What is bone matter? Compact bone substance: what is it? Cellular elements and bone development
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Bone, os, ossis, as an organ of a living organism consists of several tissues, the most important of which is bone.
Chemical composition of bone and its physical properties.
Bone substance consists of two types of chemical substances: organic (Uz), mainly ossein, and inorganic (2/z), mainly calcium salts, especially lime phosphate (more than half - 51.04%). If the bone is exposed to a solution of acids (hydrochloric, nitric, etc.), then the lime salts dissolve (decalcinatio), and the organic matter remains and retains the shape of the bone, being, however, soft and elastic. If the bone is fired, the organic substance burns out, and the inorganic substance remains, also retaining the shape of the bone and its hardness, but being very fragile. Consequently, the elasticity of bone depends on ossein, and its hardness on mineral salts. The combination of inorganic and organic substances in living bone gives it extraordinary strength and elasticity. This is also confirmed by age-related changes in bones. In young children, who have relatively more ossein, the bones are highly flexible and therefore rarely break. On the contrary, in old age, when the ratio of organic and inorganic substances changes in favor of the latter, bones become less elastic and more fragile, as a result of which bone fractures are most often observed in old people.
Bone structure.
The structural unit of bone, visible through a magnifying glass or at low magnification of a microscope, is osteon , i.e., a system of bone plates concentrically located around a central canal containing blood vessels and nerves.
Osteons do not adhere closely to each other, and the spaces between them are filled with interstitial bone plates. Osteons are not located randomly, but according to the functional load on the bone: in tubular bones parallel to the length of the bone, in spongy bones - perpendicular to the vertical axis, in flat bones of the skull - parallel to the surface of the bone and radially.
Together with the interstitial plates, osteons form the main middle layer of bone substance, covered from the inside (from the endosteum) by the inner layer of bone plates, and from the outside (from the periosteum) by the outer layer of the surrounding plates. The latter is penetrated by blood vessels coming from the periosteum into the bone substance in special perforating canals. The beginning of these canals is visible on the macerated bone in the form of numerous nutrient holes (foramina nutrfcia). The blood vessels passing through the canals ensure metabolism in the bone. Larger bone elements, visible to the naked eye on a cut or on an x-ray, are made up of osteons - crossbars of bone substance, or trabeculae. These trabeculae make up two kinds of bone substance: if the trabeculae lie tightly, then it turns out dense compact substance, substantia compacta. If the trabeculae lie loosely, forming bone cells between themselves like a sponge, then it turns out spongy, trabecular substance, substantia spongiosa, trabecularis (spongia, Greek - sponge).
The distribution of compact and cancellous substance depends on the functional conditions of the bone. The compact substance is found in those bones and in those parts of them that primarily perform the function of support (rack) and movement (levers), for example, in the diaphysis of tubular bones.
In places where, with a large volume, it is necessary to maintain lightness and at the same time strength, a spongy substance is formed, for example, in the epiphyses of tubular bones (Fig. 7).
The crossbars of the spongy substance are not arranged randomly, but regularly, also in accordance with the functional conditions in which a given bone or part of it is located. Since the bones experience a double action - pressure and muscle traction, the bone crossbars are located along the lines of compression and tension forces. According to the different directions of these forces, different bones or even parts of them have different structures. In the integumentary bones of the cranial vault, which primarily perform a protective function, the spongy substance has a special character that distinguishes it from other bones that carry all 3 skeletal functions. This spongy substance is called diploe, diploe (double), since it consists of irregularly shaped bone cells located between two bone plates - the outer, lamina externa, and the inner, lamina interna. The latter is also called vitreous, lamina vftrea, since it breaks when the skull is damaged more easily than the outer one.
Bone cells contain Bone marrow - organ of hematopoiesis and biological defense of the body. It is also involved in nutrition, development and bone growth. In tubular bones, the bone marrow is also located in the canal of these bones, therefore called the medullary cavity, cavitas medullaris.
Thus, all the internal spaces of the bone are filled with bone marrow, which forms an integral part of the bone as an organ.
