Biomedical Engineering Reference
In-Depth Information
cranial cavity that holds the brain and the spinal cavity that contains the spinal cord. The
ventral body cavity contains the thoracic and abdominopelvic cavities that are separated
by the diaphragm. The thoracic cavity contains the lungs and the mediastinum, which
contains the heart and its attached blood vessels, the trachea, the esophagus, and all other
organs in this region except for the lungs. The abdominopelvic cavity is divided by an
imaginary line into the abdominal and pelvic cavities. The former is the largest cavity in
the body and holds the stomach, small and large intestines, liver, spleen, pancreas, kidneys,
and gallbladder. The latter contains the urinary bladder, the rectum, and the internal
portions of the reproductive system.
The anatomical terms described previously are used by physicians, life scientists, and
biomedical engineers when discussing the whole human body or its major parts. Correct
use of these terms is vital for biomedical engineers to communicate with health care profes-
sionals and to understand the medical problem of concern or interest. While it is important
to be able to use the general terms that describe the human body, it is also important for
biomedical engineers to have a basic understanding of some of the more detailed aspects
of human anatomy and physiology.
3.2 CELLULAR ORGANIZATION
Although there are many smaller units such as enzymes and organelles that perform
physiological tasks or have definable structures, the smallest anatomical and physiological
unit in the human body that can, under appropriate conditions, live and reproduce on its
own is the cell. Cells were first discovered more than 300 years ago shortly after Antony
van Leeuwenhoek, a Dutch optician, invented the microscope. With his microscope, van
Leeuwenhoek was able to observe “many very small animalcules, the motions of which
were very pleasing to behold” in tartar scrapings from his teeth. Following the efforts
of van Leeuwenhoek, Robert Hooke, a Curator of Instruments for the Royal Society of
England, in the late 1600s further described cells when he used one of the earliest micro-
scopes to look at the plant cell walls that remain in cork. These observations and others
led to the cell theory developed by Theodor Schwann and Matthias Jakob Schleiden and
formalized by Rudolf Virchow in the mid-1800s. The cell theory states that (1) all organisms
are composed of one or more cells, (2) the cell is the smallest unit of life, and (3) all cells
come from previously existing cells. Thus, cells are the basic building blocks of life.
Cells are composed mostly of organic compounds and water, with more than 60 percent of
the weight in a human body coming from water. The organic compounds—carbohydrates,
lipids, proteins, and nucleic acids—that cells synthesize are the molecules that are funda-
mental to sustaining life. These molecules function as energy packets, storehouses of energy
and hereditary information, structural materials, and metabolic workers. The most common
elements found in humans (in descending order based on percent of body weight) are oxy-
gen, carbon, hydrogen, nitrogen, calcium, phosphorus, potassium, sodium, chlorine, magne-
sium, sulfur, iron, and iodine. Carbon, hydrogen, oxygen, and nitrogen contribute more than
99 percent of all the atoms in the body. Most of these elements are incorporated into organic
compounds, but some exist in other forms, such as phosphate groups and ions.
Carbohydrates are used by cells not only as structural materials but also to transport
and store energy. The three classes of carbohydrates are monosaccharides (e.g., glucose),
