The
general doctrine about bones
Tissues
and organs
In human body they distinguish some levels of the
organization:
1. molecular
level – object of the biochemistry
2. subcellular
level – object of the histology
3. cellular
level – object of the histology
4. tissues
level – object of the histology
5. organs
– object of the anatomy
6. systems
– object of the anatomy
7. organism
– object of the anatomy
connective
tissue - less elasticity - wrinkles
cartilage - less elasticity - degenerative
changes such as osteo-arthritis with associated changes. Costal cartilages
often replaced by bone: bony spurs develop in unusual places.
bone - becomes brittle, reduced in size
with less activity
muscle - ditto, plus deposition of fat.
heart
and blood vessels - arteries become tortuous, walls
become furred up with atheroma. Left ventricle is enlarged as consequence of
load. Veins often varicose.
nervous
system - Often small strokes will cause paralysis and
reduction in size of some muscles
The human body is composed of 206 bones that
perform five main functions:
1)
support
2)
protection
3)
body movement
4)
blood cell formation
5)
storage of inorganic salts and lipid
II. Cells in Osseous tissue: osteocytes,
osteoblasts, osteoclasts, osteoprogenitor, cells.
III. Cellular matrix - 1/ calcium hydroxyapatite,
2/ collagenous fibers
Diaphysis -- shaft
epiphysis
-- bone ends
epiphyseal
line
nutrient
foramen
medullary
cavity
V. Types of bone:
a. lamellar or compact bone
1. contains osteons
composed of concentric lamellae
2. each osteon has an
osteonic canal (Haversian canal) which has blood vessels and nerves
3. osteocytes found
within lacunae
4. canaliculi connect
osteocytes and function to diffuse nutrition to the osteocytes
5. communicating (also
called perforating or Volkman's) canals, connect adjacent osteons, and carry
blood vessels.
6. the diaphyses, or
shafts of long bones, are composed mostly of lamellar bone
b. Cancellous, trabecular, or spongy
bone
1. does not contain
haversian canal systems (osteons)
2. nerves and blood
vessels run randomly through the loose meshwork of bone.
Structure and Physical Properties of the bone. — Bone is one of the hardest structures of the animal body;
it possesses also a certain degree of toughness and elasticity. Its color, in a
fresh state, is pinkish-white externally, and deep red within. On examining a
section of any bone, it is seen to be composed of two kinds of tissue, one of
which is dense in texture, like ivory, and is termed compact tissue; the other consists of slender fibers and
lamellæ, which join to form a reticular structure; this, from its
resemblance to lattice-work, is called cancellous
tissue. The compact tissue is always placed on the exterior of the bone,
the cancellous in the interior. The relative quantity of these two kinds of
tissue varies in different bones, and in different parts of the same bone,
according as strength or lightness is requisite. Close examination of the
compact tissue shows it to be extremely porous, so that the difference in
structure between it and the cancellous tissue depends merely upon the
different amount of solid matter, and the size and number of spaces in each;
the cavities are small in the compact tissue and the solid matter between them
abundant, while in the cancellous tissue the spaces are large and the solid
matter is in smaller quantity.
Bone during life is permeated by vessels, and is enclosed, except where
it is coated with articular cartilage, in a fibrous membrane, the periosteum, by means of which many of
these vessels reach the hard tissue. If the periosteum be stripped from the
surface of the living bone, small bleeding points are seen which mark the
entrance of the periosteal vessels; and on section during life every part of
the bone exudes blood from the minute vessels which ramify in it. The interior
of each of the long bones of the limbs presents a cylindrical cavity filled
with marrow and lined by a highly vascular areolar structure, called the medullary membrane.
Periosteum.—The periosteum adheres to the
surface of each of the bones in nearly every part, but not to cartilaginous
extremities. When strong tendons or ligaments are attached to a bone, the
periosteum is incorporated with them. It consists of two layers closely united
together, the outer one formed chiefly of connective tissue, containing
occasionally a few fat cells; the inner one, of elastic fibers of the finer
kind, forming dense membranous networks, which again can be separated into several
layers. In young bones the periosteum is thick and very vascular, and is
intimately connected at either end of the bone with the epiphysial cartilage,
but less closely with the body of the bone, from which it is separated by a
layer of soft tissue, containing a number of granular corpuscles or osteoblasts,
by which ossification proceeds on the exterior of the young bone. Later in life
the periosteum is thinner and less vascular, and the osteoblasts are converted
into an epithelioid layer on the deep surface of the periosteum. The periosteum
serves as a nidus for the ramification of the vessels previous to their
distribution in the bone; hence the liability of bone to exfoliation or
necrosis when denuded of this membrane by injury or disease. Fine nerves and
lymphatics, which generally accompany the arteries, may also be demonstrated in
the periosteum.
