Page 84 - Atlas of Histology with Functional Correlations

remodel the cell during mitosis. These tubules are most visible and are

predominant in cilia and flagella, where they are responsible for their beating
movements. Microtubules also form the basis of centrioles and basal bodies of
the cilia.

CENTROSOME AND CENTRIOLES

The centrosome is an area of the cytoplasm located near the nucleus. It is the
major microtubule-forming center and the site for generating new

microtubules and mitotic spindles. The centrosome consists of two small
cylindrical structures called centrioles and the surrounding matrix; the centrioles
are oriented at right angles to each other. Each centriole consists of nine evenly
spaced clusters of three sets of fused microtubules arranged in a circle or a ring.

The microtubules exhibit longitudinal orientation and are parallel to each other.

Before mitosis, the centrioles in the centrosome replicate and form two pairs.
During mitosis, each pair moves to the opposite poles of the cell, where they
become microtubule-organizing centers for mitotic spindles that control the

distribution of chromosomes to the daughter cells. Beneath the cell membrane,
the centrioles induce the formation of basal bodies and organize the
development of the microtubules in cilia and flagella.

CYTOPLASMIC INCLUSIONS

The cytoplasmic inclusions are temporary structures that accumulate in the
cytoplasm of certain cells. Lipids, glycogen, crystals, pigment, or byproducts

of metabolism are inclusions and represent the nonliving parts of the cell.

NUCLEUS, NUCLEAR ENVELOPE, AND

NUCLEAR PORES

The nucleus is the largest organelle of a cell. Most cells contain a single nucleus,
but other cells may exhibit multiple nuclei. Skeletal muscle cells have multiple
nuclei, whereas mature red blood cells of mammals do not have a nucleus or are

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