CELL
CELL DIVISION
and
osteoarthritis.
Side effects include
nausea and diarrhoea. Gastrointestinal
discomfort may also occur, but can be
minimized by taking the drug with food.
cell
The 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
proteins
made in the
cell. Inside the nucleus are the
chromo-
som es
, 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 division
The processes by which
cells multiply.
Mitosis
is the most com-
mon form of cell division, giving rise to
CELL
Nucleolus
Nucleus
Centrioles
Mitochondrion
Golgi
complex
Endoplasmic
reticulum
Ribosomes
Microvilli
Lysosome
Cell
membrane
Vacuole
Vesicle
Peroxisome
Cytoskeleton
115
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