PriCells: Different types of human cells                                                            

Human primary cells are cells taken from living human beings and cultured.  These cells retain the differentiation of the original cells taken in a biopsy sample and can be used in a wide variety of types of research.  Many laboratories that sell cell cultures provide human primary cells by request and they usually list the products they offer in a catalog. Special types of cultures are available for custom orders if a researcher has very specific needs.

Collecting human primary cells starts with a sample from a subject.  Some labs rely on subjects who donate tissue specifically for scientific research after signing paperwork, indicating that they have been informed about the type of research that will be done and how their cells will be used.  These donors are screened carefully to make sure they are suitable and the lab may also recruit rare donors to ensure a steady supply of access to unusual tissue types.  Other labs may use leftovers from biopsy samples taken for diagnosis and treatment to c*te primary cells.

Human primary cells are not immortalized.  After a set number of divisions, the cells will become exhausted and the culture will die.  Typically, the lab cultures the biopsy sample long enough to confirm that it is viable and then freezes it.  When a researcher needs cells, frozen vials are shipped and the researcher revives the culture.  Being able to freeze cells allows labs to keep human primary cells in stock to meet the demand from researchers.

Histology or the study of tissues, classifies the types of human cells by the primary tissue function. 

Epithelial cells are found throughout the body, including skin and in the linings or coverings of parts of the digestive tract and of the heart, glands, blood vessels and other locations requiring smooth, dense protection. 
The digestive system includes several specialized cell types, such as the nephrons in the kidney, the villa of the small intestine and liver cells. 

The cells of the circulatory and respiratory systems are quite diverse, including red and white blood cells and the alveoli of the lung.

The muscular, skeletal and articular systems control how humans move.  Muscle cells are of three types: smooth, striated or cardiac. 

Skeletal cells are primarily bone and cartilage cells.  

The articular system includes connective tissue cells that make up ligaments and tendons.

Neurons are the principle cells of the nervous system and are characterized by the ability to receive and transmit chemical signals. 

Sensory systems include many specialized cells such as the retinal cell in the eye, and pressure and heat sensing cells in the skin.
Hearing is accomplished by a complicated series of physical sound conduction through bones and via drum heads and the connection to the nervous systems through the vibration of specialized hair cells of the inner ear. 

Other systems with specialized cells include the reproductive, endocrine, lymphatic and urinary systems.

The types of human cells may also be organized by the phase of the cell cycle they exist within.  Labile cells have specific life spans and reproduce essentially constantly.  These include digestive tract cells, bone marrow and the alveoli of the lung.

Stable cells may reproduce as required by the body. A liver cell will regenerate as necessary while a kidney cell cannot.

Permanent tissue cells are considered irreplaceable by the body and include the lens of the eye and red blood cells as examples. Somatic stem cells and neurons used to be in this category but have proven to be capable of regeneration.  All of these cells are still subject to the aging of the individual body through poorly understood mechanisms.