590 Introduction to Anatomy and Physiology
heart block a condition in which the impulses traveling
from the SA node to the ventricles are delayed,
intermittently blocked, or completely blocked by the
AV node
heart murmurs extra or unusual sounds heard by a
stethoscope during a heartbeat that may be harmless or
indicative of a problem with one of the heart valves
heat a sign of infl ammation
heat capacity the quantity of heat required to raise the
temperature of 1 gram of material by 1°C
helper T cell T lymphocyte that helps activate cytotoxic
T cells and B cells
hematocrit (hee-MAT-oh-krit) the percentage of the total
blood volume that is composed of red blood cells
hematopoiesis (HEE-ma-toh-poy-EE-sis) process of
blood cell formation
heme (heem) the iron molecule present in hemoglobin
hemodialysis (HEE-moh-digh-AL-i-sis) a procedure for
removing metabolic waste products from the body; blood
is withdrawn from an artery, pumped through a dialyzer,
and then returned to the patient through a vein
hemoglobin (HEE-moh-GLOH-bin) an essential
molecule of the red blood cell that serves as a binding
site for oxygen and carbon dioxide; composed of two
molecules: globin and heme
hemolysis (hee-MAHL-i-sis) the rupture of red blood
cells as a result of disease or old age
hemophilia (HEE-moh-FIL-ee-a) a condition in which
blood does not clot properly due to the absence of a
clotting factor
hemorrhagic stroke (HEM-oh-RAJ-ik) a stroke that
occurs when one of the arteries in the brain ruptures,
causing bleeding in the brain
hemostasis (HEE-moh-STAY-sis) the sequence of events
that causes a blood clot to form and bleeding to stop
hepatitis a disease characterized by infl ammation of and
damage to the liver
hepatocyte (HEHP-a-toh-sight) a liver cell
Hering-Breuer refl ex (HER-ing BROY-er) an involuntary
impulse triggered by stretch receptors in the bronchioles
and alveoli that halts inspiration and initiates exhalation
hernia a balloon-like section of the lining of the abdominal
cavity that protrudes through a hole or weakened section
of the muscles in the abdomen
herpes a viral infection that produces small, painful,
blisterlike sores
herpes simplex virus type 1 the form of herpes that
generates cold sores or fever blisters around the mouth
herpes simplex virus type 2 the genital form of herpes
herpes varicella (VAIR-i-SEHL-a) a highly contagious,
common childhood disease that is characterized by
extremely itchy, fl uid-fi lled blisters; chickenpox
herpes zoster (ZAHS-ter) a disease that involves a
painful, blistering rash accompanied by headache, fever,
and a general feeling of unwellness; shingles
high-risk HPVs type of HPV infections known to
sometimes cause cancer
hilum (HIGH-lum) the part of an organ, often indented,
where vessels enter and exit; found on lymph node,
spleen, kidney, lung, and other organs
hinge joint type of diarthrosis that allows only hinge-like
movements in forward and back directions
histamines (HIS-ta-meenz) molecules that trigger a
reaction to irritation of the nasal membranes, which
produces nasal congestion and drainage
histology the study of tissues
histone (HIS-tohn) a small protein that binds to DNA and
helps it coil
homeostasis (HOH-mee-oh-STAY-sis) a state of
regulated physiological balance
homeostatic imbalance a state in which there is a
diminished ability for the organ systems to keep the
body’s internal environment within normal ranges
homeostatic mechanisms the processes that maintain
homeostasis
homologous chromosomes (hoh-MAHL-uh-gus) a
pair of chromosomes that have the same genes in the
same relative positions (and possibly different alleles,
alternative forms of the genes that arise through
mutation); one member of the pair comes from the
mother and one from the father
hormonal control type of endocrine control in which
endocrine organs are stimulated by hormones from other
endocrine organs, starting with the hypothalamus
hormones chemical messengers secreted by the
endocrine glands
human anatomy the study of the form or structure of the
human body
human chorionic gonadotropin (hCG) (kor-ee-AHN-ik
GOH-nad-oh-TROH-pin) a hormone secreted by
the trophoblast cells of the embryo that prevents
deterioration of the corpus luteum and stimulates
progesterone production in the placenta
human genome the DNA sequence of a human
human immunodefi ciency virus (HIV) the virus that
causes AIDS
human papillomavirus (HPV) a sexually transmitted
disease that causes warts, especially on the genitals,
and that can cause cervical cancer; however, the virus
usually is asymptomatic
human physiology the study of how humans function
internally
humerus (HYOO-mer-us) major bone of the upper arm
humoral control type of endocrine control in which levels
of various substances in body fl uids are monitored for
homeostatic imbalance
humoral immunity immunity associated with free
antibodies that circulate in the blood; antibody-mediated
immunity
hyaline cartilage (HIGH-a-lin) type of cartilage that forms
the smooth covering on the ends of long bones
hydrogen bond electrical interactions between the positive
region around the hydrogen atom of a water molecule and
the negatively charged region of another molecule
hydrophilic (HIGH-droh-FIL-ik) term that describes a
molecule that can form favorable hydrogen bonds with
water
hydrophobic (HIGH-droh-FOH-bik) term that describes
a molecule that cannot form favorable hydrogen bonds
with water
hydrostatic pressure the pressure exerted by a liquid as
a result of its potential energy
hypercalcemia (HIGH-per-kal-SEE-mee-a) a condition
caused by the hypersecretion of parathryroid hormone
(PTH), leading to increased blood calcium levels and
increased calcium absorption by the kidneys
hyperextension backward movement of a body segment
past anatomical position in the sagittal plane
hyperglycemia (HIGH-per-gligh-SEE-mee-a) a condition
in which blood glucose levels become elevated
hyperopia (HIGH-per-OH-pee-a) the condition that
results from a fl attened eyeball shape; farsightedness