Bma Illustrated Medical Dictionary

and osteoarthritis. Side effects include
nausea and diarrhoea. Gastrointestinal
discomfort may also occur, but can be
minimized by taking the drug with food.
cellThe basic structural unit of all living
organisms. The human body consists of
billions of cells, structurally and function-
ally integrated to perform the complex
tasks necessary for life. In spite of varia-
tion in size and function, most human
cells have a similar basic structure.
Each cell is an invisibly small bag con-
taining liquid cytoplasm, surrounded by
a cell membrane that regulates the pas-
sage of useful substances (such as oxygen
and nutrients) into the cell; and waste
materials (such as carbon dioxide) and
manufactured substances (such as hor-
mones) out of the cell. Some cells, such
as those lining the small intestine, have
microvilli, projections that increase the
cells’ surface area to facilitate absorption.
All cells, except red blood cells, have a
nucleus, a control centre that governs
all major cell activities by regulating the
amount and types of proteinsmade in the
cell. Inside the nucleus are the chromo-
somes, which are made of the nucleic
acid DNA. This contains the instructions
for protein synthesis, which are carried
into the cytoplasm by a type of RNA,

another nucleic acid, and are decoded in

particles called ribosomes. The nucleus

also contains a spherical structure called

the nucleolus, which plays a role in the

production of ribosomes.

The cell also contains various organ-

elles, each with a specific role. Energy is

generated from the breakdown of sug-

ars and fatty acids by mitochondria.

Substances that would damage the cell

if they came into contact with the cyto-

plasm are contained in particles called

lysosomes and peroxisomes. A system

of membranes in the cytoplasm called

the endoplasmic reticulum transports

materials through the cell. Flattened

sacs called the Golgi complex receive

and process proteins dispatched by the

endoplasmic reticulum. Products for

export, such as enzymes and hormones,

are secreted by vesicles at the cell sur-

face. Other materials, water, and waste

products are transported and stored in

the cytoplasm by vacuoles. The cyto-

plasm itself has a network of fine tubes

(microtubules) and filaments (microfil-

aments) known as the cytoskeleton,

which gives the cell a definite shape.

cell divisionThe processes by which

cells multiply. Mitosis is the most com-

mon form of cell division, giving rise to

CELL CELL DIVISION

C

CELL

Nucleus

Centrioles

Mitochondrion

Ribosomes

Golgi
complex

Nucleolus Microvilli

Lysosome

Cell

membrane

Vacuole

Vesicle

Peroxisome

Cytoskeleton

Endoplasmic
reticulum