calcaneusThe heel bone. Itis one of the
tarsal bones and is the largest bone in
the foot. The Achilles tendonis attached
to the back of the calcaneus.
calciferolAn alternative name for vita-
min D 2 , also known as ergocalciferol
(see vitamin D).
calcificationThe deposition of calcium
salts in body tissues that is part of the
normal process of bone and teeth for-
mation and the healing of fractures.
Calcification also occurs in injured mus-
cles, in arteries affected by atherosclerosis,
and when blood calcium levels are raised
by disorders of the parathyroid glands.
calcification, dentalThe deposition of
calciumsalts in developing teeth. Pri-
mary teeth begin to calcify in a fetus at
between 3 and 6 months gestation; cal-
cification of permanent teeth (other
than the wisdom teeth) begins between
birth and 4 years. Abnormal calcification
occurs in amelogenesis imperfecta, an
inherited disorder of the enamel (see
hypoplasia, enamel), and can also result
from the absorption of high levels of
fluoride (see fluorosis).
calcinosisThe abnormal deposition of
calciumsalts in the skin, muscles, or
connective tissues,forming nodules. The
condition occurs in connective tissue
disorders such as sclerodermaor der-
matomyositis. (See also calcification.)
calcipotriolA derivative of vitamin D,
used in topical preparations for treating
the skin disorder psoriasis.
calcitoninA hormoneproduced by the
thyroid gland that helps to control
blood calciumlevels by slowing loss of
calcium fromthe bones. A synthetic form
of calcitonin is used in the treatment of
Paget’s disease. Calcitonin is also used
to reduce high blood levels of calcium
in hypercalcaemia.
calciumThe body’s most abundant min-
eral, essential for cell function, muscle
contraction, the transmission of nerve
impulses, and blood clotting. Calcium
phosphate is the hard basic constituent
of teeth and bones. Dietary sources of
calcium include dairy products, eggs,
and green, leafy vegetables. Calcium
uptake is facilitated by vitamin D.
The body’s calcium levels are controlled
by parathyroidhormone and calcitonin.Abnormally high levels in the blood
(hypercalcaemia) or abnormally low levels
(hypocalcaemia) may seriously disrupt
cell function, particularly in muscles and
nerves. (See alsomineral supplements.)
calcium channel blockersDrugs used
to treat angina pectoris, hypertension, and
types of cardiac arrhythmia. Side effects
such as headaches, swollen ankles, flush-
ing, and dizziness may occur, but tend
to diminish with continued treatment.
calculusA deposit on the teeth (see
calculus, dental) or a small, hard, crys-
talline mass that is formed in a body
cavity from certain substances in fluids
such as bile, urine, or saliva. Calculi can
occur inthe gallbladder and bile ducts
(see gallstones), the kidneys, ureters, or
bladder (see calculus, urinary tract), or in
the salivary ducts.
calculus, dentalA hard, crust-like de-
posit (also known as tartar) found on
the crowns and roots of the teeth. Cal-
culus forms when mineral salts in saliva
are deposited in existing plaque. Supra-
gingival calculus is a yellowish or white
deposit that forms above the gum mar-
gin, on the crowns of teeth near the
openings of salivary glandducts. Sub-
gingival calculus forms below the gum
margin and is brown or black. Toxins in
calculus cause gum inflammation (see
gingivitis), which may progress to de-
struction of the supporting tissues (see
periodontitis). Calculus is removed by
professional scaling. Attention to oral
hygienereduces recurrence.
calculus, urinary tractA stone in the
kidneys, ureters, or bladder formed from
substances in urine.
Most urinary tract stones are com-
posed of calcium oxalate or other salts
crystallized from the urine. These may
be associated with a diet rich in oxalic
acid (found in leafy vegetables and cof-
fee); high levels of calciumin the blood
as a result of hyperparathyroidism; or
chronic dehydration. Other types of stone
are associated with gout and some can-
cers. An infective stone is usually a result
of chronic urinary tract infection.
In developing countries, bladder stones
usually occur as a result of dietary defi-
ciencies. In developed countries, they
are usually caused by an obstruction toCALCANEUS CALCULUS, URINARY TRACTC