In our cities we have transporters and storage facilities. These are called
vesicles within cells. Secretory vesicles break off from the Golgi apparatus
with the materials manufactured by the ER, and carry these to the outer cell
membrane wall, where this material is then dumped or carried out into the
world of the body. Some vesicles act as holding tanks until the “created” or
“manufactured” product is needed. An example of this is the hormone
insulin, which is held in vesicles in the beta cells of the pancreas. When the
body’s blood glucose levels rise, these vesicles then release their stored
insulin into the blood to assist cellular utilization of glucose.
As in any city, we need protection from invaders. Many cells act as
protectors of the body. These are called immune cells. Within each cell, the
lysosomes are vesicles that contain a variety of enzymes that are used for
intracellular sanitation and elimination (digestive) functions. Macro-phages
(the white blood cells, or WBCs, for example) ingest bacteria (antigens or
pathogens). The lysosomes within your cells “eat” or “digest” (break apart)
and destroy the invader.
Now what’s a city without power? The powerhouse for a cell is its
mitochondria. These are bean- or rod-shaped organelles (specialized organs
or structures) that produce, store and release adenosine triphosphate (ATP).
This is the energy source for most chemical reactions within the cell.
Mitochondria use oxygen (oxidative metabolism) which allows ATP to be
produced.
The skeletal portions of the cells (or the “structures” of the city) are called
cytoskeleton, which is made up of proteins (chained and bound amino acids).
Within the cytoskeleton there are several structures, all of which play a role in
its flexibility, shape and size. These are called microtubules, microfilaments
and intermediate filaments.
It is noteworthy to mention that some cells have cilia, which are hair-like
extensions from the outer membrane wall. They can vary in number from one
to thousands. Their coordinated job is to move mucus. You can especially see
this in the respiratory tract where mucus is secreted by the lymphatic mucosa
of the lining of the lungs and bronchi. The action of the cilia allows the body
to keep its lungs clear of dust or other particles that could damage (or affect)
its functions.
Some cells have what are called microvilli, which are projections of the
outer cell membrane wall. This is especially true of kidneys and intestinal wall
cells where additional absorption of nutrients is necessary.