Dictionary

menstruation Bleeding that occurs each month if pregnancy does not occur. Also known as menorrhea and menses. See also menstrual cycle.

menstruation, anovular Menstruation that occurs without ovulation. Usually in anovular menstruation the egg that remains in the ovary simply disintegrates, but in some circumstances it is fertilized and a life-threatening ovarian pregnancy results.

menstruation, cessation of The ending of a woman’s menstrual cycles. Menstruation ends naturally in middle age with the onset of menopause. It can also end suddenly as a result of induced menopause. Cessation of menstruation in nonmenopausal women may be due to pregnancy, illness, disorders of the hypothalamus or pituitary gland, medication, stress, overexercise, or…

menstruation, retrograde Menstruation in which blood flows from the uterus into the Fallopian tubes, and potentially into the abdomen. This condition may play a role in the development of endometriosis. See also endometriosis.

mental 1 Pertaining to the mind. 2 Pertaining to the chin.

mental child injury See child abuse.

mental illness Any disease that affects the central nervous system, causing disturbances of thought or behavior. Mental illnesses can be caused by genetic, metabolic, structural, infectious, or environmental causes. The term mental illness is also used to describe emotional disturbances caused by traumatic or distressing events or by poor adjustment to normal life stresses. Treatment…

mental retardation The condition of having an IQ measured as below 70 to 75 and significant delays or lacks in at least two areas of adaptive skills. Mental retardation is present from childhood. Between 2 and 3 percent of the general population meet the criteria for mental retardation. Causes of mental retardation include fetal alcohol…

mercury poisoning Disease resulting from exposure to the metallic element mercury. Mercury is toxic to humans, and poisoning can occur in both acute and chronic forms. Acute mercury poisoning (less common) is associated with ulcerations of the stomach and intestine and with toxic changes in the kidney. Chronic mercury poisoning can cause diarrhea, slowed reflexes,…

mesentery In general, a fold of tissue that attaches organs to the body wall. The word mesentery usually refers to the small bowel mesentery, which anchors the small intestines to the back of the abdominal wall. Blood vessels, nerves, and lymphatics branch through the mesentery to supply the intestine. Other mesenteries exist to support the…

mesoderm The middle of the three primary germ cell layers (the other two being the ectoderm and endoderm) that make up a very young embryo. The mesoderm differentiates (specializes) to give rise to a number of tissues and structures, including bone, muscle, connective tissue, and the middle layer of the skin. See also differentiation; ectoderm;…

mesodermal Pertaining to the mesoderm or to tissues derived from the mesoderm.