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 cultivate 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.
Reference: www.wisegeek.com