Click on the alphabet and there you go!

Nail: In medicine, there are two types of nails. One is just a plain old metal nail used to hold 2 or more pieces of bone together, for example, after a fracture. The other type of nail is the horny plate on the end of the finger or toe. Each nail anatomically has a body, lateral nail folds (on the sides), a lunula (the little moon-shaped feature at the base), and a proximal skin fold (at the base).

Nail infection, fungal: The most common fungus infection of the nails is onychomycosis. Onychomycosis makes the nails look white and opaque, thickened, and brittle. Older women (perhaps because estrogen deficiency may increase the risk of infection). and men and women with diabetes or disease of the small blood vessels (peripheral vacscular disease) are at increased risk. Artificial nails (acrylic or "wraps") increase the risk because when an artificial nail is applied, the nail surface is usually abraded with an emery board damaging it, emery boards can carry infection, and. water can collect under the nail creating a moist, warm environment for fungal growth. Alternative names include tinea unguium and ringworm of the nails.

Nails, ringworm of the: See Nail infection, fungal.

Nail-patella syndrome: An hereditary condition with abnormally formed (dysplastic) or absent nails and absent or underdeveloped (hypoplastic) kneecaps (patellae). Other features include iliac horns, abnormality of the elbows interfering with full range of motion (pronation and supination) and kidney disease resembling glomerulonephritis which.is often mild but can be progressive and lead to renal failure. Nail-patella syndrome is inherited as dominant gene. This means that the disease can be transmitted by one affected parent. The nail-patella gene locus found linked genetically to the ABO blood group in 1965 is now known to be in chromosome region 9q34. Also called Turner-Kieser syndrome, and Fong disease.

Named reporting: In public health, named reporting is the reporting of infected persons by name to public health departments. This is standard practice for the surveillance of many infectious diseases such as syphilis, gonorrhea, and tuberculosis that pose a public health threat. The opposite of named reporting is anonymous testing in which the individual remains nameless.

Nanism: Once known as dwarfism, this condition is now correctly called short stature.

Nares: The nostrils. The word "nares" is straight out of Latin (still another reason why you should have taken Latin in school or, if you did, studied harder).

Nasal: Having to do with the nose. Nasal drops are intended for the nose, not (for example) the eyes. The word "nasal" came from the Latin "nasus" meaning the nose or snout.

Nasal decongestants: Drugs that shrink the swollen membranes in the nose and make it easier to breath. Decongestants can be taken orally or by nasal spray. Decongestant nasal spray should not be used for more than five days without the doctor"s advice, and if so, usually only when accompanied by a nasal steroid. Decongestant nasal sprays often cause a rebound effect if taken too long. A rebound effect is the worsening of symptoms when a drug is discontinued. This is a result of a tissue dependence on the medication.

Nasal septum: The dividing wall that runs down the middle of the nose so that there are normally two sides to the nose, each ending in a nostril.

Nasopharynx: The area of the upper throat behind the nose.

Naturopath: A person who practices naturopathy, a drugless system of therapy based on the use of physical forces such as heat, water, light, air and Messages.

Navel: The umbilicus. The word navel came from the Anglo-Saxon nafe for the hub of a wheel.

Nausea: Nausea is the urge to vomit. It can be brought by many causes including, systemic illnesses, such as influenza, medications, pain, and inner ear disease.

Neck dissection: Surgery to remove lymph nodes and other tissues in the neck.

Neck, wry: Medically called spasmodic torticollis, or torticollis. The most common of the focal dystonias. In torticollis, the muscles in the neck that control the position of the head are affected, causing the head to twist and turn to one side. In addition, the head may be pulled forward or backward.

Necropsy: A postmortem examination.

Necrosis: Death of cells or tissues. Necrosis can be due for example to ischemia (lack of blood flow).

Necrotic: Synonymous with dead. Necrotic tissue is dead tissue.

Neisseria: Group of bacteria that includes the cause of gonorrhea.

Nematodes: Roundworms.

Neo-: Prefix meaning new.

Neonatal: Pertaining to the newborn period which, by convention, is the first 4 weeks after birth.

