Types of Cells in the Human Body

Illustration of the types of cells in the body

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Cells in the human body number in the trillions and come in all shapes and sizes. These tiny structures are the basic unit of living organisms. Cells comprise tissues, tissues make up organs, organs form organ systems, and organ systems work together to create an organism and keep it alive.

Each type of cell in the human body is specially equipped for its role. Cells of the digestive system, for instance, are vastly different in structure and function from cells of the skeletal system. Cells of the body depend on each other to keep the body functioning as a unit. There are hundreds of types of cells, but the following are the 11 most common.

Stem Cells

Pluripotent stem cell on a blue background.
Pluripotent stem cell.

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Stem cells are unique in that they originate as unspecialized cells and have the ability to develop into specialized cells that can be used to build specific organs or tissues. Stem cells can divide and replicate many times in order to replenish and repair tissue. In the field of stem cell research, scientists take advantage of the renewal properties of these structures by utilizing them to generate cells for tissue repair, organ transplantation, and for the treatment of disease.

Bone Cells

Osteocyte, or bone cell, close up.
Colored scanning electron micrograph (SEM) of a freeze-fractured osteocyte (purple) surrounded by bone (gray).

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Bones are a type of mineralized connective tissue that comprise a major component of the skeletal system. Bones are made up of a matrix of collagen and calcium phosphate minerals. There are three primary types of bone cells in the body: osteoclasts, osteoblasts, and osteocytes.

Osteoclasts are large cells that decompose bone for resorption and assimilation while they heal. Osteoblasts regulate bone mineralization and produce osteoid, an organic substance of the bone matrix, which mineralizes to form bone. Osteoblasts mature to form osteocytes. Osteocytes aid in the formation of bone and help maintain calcium balance.

Blood Cells

Blood cells image.
Red and white blood cells in the bloodstream.

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From transporting oxygen throughout the body to fighting infection, blood cell activity is vital to life. Blood cells are produced by bone marrow. The three major types of cells in the blood are red blood cells, white blood cells, and platelets.

Red blood cells determine blood type and are responsible for transporting oxygen. White blood cells are immune system cells that destroy pathogens and provide immunity. Platelets help clot blood to prevent excessive blood loss due to broken or damaged blood vessels.

Muscle Cells

Smooth muscle cell image.
Immunoflourescence of a smooth muscle cell.

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Muscle cells form muscle tissue, which enables all bodily movement. The three types of muscle cells are skeletal, cardiac, and smooth. Skeletal muscle tissue attaches to bones to facilitates voluntary movement. These muscle cells are covered by connective tissue, which protects and supports muscle fiber bundles.

Cardiac muscle cells form involuntary muscle, or muscle that doesn't require conscious effort to operate, found in the heart. These cells aid in heart contraction and are joined to one another by intercalated discs that allow for heartbeat synchronization.

Smooth muscle tissue is not striated like cardiac and skeletal muscle. Smooth muscle is involuntary muscle that lines body cavities and forms the walls of many organs such as kidneys, intestines, blood vessels, and lung airways.

Fat Cells

Close up image of fat cells.
Adipocytes (fat cells) store energy as an insulating layer of fat and the majority of the cell's volume is taken up by a large lipid (fat or oil) droplet.

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Fat cells, also called adipocytes, are a major cell component of adipose tissue. Adipocytes contain droplets of stored fat (triglycerides) that can be used for energy. When fat is stored, its cells become round and swollen. When fat is used, its cells shrink. Adipose cells also have a critical endocrine function: they produce hormones that influence sex hormone metabolism, blood pressure regulation, insulin sensitivity, fat storage and use, blood clotting, and cell signaling.

Skin Cells

Skin cells close up view.
This image shows squamous cells from the surface of the skin. These are flat, keratinized, dead cells that are continuously sloughed off and replaced with new cells from below.

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The skin is composed of a layer of epithelial tissue (epidermis) that is supported by a layer of connective tissue (dermis) and an underlying subcutaneous layer. The outermost layer of the skin is composed of flat, squamous epithelial cells that are closely packed together. The skin covers a wide range of roles. It protects internal structures of the body from damage, prevents dehydration, acts as a barrier against germs, stores fat, and produces vitamins and hormones.

Nerve Cells

Nerve cells close up.

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Nerve cells or neurons are the most basic unit of the nervous system. Nerves send signals between the brain, spinal cord, and other body organs via nerve impulses. Structurally, a neuron consists of a cell body and nerve processes. The central cell body contains the neuron's nucleus, associated cytoplasm, and organelles. Nerve processes are "finger-like" projections (axons and dendrites) that extend from the cell body and transmit signals.

Endothelial Cells

Endothelial cells close up view.

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Endothelial cells form the inner lining of the cardiovascular system and lymphatic system structures. They make up the inner layer of blood vessels, lymphatic vessels, and organs including the brain, lungs, skin, and heart. Endothelial cells are responsible for angiogenesis or the creation of new blood vessels. They also regulate the movement of macromolecules, gases, and fluid between the blood and surrounding tissues as well as help manage blood pressure.

Sex Cells

Human fertilization occurring as sperm cells seek an egg cell.
This image depicts sperm entering an ovum.

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Sex cells or gametes are reproductive cells created in male and female gonads that bring new life into existence. Male sex cells or sperm are motile and have long, tail-like projections called flagella. Female sex cells or ova are non-motile and relatively large in comparison to male gametes. In sexual reproduction, sex cells unite during fertilization to form a new individual. While other body cells replicate by mitosis, gametes reproduce by meiosis.

Pancreatic Cells

Pancreas cell close up view.

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The pancreas functions as both an exocrine and endocrine organ, meaning that it discharges hormones both through ducts and directly into other organs. Pancreatic cells are important for regulating blood glucose concentration levels as well as for the digestion of proteins, carbohydrates, and fats.

Exocrine acinar cells, which are produced by the pancreas, secrete digestive enzymes that are transported by ducts to the small intestine. A very small percentage of pancreatic cells have an endocrine function or secrete hormones into cells and tissues. Pancreatic endocrine cells are found in small clusters called islets of Langerhans. Hormones produced by these cells include insulin, glucagon, and gastrin.

Cancer Cells

Cervical cancer cells close up view.
These cervical cancer cells are dividing.

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Unlike all of the other cells listed, cancer cells work to destroy the body. Cancer results from the development of abnormal cell properties that cause cells to divide uncontrollably and spread to other locations. Cancer cell development can originate from mutations stemming from exposure to chemicals, radiation, and ultraviolet light. Cancer can also have genetic origins such as chromosome replication errors and cancer-causing viruses of the DNA.

Cancer cells are allowed to spread rapidly because they develop decreased sensitivity to anti-growth signals and proliferate quickly in the absence of stop commands. They also lose the ability to undergo apoptosis or programmed cell death, making them even more formidable.