Marrow.—The marrow not only fills up the cylindrical cavities in the
bodies of the long bones, but also occupies the spaces of the cancellous tissue
and extends into the larger bony canals (Haversian canals) which contain the
bloodvessels. It differs in composition in different bones. In the bodies of
the long bones the marrow is of a yellow color, and contains, in 100 parts, 96
of fat, 1 of areolar tissue and vessels, and 3 of fluid with extractive matter;
it consists of a basis of connective tissue supporting numerous bloodvessels
and cells, most of which are fat cells but some are “marrow cells,” such as
occur in the red marrow to be immediately described. In the flat and short
bones, in the articular ends of the long bones, in the bodies of the
vertebræ, in the cranial diploë, and in the sternum and ribs the
marrow is of a red color, and contains, in 100 parts, 75 of water, and 25 of
solid matter consisting of cell-globulin, nucleoprotein, extractives, salts,
and only a small proportion of fat. The red marrow consists of a small quantity
of connective tissue, bloodvessels, and numerous cells, some few of which are
fat cells, but the great majority are roundish nucleated cells, the true
“marrow cells” of Kölliker. These marrow cells proper, or myelocytes, resemble in appearance
lymphoid corpuscles, and like them are ameboid; they generally have a hyaline
protoplasm, though some show granules either oxyphil or basophil in reaction. A
number of eosinophil cells are also present. Among the marrow cells may be seen
smaller cells, which possess a slightly pinkish hue; these are the erythroblasts or normoblasts, from which the red corpuscles of the adult are
derived, and which may be regarded as descendants of the nucleated colored
corpuscles of the embryo. Giant cells
(myeloplaxes, osteoclasts), large,
multinucleated, protoplasmic masses, are also to be found in both sorts of
adult marrow, but more particularly in red marrow. They were believed by
Kölliker to be concerned in the absorption of bone matrix, and hence the
name which he gave to them — osteoclasts.
They excavate in the bone small shallow pits or cavities, which are named Howship’s foveolæ, and in these
they are found lying. but the great majority are roundish nucleated cells, the
true “marrow cells” of Kölliker. These marrow cells proper, or myelocytes, resemble i n appearance
lymphoid corpuscles, and like them are ameboid; they generally have a hyaline
protoplasm, though some show granules either oxyphil or basophil in reaction. A
number of eosinophil cells are also present. Among the marrow cells may be seen
smaller cells, which possess a slightly pinkish hue; these are the erythroblasts or normoblasts, from which the red corpuscles of the adult are
derived, and which may be regarded as descendants of the nucleated colored
corpuscles of the embryo. Giant cells
(myeloplaxes, osteoclasts), large,
multinucleated, protoplasmic masses, are also to be found in both sorts of
adult marrow, but more particularly in red marrow. They were believed by
Kölliker to be concerned in the absorption of bone matrix, and hence the
name which he gave to them — osteoclasts.
They excavate in the bone small shallow pits or cavities, which are named Howship’s foveolæ, and in these
they are found lying.
Vessels and Nerves of Bone. — The bloodvessels of bone are very numerous. Those of the compact tissue
are derived from a close and dense network of vessels ramifying in the
periosteum. From this membrane vessels pass into the minute orifices in the
compact tissue, and run through the canals which traverse its substance. The
cancellous tissue is supplied in a similar way, but by less numerous and larger
vessels, which, perforating the outer compact tissue, are distributed to the
cavities of the spongy portion of the bone. In the long bones, numerous
apertures may be seen at the ends near the articular surfaces; some of these
give passage to the arteries of the larger set of vessels referred to; but the
most numerous and largest apertures are for some of the veins of the cancellous
tissue, which emerge apart from the arteries. The marrow in the body of a long
bone is supplied by one large artery (or sometimes more), which enters the bone
at the nutrient foramen (situated in most cases near the center of the body),
and perforates obliquely the compact structure. The medullary or nutrient
artery, usually accompanied by one or two veins, sends branches upward and
downward, which ramify in the medullary membrane, and give twigs to the
adjoining canals. The ramifications of this vessel anastomose with the arteries
of the cancellous and compact tissues. In most of the flat, and in many of the
short spongy bones, one or more large apertures are observed, which transmit to
the central parts of the bone vessels corresponding to the nutrient arteries
and veins. The veins emerge from the
long bones in three places (Kölliker): (1) one or two large veins
accompany the artery; (2) numerous large and small veins emerge at the
articular extremities; (3) many small veins pass out of the compact substance.
