Histology (hiss-TOL-o-je) Microscopic study of the structure of tis-
Homeostasis (ho'-me-o-STA-sis) The condition in which the body's
internal environment remains relatively constant, within physi-
ological limits.
Hyperthermia (hT'-per-THERM-e-a) An elevated body temperature.
Hypertonia (hT'-per-TO-ne-a) Increased muscle tone that is
expressed as spasticity or rigidity.
Hypertonic (hT'-per-TON-ik) Solution that causes cells to shrink due
to loss of water by osmosis.
Hypertrophy (hT-PER-tro-fe) An excessive enlargement or over-
growth of tissue without cell division.
Hyperventilation (hT'-per-ven-ti-LA-shun) A rate of respiration higher
than that required to maintain a normal partial pressure of carbon
dioxide in the blood.
Hypoglycemia (hT'-po-glT-SE-me-a) An abnormally low concentration
of glucose in the blood; can result from excess insulin (injected or
Hypokalemia (hT'-po-ka-LE-me-a) Deficiency of potassium ions in the
Hyponatremia (hT'-po-na-TRE-me-a) Deficiency of sodium ions in the
Hypophyseal fossa (hT'-po-FIZ-e-al FOS-a) A depression on the supe-
rior surface of the sphenoid bone that houses the pituitary gland.
Hypophysis (hT-POF-i-sis) Pituitary gland.
Hyposecretion (hT'-po-se-KRE-shun) Underactivity of glands resulting
in diminished secretion.
Hypothalamus (hT'-po-THAL-a-mus) A portion of the diencephalon,
lying beneath the thalamus and forming the floor and part of the
wall of the third ventricle.
Hypothermia (hT'-po-THER-me-a) Lowering of body temperature
below 35 °C (95 °F); in surgical procedures, it refers to deliberate
cooling of the body to slow down metabolism and reduce oxygen
needs of tissues.
Hypotonia (hT'-po-TO-ne-a) Decreased or lost muscle tone in which
muscles appear flaccid.
Hypotonic (hT'-po-TON-ik) Solution that causes cells to swell and
perhaps rupture due to gain of water by osmosis.
Hypoventilation (hT-po-ven-ti-LA-shun) A rate of respiration lower
than that required to maintain a normal partial pressure of carbon
dioxide in plasma.
Hypovolemic shock (hT-po-vo-LE-mik) A type of shock characterized
by decreased blood volume; may be caused by acute hemor-
rhage or excessive loss of other body fluids, for example, by
vomiting, diarrhea, or excessive sweating.
Hypoxia (hT-POKS-e-a) Lack of adequate oxygen at the tissue level.
Hysterectomy (hiss-te-REK-to-me) The surgical removal of the uterus.
Homologous chromosomes (ho-MOL-o-gus) Two chromosomes that
belong to a pair.
Homozygous (ho-mo-ZT-gus) Possessing the same alleles on homolo-
gous chromosomes for a particular hereditary trait.
Hormone (HOR-mon) A secretion of endocrine cells that alters the
physiological activity of target cells of the body.
Horn An area of gray matter (anterior, lateral, or posterior) in the
spinal cord.
Human chorionic gonadotropin (hCG) (ko-re-ON-ik go-nad-o-TRO-pin)
A hormone produced by the developing placenta that maintains
the corpus luteum.
Human growth hormone (hGH) Hormone secreted by the anterior
pituitary that stimulates growth of body tissues, especially
skeletal and muscular tissues. Also known as somatotropin and
somatotropic hormone (STH).
Hyaluronic acid (hT'a-loo-RON-ik) A viscous, amorphous extracellular
material that binds cells together, lubricates joints, and maintains
the shape of the eyeballs.
Hymen (HT-men) A thin fold of vascularized mucous membrane at
the vaginal orifice.
Hypercalcemia (hT'-per-kal-SE-me-a) An excess of calcium in the blood.
Hypercapnia (hT'-per-KAP-ne-a) An abnormal increase in the amount
of carbon dioxide in the blood.
Hyperextension (hT'-per-ek-STEN-shun) Continuation of extension
beyond the anatomical position, as in bending the head back-
Hyperglycemia (hT'-per-glT-SE-me-a) An elevated blood glucose level.
Hyperkalemia (hT'-per-ka-LE-me-a) An excess of potassium ions in
the blood.
Hypermetropia (hT'-per-me-TRO-pe-a) A condition in which visual
images are focused behind the retina, with resulting defective
vision of near objects; farsightedness.
Hyperplasia (hT'-per-PLA-ze-a) An abnormal increase in the number
of normal cells in a tissue or organ, increasing its size.
Hyperpolarization (hT'-per-POL-a-ri-za'-shun) Increase in the internal
negativity across a cell membrane, thus increasing the voltage
and moving it farther away from the threshold value.
Hypersecretion (hT'-per-se-KRE-shun) Overactivity of glands resulting
in excessive secretion.
Hypersensitivity (hT'-per-sen-si-TI-vi-te) Overreaction to an allergen
that results in pathological changes in tissues. Also called allergy.
Hypertension (hT'-per-TEN-shun) High blood pressure.
Ileocecal sphincter (il-e-o-SE-kal) A fold of mucous membrane that
guards the opening from the ileum into the large intestine. Also
called the ileocecal valve.
Ileum (IL-e-um) The terminal part of the small intestine.
Immunity (im-O-ni-te) The state of being resistant to injury, particu-
larly by poisons, foreign proteins, and invading pathogens.
Immunoglobulin (Ig) (im-u-no-GLOB-u-lin) An antibody synthesized
by plasma cells derived from B lymphocytes in response to the
introduction of an antigen. Immunoglobulins are divided into five
kinds (IgG, IgM, IgA, IgD, IgE).
Immunology (im'-u-NOL-o-je) The study of the responses of the body
when challenged by antigens.
Implantation (im-plan-TA-shun) The insertion of a tissue or a part into
the body. The attachment of the blastocyst to the stratum basalis
of the endometrium about 6 days after fertilization.
532 Glossary
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