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128 Human Body

A human body is made up of 100 trillion. CELLS of

different types. Similar cells are grouped to form tissue,

and tissues form. ORGANS. Using modern. IMAGING

technology, we can look into the body and see it work.

WHAT CONTROLS CELLS?

Most cells have a control centre called a nucleus. The

nucleus holds the DNA which makes up the genes.

Depending on the type of cell, certain genes are

switched on or off. The active genes send instructions

out of the nucleus, controlling all the chemical

reactions that happen in the rest of the cell.

WHAT MAKES HUMANS SPECIAL?

Humans are unique in the animal world. We are the

only mammals to walk on two legs, our brains are

unusually large, and our skin is almost hairless. Yet

in most ways we are just like other mammals, with

two pairs of limbs, two eyes and ears, and the usual

mammalian internal organs.

WHY ARE WE ALL DIFFERENT?

Apart from identical twins, no two people in the

world are exactly alike. We differ in many subtle

ways because we each have a unique set of genes,

inherited from our mother and father. Our genes

control the way we grow and develop from embryos

into adults.

WHAT IS TISSUE?

Cells of the same type are often grouped together in

a pattern, to form tissue. Muscle is made up of bundles

of muscle cells. Skin consists of sheets of skin cells.

Blood is a liquid tissue of cells suspended in a watery

fluid. There are four main types: epithelial tissue,

connective tissue, muscular tissue, and nervous tissue.

MRI BODY SCAN 3

This magnetic resonance imaging (MRI) scan shows the

insides of a nine-year-old boy. It was produced using a

scanning machine containing giant magnets, which cause

atoms in the body to release radio waves that the scanner

detects. This image of the whole body is made up of a number of

MRI scans made down the length of the body and then put together.

The microscopic units that make up all

living things are called cells. In the body,

there are hundreds of different types of cell,

each designed to perform a specific task.

4 FIBROBLAST CELLS

These cells are called

fibroblasts and are found

in connective tissue,

which holds together

and supports the body’s

organs. This picture has

been coloured to

show each cell’s

nucleus (in blue)

and cytoplasm, or

body (in orange).

BODY

CELLS

The bladder

is the organ

where urine is

stored until

released

during

urination

The brain

controls the

body’s activity

and produces

thought and

emotion

Vertebrae

make up the

backbone

The bones

of the skeleton

support the

body and give

it shape

The liver is a

large organ that

processes body

chemicals

The lungs

take in oxygen

from the air

Tongue