In the flat cranial bones the veins are large, very numerous, and run in
tortuous canals in the diploic tissue, the sides of the canals being formed by
thin lamellæ of bone, perforated here and there for the passage of
branches from the adjacent cancelli. The same condition is also found in all
cancellous tissue, the veins being enclosed and supported by osseous material,
and having exceedingly thin coats. When a bone is divided, the vessels remain
patulous, and do not contract in the canals in which they are contained. Lymphatic vessels, in addition to those
found in the periosteum, have been traced by Cruikshank into the substance of
bone, and Klein describes them as running in the Haversian canals. Nerves are distributed freely to the
periosteum, and accompany the nutrient arteries into the interior of the bone.
They are said by Kölliker to be most numerous in the articular extremities
of the long bones, in the vertebræ, and in the larger flat bones.
Minute Anatomy. — A transverse section of dense bone may be cut with a
saw and ground down until it is sufficiently thin.
If this be examined with a rather low power the bone will be seen to be
mapped out into a number of circular districts each consisting of a central
hole surrounded by a number of concentric rings. These districts are termed
Haversian systems; the central hole is an Haversian canal, and the rings are
layers of bony tissue arranged concentrically around the central canal, and
termed lamellæ. Moreover, on closer examination it will be found that
between these lamellæ, and therefore also arranged concentrically around
the central canal, are a number of little dark spots, the lacunæ, and
that these lacunæ are connected with each other and with the central
Haversian canal by a number of fine dark lines, which radiate like the spokes
of a wheel and are called canaliculi. Filling in the irregular intervals which
are left between these circular systems are other lamellæ, with their
lacunæ and canaliculi running in various directions, but more or less
curved (Fig. 73); they are termed interstitial
lamellæ. Again, other lamellæ, found on the surface of the bone,
are arranged parallel to its circumference; they are termed circumferential, or
by some authors primary or fundamental lamellæ, to distinguish them from
those laid down around the axes of the Haversian canals, which are then termed
secondary or special lamellæ.
The Haversian canals, seen in
a transverse section of bone as round holes at or about the center of each
Haversian system, may be demonstrated to be true canals if a longitudinal section
be made. It will then be seen that the canals run parallel with the
longitudinal axis of the bone for a short distance and then branch and
communicate. They vary considerably in size, some being as much as
The lamellæ are thin
plates of bony tissue encircling the central canal, and may be compared, for
the sake of illustration, to a number of sheets of paper pasted one over
another around a central hollow cylinder. After macerating a piece of bone in
dilute mineral acid, these lamellæ may be stripped off in a longitudinal
direction as thin films. If one of these be examined with a high power of the
microscope, it will be found to be composed of a finely reticular structure,
made up of very slender transparent fibers, decussating obliquely; and
coalescing at the points of intersection; these fibers are composed of fine
fibrils identical with those of white connective tissue. The intercellular
matrix between the fibers is impregnated by calcareous deposit which the acid dissolves.
In many places the various lamellæ may be seen to be held together by
tapering fibers, which run obliquely through them, pinning or bolting them
together; they were first described by Sharpey, and were named by him perforating fibers.
The Lacunæ are situated
between the lamellæ, and consist of a number of oblong spaces. In an
ordinary microscopic section, viewed by transmitted light, they appear as
fusiform opaque spots. Each lacuna is occupied during life by a branched cell,
termed a bone-cell or bone-corpuscle, the processes from
which extend into the canaliculi.
The Canaliculi are exceedingly minute channels, crossing the
lamellæ and connecting the lacunæ with neighboring lacunæ and
also with the Haversian canal. From the Haversian canal a number of canaliculi
are given off, which radiate from it, and open into the first set of
lacunæ between the first and second lamellæ. From these
lacunæ a second set of canaliculi is given off; these run outward to the
next series of lacunæ, and so on until the periphery of the Haversian
system is reached; here the canaliculi given off from the last series of
lacunæ do not communicate with the lacunæ of neighboring Haversian
systems, but after passing outward for a short distance form loops and return
to their own lacunæ. Thus every part of an Haversian system is supplied
with nutrient fluids derived from the vessels in the Haversian canal and
distributed through the canaliculi and lacunæ.
