Estimated reading time: 7 minutes
Humans are complex organisms made up of trillions of cells, each with its own structure and function. It is estimated that the number of cells is around 30 trillion.
There are over 200 different cell types in the human body. This means that each cell type has a unique and special function. For this reason, each of the 200 types has a different structure, size, shape, and function.
The cells die continuously, and new ones are made simultaneously. In addition, the actual number of cells varies from person to person, depending on age, height, weight, health, and environmental factors. Fortunately, a healthy human body can maintain a balance between the number of cells produced and the number of cells that die.
All cells work together for the human body to function efficiently and every cell type is just as important.
1. Stem cells
Before a cell can specialize, it first begins as a stem cell. The unique feature of stem cells is that they are pluripotent, meaning they have the potential to become any type of cell in the body.
The process of transforming stem cells into any kind of cell is known as cell differentiation and is controlled by a combination of internal genetics and external factors, such as chemicals and physical contact with other cells. The stem cells can divide and reproduce over long periods of time.
There are two types of stem cells: embryonic stem cells and adult stem cells. The embryonic stem cells come from embryos. Generally used for research purposes, embryonic stem cells are harvested from fertilized eggs. The adult (or somatic) stem cells are present throughout the human body, repairing and maintaining the surrounding specialized tissues.
2. Red blood cells
The red blood cells are known as erythrocytes and are the most common type of blood cell. They have the shape of a biconcave disc. The red blood cells are flexible, allowing them to seep through thin blood capillaries.
The main role of the red blood cells is to transport oxygen around the body using hemoglobin. They also help control blood pH. They release an enzyme called carbonic anhydrase, which causes the water in the blood to carry carbon dioxide to the lungs.
3. White blood cells
The white blood cells are known as leukocytes and are a vital component of the immune system. There are two categories: granulocytes and agranulocytes. The granulocytes contain granules in the cytoplasm, while the agranulocytes do not. The granulocytes include neutrophils, eosinophils, and basophils. The agranulocytes include lymphocytes and monocytes.
4. Platelets
The platelets are fragments of cells rather than real cells, but they are vital in controlling bleeding. There are fragments of large cells called megakaryocytes, which are produced in the bone marrow. They have surface proteins that allow them to bind to each other and to the walls of damaged blood vessels.
5. Nerve cells
The nerve cells, commonly known as neurons, transmit information throughout the body in the form of electrical signals or nerve impulses. Structurally, the neurons have four specific regions: cell body, dendrites, axons, and terminal axons. The cell body contains a nucleus and is responsible for the synthesis of neuronal proteins. The axon is long and thin. The axons are responsible for conducting electrical impulses, and impulses are received by the dendrites, which are multiple branching structures that protrude from the cell body.
6. Neuroglial cells
The neuroglial cells, more commonly known as glial cells or glia, are cells of the nervous system that are not involved in conducting the nerve impulses. The glial cells are smaller than neurons and have no axons or dendrites. They have a variety of roles in the nervous system, modulate synaptic action and impulse propagation rate, and help recover neuronal damage.
There are four types of glial cells in the central nervous system: astrocytes, oligodendrocytes, microglial, and ependymal.
7. Muscle cells
There are three types of muscle cells, known as myocytes, in the human body: skeletal, cardiac, and smooth muscles.
The skeletal muscle cells are attached to bones and tendons and can reach up to 30 cm in length, being responsible for voluntary movements. The cardiac muscle cells make up the most important muscle tissue in the whole body, namely the heart tissue. The smooth muscle cells are responsible for involuntary contractions in the visceral organs such as the bladder and lungs and walls of blood vessels.
8. Cartilage cells
The cartilage cells, also known as chondrocytes, make up the cartilage, a firm tissue that is vital to the structure of the body. The cartilage is found in the joints between the bones, ears, and nose, in the airways, as well as in other locations. For example, the cartilage can be found between the vertebrae in the spine.
9. Bone cells
There are four types of bone cells in the body: osteoblasts, osteoclasts, osteocytes, and liners.
The osteoblasts are involved in the generation of new bone. The osteoclasts are involved in bone resorption. The osteoclasts break down the bone into sealed compartments on its surface and release enzymes and acids. The osteocytes are cells that are found inside the bone. The lining cells align the surface of the bone and are responsible for releasing calcium from the bone into the bloodstream as it decreases. They also protect the bone from chemicals in the blood, which could damage the bone structure.
10. Skin cells
There are many different types of cells in the skin epidermis.
Keratinocytes: These cells makeup 95% of the epidermis and are sometimes known as basal cells because they are found in the base layer of the epidermis. They generate protein keratin but are also important in protecting the body by blocking toxins and pathogens and preventing heat and moisture loss. It also stimulates inflammation and secretes inhibitory cytokines.
Melanocytes: The role of melanocytes in the skin is to produce melanin pigment, which causes skin discoloration.
Langerhans cells: These are dendritic cells involved in antigen processing when the skin becomes infected, acting as cells that process the antigen.
Merkel cells: They act as mechanosensory cells and are involved in tactile reception (the ability to feel).
11. Endothelial cells
The endothelial cells are the cells that make up the lining of blood vessels. They have a central nucleus and are connected to each other by intercellular junctions. The endothelial cells are highly adaptable, being able to migrate and adjust their number and arrangements to meet the body’s needs. This allows the growth and repair of body tissues, as new networks of blood vessels can be easily formed.
12. Epithelial cells
The epithelial cells make up the mucous membranes of body cavities, such as the lungs, small intestine, and stomach. They join to form epithelia.
The epithelial cells can become sensory cells, detecting stimuli such as smell. The epithelial cells can also specialize to become secretory cells, which release mucous membranes, hormones, and enzymes into the body. These cells contain vesicles of hormones or enzymes ready to be released.
13. Fat cells
The fat cells also called adipocytes and lipocytes, are the cells in the body that specialize in storing energy in the form of adipose tissue or fat. There are two types of fat cells: white cells and brown cells.
The white fat cells or unilocular cells are cytoplasm-containing vacuolar cells. They vary in size, but on average are about 0.1 mm in diameter. The brown fat cells or multilocular cells have multiple vacuoles and are shaped like polygons. The key role is to generate heat and, therefore, the cells contain many mitochondria, which gives them a brown color.
14. Sex cells
Sexual reproduction is the result of the fusion of two different types of sex cells called gametes. The male sex cells are commonly known as sperm, and the female sex cells are known as eggs or ova. When they merge, fertilization occurs, and a zygote is formed.
Sperm and eggs are very different from each other structurally. The sperm are smaller, the eggs are very large compared to other cell bodies.
If you want to find out about thalassemia, check out our article on this topic: All about thalassemia.
[Photo from Pixabay]
