Cells, Tissues & Organs

Building Materials for the Human Body

heart muscle tissue
Nuclei from the cells are readily apparent in this heart muscle tissue.. STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY / Getty Images

Medical and first aid articles regularly use terms that don't always make sense out of context or if you're just not familiar with them. If they don't make sense in the piece, it could completely change how much you understand.

Here to help you with the most basic of all anatomical terms are the basic building materials of the body: cells, tissues, and organs. Once you have these down, we can move on to organ systems or get more specific, like the nervous system.


Cells are the smallest unit of life. To understand what a cell looks like, picture a chicken egg. It has an outer membrane (in the case of an egg, it's a hard shell, but most cells aren't like that); it's filled with nutrient-rich fluid (whites of the egg versus cytoplasm in a cell) and has a nucleus (egg yolk).

Not all cells look alike. Nerve cells are long, thin and covered in myelin, a natural insulation. Muscle cells are thick and elongated. Red blood cells are flat and oval-shaped. The shapes of the cells help them with their individual functions.

Each cell serves a single purpose in the body. Muscle cells contract and nerve cells transmit impulses. Red blood cells bind to oxygen, while white blood cells fight infection.


When cells of a certain type are grouped together, the resulting structure is called tissue. There is muscle tissue, which is made of strands of muscle cells.

Adipose tissue is one layer of skin made of fat cells. Connective tissue is a term used for various types of tough, fibrous matter like tendons or ligaments.

Most of the time in first aid, we refer to tissues more than cells. Cells are typically microscopic, while tissues can be seen and manipulated.

When you look at a laceration to determine if it needs stitches, you are looking for adipose tissue in the wound. Indeed, stitches hold together the tissue, not the individual cells.


When different types of tissues are organized together to perform a complex function, it's called an organ. The heart is an organ. It has muscle tissue, connective tissue and nerve tissue all working together to pump blood.

Organs can do more than one function and each function can be pretty complicated. The eyes sense color, movement and light. They move and focus. The biggest organ in (or on) the human body is the skin. It's a great example of layers of tissue working together to do several functions:

  • holds in fluids
  • regulates heat
  • senses heat and pressure

The organization of the anatomy starts with these three building blocks. Whether your talking about delicate tissue of the brain or the hardness of bone, it's still made of cells banded together into tissue and organized into organs.

Continue Reading