The bone cells are contained
in the lacunæ, which, however, they do not completely fill. They are
flattened nucleated branched cells, homologous with those of connective tissue;
the branches, especially in young bones, pass into the canaliculi from the
lacunæ.
In thin plates of bone (as in the walls of the spaces of cancellous
tissue) the Haversian canals are absent, and the canaliculi open into the
spaces of the cancellous tissue (medullary spaces), which thus have the same
function as the Haversian canals.
Chemical Composition. — Bone consists of an animal
and an earthy part intimately combined together.
The animal part may be obtained by immersing a bone for a considerable
time in dilute mineral acid, after which process the bone comes out exactly the
same shape as before, but perfectly flexible, so that a long bone (one of the
ribs, for example) can easily be tied in a knot. If now a transverse section is
made the same general arrangement of the Haversian canals, lamellæ, lacunæ,
and canaliculi is seen.
The earthy part may be separately obtained by calcination, by which the
animal matter is completely burnt out. The bone will still retain its original
form, but it will be white and brittle, will have lost about one-third of its
original weight, and will crumble down with the slightest force. The earthy
matter is composed chiefly of calcium phosphate, about 58 per cent. of the
weight of the bone, calcium carbonate about 7 per cent., calcium fluoride and
magnesium phosphate from 1 to 2 per cent. each and sodium chloride less than 1
per cent.; they confer on bone its hardness and rigidity, while the animal
matter (ossein) determines its
tenacity. Ossification.—Some bones
are preceded by membrane, such as those forming the roof and sides of the
skull; others, such as the bones of the limbs, are preceded by rods of
cartilage. Hence two kinds of ossification are described: the intramembranous and the intracartilaginous.
According to their structure bones
are dividing into long bone, short bone, flat bone, irregular
bone, pneumatized bone, sesamoid bone.
Bone is covered by periosteum. An individual bone is composed of
bones tissue, cartilage, fibrous connective tissue, and blood and nerve tissue.
Because most of the bone is made of inorganic salts a bones seems nonliving,
but the bone is a system of tissues that form together and the bones make the
skeletal system.
On long bones, such as those in the arms and legs
the large expanded portions are called epiphyses. These are the regions of the
bones that articulate with other bones. The shaft of the bones between the
epiphyses is called the diaphysis. Except of the articular cartilage that
covers the epiphyes the entire bones is covered in a tough, vascular tissue
called periosteum. Periosteum fibres interlock with fibres of tendons and
muscles that are connected to the bone. The wall of the diaphysis is composed of
a strong, tightly packed, and resistant to bending tissue called compact bone.
The epiphyses, on the other hand, are formed mostly by spongy bone. Spongy bone
is made of many small bone plates that have irregular interconnected spaces
that help keep bones light but very strong. The compact bone in the diaphysis
of long bones forms a tube or channel called the medullary cavity. This cavity
is continuos through the length of the diaphysis and then fades into the spongy
bone. The medullary cavity is filled with a special type of soft connective
tissue called marrow.
Bones usually developed from separate centers of
ossification termed epiphyses, and consist of cancellous tissue surrounded by
thin compact bone. The medullary canal and the spaces in the cancellous tissue
are filled with marrow. The long bones are not straight, but curved, the curve
generally taking place in two planes, thus affording greater strength to the
bone. The bones belonging to this class are: the clavicle, humerus, radius,
ulna, femur, tibia, fibula, metacarpals, metatarsals, and phalanges.
Short Bones. — Where a part
of the skeleton is intended for strength and compactness combined with limited
movement, it is constructed of a number of short bones, as in the carpus and
tarsus. These consist of cancellous tissue covered by a thin crust of compact
substance. The patellæ, together with the other sesamoid bones, are by
some regarded as short bones.
Flat Bones. — Where the
principal requirement is either extensive protection or the provision of broad
surfaces for muscular attachment, the bones are expanded into broad, flat
plates, as in the skull and the scapula. These bones are composed of two thin
layers of compact tissue enclosing between them a variable quantity of
cancellous tissue. In the cranial bones, the layers of compact tissue are
familiarly known as the tables of the skull; the outer one is thick and tough;
the inner is thin, dense, and brittle, and hence is termed the vitreous table.
