Glossary G-9pituitary gland. The hypothalamus regulates the
pituitary gland and contributes to the regulation of the
autonomic nervous system, among its many functions.
hypothermia (hi 0 p ̆o-ther 9 me- ̆a) A low body
temperature. This is a dangerous condition
that is defended against by shivering and other
physiological mechanisms that generate body heat.
hypoventilation (hi 9 po-ven-ti-la 9 shun) Inadequate
pulmonary ventilation, such that the plasma
concentration of carbon dioxide (partial pressure of
carbon dioxide) is abnormally increased.
hypovolemic (hi 0 po-vo-le 9 mik) shock A rapid fall
in blood pressure as a result of diminished blood
volume.
hypoxemia (hi 0 pok-se 9 me- ̆a) A low oxygen
concentration of the arterial blood.
hypoxic (hi-pok 9 sik) drive The stimulation of
breathing by a fall in the plasma concentration of
oxygen (partial pressure of oxygen), as may occur at
high altitudes.I
ileogastric (il 0 e-o-gas 9 trik) reflex The reflex in
which distension of the ileum causes decreased
gastric motility.
immediate hypersensitivity Hypersensitivity
(allergy) that is mediated by antibodies of the IgE
class and that results in the release of histamine and
related compounds from tissue cells.
immunization (im 0 y ̆u-n ̆ı-za 9 shun) The process of
increasing one’s resistance to pathogens. In active
immunity, a person is injected with antigens that
stimulate the development of clones of specific B
or T lymphocytes; in passive immunity, a person
is injected with antibodies made by another
organism.
immunoassay (im 0 y ̆u-no-as 9 a) Any of a number of
laboratory or clinical techniques that employ specific
bonding between an antigen and its homologous
antibody in order to identify and quantify a substance
in a sample.
immunoglobulins (im 0 y ̆u-no-glob 9 y ̆u-linz)
Subclasses of the gamma globulin fraction of plasma
proteins that have antibody functions, providing
humoral immunity.
immunosurveillance (im 0 y ̆u-no-ser-va 9 lens) The
function of the immune system to recognize and
attack malignant cells that produce antigens not
recognized as “self.” This function is believed to be
cell mediated rather than humoral.
implantation (im 0 plan-ta 9 shun) The process by
which a blastocyst attaches itself to and penetrates
the endometrium of the uterus.
incretins Hormones secreted by the gastrointestinal
tract that stimulate the pancreatic islets to secrete
insulin. This causes the plasma insulin to rise
ahead of the arrival of food-derived glucose. The
incretins have been identified as glucose-dependent
insulinotropic peptide (GIP) and glucagon-like
peptide-1 (GLP-1).
infarct (in 9 farkt) An area of necrotic (dead) tissue
produced by inadequate blood flow (ischemia).
inhibin (in-hib 9 in) Believed to be a water-soluble
hormone secreted by the seminiferous tubules
of the testes that specifically exerts negative
feedback control of FSH secretion from the anterior
pituitary.
innate immunity Also called nonspecific
immunity, this refers to the parts of the immune
system that are inherited and can combat pathogens
without prior exposure to them.hyaline (hi 9 ̆a-l ̄ın) membrane disease A disease
affecting premature infants who lack pulmonary
surfactant. It is characterized by collapse of the
alveoli (atelectasis) and pulmonary edema; also
called respiratory distress syndrome.
hydrocortisone (hi 0 dr ̆o-kor 9 t ̆ı-s ̄on) The principal
corticosteroid hormone secreted by the adrenal
cortex, with glucocorticoid action; also called
cortisol.
hydrolysis (hi-drol 9 i-sis) The splitting of a larger
molecule into its subunits, in a reaction that also
results in the breaking of a water molecule.
hydrophilic (hi 0 dr ̆o-fil 9 ik) Denoting a substance
that readily absorbs water; literally, “water loving.”
hydrophobic (hi 0 dr ̆o-fo 9 bik) Denoting a substance
that repels, and that is repelled by, water; literally,
“water fearing.”
hyperbaric (hi 0 per-bar 9 ik) oxygen Oxygen gas
present at greater than atmospheric pressure.
hypercapnia (hi 0 per-kap 9 ne- ̆a) Excessive
concentration of carbon dioxide in the blood.
hyperemia (hi 0 per-e 9 -me- ̆a) Excessive blood flow
to a part of the body.
hyperglycemia (hi 0 per-gli-se 9 me- ̆a) An
abnormally increased concentration of glucose in the
blood.
hyperkalemia (hi 0 per-ka ̆-le 9 me- ̆a) An abnormally
high concentration of potassium in the blood.
hyperopia (hi 0 per-o 9 pe- ̆a) A refractive disorder in
which rays of light are brought to a focus behind the
retina as a result of the eyeball being too short; also
called farsightedness.
hyperplasia (hi 0 per-pla 9 ze- ̆a) An increase in organ
size because of an increase in the number of cells as
a result of mitotic cell division.
hyperpnea (hi 0 perp 9 ne- ̆a) Increased total minute
volume during exercise. Unlike hyperventilation, the
arterial blood carbon dioxide values are not changed
during hyperpnea because the increased ventilation is
matched to an increased metabolic rate.
hyperpolarization (hi 0 per-po 0 lar- ̆ı-za 9 shun)
An increase in the negativity of the inside of a cell
membrane with respect to the resting membrane
potential.
