Cell division and growth normally occur at approximately the same rate as cell death.
Cell Division
and Cancer
Cell division and growth normally
occur at approximately the same rate as cell death. However, when cell
division and growth are higher than the cell death rate, tissues enlarge. A
neoplasm or tumor is a mass of tissue
produced by abnormal cell growth and divi-sion. A tumor is called benign when it remains within the
epithelium or a capsule made of connective tissue. This type of tumor seldom
becomes life threatening and can usually be surgically removed if it affects
tis-sue function.
Malignant tumors spread into
surrounding tis-sues in a process called invasion.
The primary tumor may result in malignant cells traveling to other organs or
tissue to establish secondary tumors. This process, called metastasis, is not easily controlled. Cancerdevel-ops (FIGURE 3-19) and exhibits mutations disrupting normal cell growth. Usually, all
tumor cells are daugh-ter cells of just one malignant cell. Malignancy often
occurs when a normal gene mutates. These modified genes are called oncogenes. Genes that promote cell
division are called proto-oncogenes,
and oncogenes are created by these genes. Oncogenes often code for the proteins
controlling cell division.
Most cancers are caused by
mutations of the genes inside somatic
cells. This is linked to mutations occurring during cell division. A small
number of errors occur while DNA is being replicated before cell division. A mutation is defined as a DNA sequence
with replication errors inside it. Mutations may also be caused by chemicals,
toxins, radiation, and viruses. Cancer most commonly develops in tis-sues that
experience frequent cell divisions such as epithelial cells. Multiple
mutations, occurring overmany cell generations, result in cancer. This is why
older people more commonly develop cancer than younger people.
Cancer cells change shape as they
grow and grad-uallyresemble normal cells less and less. Tumor cells escape the
primary tumor to invade the surrounding tissue—this is the manner in which
metastasis begins. If tumor cells penetrate blood vessels, they circulate
throughout the body. If they enter the lymphatic sys-tem, they accumulate in
lymph nodes. The presence of tumor cells stimulates the growth of new blood
vessels where the cells situate themselves. This supplies them with more
nutrients and accelerates their growth and further metastasis.
As metastasis increases, organ
function changes. Cancer cells grow and multiply by taking nutrients and space
from normal cells, causing weight loss in most cancer patients as the normal
cells deteriorate. When cancer cells compress vital organs or have replaced
healthy cells in vital organs, death may occur. Cancer often begins where stem
cells divide, because a greater chance of error occurs the more frequently that
chromosomes are copied for cell division.
To prevent the development of
cancer in cells, the body uses two major mechanisms. The first involves DNA
repair enzymes, which detect and correct errors that occurred during
replication. If these enzymes are made less effective because of their
controlling genes becoming mutated, this first mechanism of fighting against
cancer cannot be effective. The second mechanism is apoptosis, which is a self-destructive process that destroys cells
containing abnormal DNA. There-fore, mutated cells are made to self-destruct
before cancer can develop. Apoptosis also occurs in normal cells that have a
limited life span. However, mutations of genes that influence apoptosis may
result in per-sistently mutated cells, which can continue to divide and
proliferate.
Tumor suppressor genes are
normal genes thatslow or even stop cell division. They can be affected by
mutations that cause them to have reduced actions. In human cancer cells, many
types of oncogenes and altered tumor suppressor genes have been identified.
Cancer therapy focuses on the confinement of malignant cells and then their
destruction. Cancerous tissue is killed by lasers, X-rays, and drugs
(chemotherapy) and removed by surgery. However, many cancers cannot be
com-pletely destroyed. Some of the adverse effects of cancer therapies include
the destruction of nor-mal cells in rapidly growing tissues such as bone
marrow. This can lead to anemia, because of the reduced numbers of red blood
cells.
Related Topics
TH 2019 - 2024 pharmacy180.com; Developed by Therithal info.