The intervening cancellous tissue is called the diploë, and this, in
certain regions of the skull, becomes absorbed so as to leave spaces filled
with air (air-sinuses) between the two tables. The flat bones are: the
occipital, parietal, frontal, nasal, lacrimal, vomer, scapula, os coxæ
(hip bone), sternum, ribs, and, according to some, the patella.
Irregular Bones. — The irregular
bones are such as, from their peculiar form, cannot be grouped under the
preceding heads. They consist of cancellous tissue enclosed within a thin layer
of compact bone. The irregular bones are: the vertebra, sacrum, coccyx,
temporal, sphenoid, ethmoid, zygomatic, maxilla, mandible, palatine, inferior
nasal concha, and hyoid. Surfaces of Bones.—If
the surface of a bone be examined, certain eminences and depressions are seen.
These eminences and depressions are of two kinds: articular and non-articular.
Well-marked examples of articular eminences are found in the heads of the
humerus and femur; and of articular depressions in the glenoid cavity of the
scapula, and the acetabulum of the hip bone. Non-articular eminences are
designated according to their form. Thus, a broad, rough, uneven elevation is
called a tuberosity, protuberance, or process, a small, rough prominence, a
tubercle; a sharp, slender pointed eminence, a spine; a narrow, rough
elevation, running some way along the surface, a ridge, crest, or line.
Non-articular depressions are also of variable form, and are described as
fossæ, pits, depressions, grooves, furrows, fissures, notches, etc. These
non-articular eminences and depressions serve to increase the extent of surface
for the attachment of ligaments and muscles, and are usually well-marked in
proportion to the muscularity of the subject. A short perforation is called a
foramen, a longer passage a canal.
Development of Bone
Bone
formation is due to the osteoblasts
which are specialized mesenchymal cells. Osteobiasts secrete an intercellular
substance, the osteoid, which
consists initially of soft around substance and collagen fibers. Osteobiasts
develop into osteocytes, the
definitive bone cells. At the same time multinucleated osteoclasts develop, cells connected with resorbing and remodelling
bone. We distinguish direct or Intramembranous ossification from Indirect or
chondral ossification.
Intramembranous ossification, osteogenesis membranacea is the development of
bone from connective tissue. The latter contains many mesenchymal cells which
develop via osteobiasts into osteocytes. At the same time osteoclasts develop
and collagen fibers also appear. The original bone is fibrous and it is
subsequently remodelled into lamellar bone. The skull cap, the facial bones and
the clavicles develop as membranous bones. Preformed cartilaginous skeletal
parts are necessary for chondral ossKlcatlon, osreogenesis cartilaginea when they become replaced by bone. Growth is possible
only as long as cartilage still remains. The prerequisites for replacement bone
formation are chondroclasts,
differentiated connective tissue cells, which remove cartilage and enable the
osteobiasts to form bone. Two types of replacement bone formation are
recognized endochondral and perichondral.
Endochrondral ossification begins
within cartilage, and occurs near the epiphyses. Just before ossification
begins the mass is entirely cartilaginous, and in a long bone, which may be
taken as an example, the process commences in the center and proceeds toward
the extremities, which for some time remain cartilaginous. Subsequently a
similar process commences in one or more places in those extremities and gradually
extends through them. The extremities do not, however, become joined to the
body of the bone by bony tissue until growth has ceased; between the body and
either extremity a layer of cartilaginous tissue termed the epiphysial
cartilage persists for a definite period.
The
first step in the ossification of the cartilage is that the cartilage cells, at
the point where ossification is commencing and which is termed a center of
ossification, enlarge and arrange themselves in rows. The matrix in which they
are imbedded increases in quantity, so that the cells become further separated
from each other. A deposit of calcareous material now takes place in this
matrix, between the rows of cells, so that they become separated from each
other by longitudinal columns of calcified matrix, presenting a granular and
opaque appearance. Here and there the matrix between two cells of the same row
also becomes calcified, and transverse bars of calcified substance stretch
across from one calcareous column to another. Thus there are longitudinal
groups of the cartilage cells enclosed in oblong cavities, the walls of which
are formed of calcified matrix which cuts off all nutrition from the cells; the
cells, in consequence, atrophy, leaving spaces called the primary areolæ.
