TYPES OF HUMAN CELL
NERVE CELLS
The cells that make up the nervous system and the brain are nerve cells
or neurons. Electrical messages pass between nerve cells along long filaments
called axons. To cross the gaps between nerve cells (the synapse) that electrical signal is converted into a
chemical signal. These cells enable us to feel sensations, such as pain, and
they also enable us to move.
BONE CELLS
The cells that make up bone matrix – the hard structure that makes bones
strong – consist of three main types. Your bone mass is constantly changing and
reforming and each of the three bone cells plays its part in this process.
First the osteoblasts, which come from bone marrow, build up bone mass and
structure. These cells then become buried in the matrix at which point they become known as osteocytes. Osteocytes make up around 90 per cent of the cells in
your skeleton and are responsible for maintaining the bone material. Finally,
while the osteoblasts add to bone mass, osteoclasts are the cells capable of
dissolving bone and changing its
mass.
PHOTORECEPTOR CELLS
The cones and rods on the retina at the back of the eye are known as
photoreceptor cells. These contain
light- sensitive pigments that convert the image that enters the eye into nerve
signals, which the brain interprets as pictures. The rods enable you to
perceive light, dark and movement, while the cones bring colour to your world.
LIVER CELLS
The cells in your liver are responsible for regulating the composition of
your blood. These cells filter out
toxins as well as controlling fat, sugar and amino acid levels. Around 80 per cent of the liver’s mass
consists of hepatocytes, which are the liver’s specialised cells that are
involved with the production of proteins
and bile.
MUSCLE CELLS
Therearethreetypes of muscle cell – skeletal, cardiac and smooth–and
eachdiffers depending onthefunction it
performs and its location inthe body. Skeletal muscles contain long fibres
thatattach to bone. When triggered by anervesignal, the muscle contracts and
pulls thebone withit, making you move. Wecan control skeletal muscles because they are voluntary. Cardiac muscles, meanwhile, areinvoluntary, whichis fortunate because they areused to keep your heart
beating. Found in thewalls of
theheart, these muscles createtheir own stimuli to contract without input from
the brain. Smooth muscles, whicharepretty slowand also involuntary, makeup the
linings of hollow structures suchas blood vessels and your digestive tract. Their wave-likecontraction aids the
transport of blood around thebody and the digestion
of food.
FAT CELLS
These cells – also known as adipocytes or lipocytes – make up your
adipose tissue, or body fat, which can cushion,
insulate and protect the body. This tissue is found beneath your skin and also
surrounding your other organs. The size of a fat cell can increase or decrease depending on the amount of energy
it stores. If we gain weight the cells fill with more watery fat, and eventually the number of fat cells will begin to
increase. There are two types of adipose tissue: white and brown. The white
adipose tissue stores energy and insulates the body by maintaining body heat.
The brown adipose tissue, on the other hand, can actually create heat and isn’t
burned for energy – this is why animals are able to hibernate for months on end without food.
EPITHELIAL CELLS
Epithelial cells make up the epithelial tissue that lines and protects
your organs and constitute the
primary material of your skin. These tissues form a barrier between the
precious organs and unwanted
pathogens or other fluids. As well as covering your skin, you’ll find
epithelial cells inside your nose, around your lungs and in your mouth.
RED BLOOD CELLS
Unlike all theother cells in your body, your red blood cells (also known
as erythrocytes) do not contain a
nucleus. You aretopped up with around 25 trillion red blood cells – that’s a
third of all your cells, making them
the most common cell in your body.
Formed in the bonemarrow, these cells
are important because they carry
oxygen to all thetissues in your body. Oxygen is carried in haemoglobin,
apigmented protein that gives blood
cells their red colour.
