Cells are the basic unit of life on earth. In humans there are trillions of cells and each cell type has their own structure and function. ( For ultra structure of a human cell please read here ). Each type of a cell has a shape and size based on the function it carries in the body. In multicellular organisms ( organisms with many number of cells) like humans, there is a division of labor among the different body parts. This means different body part’s of our body has a different task to perform. For example, eyes ensure we see all the objects , heart takes the responsibility to pump blood throughout the body etc. So the cells present in particular organ mostly exhibit a unique shape and ensures proper function of that organ.
Interestingly, all the cells are known to contain similar organelles in them but perform a different function depending upon the organ or place they are present. The function of a cell is decided by the proteins and other regulatory components present in the cells at a particular moment, which eventually depends on the expression or regulation of DNA in those cells.
Different types of cells in humans
When one considers the complexity of our body, it is not surprising to know that there are more than 200 types of cells which come sin all sizes and shapes. These tiny little structures are really amazing functional units of cells, they have the ability to work as independent units in producing their own energy and proteins. Apart from this they also work efficiently as a part of the huge network of cells that create tissues, then tissues contribute to form organs and organs work in harmony to create a functional living organism.
Here we will look into small section of cell types present in our body:
Nerve cells: They are the basic unit of nervous system, also called as Neurons which act as communication system of our body. These are thin, long cells which is helpful to carry electrical signal over long distances. Neurons signals between brain, spinal and different body organs. Structurally, neurons can be divided into central body and nerve processes. The central body contains the nucleus and other organelles, whereas the nerve processes are long finger like projections called axons or dendrites that extends away from central body, which helps to transmit nerve signal.
Eye cells : The cells present in the eye are called as rods and cones. They are primarily responsible for detecting light. which send signals to the brain through retinal ganglion cells (RGCs) so the brain can form our perception of images. Rod cells work at low level of light intensity whereas cone cells require high levels of light to function. Rod cell doesn’t help us to see color, which is the sole function of cone cells along with providing the sharpness of the objects. Together rod and cones form the foundation of our normal everyday vision.
Sex cells: Sex cells – egg and sperm, are reproductive cells produced in male and female reproductive organs respectively. Sperms are long slender structures with long tail called flagella, which allows them to move or swim. Female egg or ovum are large structures compared to sperm and are non motile.
Blood Cells: There are three types of blood cells: red blood cells, white blood cells, and platelets. Red blood cells (RBC’s) are doughnut shaped cells present in huge numbers are responsible for transporting of oxygen to all parts of body. White blood cells (WBC’s) have the ability to fight infections by destroying invading pathogens and forms a major part of immune system of our body. Platelets helps in clotting of blood in case of damage to any of our blond vessels.
Muscle cells: These cells can contract and relax to produce movement. Also called as myocytes, muscle cells are long, tubular cells responsible for many functions such as movement and providing support to the body.
Stem Cells : Stems cells are special cells in our body which can either renew themselves or possess the ability to become any of the 200 different cell types of our body. They play a very important role in repair of any damaged tissue or organ due to their ability to divide and replicate innumerable times. This special feature of self renewal of cells can be exploited to repair any damaged tissue or for curing some diseases.
Lifespan of some cell types:
Different types of our cells have different lifespan. Some are worn out quickly and some have longer lifespan. few cell types are replenished by stem cells.
Blood cells : white blood cells have lifespan of less than a day
Skin cells : 30 days
Liver cells: 12-18 months
Muscle cells : 15 Years
Neurons: Lifetime for some nerve cells.