Medically Reviewed by Dr. Elisabeth Vincent Hamelin
The body is made up of many billions of cells. Different cells can have different looks and tasks. Together, the cells form tissues. There are several different types of tissues, such as muscle tissue, bone tissue, and adipose tissue. The tissues together form organs, such as the heart and lungs.
- 1 Then the cell looks like
- 2 Cell division
- 3 Chromosomes consist of DNA
- 4 Stem cells are immature cells
- 5 Tissues
- 6 Support tissue protects and holds the body together
- 7 Nerve tissue forms nerve signals
Then the cell looks like
A cell consists of several different parts. The various parts are important for the cell to function.
The cell membrane
The outermost shell of the cell is called cell membrane. The cell membrane is not completely dense. Small particles can be sent out or in through special channels. The cell membrane also contains so-called receptors that receive important information to the cell’s interior.
The cytoplasm is located inside the cell membrane
Inside the cell membrane is a viscous liquid called cytoplasm. The cytoplasm consists of water, salts, nutrients and proteins. The cytoplasm also contains several small structures that the cell needs to survive. The different parts are called organelles, and each type of organelle has its special purpose.
These are some of the most important organelles:
- Mitochondria that form energy for the body’s important processes.
- Endoplasmic network. Here the production and transport of various substances takes place.
- Ribosomes that form proteins. The ribosomes are found in the cytoplasm and also in the endoplasmic network.
- The Golgi apparatus that receives, stores and sends proteins away.
- Lysosomes that take care of old cell parts and bacteria in the cell.
The cell nucleus contains your genes
The cytoplasm also contains the cell nucleus. The cell nucleus contains the genetic mass, DNA. Parts of the genetic mass are called genes. The genes contain information on how the body should be built up and function. It is the genes that determine how you look and contribute to what traits you have.
Most cells have a cell nucleus, but the red blood cells lack a cell nucleus. Some cells have several nuclei, such as the cells that build up the skeletal muscles.
Different cells have different tasks
Not all cells are the same. They have different tasks and therefore they also have a slightly different appearance. Nerve cells, for example, have projections similar to long strands. Some cells have flickering hair on the surface, such as the cells in the trachea. The body also contains, for example, muscle cells, blood cells and bone cells, all of which are adapted to fulfill their various tasks.
All cells have a limited life span. Cells that die are replaced by new cells formed by dividing cells. This process is called cell division.
It takes different time for different types of cells to renew themselves by division. For example, it takes two to four weeks for the top layer of cells on the skin to be replaced. Renewal of liver cells takes longer. Some cells do not divide at all and cannot be renewed by cell division, such as nerve cells.
The genes control cell division
Cell division is tightly regulated and controlled by genes. Some genes control when the cell divides. Other genes control when it’s time for the cell to stop dividing. There are also genes that control when the cell needs to repair a damage so that the damage is not passed on at the next cell division.
Sometimes cell division does not work properly
For the most part, cell division works as it should, but sometimes it can be wrong. There may have been damage inside the cell so that it has changed. Changed cells that continue to divide can lead to cancer. Here you can read more about how cancer occurs.
Chromosomes consist of DNA
The genetic mass, DNA, is in the nucleus of the cell. DNA consists of thin filaments. When dividing the cell, the threads roll together into chromosomes. A cell usually contains 23 pairs of chromosomes, thus a total of 46. In each pair, one chromosome comes from the mother, and the other from the father.
X chromosomes and γ chromosomes
One of the chromosomes is called sex chromosomes. In women, both sex chromosomes are the same and are called X chromosomes. Men have an X chromosome and a Y chromosome.
Egg cells and sperm contain half the amount of genetic material, that is 23 chromosomes each. When the egg cell is joined with a sperm at fertilization, a cell with a complete chromosome set, 23 pairs, is thus formed, 46 in total.
Sometimes the number of chromosomes is more or less than 46
Some people have chromosome abnormalities. This means that you do not have 46 whole chromosomes but more or fewer chromosomes. It may also mean that the chromosomes have a different shape. Sometimes, chromosome abnormalities can mean that you have a disability and that different organs in the body do not function properly. Sometimes, chromosome abnormalities have no effect on a person’s health.
Stem cells are immature cells
Stem cells are cells that have not specialized. This means that it is not yet decided how they will work. Stem cells can be divided and developed into many different types of cells.
