Question

Mr. Smith's mother had a right radical mastectomy due to breast cancer

• What are the four mechanisms of cellular adaptation? Explain.
• What is the general classification of neoplasms according to their tissue of origin?

Answer 1

The four mechanisms of cellular adaptation are:-
1.Atrophy
2.Hypertrophy
3.Hyperplasia
4.Neoplasia
Now we will discuss each one these separately.

1.Atrophy

A reduction in cell size is known as Atrophy. The entire organ will decrease in size if many cells of the organ ho under atrophy.Tissue and organs prone to atrophy include skeletal muscle, cardiac muscle, secondary sex organs, and the brain.

Atrophy can be attributed to:-
Low protein synthesis
High protein degradation in cells.

Some of the causes of atrophy are:-

Decreased workload which causes Atrophy of Disuse e.g. limb atrophy after immobilization for fracture

Loss of innervation which cause Denervation atrophy e.g.thenar muscle atrophy after medial nerve injury

Very low bood supply because of atherosclerosis of vessels with aging leads to cerebral atrophy

Inadequate nutrition leads to marasmus

Loss of endocrine stimulation causes loss of estrogen stimulation after menopause and causes atrophy of endometrium, vaginal epithelium and breast

Aging which causes senile atrophy an lead to cell loss in brain and heart

2.Hypertrophy

Increase in cell size and volume is called as Hypertrophy.The whole organ will increase in size if many cells of the organ gets hypertrophied. Hypertrophy may include an increase in intracellular protein as well as cytosol ,cytoplasmic components.

Following are the types of hypertrophy:-

Physiologic hypertrophy: Occurs due to a normal stress.e.g.increase in size of skeletal muscle with exercise.

Pathological hypertrophy: It occurs due to an abnormal stress.e.g. increase in the size of the heart in case of cardiac failure.

3.Hyperplasia

An increase in the number of cells is called Hyperplasia.Increased cell mitosis or division leads to this.

Following are the types of hyperplasia:-

Physiologic hyperplasia: Occurs due to a normal stress.e.g.The size of the breasts increase the during pregnancy, thickness of endometrium increases during menstrual cycle.

Pathologic hyperplasia: Occurs due to an abnormal stress.e.g.In the case of pituitary adenoma due to production of ACTH there is growth of the adrenal gland

4.Metaplasia

When a cell of a specific type is replaced by another cell type,which may be less differentiated then it is called as Metaplasia.

Following are the types of Metaplasia:-

a.Squamous metaplasia: result from chornic irritation

In a chronic smoker the ciliated columnar epithelium of trachea and bronchi are replaced by stratified squamous epithelial cells

In vitamin A deficiency the squamous metaplasia occurs in respiratory epithelium.In this there is replacement of thin squamous conjunctival lining with stratified keratinizing squamous epithelium.

However the metaplastic squamous epithelium has survival advantages some important protective mechanisms are lost – eg.In respiratory tract squamous metaplasia the secretion of mucus is lost.

b. Columnar metaplasia:

Barrett esophagus is an example of columnar metaplasia.In this there is non-ciliated, mucin producing columnar metaplasia of distal esophagus due to chronic gastroesophageal acid reflux.

c. Myeloid metaplasia:

Proliferation of hematopoietic tissue outside bone marrow, eg. liver and spleen

Occurs in chronic idiopathic myelofibrosis

d. Connective tissue metaplasia:

Formation of cartilage, bone, or adipose tissues that normally don't have these tissues.
E.g. Myositis ossificans -muscle changes to bone during fracture healing

According to tissue of origin neoplasms are grouped into six major categories:

Carcinoma

Sarcoma

Myeloma

Leukemia

Lymphoma

Mixed Types

Carcinoma

Carcinoma can be defined as a malignant neoplasm of epithelial origin.

Epithelial tissue is encountered in the whole body. It is found in the skin and the covering and lining of organs and internal pathways, such as the GIT.

Carcinomas are divided into two major subtypes:
Adenocarcinoma : These develops in an organ or gland
Squamous cell carcinoma : These develops in the squamous epithelium.

Adenocarcinomas usually occur in mucus membranes.They are first seen as a thick plaque-like white mucosa. They can be spread easily through the soft tissue where they occur.

Sarcoma

A cancer which is arised in connective tissues can be referred to as Sarcoma. It generally occurs in young adults.The most common sarcoma often develops as a painful mass on the bone. Sarcoma tumors are liike the tissue in which they grow.

Following are the examples of sarcomas:-

Osteosarcoma or osteogenic sarcoma-occurs in bone

Chondrosarcoma occurs in cartilage

Leiomyosarcoma occurs in smooth muscle

Rhabdomyosarcoma occurs in skeletal muscle

Mesothelial sarcoma or mesothelioma occurs in membranous lining of body cavities

Fibrosarcoma occurs in fibrous tissue

Angiosarcoma or hemangioendothelioma occurs in blood vessels

Liposarcoma occurs inadipose tissue

Glioma or astrocytoma neurogenic occurs in connective tissue

Myxosarcoma occurs in primitive embryonic connective tissue

Mesenchymous or mixed mesodermal tumor occurs in mixed connective tissue types

Myeloma

Myeloma arises in the plasma cells of bone marrow.

Leukemia

These are cancers of the bone marrow .The disease is often associated with the overproduction of immature white blood cells. These immature white blood cells are not efficient as the normal ones, therefore the patient is often prone to infection.

Following are the examples of leukemia include:

Myelogenous leukemia- Neoplasmsof the myeloid cells

Lymphocytic leukemia -Neoplasms of the lymphoid and lymphocytic cells

Polycythemia vera -Neoplasms of different blood cells with red cells more.

Lymphoma

Lymphomas origina in the glands or nodes of the lymphatic system, a network of vessels, nodes, and organs like spleen, tonsils, and thymus that produce infection-fighting white blood cells, or lymphocytes.Lymphomas may also occur in specific organs such as the stomach, breast or brain. These lymphomas are called as extranodal lymphomas. The lymphomas are divided into two categories: Hodgkin lymphoma and Non-Hodgkin lymphoma.

Mixed Types

Some components of the cancer can be of one type and some components can be of other type of neoplasms. Some examples are:-

adenosquamous carcinoma

mixed mesodermal tumor

carcinosarcoma

teratocarcinoma