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Dr. Kennedy's Vocabulary Course for 11/18/2013
(A B C D E F G H I J K L M)
 
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Ron Kennedy, M.D.
 
Vocabulary Search:Phrase  Any Words
 
 
Meiosis:  The process chromosomes undertake during germ-cell formation (egg + sperm) to halve the chromosome number from 46 to 23 and combine with the corresponding egg or sperm to recreate a new cell with 46 chromosomes, half from egg, half from sperm. As division continues two new cells are created. If the new cell is to be female X chromosomes pair; if to be male the X and Y chromosomes pair.
Meiotic drive:  Preferential selection during meiosis (germ cell production). In meiotic drive there is preferential production of certain gametes. This alters the segregation of genes from the Mendelian expectations. Meiotic drive is a mechanism for transmission distortion. In other words the final genome of the new animal is not a simple statistical dice roll for which genes are included.
Meiotic nondisjunction:  Failure of two members of a chromosome pair to separate from one another during meiosis, causing both chromosomes to go to a single daughter cell. Meiotic nondisjunction is responsible for the extra chromosome 21 in trisomy 21 (Down syndrome) and for extra and missing chromosomes that cause other birth defects and many miscarriages.
Melan- (prefix):  Prefix meaning dark or black. It comes from the Greek "melas", black. Examples of terms containing melan- include melancholia, melanin, melanocytes, melanoma and melena.
Melancholia:  An old term for depression.
Melanin:  The pigment that gives human skin, hair, and eyes their color. Dark-skinned people have more melanin in their skin than light-skinned people have. Melanin is produced by cells called melanocytes. It provides some protection again skin damage from the sun, and the melanocytes increase their production of melanin in response to sun exposure. Freckles, which occur in people of all races, are small, concentrated areas of increased melanin production. Protection from the sun comes at a cost however. Increased melanin means a reduction of vitamin D production. So-called "old age spots" occur when melanocytes burst and release their malanin content which creates a permanent stain in the skin.
Melanocyte:  A cell in the skin that produces and contains the pigment melanin.
Melanoderma:  Various forms of increased skin pigmentation (darkening of the skin). This is directly due to an increased amount of melanin pigment in the skin when there is increased production of melanin by the melanocytes (the cells that make melanin) or if there is a rise in the number of melanocytes.
Melanoma:  The most dangerous form of skin cancer, a malignancy of the melanocyte, the cell that produces pigment in the skin. Melanoma is most common in people with fair skin, but can occur in people with all skin colors. Most melanomas present as a dark, mole-like spot that spreads and, unlike a mole, has an irregular border. The tendency toward melanoma may be inherited, and the risk increases with overexposure to the sun and sunburn. Fair-skinned people and people with a family history of melanoma should always use a high-SPF sunscreen when outdoors. Everyone who has concern about an unusual mole-like spot should see their doctor. Detected early, melanoma is almost always treatable. Undetected, melanoma can spread rapidly and be fatal. People with a history of skin cancer of any kind should have periodic visual exams by a dermatologist.
Melanoma thickness:  A method for determining the prognosis of melanomas. The thickness of a melanoma is related to the 5-year survival rate after surgical removal of the tumor. Also called Breslow thickness, named for the physician Alexander Breslow who in 1975 observed that as the thickness of the tumor increases, the chance of survival goes down.
Melanoma types:  juvenile, acral-lentiginous, amelanotic, benign, choroidal, ciliary body. conjunctival, eye, intraocular, iris, lentigo maligna, malignant, nodular, ocular, superficial spreading, and uveal.
Melanoma vaccine:  A cancer vaccine prepared from human melanoma cancer cells. It may be used alone or with other therapy in treating melanoma.
Melanosis coli:  A benign, reversible condition usually, but not always, associated with long-term use of anthranoid laxatives in which pigment deposition in the lamina propria of the large intestine results in a brown to black discoloration of the lining of the large intestine. Melanosis coli is sometimes called pseudomelanosis coli since the pigment deposited is lipofuscin and not melanin as the name implies. Melanosis coli produces no symptoms and is indicative of chronic anthranoid (senna) laxative use.
MELAS syndrome:  Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes syndrome, a rare form of dementia caused by mutations in the genetic material (DNA) in the mitochondria.
Melasma:  Pigmentation of the cheeks of the face (malar area). When it occurs during pregnancy it is referred to as chloasma or the mask of pregnancy. Melasma darkens with sun exposure.
Melatonin:  A hormone that is produced by the pineal gland and is intimately involved in regulating the sleeping and waking cycles, among other processes.
MELD:  Acronym for Model End Stage Liver Disease. A disease severity scoring system for adults with liver disease, designed to improve the organ allocation in transplantation based on the severity of liver disease rather than the length of time on the waiting list. The MELD score is based only on laboratory data in order to be as objective as possible.
Melena:  Stool or vomit that is stained black by blood pigment or dark blood products.



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