Gynecomastia (gTn'-e-kC-MAS-te-a) Excessive growth (benign) of
the male mammary glands due to secretion of estrogens by an
adrenal gland tumor (feminizing adenoma).
Gyrus (Jf-rus) One of the folds of the cerebral cortex of the brain.
P lu r a l
is gyri (Jf-rT). Also called a convolution.
Hair A threadlike structure composed of dead, keratinized cells
produced by hair follicles that develops in the dermis. Also called
a pilus (Pf-lus).
Hair follicle (FOL-li-kul) Structure, composed of epithelium and sur-
rounding the root of a hair, from which hair develops.
Hair root plexus (PLEK-sus) A network of dendrites arranged around
the root of a hair as free or naked nerve endings that are stimu-
lated when a hair shaft is moved.
Hand The terminal portion of an upper limb, including the carpus,
metacarpus, and phalanges.
Haploid (HAP-loyd) Having half the number of chromosomes charac-
teristically found in the somatic cells of an organism; characteris-
tic of mature gametes. Symbolized
Hard palate (PAL-at) The anterior portion of the roof of the mouth,
formed by the maxillae and palatine bones and lined by mucous
Head The superior part of a human, cephalic to the neck. The supe-
rior or proximal part of a structure.
Heart A hollow muscular organ lying slightly to the left of the midline
of the chest that pumps the blood through the cardiovascular
Heart block An arrhythmia (dysrhythmia) of the heart in which the
atria and ventricles contract independently because of a block-
ing of electrical impulses through the heart at some point in the
Heart murmur (MER-mer) An abnormal sound that consists of a flow
noise that is heard before, between, or after the normal heart
sounds, or that may mask normal heart sounds.
Heat exhaustion Condition characterized by cool, clammy skin, pro-
fuse perspiration, and fluid and electrolyte (especially sodium and
chloride) loss that results in muscle cramps, dizziness, vomiting,
and fainting. Also called heat prostration.
Heat stroke Condition produced when the body cannot easily lose
heat and characterized by reduced perspiration and elevated
body temperature. Also called sunstroke.
Hematocrit (Hct) (he-MAT-o-krit) The percentage of blood made up of
red blood cells. Usually measured by centrifuging a blood sample
in a graduated tube and then reading the volume of red blood
cells and dividing it by the total volume of blood in the sample.
Hematology (he'-ma-TOL-o-je) The study of blood.
Hemiplegia (hem-i-PLE-je-a) Paralysis of the upper limb, trunk, and
lower limb on one side of the body.
Hemoglobin (Hb) (he'-mo-GLO-bin) A substance in red blood cells
consisting of the protein globin and the iron-containing red pig-
ment heme that transports most of the oxygen and some carbon
dioxide in blood.
Hemolysis (he-MOL-i-sis) The escape of hemoglobin from the interior
of a red blood cell into the surrounding medium; results from
disruption of the cell membrane by toxins or drugs, freezing or
thawing, or hypotonic solutions.
Hemolytic disease of the newborn A hemolytic anemia of a newborn
child that results from the destruction of the infant's erythrocytes
(red blood cells) by antibodies produced by the mother; usually
the antibodies are due to an Rh blood type incompatibility. Also
called erythroblastosis fetalis (e-rith'-ro-blas-TO-sis fe-TAL-is).
Hemophilia (he'-mo-FIL-e-a) A hereditary blood disorder where there
is a deficient production of certain factors involved in blood clot-
ting, resulting in excessive bleeding into joints, deep tissues, and
Hemopoiesis (he-mo-poy-E-sis) Blood cell production, which occurs
in red bone marrow after birth. Also called hematopoiesis (hem'-
Hemorrhage (HEM-or-rij) Bleeding; the escape of blood from blood
vessels, especially when the loss is profuse.
Hemorrhoids (HEM-o-royds) Dilated or varicosed blood vessels (usu-
ally veins) in the anal region. Also called piles.
Hemostasis (he-MO-sta-sis) The stoppage of bleeding.
Heparin (HEP-a-rin) An anticoagulant given to slow the conversion of
prothrombin to thrombin, thus reducing the risk of blood clot for-
mation; found in basophils, mast cells, and various other tissues,
especially the liver and lungs.
Hepatic (he-PAT-ik) Refers to the liver.
Hepatic duct A duct that receives bile from the bile capillaries. Small
hepatic ducts merge to form the larger right and left hepatic
ducts that unite to leave the liver as the common hepatic duct.
Hepatic portal circulation The flow of blood from the gastrointestinal
organs to the liver before returning to the heart.
Hepatocyte (he-PAT-o-cyte) A liver cell.
Hernia (HER-ne-a) The protrusion or projection of an organ or part of
an organ through a membrane or cavity wall, usually the abdomi-
Herniated disc (HER-ne-a'-ted) A rupture of an intervertebral disc
so that the nucleus pulposus protrudes into the vertebral cavity.
Also called a slipped disc.
Heterozygous (he-ter-o-Zf-gus) Possessing different alleles on
homologous chromosomes for a particular hereditary trait.
Hiatus (hf-A-tus) An opening; a foramen.
Hinge joint A synovial joint in which a convex surface of one bone
fits into a concave surface of another bone, such as the elbow,
knee, ankle, and interphalangeal joints. Also called a ginglymus
Hirsutism (HER-soot-izm) An excessive growth of hair in females and
children, with a distribution similar to that in adult males, due to
the conversion of vellus hairs into large terminal hairs in response
to higher-than-normal levels of androgens.
Histamine (HISS-ta-men) Substance found in many cells, especially
mast cells, basophils, and platelets, released when the cells are
injured; results in vasodilation, increased permeability of blood
vessels, and constriction of bronchioles.