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  • Manifestations: in medicine, symptoms.
  • Mauzerall-Granick method: This is a newer test than the Watson-Schwartz test, and is used to screen for elevated porphobilinogen (PBG) in the urine. PBG is the screening test used to diagnose an acute porphyria.
  • Melanin: the pigment responsible for the colour of the skin. The more melanin that is present, the darker the skin.
  • Menses: menstrual flow; the monthly flow of blood and cellular debris from the uterus that begins at puberty in women.
  • Menstrual cycle: a cycle of physiological changes that lasts about 28 days and occurs in females during their childbearing years, preparing the uterus for pregnancy.
  • Metabolic pathway:  the sequence by which the chemical changes in living cells provide energy for vital processes in the body.
  • Metabolites: substances that are part of the chemical reactions within one's body.
  • Metoclopramide: a medication sometimes used  to treat heartburn caused by gastroesophageal reflux.
  • Mitochondria: structures found within all cells (except red blood cells), which use oxygen to produce the energy needed for cellular metabolism.
  • Molecule: the smallest particle of a substance that retains the chemical and physical properties of the substance and is composed of two or more atoms; a group of like or different atoms held together by chemical forces.
  • Mutation: an alteration in DNA that is permanent and potentially inheritable and may change the function of the gene in which it is located.
  • Mutilation: permanent physical injury that affects the appearance or function of any part of the body.
  • Myoglobin: the protein that carries oxygen in muscle cells.