Glossary
G-11
Hydrogen bond
Weak bond in which a hydrogen atom forms a bridge
between two electron-hungry atoms. An important intramolecular bond.
Hydrogen ion (H
1
)
A hydrogen atom minus its electron and therefore
carrying a positive charge (i.e., a proton).
Hydrolysis
(hi
0
drah
9
lă-sis) Process in which water is used to split a sub-
stance into smaller particles.
Hydrophilic
(hi
0
dro-fil
9
ik) Refers to molecules, or portions of molecules,
that interact with water and charged particles.
Hydrophobic
(hi
0
dro-fo
9
bik) Refers to molecules, or portions of mol-
ecules, that interact only with nonpolar molecules.
Hydrostatic pressure
(hi
0
dro-stă
9
tic) Pressure of fluid in a system.
Hydroxyl ion (OH
2
)
(hi-drok
9
sil) An ion liberated when a hydroxide (a
common inorganic base) is dissolved in water.
Hyperalgesia
Pain amplification.
Hypercapnia
(hi
0
per-kap
9
ne-ah) High carbon dioxide levels in the blood.
Hyperemia
An increase in blood flow into a tissue or organ; congested
with blood.
Hyperglycemic
(hi
0
per-gli-se
9
mik) Term used to describe hormones
such as glucagon that elevate blood glucose level.
Hyperopia
(hi
0
per-o
9
pe-ah) A condition in which visual images are
routinely focused behind rather than on the retina; commonly known as
farsightedness.
Hyperplasia
(hi
0
per-pla
9
ze-ah) Accelerated growth, e.g., in anemia, the
bone marrow produces red blood cells at a faster rate.
Hyperpnea
(hi
0
perp-ne
9
ah) An increase in ventilation in response to
metabolic need (e.g., during exercise).
Hyperpolarization
An increase in membrane potential in which the
membrane becomes more negative than resting membrane potential.
Hypersensitivity
Overzealous immune response to an otherwise harm-
less antigen.
Hypertension
(hi
0
per-ten
9
shun) High blood pressure.
Hypertonic
(hi
0
per-ton
9
ik) Excessive, above normal, tone or tension.
Hypertonic solution
A solution that has a higher concentration of non-
penetrating solutes than the reference cell; having greater osmotic pres-
sure than the reference solution (blood plasma or interstitial fluid).
Hypertrophy
(hi-per
9
trah-fe) Increase in size of a tissue or organ inde-
pendent of the body’s general growth.
Hyperventilation
An increase in the depth and rate of breathing that is
in excess of the body’s need for removal of carbon dioxide.
Hypocapnia
Low carbon dioxide levels in the blood.
Hypodermis
(superficial fascia) Subcutaneous tissue just deep to the
skin; consists of adipose plus some areolar connective tissue.
Hypoglycemic
(hi
0
po-gli-se
9
mik) Term used to describe hormones such
as insulin that decrease blood glucose level.
Hyponatremia
Abnormally low concentrations of sodium ions in extra-
cellular fluid.
Hypoproteinemia
(hi
0
po-pro
0
te-ĭ-ne
9
me-ah) A condition of unusually
low levels of plasma proteins causing a reduction in colloid osmotic pres-
sure; results in tissue edema.
Hypotension
Low blood pressure.
Hypothalamic-hypophyseal tract
(hi
0
po-thah-lam
9
ik hi
0
po-fiz
9
-e-al)
Nerve bundles that run through the infundibulum and connect the pos-
terior pituitary to the hypothalamus.
Hypothalamus
(hi
0
po-thal
9
ah-mus) Region of the diencephalon form-
ing the floor of the third ventricle of the brain.
Hematopoiesis
(hem
0
ah-to-poi-e
9
sis) Blood cell formation; hemopoiesis.
Hematopoietic stem cell
(hem
0
ah-to-poi-et
9
ik) Bone marrow cell that
gives rise to all the formed elements of blood; hemocytoblast.
Heme
(hēm) Iron-containing pigment that is essential to oxygen trans-
port by hemoglobin.
Hemoglobin
(he
9
muh-glo-bin) Oxygen-transporting protein of eryth-
rocytes.
Hemolysis
(he-mah
9
lĕ-sis) Rupture of erythrocytes.
Hemophilia
(he
0
mo-fil
9
e-ah) A term loosely applied to several different
hereditary bleeding disorders that exhibit similar signs and symptoms.
Hemopoiesis
(he
0
mo-poi-e
9
sis)
See
Hematopoiesis.
Hemorrhage
(hem
9
or-ij) Loss of blood from the vessels by flow through
ruptured walls; bleeding.
Hemostasis
(he
0
mo-sta
9
sis) Stoppage of bleeding.
Heparin
Natural anticoagulant secreted into blood plasma.
Hepatic portal system
(hĕ-pat
9
ik) Circulation in which the hepatic por-
tal vein carries dissolved nutrients to the liver tissues for processing.
Hepatitis
(hep
0
ah-ti
9
tis) Inflammation of the liver.
Hernia
(her
9
ne-ah) Abnormal protrusion of an organ or a body part
through the containing wall of its cavity.
Heterozygous
(het
0
er-o-zi
9
gus) Having different allelic genes at a given
locus or (by extension) many loci.
Hilton’s law
Any nerve serving a muscle that produces movement at a
joint also innervates the joint and the skin over the joint.
Hilum
(hi
9
lum) ±e indented region of an organ from which blood and/
or lymphatic vessels and nerves enter and exit.
Hippocampus
Limbic system structure that plays a role in converting
new information into long-term memories.
Histamine
(his
9
tuh-mēn) A chemical messenger (neurotransmitter or
paracrine); causes vasodilation and increased capillary permeability; in
stomach causes acid secretion.
Histology
(his-tol
9
o-je) Branch of anatomy dealing with the microscopic
structure of tissues.
HIV (human immunodeficiency virus)
Virus that destroys helper T
cells, thus depressing adaptive immunity; symptomatic AIDS gradually
appears when lymph nodes can no longer contain the virus.
Holocrine glands
(hol
9
o-krin) Glands that accumulate their secretions
within their cells; secretions are discharged only upon rupture and death
of the cell.
Homeostasis
(ho
0
me-o-sta
9
sis) A state of body equilibrium or stable in-
ternal environment of the body.
Homologous
(ho-mol
9
ŏ-gus) Parts or organs corresponding in structure
but not necessarily in function.
Homozygous
(ho-mo-zi
9
gus) Having identical genes at one or more
loci.
Hormones
Steroidal or amino acid–based molecules released to the
blood that act as chemical messengers to regulate specific body functions.
Humoral immunity
(hu
9
mer-ul) Immunity conferred by antibodies
present in blood plasma and other body fluids.
Huntington’s disease
Hereditary disorder leading to degeneration of
the basal nuclei and the cerebral cortex.
Hyaline cartilage
(hi
9
ah-līn) ±e most abundant cartilage type in the
body; provides firm support with some pliability.
Hydrochloric acid (HCl)
(hi
0
dro-klor
9
ik) Acid that aids protein diges-
tion in the stomach; produced by parietal cells.
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