We are going to look at some of the terms that are used when studying cells. The internal structures and their functions will be covered, and we will also look at stem cells and compare adult and embryonic stem cells.


Think back for a minute to when you first started learning the meanings to different word parts in medical terminology. Do you recall what the suffix -logy means? Hopefully you remember that it means the study of. What about the meaning for the combining form, cyto? With some luck, you know it means cells. Putting this together, you would realize that cytology is the study of cells.

There are so many different types of cells in the body. Each cell is composed of many internal structures that allow the cells to carry out their purpose. We are going to look at some of the main components of the cell and their functions.

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Parts of the Cell

Let’s think about how a factory operates for a minute. Each product starts out as a set of directions that everyone in the factory has to follow in order to create the product. Every worker in the factory is responsible for adding one part in the process of creating the product. As long as the directions are accurate and everyone follows them correctly, the factory puts out the desired product. This is a lot like the structure and function of our cells.

Within each cell is a starting point where the instructions can be found. The nucleus is the brain of the cell that contains the instructions for how each part of the cell should function. We refer to these instructions as our DNA.

The nucleus is the processing center that converts DNA into RNA. RNA is like a messenger that tells the other parts of the cell what to do when making the desired product. The RNA is converted into protein as it exits the nucleus. Protein is the product that the cell wants to produce.

The ribosomes are the sites where protein synthesis takes place. Most ribosomes are located on another structure in the cell called the endoplasmic reticulum, or ER for short. The ER with ribosomes is called the rough ER, and that is where protein is made. The ER without ribosomes is called the smooth ER, and that is where lipids or fats are made. Now that the cell has its product (protein), it has to package it so that it can be sent out of the cell.

The protein is now sent to the Golgi apparatus, where it is refined, packaged and transported towards the exit from the cell. The Golgi apparatus is a lot like the inspector, packer and package handler all in one. The proteins are now enclosed in transport vesicles, which are a lot like delivery trucks.

The transport vesicles carry the proteins to the surface of the cell for them to be released from the cell. The surface of the cell is what we refer to as the cell membrane. The cell membrane is like the gate of the cell, just like most factories have gates to determine what can come in and what goes out. It is there as a safeguard against everything outside the cell and an enclosure for everything inside the cell.

The cell membrane is a phospholipid bilayer, which means that only certain items are able to easily cross it. All of the internal structures inside of the cell are in what is called the cytoplasm, which is the gel-like substance inside of the cell.

Stem Cells

If you follow science or politics, then you have heard quite a bit about stem cell research. You may have wondered, ‘What are stem cells?’ and ‘Why the big fuss?’ Here is part of the answer. Stem cells are cells in the body that have yet to become any particular type of cell.

Stem cells have the ability to become different types of cells in the body. In other words, these are cells that can differentiate to become nerve cells, muscle cells, skin cells, etc. There are two major categories of stem cells.

The first category is adult stem cells. These are stem cells that are present in our bodies after we have completely developed. Adult stem cells have the ability to become any type of cell that originates from the tissue or organ in which the stem cell is located.

For instance, a hematopoietic stem cell can become any type of blood cell. But they are limited to only becoming one of those types of cells. So, adult stem cells have started to differentiate into a type of cell, but they haven’t completely become one type of cell.

The second category is embryonic stem cells. These are stem cells that are present in an embryo during development in the womb. They are pluripotent, which means they have the ability to become every type of cell in the body. These cells can differentiate to become whatever cells the body needs.

Lesson Summary

We learned quite a bit about the cells in this lesson. Cytology is the study of the cell. We now know that the nucleus is the center of the cell that contains the instructions for the cell. DNA is the instruction set for the cell. It gets converted into RNA, which is a messenger, and then into protein, which is the final product of the cell.

Ribosomes are the site of protein synthesis. They are usually located on the endoplasmic reticulum, or ER. The Golgi apparatus refines, packages and ships the proteins in transport vesicles, which are like delivery trucks. The gate of the cell is the cell membrane, which determines what can enter and exit the cell. Cytoplasm is the gel-like substance inside the cell where internal structures can be found.

We also discussed the fact that stem cells are cells that are capable of becoming more than one type of cell. Adult stem cells are cells that can become any type of cell that originates from the tissue or organ it comes from. Embryonic stem cells are cells present in embryos during development that haven’t differentiated yet. They are pluripotent, meaning that they can become any type of cell in the body.

Learning Outcomes

Once you’ve finished with this lesson, you should have the ability to:

  • Define cytology
  • Describe the components of cells and their functions
  • Recall what stem cells are
  • Differentiate between adult and embryonic stem cells