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Looking inside your body
Under the skin, the human body is made up of about 200 different cell types. These are classified into four tissue types – epithelial, muscle, nerve and connective – and they can vary widely.
Epithelial tissue covers the whole surface of the body. There is not much space between the cells.
Muscle tissue can relax and contract. This ability means they bring about movement.
There are three different muscle tissue categories – smooth muscle, skeletal muscle and cardiac muscle tissue. The cells that make up these tissues are all a little different.
Nerve tissue is made up two cell types:
- A nerve cell that can transmit an electrical pulse is known as a neuron
- A nerve cell that cannot transmit an electrical pulse is called a neuroglia or glial cell, and makes up the support tissues for the neurons
Connective tissue includes bone, cartilage, blood and lymph, as well as other cell types. These different cells have a variety of tasks, like keeping organs in position, cushioning, and forming ligaments and tendons.
Sometimes we need to separate out different types of cells, for example, in blood. If a sample of blood is spun rapidly the red blood cells and platelets sink to the bottom leaving the straw-colored plasma at the top. This is an example of different cells that are not tightly attached to each other.
Other cells in the body are tightly attached to each other, as in cartilage or organs. Cells can be separated in these cases, but it requires a great deal more effort, for example, in a biopsy, where a small piece of tissue is cut and can be viewed under a microscope to see the individual cells.
Which imaging technique?
Different cell characteristics are important when considering the type of medical imaging technique to use to see them.
X-rays are good for showing dense tissues that absorb the X-rays. This is why they are useful for looking at broken bones.
Computed tomography (CT) uses x-rays images, but because they involve more than one image, greater detail of tissues like blood vessels, lungs and bones can be seen.
Magnetic resonance imaging (MRI) can see right through bone and other hard tissues so they can show things like brain tumours, nerve damage and swelling.
Ultrasound scans are good at showing muscle, soft tissue and the difference between solid and fluid-filled spaces.