An embryo contains stem cells during the first few days
An embryo is an egg that has been fertilized and started to divide. The embryo contains stem cells during the first few days. Then every single cell can give rise to a new person. The cells then begin to have more specific properties and develop into, for example, muscle cells, brain cells and skin cells.
The stem cells have several tasks in the body
Stem cells have several tasks. For example, they make young people grow. Adult stem cells can repair cells that have died or are damaged. There are stem cells in the skin and intestinal mucosa that can form new tissue. The ability of stem cells to form different types of cells decreases with the age of a person.
Stem cell transplantation is used as a treatment for certain types of cancer and other unusual diseases. Here you can read more about it.
Tissues are made up of cells that have similar appearance and properties. Various tissues then build up the organs and body parts.
The body’s tissues can be divided into four groups:
- supporting tissue
- nerve tissue
- muscle tissue
Epithelial tissue is found in skin and mucous membranes
Epithelial tissue is found on the body’s surfaces, both inside and outside. It acts as a shelter. For example, epithelium is found in the skin, the mucous membranes of the mouth, the trachea and the gastrointestinal tract.
In epithelial tissue, the cells lie tightly on top of a layer called basement membrane. The basement membrane is stuck in the tissues that are underneath. The epithelium becomes more resilient the more layers it has. The cells closest to the basement membrane are renewed by cell division. In this way, the epithelium does not disappear when the cells at the top die and become loose over time.
The epithelium has several important tasks
Epithelium such as skin and mucous membranes protect various tissues and organs. Some mucous membranes contain glands that form different types of fluids. For example, the mucous membrane of the mouth contains glands that form saliva and the stomach contains glands that form gastric juice.
Epithelium can also absorb nutrients. The intestinal epithelium is an example of that. Epithelium can also receive different signals for sight, smell, taste and hearing.
Support tissue protects and holds the body together
The most important tasks of the supporting tissues are to support, protect and hold different parts of the body.
Here are the different types of support tissue:
- connective tissue
- adipose tissue
- cartilage tissue
- bone tissue.
Common to all types of support tissue is that the tissue consists of quite a few cells that are in a so-called basic substance. The basic substance is what exists between the cells. In the blood, the plasma is the basic substance and the blood is therefore liquid. In the bone, there are hard calcium crystals in the basic substance and the tissue therefore becomes hard. It is thus the basic substance that determines the properties of the tissue.
Tissues are available in ligaments and tendons
Adhesive tissue contains a lot of fibers that make the tissue both strong and elastic. For example, connective tissue is found in the subcutaneous tissue and in tendons and ligaments.
Adipose tissue stores energy
Adipose tissue contains many cells. The cells can be filled with fat droplets and in this way store energy that the body may need. Adipose tissue is found in the subcutaneous tissue and prevents heat from escaping from the body. Various organs in the abdomen are also protected by adipose tissue.
Cartilage tissue protects the joints
Cartilage tissue is both firm and flexible. Among other things, the tissue covers the surfaces of the joints and makes them more durable. Cartilage tissue is also found in the trachea and between the vertebrae of the spine.
Bone tissue builds up the skeleton
Bone tissue builds up our skeleton. The tissue contains a lot of calcium crystals. It makes it tough and very strong.
Nerve tissue forms nerve signals
The brain, spinal cord and nerves are made up of nerve tissue. The nerve tissue contains nerve cells and so-called glial cells. Nerve cells can form nerve signals. The nerve signals are passed on to other nerve cells or to different muscles. In this way, information is sent between the brain and different parts of the body. The nerve cells therefore have long projections that reach far out of the cell. The projections can be over one meter long. The projections are called axons.
The body contains three types of muscle tissue:
- Skeletal muscles build up the large muscles found in, for example, arms and legs.
- Heart muscles build up the heart.
- Smooth muscles are found, for example, in the walls of the blood vessels, the trachea, the bladder and the gastrointestinal tract.
The cells in the muscle tissue are long. They are called muscle fibers. The muscle becomes shorter as the muscle fibers contract. Then force and movement occur.
Blood is fluid tissue
Blood contains a liquid basic substance called plasma. The blood also contains several different types of cells. One type of cells is the red blood cells. They carry oxygen in the body. The blood also contains various types of white blood cells that participate in the immune system, and platelets that help to deliver the blood.