Webster's New World Medical Dictionary

part of the blood; leukapheresis, harvesting leuko-
cytes or white blood cells; granulocytapheresis, har-
vesting granulocytes; lymphocytapheresis,
harvesting lymphocytes; lymphoplasmapheresis,
harvesting lymphocytes and plasma; and platelet-
pheresis, harvesting platelets.
aphonia
Inability to speak.
apical
The adjective for apex, the tip of a pyram-
idal or rounded structure, such as the lung or the
heart. For example, an apical lung tumor is a tumor
located at the top of the lung.
aplasia
Failure to develop. See also 
atrophy.
aplasia of the breast
See 
amastia.
aplastic anemia
See 
anemia, aplastic.
apnea
The absence of breathing (respiration).
apnea, sleep
See 
sleep apnea.
apophysitis calcaneus
Inflammation of the
growth plate of the calcaneus, the bone at the back
of the heel, where the Achilles tendon attaches.
Apophysitis calcaneus occurs mainly in older chil-
dren and adolescents, especially active boys. It can
be very painful, although it may be dismissed as
“growing pains.” Treatment includes activity limita-
tion, medication, shoe inserts, heel lifts, and some-
times casting if it becomes especially severe.
Fortunately, it usually disappears as the child gets
older. Also known as Sever condition. See also
Achilles tendon.
apoptosis
A form of cell death in which a pro-
grammed sequence of events leads to the elimination
27
apoptosis
02_189283 ch01.qxp 4/18/08 10:03 PM Page 27
http://www.rashidislamiccenter.com
http://www.allofislam.com/

---

of cells without releasing harmful substances into
the surrounding area. Apoptosis plays a crucial role
in developing and maintaining the health of the body
by eliminating old cells, unnecessary cells, and
unhealthy cells. The human body replaces perhaps
one million cells per second. Too little or too much
apoptosis can play a role in many diseases. When
apoptosis does not work correctly, cells that should
be eliminated may persist and become immortal, 
for example, in cancer and leukemia. When apopto-
sis works overly well, it kills too many cells and
inflicts grave tissue damage. This is the case in
strokes and neurodegenerative disorders such as
Alzheimer’s, Huntington’s, and Parkinson’s diseases.
Also known as programmed cell death and cell 
suicide.
appendectomy
Surgical removal of the appen-
dix. An appendectomy is performed because of
probable appendicitis. See also 
appendicitis.
appendicitis
Inflammation of the appendix, usu-
ally associated with infection of the appendix.
Appendicitis often causes fever, loss of appetite, and
pain. Appendicitis may be suspected because of the
medical history and physical examination. The pain
of appendicitis can be located in various areas of
the belly. If the appendix ruptures and infection
spreads throughout the abdomen, the pain becomes
widespread as the entire lining of the abdomen
becomes inflamed. Ultrasonography and computer-
ized tomography may be helpful in diagnosis.