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Macrocytic anemia:
Low red
blood cell count, characterized by the presence in the blood of larger than
normal red blood cells.
Macrophage:
Phagocytic cell derived from a monocyte which may be fixed or wandering.
Macula:
A small
area of the retina where vision is the keenest. The macula is located in the
center of the retina and provides central vision. Activities that require
central vision include driving, reading and other activities that require
sharp, straight-ahead vision.
Magnetic
Resonance Imaging (MRI):
A
diagnostic procedure that uses a special imaging technique with a powerful
magnet and a computer to provide clear images of soft tissues. Tissues that
are well-visualized using MRI include the brain and spinal cord, abdomen,
and joints.
Malabsorption syndrome:
A disease
or condition that results in poor absorption of nutrients from food.
Malaise: Discomfort,
uneasiness and indisposition often indicative of malaria.
Malaria:
An
infectious disease caused by parasitic microorganisms called plasmodia.
Malaria can be spread among humans through the sting of certain types of
mosquitos (Anopheles) or by a contaminated needle or transfusion. Malaria is
a major health problem in the tropics and subtropics, affecting over 200
million people world wide.
Malignant:
Referring to diseases that tend to become worse and cause death; cancerous
Malnutrition: A state
of bad or poor nutrition that may be due to inadequate food intake,
imbalance of nutrients, malabsorption of nutrients, improper distribution of
nutrients increased nutrient requirements, increased nutrient loses or
over-nutrition.
Megaloblastic anemia:
Low red
blood cell count, characterized by the presence in the blood of large,
immature, nucleated cells (megaloblasts) that are forerunners of red blood
cells. Red blood cells, when mature, have no nucleus.
Melanin:
A dark
brown pigment found in the skin.
Membrane
potential:
The
electrical potential difference across a membrane. The membrane potential is
a result of the concentration differences between potassium and sodium
across cell membranes which are maintained by ion pumps. A large proportion
of the body's resting energy expenditure is devoted to maintaining the
membrane potential, which is critical for nerve impulse transmission, muscle
contraction, heart function, and the transport of nutrients and metabolites
in and out of cells.
Menstruation:
The
cyclic loss of blood by a woman, from her uterus (womb) when she is not
pregnant. Menstruation generally occurs every 4 weeks after a woman has
reached sexual maturity and prior to menopause.
Meta-analysis:
A
mathematical or statistical analysis, used to pool the results of all
studies investigating a particular effect (e.g., the effect of folic acid
supplementation on homocysteine levels) and provide an overall estimate of
that effect.
Metabolism:
Physical
and chemical processes within the body involving energy production and
utilization.
Metabolite:
A
compound derived from the metabolism of another compound is said to be a
metabolite of that compound.
Metastasize:
To spread
from one part of the body to another. Cancer is said to metastasize when it
spreads from the primary site of origin to a distant anatomical site.
Methionine:
A sulfur
containing amino acid, required for protein synthesis and other vital
metabolic processes. It can be obtained through the diet in protein or
synthesized from homocysteine.
Methylation:
A
biochemical reaction resulting in the addition of a methyl group (-CH3)
to another molecule.
Migraine
headache:
A type of
headache thought to be related to abnormal sensitivity of blood vessels
(arteries) in the brain to various triggers resulting in rapid changes in
the artery size due to spasm (constriction). Other arteries in the brain and
scalp then open (dilate), and throbbing pain is perceived in the head. The
tendency toward migraine appears to involve serotonin, a neurotransmitter
that can trigger the release of vasoactive substances in the blood vessels.
Minerals:
Nutritionally significant elements. Elements are composed of only one kind
of atom. Minerals are inorganic, i.e., they do not contain carbon as do
vitamins and other organic compounds.
Mitochondria:
Energy-producing structures within cells. Mitochondria possess two sets of
membranes, a smooth continuous outer membrane, and an inner membrane
arranged in folds. Among other critical functions, mitochondria convert
nutrients into energy via the electron transport chain.
mm Hg:
Millimeters of mercury. The unit of measure for blood pressure.
Mole:
The
fundamental unit for measuring chemical compounds (abbreviated mol). One
mole equals the molecular weight of a compound in grams. The number of
molecules in a mole is equal to 6.02 x 1023 (Avogadro's number).
Multifactorial:
Refers to
a disorder or condition that has a number of different causes.
Multiple
sclerosis (MS):
An
autoimmune disorder, which results in the demyelinization of nerves. In MS,
the myelin shealth that allows for efficient transmission of nerve impulses
is damaged, resulting in progressive neurological symptoms such as,
numbness, tingling, loss of control of certain bodily functions, and
paralysis.
Mutation:
A change
in a gene, in other words, a change in the sequence of base pairs in the DNA
that makes up a gene. Mutations in a gene may or may not result in an
altered gene product.
Myelin:
The fatty
substance that covers myelinated nerves. Myelin is a layered tissue
surrounding the axons or nerve fibers. This sheath acts as a conduit in an
electrical system, allowing rapid and efficient transmission of nerve
impulses. Myelination refers to the process in which nerves acquire a myelin
sheath.
Myocardial infarction (MI):
Commonly
known as a "heart attack", a myocardial infarction refers to changes that
occur in the heart muscle due to an interruption in its blood supply. An MI
is often the result of a clot that lodges in a coronary artery, resulting in
deprivation of oxygen to a portion of the heart muscle (ischemia), and
ultimately the death (necrosis) of a portion of the heart muscle, if the
oxygen supply is not restored within a few minutes.
Myocarditis:
An
inflammation of the heart muscle.
Myoglobin:
A heme-containing
pigment in muscle cells that binds and stores oxygen.
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