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 comprise organs, organs form organ systems, and organ systems work together in an organism. There are hundreds of different types of cells in the body and the structure of a cell is perfectly suited for the role it performs. Cells of the digestive system, for instance, are different in structure and function from cells of the skeletal system. No matter the differences, cells of the body depend on each another, either directly or indirectly, to keep the body functioning as one unit. The following are examples of different types of cells in the body.
Stem Cells
Stem cells are unique cells of the body in that they are unspecialized and have the ability to develop into specialized cells for specific organs or to develop into tissues. Stem cells are able to divide and replicate many times in order to replenish and repair tissue. In the field of stem cell research, scientists are attempting to take advantage of the renewal properties of stem cells by utilizing them to generate cells for tissue repair, organ transplantation, and for the treatment of disease.
Bone Cells
Bones are a type of mineralized connective tissue and a major component of the skeletal system. Bone cells form bone, which is composed of a matrix of collagen and calcium phosphate minerals. There are three primary types of bone cells in the body. Osteoclasts are large cells that decompose bone for resorption and assimilation. Osteoblasts regulate bone mineralization and produce osteoid (organic substance of 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
From transporting oxygen throughout the body to fighting infection, cells of the bloodare vital to life. 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 also responsible for transporting oxygen to cells. White blood cells are immune systemcells that destroy pathogens and provide immunity. Platelets help to clot blood and prevent excessive blood loss due to broken or damaged blood vessels. Blood cells are produced by bone marrow.
Muscle Cells
Muscle cells form muscle tissue, which is important for bodily movement. Skeletal muscle tissue attaches to bones enabling voluntary movement. Skeletal muscle cells are covered by connective tissue, which protects and supports the muscle fiber bundles. Cardiac muscle cells form involuntary cardiac muscle found in the heart. These cells aid in heart contraction and are joined to one another by intercalated discs, which allow for synchronization of the heartbeat. 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 (kidneys, intestines, blood vessels, lung airways, and so on).
Fat Cells
Fat cells, also called adipocytes, are the major cell component of adipose tissue. Adipocytes contain droplets of stored fat (triglycerides) that can be used for energy. When fat is being stored, fat cells swell and become round in shape. When fat is being used, these cells shrink in size. Adipose cells also have an endocrine function as they produce hormones that influence sex hormone metabolism, blood pressure regulation, insulin sensitivity, fat storage and use, blood clotting, and cell signaling.
Skin Cells
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 protects the 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 or neurons are the basic units of the nervous system. Nerves send signals among the brain, spinal cord, and other body organs via nerve impulses. A neuron consists of two major parts: 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 are able to conduct and transmit signals.
Endothelial Cells
Endothelial cells form the inner lining of the cardiovascular system and lymphatic system structures. These cells 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, and help to regulate blood pressure.
Sex Cells
Sex cells or gametes are reproductive cells produced in male and female gonads. Male sex cells or sperm are motile and have a long, tail-like projection called a flagellum. Female sex cells or ova are non-motile and relatively large in comparison to the male gamete. 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
The pancreas functions as both an exocrine and endocrine organ. Exocrine acinar cells produce and secrete digestive enzymes that are transported by ducts to the small intestine. A very small percentage of pancreatic cells have an endocrine function and secrete hormones. Pancreatic endocrine cells are found in small clusters called islets of Langerhans. Hormones produced by these cells include insulin, glucagon, and gastrin. Pancreatic cells are important for regulating blood glucose concentration levels as well as for the digestion of proteins, carbohydrates, and fats.
Cancer Cells
Cancer results from the development of abnormal properties in normal cells that enable them to divide uncontrollably and spread to other locations. Cancer celldevelopment can be caused by mutations that occur from factors such as chemicals, radiation, ultraviolet light, chromosome replication errors, or viral infection. Cancer cells lose sensitivity to anti-growth signals, proliferate rapidly, and lose the ability to undergo apoptosis or programmed cell death.