Neonatal mortality rate: The number of children dying under 28 days of age divided by the number of live births that year. The neonatal mortality rate in the United States, which was 8.4 per 1,000 live births in 1980, declined to 5.8 per 1,000 live births in 1990.

Neonate: A newborn baby.

Neonatologist: A specialist in the care of the newborn.

Neonatology: The art and science of caring medically for the newborn.

Neoplasia: Abnormal new growth of cells.

Neoplasm: Literally, a new growth. Neoplasm is another word for a tumor.

Nephrectomy: Surgery to remove the kidney. Radical nephrectomy removed the kidney, the adrenal gland, nearby lymph nodes, and other surrounding tissue. Simple nephrectomy removes just the affected kidney. Partial nephrectomy removes the tumor, but not the entire kidney.

Nephritis: Inflammation of the kidney.

Nephro-: Having to do with the kidney. From the Greek nephros meaning kidney.

Nephrologist: A medical specialist in nephrology (the study of the kidney or "kidney-ology").

Nephrology: The art and science of the care of the kidney.

Nephron: A key unit, both anatomically and functionally, of the kidney.

Nephrosclerosis: Hardening (sclerosis) of the kidney usually due to disease of the blood vessels in it from atherosclerosis.

Nephrosis: Non-inflammatory, non-neoplastic disease of the kidney.

Nephrolithiasis: Kidney stones.

Nephrotomogram: A series of special x-rays of the kidneys. The x-rays are taken from different angles. They show the kidneys clearly, without the shadows of the organs around them.

Nerve: A nerve is a bundle of fibers that uses electrical and chemical signals to transmit sensory and motor information from one body part to another. (see nervous system).

Nerve Growth Factor: A substance that occurs naturally in the body and enhances the growth and survival of cholinergic nerves.

Nervous colon syndrome: A common gastrointestinal disorder characterized by abdominal pain, bloating, mucous in stools, and irregular bowel habits with alternating diarrhea and constipation, symptoms that tend to be chronic and wax and wane over the years. Although nervous colon syndrome can cause chronic recurrent discomfort, it appears to be an abnormal condition of gut contractions (motility) and does not lead to any serious organ problems. Diagnosis usually involves excluding other illnesses. Treatment is directed toward relief of symptoms and includes high fiber diet, exercise, relaxation techniques, avoidance of caffeine, milk products and sweeteners, and medications. Alternative names include irritable bowel syndrome, spastic colitis, and mucus colitis.

Nervous system: The nervous system is the body tissue that records and distributes information in the body using electrical and chemical transmission. It has two parts. The "central" nervous system is comprised of the brain and spinal cord. The "peripheral" nervous system is the nerve tissue that transmits sensation and motor information back and forth from the body to the central nervous system.

Nervous system, autonomic: Part of the nervous system once thought functionally independent of the brain. The autonomic nervous system regulates key functions including the activity of the cardiac (heart) muscle, smooth muscles (e.g., of the gut), and glands. The autonomic nervous system has two divisions: (1) the sympathetic nervous system, which accelerates the heart rate, constricts blood vessels, and raises blood pressure; and (2) the parasympathetic nervous system, which slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles.

Nervous system, parasympathetic: A part of the nervous system that slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles. The parasympathetic nervous system together with the sympathetic nervous system (that accelerates the heart rate, constricts blood vessels, and raises blood pressure) constitute the autonomic nervous system.

Nervous system, sympathetic: A part of the nervous system that accelerates the heart rate, constricts blood vessels, and raises blood pressure. The sympathetic nervous system together with the parasympathetic nervous system (that slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles) constitute the autonomic nervous system.

Neural: Having to do with nerve cells.

Neural tube defect (NTD): Abnormal development during embryonic life of the neural tube, the structure which gives rise to the central nervous system (the brain and spinal cord), resulting in anencephaly (absence of the cranial vault and absence of most or all of the cerebral hemispheres of the brain) and spina bifida/meningomyelocele (open spina with exposure and protusion of the spinal cord). The risk of NTDs can be decreased by the mother eating ample folic acid during pregnancy.