At the
same time that this process is going on in the center of the solid bar of
cartilage, certain changes are taking place on its surface. This is covered by
a very vascular membrane, the perichondrium, entirely similar to the embryonic
connective tissue already described as constituting the basis of membrane bone;
on the inner surface of this — that is to say, on the surface
in contact with the cartilage — are gathered the formative
cells, the osteoblasts. By the agency of these cells a thin layer of bony
tissue is formed between the perichondrium and the cartilage, by the
intramembranous mode of ossification just described. There are then, in this
first stage of ossification, two processes going on simultaneously: in the
center of the cartilage the formation of a number of oblong spaces, formed of
calcified matrix and containing the withered cartilage cells, and on the
surface of the cartilage the formation of a layer of true membrane bone. The
second stage consists in the prolongation into the cartilage of processes of
the deeper or osteogenetic layer of the perichondrium, which has now become
periosteum. The processes consist of bloodvessels and cells — osteoblasts, or bone-formers,
and osteoclasts, or bone-destroyers. The latter are similar to the giant cells
(myeloplaxes) found in marrow, and they excavate passages through the
new-formed bony layer by absorption, and pass through it into the calcified
matrix. Wherever these processes come in contact with the calcified walls of
the primary areolæ they absorb them, and thus cause a fusion of the
original cavities and the formation of larger spaces, which are termed the
secondary areolæ or medullary spaces. These secondary spaces become
filled with embryonic marrow, consisting of osteoblasts and vessels, derived,
in the manner described above, from the osteogenetic layer of the periosteum.
Thus
far there has been traced the formation of enlarged spaces (secondary
areolæ), the perforated walls of which are still formed by calcified
cartilage matrix, containing an embryonic marrow derived from the processes
sent in from the osteogenetic layer of the periosteum, and consisting of
bloodvessels and osteoblasts. The walls of these secondary areolæ are at
this time of only inconsiderable thickness, but they become thickened by the
deposition of layers of true bone on their surface. This process takes place in
the following manner: Some of the osteoblasts of the embryonic marrow, after
undergoing rapid division, arrange themselves as an epithelioid layer on the
surface of the wall of the space. This layer of osteoblasts forms a bony
stratum, and thus the wall of the space becomes gradually covered with a layer
of true osseous substance in which some of the bone-forming cells are included
as bone corpuscles. The next stage in the process consists in the removal of
these primary bone spicules by the osteoclasts. One of these giant cells may be
found lying in a Howship’s foveola at the free end of each spicule. The removal
of the primary spicules goes on pari passu with the formation of permanent bone
by the periosteum, and in this way the medullary cavity of the body of the bone
is formed.
The number of ossific centers varies in different bones. In most of the
short bones ossification commences at a single point near the center, and
proceeds toward the surface. In the long bones there is a central point of
ossification for the body or diaphysis: and one or more for each extremity, the
epiphysis. That for the body is the first to appear. The times of union of the
epiphyses with the body vary inversely with the dates at which their
ossifications began (with the exception of the fibula) and regulate the
direction of the nutrient arteries of the bones. Thus, the nutrient arteries of
the bones of the arm and forearm are directed toward the elbow, since the
epiphyses at this joint become united to the bodies before those at the
opposite extremities. In the lower limb, on the other hand, the nutrient
arteries are directed away from the knee: that is, upward in the femur,
downward in the tibia and fibula; and in them it is observed that the upper
epiphysis of the femur, and the lower epiphyses of the tibia and fibula, unite
first with the bodies. Where there is only one epiphysis, the nutrient artery
is directed toward the other end of the bone; as toward the acromial end of the
clavicle, toward the distal ends of the metacarpal bone of the thumb and the
metatarsal bone of the great toe, and toward the proximal ends of the other
metacarpal and metatarsal bones.
Parsons groups epiphyses under three headings, viz.: (1) pressure
epiphyses, appearing at the articular ends of the bones and transmitting “the
weight of the body from bone to bone;” (2) traction epiphyses, associated with
the insertion of muscles and “originally sesamoid structures though not
necessarily sesamoid bones;” and (3) atavistic epiphyses, representing parts of
the skeleton, which at one time formed separate bones, but which have lost
their function, “and only appear as separate ossifications in early life.”
Epiphyses are found at the ends of long
bones, whilst the shafts are called diaphyses.
