Page 72 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy and Physiology of the Cell / 57

Regulation of Cell Growth insulin‐like growth factors stimulate carti­
and Replication
lage proliferation at growth plates in bone
VetBooks.ir Most cell types in the body can grow beyond to promote an increase in body size.
Unregulated cell growth and replication
normal size (hypertrophy). However, not all are factors in the development of cancer.
cell types in the mature animal have the A mass of cells undergoing uncontrolled
same ability to replicate and produce two growth is a tumor. A tumor is said to be
new daughter cells. Some cell types, for benign if it is local and does not invade
example the epithelium lining the small other tissues. Malignant tumors are
intestine and certain blood cells, are con­ capable of invading surrounding tissues
tinuously replicating to replace cells that and spreading to other sites throughout
are lost from the body or die. Other cell the body (metastasis).
types, for example cardiac and skeletal Sometimes normal cells must undergo
muscle cells, do not normally replicate and spontaneous, or programmed, death and
produce new daughter cells. What deter­ be removed without an inflammatory
mines the ability of cells to replicate and response so that normal function of a tis­
divide is not fully understood. However, a sue or organ can proceed. For example a
variety of chemical signals stimulate cell corpus luteum formed in an ovary during
growth and, in some cases, cell division. an estrous cycle must cease to function
Chemical signals with these capabilities before another estrous cycle can begin.
are said to be growth factors. Typically, The term apoptosis is applied to sponta­
growth factors stimulate only certain neous or programmed death of normal
populations of cells. For example, colony‐ cells. In some cases the development of
stimulating growth factors stimulate bone tumors may also include a decrease in the
marrow cells to produce blood cells, while rate of normal apoptosis.