Neuralgia: Pain along the course of a nerve. Facial neuralgia is severe pain usually occurrring in bursts from the trigeminal nerve, the chief sensory nerve of the face.

Neuritis: Inflammation of nerves.

Neuroblastoma: Childhood tumor of adrenal or related tissue in the nervous system.

Neurofibromatosis (NF1): Hereditary disorder characterized by cafe-au-lait (coffee-with-milk spots on the skin and a tendency to tumors) also known as von Recklinghausen's disease.

Neurogenic: Starting with or having to do with the nerves or the nervous system.

Neurologist: A doctor who specializes in the diagnosis and treatment of disorders of the nervous system.

Neuroma: A tumor that arises in nerve cells.

Neuroma, optic: A benign tumor of the optic nerve.

Neurosurgeon: A doctor who specializes in surgery on the brain and other parts of the nervous system.

Neurosyphilis: The neurologic complications in the last ("tertiary") phase of syphilis involving the central nervous system.

Neurosyphilis, tabes: Also known as tabes dorsalis, the slowly progressive degeneration of the spinal cord that occurs in the late (tertiary) phase of syphilis a decade or more after contracting the infection. Among the terrible features are lancinating lightning-like pain, ataxia (wobbliness), deterioration of the nerve to the eye (the optic nerve) leading to blindness, urinary incontinence, loss of the sense of position, and degeneration of the joints (Charcot’s joints). Tabes is the Latin word for decay. The term tabes dorsalis was devised in 1836 when the cause of the condition was thought to be wastage of the dorsal (posterior) columns of the spinal cord, well before it was recognized as part of late syphilis.

Neurotoxic: Poisonous to nerves or nerve tissue. (example: lead)

Neutropenia: Not enough neutrophils.

Neutrophil: A type of white blood cell.

Neutrophilia: Too many neutrophils.

Nevus: A pigmented spot on the skin, such as a mole. The plural of nevus is nevi.

Newborn screening: Tests of newborns to detect those at increased risk for disorders such as PKU (phenylketonuria) and hypothyroidism.

NIH: The National Institutes of Health.

Nipple: The pigmented projection on the surface of the breast. Ducts which conduct milk from milk glands to the surface of the breast exit through the nipple. The surrounding flat area of pigmentation is the areola.

Nipple, supernumerary: An extra nipple.

Nitrogenous base: A molecule that contains nitrogen and has the chemical properties of a base. The nitrogenous bases in DNA are adenine (A), guanine (G), thymine (T), and cytosine ©. The nitrogenous bases in RNA are the same with one exception: adenine (A), guanine (G), uracil (U), and cytosine ©

Nitrosoureas: A group of anticancer drugs that can cross the blood-brain barrier. Carmustine (BCNU) and lomustine (CCNU) are nitrosoureas.

NMR: Nuclear Magnetic Resonance. An imaging technique that does not use radiation.

Nocturia: Excessive urinating at night.

Node: Literally a knot, a node is a collection of tissue. For example a lymph node, is a collection of lymphoid tissue.

Node, AV: Atrioventricular node. Specialized heart tissue which acts as an electrical relay station between the upper chambers of the heart (atria) and the lower chambers of the heart (ventricles). Electrical signals from the sinoatrial (SA) node and the atria must pass through the AV node to reach the ventricles.

Node, SA: Sinoatrial node. The pacemaker of the heart, located in the right atrium (upper chamber of the heart). The electrical signals initiated in the SA node are transmitted throuhg the atria and the ventricles to stimulate heart muscle contractions (heartbeats).

Nodular: Bumpy.

Nodule: A small node, a bump.

Nondisjunction: Failure of paired chromosomes to disjoin (separate) during cell division so both chromosomes go to one daughter cell and none to the other. Nondisjunction causes errors in chromosome number such as trisomy 21 (Down syndrome) and monsomy X (Turner syndrome).

Nonmelanoma skin cancer: Skin cancer that does not involve melanocytes. Basal cell cancer and squamous cell cancer are nonmelanoma skin cancers.

Nonseminoma: A classification of testicular cancers that arise in specialized sex cells called germ cells. Nonseminomas include embryonal carcinoma, teratoma, choriocarcinoma, and yolk sac tumor.

