Bones – Tissue and Systems

This article describes the basic anatomy and function of the skeletal system as it relates to understanding symptoms of bone cancer.  Understanding the function and form of bones will help to better interpret dysfunction and symptoms of bone tumors.

There are many different kinds of bone tumors and not all of them are cancer.  A cancer is generally defined by its lack of respect for boundaries and invasive behavior into adjacent or remote tissues.  A growth or cyst of a bone is not necessarily cancerous if it does not meet these and other certain criteria when examined under the microscope.

The skeletal system performs several important functions for the body.

A list of the functions of bones includes:

  • Protection: The bones provide protection in several ways.  The skull is composed of dual layer bones that encase the brain and maintain a fixed volume internally.  This fixed volume allows the brain to regulate pressure and fluid volume around it by sensitive feedback it gets from pressure sensors.  Protection is provided to very sensitive structures such as the spinal cord by the spinal column of bones.  The spinal column is a very complex set of bones that house the spinal cord while providing flexibility.
  • Stability: Bone density increases with age to a peak and then begins to decline with age.  The normal curve of the spin (i.e. primary and secondary curvatures) can become abnormal with age and development such as excessive lateral curve (also known as scoliosis), excessive secondary curve of the cervical spine (also known as kyphosis), or excessive curvature of the lumbar spine (also known as lordosis).  Bone health is essential to adequate stability of the body.
  • Allows fulcrum and levels for movement:  The bones and the tendinos attachments of muscles creates a series of levers that create mechanical advantage and allow ease of movement.  Disease of bones creates instability and may impair the mechanisms of movement.
  • Production of blood cells in the bone marrow (also known as hematopoiesis):  The bone contains bone marrow which is the center for blood cell production in the adult.  During development as a fetus the yolk sac produces blood cells.  Older in development the liver and spleen to play a small role in blood cell production as well.  The main blood cells produced include red blood cells, the white blood cells and platelets.  Red blood cells function to carry oxygen.  White blood cells help the immune system fight foreign invaders such as bacteria and viruses.

There are several pre-cursors and different types of cells made in each of these categories, particularly the white blood cells where the cells go through several generations and can end up as one of several different kinds of players in the immune system.  The bone marrow produces megakaryocytes which then each produce many platelets.  The platelets function to help clotting and the process of hemostasis.  The platelets are cell fragments that basically function as small plugs in the scaffolding of a clot and fibrin network. Impairment of bone marrow can be devastating and even fatal.  Without adequate bone marrow function the most immediate consequence is abnormal immune function and susceptibility to severe opportunistic infection. Inadequate red blood cell production will cause anemia, pale skin, weakness and over time heart failure.  Inadequate platelet production and/or function will cause easy bleeding, bruising, and spontaneous bleeding into spaces such as joints.

  • A storage facility for important inorganic solutes: The bones house several important minerals, notably calcium and phosphorus but there are many more.  The bone serves gains strength from calcium but it is also a storage facility and when calcium levels are low some can be released from the bone, mostly under the influence of parathyroid hormone which activates osteoclasts.  Difficulties arise if too much minerals are released the bone density decreases.  A test that is commonly done to check for weak or thin bones (also known as osteoporosis) is called a bone density scan.  This creates a score (i.e. z-score or a standardized scoring system) that compares your bone density with other people your approximate age and sex.
  • Store bone marrow and fat
  • Provide form and shape for the body: Key features of cosmesis and bodily form are obtained from bones.  When bones function abnormally or lose their normal contour with a fracture or tumor, it can create significant shape alterations that can be very challenging.
  • Sensory assistance with transmission of vibrations and sound: The bones play key functions with sensory ability.  The small bones of the inner ear (i.e. stapes, incus, malleus also collectively known as ossicles) assist in mechanical sound transmission.  Vibration and position sense is also obtained from bones.

Bones are very sensitive to injury and injuries, tumors or fractures are very painful.  Pain from a tumor is often the first sign of a bone cancer.  There are many different kinds of bone cancers and potential causes for each of these.  Fortunately, the symptoms of most of these are quite similar and can facilitate recognition.  Sometimes the tumor is “noticed” after a minor injury or accident such as bumping the leg on something that causes pain.  The person that feels a bump there and attributes it to the minor trauma when in fact it has been there for some time and they never really noticed it.

REFERENCES:

  1. www.cancer.gov/cancertopics/factsheet/Sites-Types/bone
  2. www.nlm.nih.gov/medlineplus/bonecancer.html
  3. Ferguson WS, Goorin AM. Current treatment of osteosarcoma. Cancer Invest 2001; 19:292
  4. Blanco Sequeiros R, Klemola R, Ojala R, et al. MRI-guided trephine biopsy and fine-needle aspiration in the diagnosis of bone lesions in low-field (0.23 T) MRI system using optical instrument tracking. EurRadiol 2002; 12:830.
  5. This article was originally published on September 3, 2012 and last revision and update was 9/4/2015.