Bma Illustrated Medical Dictionary

sievertA unit for measuring doses of

ionizing radiation. (See radiation units).

sightSee vision.

sight, partialLoss of vision short of

total blindness. Partial sight may involve

loss of visual acuityand/or visual field.

sigmoid colonThe S-shaped part of

the colon, in the lower abdomen, extend-

ing from the brim of the pelvis, usually

down to the 3rd segment of the sacrum.

It is connected to the descending colon

above, and the rectum below.

sigmoidoscopyA form of endoscopy in

which a viewing instrument is inserted

through the anus to examine the rectum

and sigmoidcolon.

signAn objective indication of a dis-

ease or disorder (for example, jaundice)

that is observed or detected by a doctor,

as opposed to a symptom(for example,

pain), which is noticed by the patient.

sildenafilCommonly known by its brand

name Viagra, a drug used in the treat-

ment of impotence. Because of the risk

of potentially serious side effects in cer-

tain people, the drug must only be used

on medical advice.

siliconeA long-chain, carbon-containing

compound of silicon and oxygen. Synth-

etic silicones are sometimes used as

implants in cosmetic surgery.

silicosisA lung disease caused by the

inhalation of dusts containing silica.

(See also pneumoconiosis.)

silver sulfadiazineAn antibacterial

drugapplied as a cream to prevent infec-

tionafter skin grafts or in burns, leg

ulcers, and pressure sores. Side effects

may include permanent grey skin dis-

coloration, rashes, or itching.

simvastatinA lipid-lowering drugthat

acts on the liver enzymes that produce

cholesterol. It may cause bowel upsets,

headaches, and muscle pains.

sinewA nonmedical term for a tendon.

singer’s nodes Small, greyish-white

nodules that develop on the vocal cords

as the result of constant voice strain. In

acute cases, treatment consists of rest-

ing the voice. In chronic cases, surgical

removal of the nodes may be necessary.

sinoatrial nodeThe natural pacemaker

of the heart. The sinoatrial node consists

of a cluster of specialized muscle cells

in the right atrial wall. These cells regu-

larly emit electrical impulses, which

initiate the contractions of the heart.

sinusA cavity in a bone, in particular

one of the air-filled spaces in the bones

surrounding the nose (see sinus, facial).

The term sinus also refers to any wide

channel that contains blood, or to an

abnormal, often infected, tract.

sinus bradycardiaA slow, but regular

heart-rate (less than 60 beats per min-

ute) caused by reduced electrical activity

in the sinoatrial node. Sinus bradycardia

is normal in athletes, but in others it may

be caused by hypothyroidism, a myo-

cardial infarction, or by drugs such as

beta-blockersor digoxin.

sinus, facialAny of the air-filled cavi-

ties in the bones surrounding the nose.

These include 2 frontal sinuses in the

SIEVERT SINUS, FACIAL

S

SINUS, FACIAL

FRONT VIEW SIDE VIEW

Frontal

sinus

Frontal

sinus

Maxillary

sinus

Maxillary

sinus

Sphenoid

sinus

Ethmoid

sinuses

Ethmoid

sinuses