and inflamed spinal cord due to meningitis (bottom detail).

Illustration of the spread of meningococcal disease (bacterial meningitis) in an infant. The bacteria enter the bloodstream and circulate throughout the body (left). The bacteria infect the meninges that cover the brain and spinal cord, causing inflammation (right). Bacterial meningitis is the most deadly type of meningitis, particularly among infants.