Phagocytosis is the engulfing of solid particles by a cell. For example, bacteria
could be surrounded and ingested by a cell. The mechanism of phagocytosis is similar
to that of pinocytosis. However, in phagocytosis, the cell acts to surround the particle
with the cell membrane and form a vesicle (sac) containing the particle and cytoplasm.
Then, the vesicle breaks away from the cell wall and moves toward the center of the
cell. Figure 2-4 illustrates phagocytosis.
Figure 2-4. Phagocytosis.
Section III. TISSUE
2-8. DEFINITION OF TISSUE
A tissue is composed of a group of cells, which are the same or similar in nature.
For example, liver cells are bound together into a tissue called liver, and bone cells are
bound together with a large amount of lime salts to form bony tissue. The various
tissues of the body have different characteristics because the cells that make up these
tissues are different both in structure and in function.
2-9. TYPES OF TISSUE
There are four primary tissues as follows: epithelial, connective, muscular, and
a. Epithelial (Figure 2-5). This tissue covers the outer surface of the body and
forms the lining of the intestinal and respiratory systems. A special form called
endothelium lines the heart and blood vessels. As serous membranes, it lines the
cavities of the abdomen, the chest, and the heart, and covers the organs that lie in
these cavities. Epithelial tissue forms the glands and parts of the sense organs.
According to its location, this tissue has different functions. As the skin, it protects
underlying structures; in the small intestine, it absorbs; in the lungs, it is a highly
permeable membrane; in glands, it secretes; and in the kidneys and liver, it both
secretes and excretes. There are three types of epithelial tissue based on the shape of
the cells. These are squamous (flat), cuboidal, and columnar. These cells are further