Histology and Cell Structure
Introductory Note: Knowledge
of Cell Structure is an essential part of the basic
Anatomy and Physiology theory required for successful
completion of accredited courses in many bodywork therapies,
such as Massage, Reflexology, Aromatherapy, Indian Head
Massage, and others. At least a general knowledge of
cell structure and the associated terminology and processes
is important for everyone interested in health sciences.
These concepts feature in literature describing the
latest advances in research and associated conclusions
and proposals.
This article describes the basic structure of a general
human cell and some of the organelles within it.
Histology
Histology is the microscopic study of the structure
of tissues using special staining techniques combined
with light and electron microscopy. The detail of even
the general cell structure summarised below cannot be
observed without the use of these modern techniques.
Cell Structure
The structure of cells varies according to the type
and purpose of the cell (for example, which functions it is performing
and in which part of the body).
All cells contain organelles.
These are structures within the cell that are specialised for particular
functions.
The following diagram illustrates a single cell and
simple representations of key organelles:
It is also important to know something about each
of these organelles:
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Organelle
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Structure/Function
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Cell Membrane
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The cell membrane keeps the cell together
by containing the organelles within it. Cell membranes are
selectively-permeable, allowing materials to move both into
and outside of the cell.
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Centrosomes
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The centrosomes contain the centrioles,
which are responsible for cell-division.
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Cytoplasm
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Cytoplasm is a jelly-like substance that
is sometimes described as "the cell-matrix". It
holds the organelles in place within the cell.
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Goli Apparatus
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The goli apparatus of a cell is usually connected
to an endoplasmic reticulum (ER) because it stores
and then transports the proteins produced in the ER.
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Lysosomes
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Lysosomes are tiny sacs filled with enzymes
that enable the cell to utilize its nutrients. Lysosomes also
destroy the cell after it has died, though there are some
circumstances (diseases/conditions) in which lysosomes begin
to 'break-down' living cells.
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Microvilli
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"Microvilli" is the pural form;
"Microvillus" is the singular form.
Microvilli are finger-like projections on the
outer-surface of the cell.
Not all cells have microvilli.
Their function is to increase the surface area of the cell,
which is the area through which diffusion of materials both
into, and out of, the cell is possible.
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Mitochondria
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"Mitochondria" is a plural term;
which is appropriate as these are not found alone.
The quantity of mitochondria within cells varies
with the type of cell.
These are the energy producers within the cell. They generate
energy in the form of Adenosine Tri-Phosphate (ATP). Generally,
the more energy a cell needs, the more mitochondria it contains.
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Nuclear Membrane
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The nuclear membrane separates the nucleus
and the nucleolus from the rest of the contents of the cell.
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Nuclear Pore
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Nuclear pores permit substances (such as
nutrients, waste, and cellular information) to pass both into,
and out of, the nucleus.
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Nucleolus
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The nucleolus is responsible for the cell
organelles (e.g. lysosomes, ribosomes, etc.).
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Nucleus
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The nucleus is the "Control Center"
of the cell, which contains DNA (genetic information)
in the form of genes, and also information for
the formation of proteins.
Information is carried on chromosomes, which are a form of
DNA.
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Ribosomes
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Ribosomes interpret cellular information
from the nucleus and so synthesize appropriate proteins, as
required.
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Rough Endoplasmic Reticulum (RER)
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"Rough" indicates that there are
ribosomes attached to the surfaces of the endoplasmic
reticulum. The endoplasmic reticulum is where proteins
and lipids are produced within the cell, and is also concerned
with the transport of these materials within the cell.
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Smooth Endoplasmic Reticulum (SER)
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"Smooth" indicates that there are
no ribosomes attached to the surfaces of the endoplasmic
reticulum.The endoplasmic reticulum is where proteins
and lipids are produced within the cell, and is also concerned
with the transport of these materials within the cell.
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Other components of a typical cell not shown on
the above simple diagram include:
Cilium; Cytosol (component of cytoplasma); Glycogen granules;
Intermediate filament; Microtubule; Microfilament; Pericentriolar
area (around the Centrioles); Peroxisome; Secretory vesicle. |
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Cell Membrane
A simple representation of the structure of animal cell membranes
is shown below.
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This is illustrates a cross-section of the phospholipid bilayer
that forms the membrane around the outside of all animal (including
human) cells.
This plasma membrane consists mainly of phospholipids and
proteins, most of the membrane proteins being
glycoproteins.
The two components of the phospholipids are the
heads (represented by black circles), and
the
fatty acid tails (that extend into the phospholipid bilayer).
Other molecules present in the plasma membrane generally
include cholesterol (as illustrated) and glycolipids.
Note that this membrane is non-rigid; if it had a
cell-wall then it would be rigid - but a plant cell
!
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Integral Proteins extend through the bilipid layer
and among the fatty acid tails of the phospholipids
- though not necessarily all the way through the
plasma membrane.
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Peripheral Proteins are loosely attached to (either
the interior or exterior) surface of the plasma membrane.
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