Biomedical Engineering Reference
In-Depth Information
vessels in the marrow, that enter the Haversian canals from both periosteum and
the marrow.
Gajda
et al
. [128] investigated the development of sensory innervation in long
bones, see Figure 1.18. Their model was rat tibia in fetuses and in juvenile indi-
viduals on postnatal days. A double immunostaining method was applied to study
the co-localization of the neuronal growth marker GAP-43 and the pan-neuronal
marker PGP 9.5 (9.5) as well as that of two sensory fiber-associated neuropeptides,
calcitonin gene-related peptide (CGRP) and SP. The earliest, not yet chemically
coded, nerve fibers were observed in the perichondrium of the proximal epiph-
ysis. Further development of the innervation was characterized by the successive
appearance of nerve fibers in the perichondrium/periosteum of the shaft, the
bone marrow cavity and intercondylar eminence, the metaphyses, the cartilage
canals penetrating into the epiphyses, and finally in the secondary ossification
centers and epiphyseal bone marrow. Maturation of the fibers, manifested by their
immunoreactivity for CGRP and SP, was investigated in these cases also.
1.3.4
Bone Cells
1.3.4.1
Cells
The living cells are divided into two types: prokaryotic and eukaryotic. The prokary-
otes are organisms that lack a cell nucleus (karyon). Prokaryotes are divided into the
bacteria and archea. Animals, plants, fungi, and protists are eukaryotes - organisms
whose cells are organized into complex structures enclosed within membranes.
The defining membrane-bound structure that differentiates eukaryotic cells from
prokaryotic cells is the nucleus. The cells of protozoa, higher plants, and animals
are highly structured. These cells tend to be larger than the cells of bacteria, and
have developed special packaging and transport mechanisms that are appropriate
to their larger size. There are many different cell types: approximately 210 distinct
cell types in the adult human body.
In Figures 1.19 and 1.20, the animal and plant cells may be compared. It is seen
that a cell wall - a thick, rigid membrane - surrounds a plant cell. This layer of
cellulose fiber gives the cell most of its support and structure. The cell wall also
bonds with other cell walls to form the structure of the plant.
Existence of wall in the plant cell provides the main difference between plant
and animal body from a mechanical point of view. The wall in plant cell gives the
plant support and structure. The animal body whose cells have no walls should be
supported by special tissues - the bones in the case of vertebrates.
The cytoskeleton (a cellular skeleton or cell scaffolding) is present in all cells,
being contained within the cytoplasm. It is a dynamic structure made out of protein
molecules that protects the cell, maintains the cell shape, enables cellular motion
(using structures such as flagella, cilia, and lamellipodia), and plays important roles
in both intracellular transport (such as the movement of vesicles and organelles)
and cellular division. Microfilaments (or actin filaments) are the thinnest filaments
of the cytoskeleton found in the cytoplasm of all eukaryotic cells [130-135].
