Clinical Applications of Human Anatomy and Physiology for Healthcare Professionals. Jassin M. Jouria

or overcome normal blood cells in the bloodstream or bone marrow. Over time, the number of damaged or abnormal cancerous cells gradually overcome and replace healthy cells.

      A carcinoma is defined as a cancer of epithelial cells. Carcinomas also affect endocrine glands or any gland that secretes hormones. Some of the most common types of carcinomas include:

      •Skin cancer – such as melanoma

      •Stomach cancer

      •Lung cancer

      •Prostate cancer

      •Colon cancer

      Carcinomas are more commonly found in older individuals than younger individuals.

      Sarcomas are defined as cancers of muscle dermal cells or the cells that form connective tissues and muscles.

      This type of cancer can form in smooth muscles found in digestive organs (Leimyosarcoma) or in bone cells, resulting in bone cancer (osteosarcoma).

      This type of cancer is more commonly found in younger people than older people.

      A number of factors can contribute to an increased risk of developing cancer:

      •Genetics

      •Environment

      •Diet

      •Geography

Men	Women
Prostate	Breast
Lung	Lung
Colon and rectum	Colon and rectum
Bladder	Uterus
Non-Hodgkin’s lymphoma	Non-Hodgkin’s lymphoma

      Some cancers are often gender specific. For example, see the list above. Other causes of cancer include viral infections and inflammatory diseases.

      Body defenses against cancer

      The body’s immune system is the front line of defense against a cancerous cell. In most cases, it is believed that the immune system is able to recognize the development of common abnormal cell structures and destroy them before they can reproduce or replicate and spread.

      Figure 2-13 Different types of Sarcoma.

      However, cancers are not limited to individuals with compromised immune systems or system function. Otherwise healthy individuals with strong immune systems may also develop cancers.

      When the body senses a cancerous or abnormal cell, it responds to tumor antigens. Antigens are described as a foreign substance that is quickly recognized by the immune system and targeted for destruction. While antigens are typically found on all cellular surfaces, the body’s immune system doesn’t typically react to its own cellular structures. However, when the cell becomes cancerous, new or previously unknown antigens appear on the surface of that cell.

      Think of these antigens as a beacon that attract components of the immune system, much like a great white shark attracted to the scent of blood in the water, which them prepare for attack.

      In some cases, the body’s own immune system, through this mechanism of action, is capable of destroying abnormal cellular development and even cancerous cells before they become established in the body. However, after a cancerous cell reproduces or forms a mass, the body’s immune system is often unable to halt its progress.

A number of cancers have been identified through their tumor antigens,11 including malignant melanoma and bone cancer. Individuals with such types of cancer typically produce antibodies against those specific tumor antigens. Nevertheless, the body’s immune system is more capable of destroying cancerous cells early on in some types of cancers such as corneal carcinoma (cancerous tumor development in the uterus from parts of the developing embryo).

      Figure 2-14 Cancer cells.

      Blood tests can determine the presence of tumor antigens. Antigens are also commonly defined as tumor markers. Measuring tumor markers is a way to screen individuals with no previous symptoms of cancer, and are often capable of aiding in diagnosis and evaluating treatment responses.

       ■How do Cells Function?

      Cells have the ability to move things from one point to another. One major function of cells is the ability to engage in transportation of vital components necessary for cellular health and wellness. Two specific types of transportation are common to all cellular function:

      •Active transport

      •Passive transport

      Figure 2-15 Passive and active transport.

      Active transport is defined as something that occurs when the cell must utilize energy for transportation. This involves literal movement of molecules across a cellular membrane.

      Because the inside and outside of cells are composed of different substances, cells are often required to work very hard and use energy to maintain adequate balances of molecules and ions inside and out.

      One of the most common forms of active transportation occurs across the cellular membrane. Literally thousands of proteins are embedded into the lipid bilayer of the cell. These proteins are likened to workhorses and are positioned in such a way that one portion of such proteins remains on the inside and the other portion of the protein protrudes to the outside of the cellular membrane. Only when the bilayer is crossed are the proteins capable of moving ions and molecules into or outside of the cell.

      However, these proteins, often called membrane proteins, are not created equal. For example, one proteins may only be able to move glucose, while another is responsible for the movement of calcium. Hundreds of membrane proteins are found in the body, each charged with a specific function.

      When pressure or concentration differs between the inside and outside of the cell (especially in the case of neurons), the proteins are working “against” concentrated gradients. This is typical when an ion wants to move from an area of lower concentrations to an area of higher concentrations. In this situation, membrane proteins must consistently push ions into or out of the cell in order to prepare the neuron membrane to transmit an electrical impulse.

      Passive transportation is another cellular function. While active transport relies on energy, passive transport is achieved through several different methods:

      •Osmosis

      •Filtration

      •Diffusion

      Osmosis is defined as a process by which molecules pass from semi-permeable membranes with less concentrated solutions into an area of higher concentration. This results in equalization of concentration on both sides (inside and outside) of the membrane.

      Figure 2-16 Osmosis and reverse osmosis.

      Osmosis is primarily defined as a water-based movement. The balance of ions inside and outside of the cell needs to be the same. If ions are not balanced, water molecules want to enter, which can cause swelling and literally explode or pop the cell.

      Diffusion defines a process where molecules move from an area of higher concentration to lower concentration. Think of the unloading of passengers from a train. A high volume of passengers surge from the train car and disperse throughout the train station, decreasing the volume of passengers