BODY TISSUES
There are hundreds of cell types in a complex multicellular organism like ours. All of these cells are derived from a single cell, the fertilized oocyte or zygote. This cell, during embryonic development, becomes multiplied through numerous mitotic cycles.
During embryonic and fetal development, undifferentiated and totipotent cells gradually undergo a process called differentiation, during which some genes are silenced or repressed and others are activated.
Groups of cells that have undergone activation of sets of genes begin to produce new proteins or greatly increase the production of pre-existing proteins. Due to these processes, these groups of cells acquire new structural and functional properties (their morphology, type of organization, function), developing “cell families”.
Families of cells with similar structure, function and behavior constitute the body’s tissues. These tissues have been classified based on their morphology, location, functions and embryological origin. Four basic tissues: epithelial tissue, connective tissue, muscular tissue and nervous tissue are commonly recognized.
Their designation is useful for systematizing the tissues and for teaching purposes.