hypersensitivity (hi 0 per-sen 0 s ̆ı-tiv 9 ̆ı-te) Another
name for allergy; an abnormal immune response
that may be immediate (due to antibodies of the IgE
class) or delayed (due to cell-mediated immunity).
hypertension (hi 0 per-ten 9 shun) High blood
pressure. Classified as either primary, or essential,
hypertension of unknown cause or secondary
hypertension that develops as a result of other,
known disease processes.
hypertonic (hi 0 per-ton 9 ik) Denoting a solution
with a greater solute concentration, and thus a greater
osmotic pressure, than plasma.
hypertrophy (hi-per 9 tr ̆o-fe) Growth of an
organ because of an increase in the size of its cells.
hyperventilation (hi-per-ven 0 t ̆ı-la 9 shun) A high
rate and depth of breathing that results in a decrease
in the blood carbon dioxide concentration to below
normal.
hypotension (hi 0 po-ten 9 shun) Abnormally low
blood pressure.
hypothalamo-hypophyseal (hi 0 po-th ̆a-lam 9 o-
hi 0 po-f ̆ı-se 9 al) portal system A vascular system that
transports releasing and inhibiting hormones from
the hypothalamus to the anterior pituitary.
hypothalamo-hypophyseal tract The tract of
nerve fibers (axons) that transports antidiuretic
hormone and oxytocin from the hypothalamus to the
posterior pituitary.
hypothalamus (hi 0 po-thal 9 ̆a-mus) An area of
the brain lying below the thalamus and above thehematopoiesis (he-ma-to-poy-e 9 sis) The formation
of new blood cells, including erythropoiesis (the
formation of new red blood cells) and leukopoiesis
(the formation of new white blood cells).
heme (h ̄em) The iron-containing red pigment that,
together with the protein globin, forms hemoglobin.
hemoglobin (he 9 m ̆o-glo 0 bin) The combination
of heme pigment and protein within red blood cells
that acts to transport oxygen and (to a lesser degree)
carbon dioxide. Hemoglobin
also serves as a weak buffer within red blood cells.
Henderson-Hasselbalch (hen 9 der-son-has 9 el-balk)
equation A formula used to determine the blood pH
produced by a given ratio of bicarbonate to carbon
dioxide concentrations.
Henry’s law The statement that the concentration
of gas dissolved in a fluid is directly proportional to
the partial pressure of that gas.
heparin (hep 9 ar-in) A mucopolysaccharide found
in many tissues, but in greatest abundance in the lungs
and liver. It is used medically as an anticoagulant.
hepatic (h ̆e-pat 9 ik) Pertaining to the liver.
hepatitis (hep 0 ̆a-ti 9 tis) Inflammation of the liver.
Hering-Breuer reflex A reflex in which distension
of the lungs stimulates stretch receptors, which in
turn act to inhibit further distension of the lungs.
hermaphrodite (her-maf 9 r ̆o-d ̄ıt) An organism with
both testicular and ovarian tissue.
heterochromatin (het 0 ̆e-ro-kro 9 m ̆a-tin) A
condensed, inactive form of chromatin.
hiatal hernia (hi-a 9 tal her 9 ne- ̆a) A protrusion of
an abdominal structure through the esophageal hiatus
of the diaphragm into the thoracic cavity.
high-density lipoproteins (lip 0 o-pro 9 te-inz)
(HDLs) Combinations of lipids and proteins that
migrate rapidly to the bottom of a test tube during
centrifugation. HDLs are carrier proteins that are
believed to transport cholesterol away from blood
vessels to the liver, and thus to offer some protection
from atherosclerosis.
histamine (his 9 t ̆a-m ̄en) A compound secreted by
tissue mast cells and other connective tissue cells
that stimulates vasodilation and increases capillary
permeability. It is responsible for many of the
symptoms of inflammation and allergy.
histocompatibility (his 0 to-kom-pat 0 ̆ı-bil 9 ̆ı-te)
antigens A group of cell-surface antigens found
on all cells of the body except mature red blood
cells. They are important for the function of
T lymphocytes, and the greater their variance, the
greater will be the likelihood of transplant rejection.
histone (his 9 to ̄on) A basic protein associated with
DNA that is believed to repress genetic expression.
homeostasis (ho 0 me-o-sta 9 sis) The dynamic
constancy of the internal environment, the
maintenance of which is the principal function of
physiological regulatory mechanisms. The concept of
homeostasis provides a framework for understanding
most physiological processes.
homologous (h ̆o-mol 9 - ̆o-gus) chromosomes The
matching pairs of chromosomes in a diploid cell.
hormone (hor 9 m ̄on) A regulatory chemical
produced in an endocrine gland that is secreted into
the blood and carried to target cells that respond to
the hormone by an alteration in their metabolism.
hormone-response element A specific region
of DNA that binds to a particular nuclear hormone
receptor when that receptor is activated by
bonding with its hormone. This stimulates genetic
transcription (RNA synthesis).
humoral immunity (hyoo 9 -mor-al ̆ı-myoo 9 n ̄ı-te)
The form of acquired immunity in which antibody
molecules are secreted in response to antigenic
stimulation (as opposed to cell- mediated immunity).fox36375_glo_G1-G19.indd 9fox36375_glo_G1-G19.indd 9 2/4/15 12:29 PM2/4/15 12:29 PM