Nonsense mutation: A change in a DNA that prematurely stops the eading of messenger RNA. A nonsense mutation creates a stop codon (a triplet of bases that signals stop).

Nonsmall cell lung cancer: A general classification for squamous cell carcinoma, adenocarcinoma, and large cell carcinoma.

Normal range: Normal results can fall outside the normal range. By convention, the normal range is set to cover ninety-five percent (95%) of values from a normal population. Five percent (5%) of normal results therefore fall outside the normal range.

North Asian tick-borne rickettsiosis: One of the tick-borne rickettsial diseases of the eastern hemisphere, similar to Rocky Mountain spotted fever, but less severe, with fever, a small ulcer (eschar) at the site of the tick bite, swollen glands nearby (satellite lymphadenopathy), and a red raised (maculopapular) rash.

Northern blot: A technique in molecular biology, used mainly to separate and identify pieces of RNA. Called a Northern blot because it is similar to a Southern blot (which is named after its inventor, the British biologist M.E. Southern).

Nosebleed: Its medical name is epistaxis.

Nosebleed, causes of: The nose is a part of the body that is very rich in blood vessels (vascular) and is situated in a vulnerable position on the face. As a result, any trauma to the face can cause bleeding which may be profuse. Nosebleeds can occur spontaneously when the nasal membranes dry out, crust, and crack, as is common in dry climates, or during the winter months when the air is dry and warm from household heaters. People are more susceptible if they are taking medications which prevent normal blood clotting (coumadin, warfarin, aspirin, or any anti-inflammatory medication). Other predisposing factors include infection, trauma, allergic and non-allergic rhinitis, hypertension., alcohol abuse and inherited bleeding problems.

Nosebleed, treatment of: To stop a nosebleed, you should: 1. Pinch all the soft parts of the nose together between your thumb and index finger. 2. Press firmly toward the face - compressing the pinched parts of the nose against the bones of the face. 3. Hold the nose for at least 5 minutes (timed by the clock). Repeat as necessary until the nose has stopped bleeding. 4. Sit quietly, keeping the head higher than the level of the heart; that is, sit up or lie with the head elevated. Do not lay flat or put your head between your legs. 5. Apply ice (crushed in a plastic bag or washcloth) to nose and cheeks.

Nose job: Plastic surgery on the nose known medically as a rhinoplasty.

Nose, runny: Rhinorrhea is the medical term for this common problem. From the Greek words "rhinos" meaning "of the nose" and "rhoia" meaning "a flowing."

Nosocomial: Hospital-acquired. A nosocomial infection is one contracted in the hospital.

NSAIDS: Abbreviation for nonsteroidal anti-inflammatory drugs. This is a large group of medications used to treat conditions associated with inflammation.

NTD: Neural tube defect.

Nucleic acid: DNA or RNA.

Nucleosome: Structure responsible in part for the compactness of a chromosome. Each nucleosome consists of a sequence of DNA wrapped around a core of histone (a type of protein).

Nucleotide: A subunit of DNA or RNA. A nucleotide consists of a nitrogenous base (A, G, T, or C in DNA; A, G, U, or C in RNA), a phosphate molecule, and a sugar molecule (deoxyribose in DNA and ribose in RNA). Thousands of nucleotides are linked to form a DNA or RNA molecule.

Nucleus: In cell biology, the structure that houses the chromosomes. In neuroanatomy, a group of nerve cells.

Nullipara: A woman who has not given birth to a viable child.

Null mutation: Change in a gene that leads to nothing, for example to no enzyme or to a nonfunctioning enzyme.

Nurse: A person skilled in nursing. Also, to feed at the breast (suckle) as an infant.

Nursing: Profession (better known than defined) concerned with the provision of services essential to the maintenance and restoration of health by attending the needs of sick persons. Also, feeding a infant at the breast.

Nutrition: The science of taking in and utilizing foods.

Nutritionist: A specialist in nutrition.

Nystagmus: Rapid rhythmic repetitious involuntary (unwilled) eye movements. Nystagmus can be horizontal, vertical or rotary.