b. Meiosis. Sex cells mature and propagate by a different process than somatic
cells. This process is called meiosis. In meiosis, the series of nuclear changes within
the sex cell results in the production of new cells with half the number of chromosomes
present in the original sex cell. Meiosis occurs in both female and male sex cells,
resulting in the formation of ova and spermatozoa, respectively. The union of a mature
spermatazoa and a mature ovum results in the formation of a new individual. As a
result of meiosis, the chromosome number remains constant from one generation to the
next. For this reason, meiosis is sometimes called reduction division.
Somatic cells are usually classified as either epithelial, muscle, nerve, or
connective. Cells arranged or organized to perform one or more specific functions are
called a tissue. The four basic tissue types found in the human body are classified
according to the type of cells that comprise them and have these specialized functions.
a. Epithelial Tissue. Forms linings and coverings of various body parts and
b. Muscle Tissue. Contracts to cause movement and to maintain body posture.
c. Nerve Tissue. Conducts messages (impulses) to and from the central
d. Connective Tissue. Serves as filler and binder substances of the body and
forms the supporting framework of the body and the body organs.
Section III. BONES
BONES OF THE SKELETON
a. The normal adult human body has approximately 206 bones. This includes
the auditory ossicles and the patella, but excludes the small sesamoid bones.
Figure 1-10 shows a human skeleton in anatomical position.
b. The skeleton may be divided into the appendicular and the axial skeleton.
The appendicular skeleton includes the bones of the upper and lower free extremities,
the shoulder (pectoral girdle), and the pelvic girdle. The axial skeleton includes the
bones of the skull, the vertebral column, the thoracic cage, the auditory ossicles, and
the hyoid bone.