Pericnondrai ossification, which originates in the perichondrium. The epiphyslal disk (growth plate), which is
necessary for growth in length, forms a layer between the epiphysis and the
diaphysis. That part of the shall adjacent to the epiphysial disk is called the
melaphysis and develops fiist on an
endochondral basis. Within the epiphysial cartilage, the processes of
ossification occur in separate zones. First, in the epiphysis is the zone of the capping, hyaline cartilaginous
material, which has not been influenced by bone formation. Next to this area of
'resting cartilage' is the zone or cartilage
cell columns, the growth zone. Here cartilage cells divide and so increase
in number. The next layer, which lies nearer to the shaft, is the zone of large vesicular cartilage cells,
in which calcification is occurring. This is contiguous with the zone of cartilage destruction, where
cartilage is broken down by chondroclasts and replaced by bone-forming osteobiasts.
A cartilage remnant persists, which enables endochondral bone and perichondral
bone to be distinguished in the diaphysis. It Is
secondarily replaced by perichondral bone. Endochondral bone is destroyed by
the immigrant osteoclasts. In crease in thickness in the region of the
diaphysis is brought about by deposition of new bony materal on the outer
surface beneath the cellular layer of the periosteum. The bone marrow cavity becomes larger as a result
of bone destruction. Hormones regulate all growth processes.
Bone and joint health is a
concern for almost everyone over the age of 30.
Studies show that bone density is determined by the mid-twenties for
both men and women and that bone mineral loss occurs naturally as we age. This is also true for the “building blocks”
that make-up our joints and connective tissue.
Flexibility: Stretching can
increase flexibility. Bone strength: Weight-bearing exercise strengthens bones and helps prevent osteoporosis. Exercising
on a regular basis can help build your bones, but the kind of exercise
is what makes a difference. There are basically two kinds of exercise - aerobic
and weight-bearing. Some aerobic exercises, like swimming and bicycling
outdoors or on a stationary bike, are certainly good for you, but they don't do
much for your bones.
The ones that help build
and strengthen bone are the weight-bearing kind. Weight-bearing exercises, some
of which can be aerobic, are those that force you to put weight, and therefore
stress, on your muscles and bones. Weight-lifting walking, hiking, and step
aerobic classes are all activities that require your muscles to work against
gravity. For weights you can even use soup cans and water bottles.See the list
below for more good examples of this kind of exercise. Weight-bearing exercises
that may be right for you: gardening, stair climbing, chair exercises, tennis,
walking, weight lifting erobics, dancing.
Ideally, you should do some
kind of weight-bearing exercise on a regular basis. In addition, weight-bearing
exercise stimulates the formation of new
bone. Exercise strengthens the muscles that pull or tug on bones, an action
that keeps bones strong. Exercise improves balance, strength, and
co-ordination, which reduces the risk of falling and breaking a bone. Talk to
your doctor about the best weight-bearing exercise for you. In general,
exercise is a good thing. However, if you already have osteoporosis, or if you
have any other medical conditions, some activities may not be good choices for
you. Have a discussion with your doctor or other healthcare provider about the
exercises and activities that would be best for you, especially before starting
any new exercise programme.
When you start any new
programme, start slowly and build gradually. If you develop any pain, check
with your doctor or other health care provider immediately. Exercise to prevent
falls. Exercise counts in fall prevention. You've probably heard about the
benefits of exercise. It helps make your bones stronger, improves your overall
health, and can even brighten your outlook. But did you know that exercise
might reduce your risk of falling by improving your balance, muscle strength,
and co-ordination? It may even help you avoid a serious injury if you do fall.
Tips for developing an exercise programme that works for you
1. Talk to your healthcare
provider before you start. While the right exercise program offers great
benefits, the wrong exercises can lead to injury or serious illness. Discuss
your exercise plan with your healthcare provider and keep in mind these special
precautions:
2. Anyone more than age 40
should have a thorough medical exam before beginning an exercise programme. If
a woman has a significant amount of bone
loss, some exercises may actually increase her risk of fracture. For
example, sit-ups and toe touches increase the risk of fracture in women with
osteoporosis of the spine. A woman at high risk for heart disease may
need a stress test before starting an exercise programme.
Tai chi (a popular exercise
using gentle, slow movements to relax muscles): This improves balance,
flexibility, and state of mind.
Weight-bearing, low-impact
aerobic exercises such as walking, dancing, and climbing stairs: These increase
muscle strength and co-ordination, improve balance, and make bones stronger,
without putting too much stress on joints and muscles.
Consider one of the most
natural forms of exercise - walking. This is an easy, effective way to strengthen muscles, increase bone strength,
and improve overall health.