Page 19 - 84 human physiolofy part-1

Cell Physiology

move. The cytoskeleton allows certain cells such as neutrophils and macrophages to make amoeboid
movements.

The network is composed of three elements:
microtubules, actin filaments, and intermediate fibers.

• Microtubules

Microtubules function as the framework along
which organelles and vesicles move within a cell. They
are the thickest of the cytoskeleton structures. They are
long hollow cylinders, composed of protein subunits,
called tubulin. Microtubules form mitotic spindles, the
machinery that partitions chromosomes between two
cells in the process of cell division. Without mitotic
spindles cells could not reproduce.

Microtubules, intermediate filaments, and
microfilaments are three protein fibers of decreasing
diameter, respectively. All are involved in establishing A photograph of microtubules.
the shape or movements of the cytoskeleton, the
internal structure of the cell.

• Microfilaments

Microfilaments provide mechanical
support for the cell, determine the cell
shape, and in some cases enable cell
movements. They have an arrow-like
appearance, with a fast growing plus or
barbed end and a slow growing minus or
pointed end. They are made of the protein
actin and are involved in cell motility. They
are found in almost every cell, but are
predominant in muscle cells and in the cells
that move by changing shape, such as
phagocytes (white blood cells that scour the
body for bacteria and other foreign
invaders).
A photograph of microfilaments. (GFDL - Y tambe)

Organelles

Organelles are bodies embedded in the cytoplasm that serve to physically separate the various
metabolic activities that occur within cells. The organelles are each like separate little factories, each
organelle is responsible for producing a certain product that is used elsewhere in the cell or body.

Cells of all living things are divided into two broad categories: prokaryotes and eukaryotes.
Bacteria (and archea) are prokaryotes, which means they lack a nucleus or other membrane-bound

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