There are two types of bone marrow: red and yellow.
Red bone marrow, medulla ossium rubra (for structural details, see the histology course), has the appearance of a tender red mass consisting of reticular tissue, in the loops of which there are cellular elements that are directly related to hematopoiesis (stem cells) and bone formation (bone builders - osteoblasts and bone destroyers - osteoclasts). It is penetrated by nerves and blood vessels that, in addition to the bone marrow, supply the inner layers of the bone. Blood vessels and blood elements give bone marrow its red color.
Yellow bone marrow, medulla ossium flava, owes its color to the fat cells of which it is mainly composed.
During the period of development and growth of the body, when greater hematopoietic and bone-forming functions are required, red bone marrow predominates (fetuses and newborns have only red marrow). As the child grows, the red marrow is gradually replaced by yellow marrow, which in adults completely fills the medullary cavity of the tubular bones.
The outside of the bone, with the exception of the articular surfaces, is covered with periosteum, periosteum.
Periosteum- this is a thin, strong connective tissue film of pale pink color, surrounding the bone from the outside and attached to it with the help of connective tissue bundles - perforating fibers that penetrate the bone through special tubules. It consists of two layers: outer fibrous (fibrous) and inner bone-forming (osteogenic, or cambial). It is rich in nerves and blood vessels, due to which it participates in the nutrition and growth of bone thickness. Nutrition is carried out by blood vessels penetrating in large numbers from the periosteum into the outer compact substance of the bone through numerous nutrient openings (foramina nutricia), and bone growth is carried out by osteoblasts located in the inner layer adjacent to the bone (cambium). The articular surfaces of the bone, free from periosteum, are covered by articular cartilage, cartilage articularis.
Thus, the concept of bone as an organ includes bone tissue, which forms the main mass of the bone, as well as bone marrow, periosteum, articular cartilage and numerous nerves and vessels.
Test questions for the lecture:
1. The concept of bone (hard) and connective tissue skeleton,
2. General overview of the human skeleton, classification of bones.
3. The structure of bone as an organ, periosteum, bone marrow.
4. Osteon structure: Haversian canals, bone plates; bone cells - osteoblasts, osteocytes, osteoclasts.
5. Bone structure; diaphysis, metaphysis, epiphysis, apophysis, compact and spongy substance.
6. Chemical composition of bone.
Lecture No. 5
Bone in x-ray image. The influence of labor and sports on the structure of the bones of a living person. The relationship between social and biological factors in the structure of bones.
Purpose of the lecture. Consider the structure of bone in the whole organism.
lecture plan:
1. Consider the x-ray anatomy of bones.
2. Consider the dependence of bone development on internal and external factors.
3. Reveal the structural and functional relationships between the active and passive parts of the musculoskeletal system.
4. Reveal the role of the Russian scientist P.F. Lesgaft in the study of the interdependence of the muscular and skeletal systems.
5. Consider the relationship between social and biological factors in the formation of the human skeleton.
X-RAY ANATOMY OF BONES.
On radiographs, compact and spongy substances are clearly distinguishable. The first gives an intense contrasting shadow, corresponding to the plane of the cortical layer, and in the area of substantia spongiosa the shadow has a network-like character (see Fig. 1).
Compact substance of the epiphyses of tubular bones and the compact substance of bones, built primarily from spongy substance (bones of the wrist, tarsus, vertebrae), has the appearance of a thin layer bordering the spongy substance. This thin cortical layer on the articular sockets appears thicker than on the articular heads.
In the diaphyses of tubular bones, compact the substance varies in thickness: in the middle part it is thicker, tapering towards the ends. In this case, between the two shadows of the cortical layer, a bone marrow cavity is noticeable in the form of some clearing against the background of the general shadow of the bone. If this cavity is not traced throughout its entire length, this indicates the presence of a pathological process.
X-ray contours of the compact substance of the diaphysis clear and smooth. At the attachment points of ligaments and muscles, the contours of the bone are uneven. Against the background of the cortical layer of the diaphysis, thin stripes of clearing are noticeable, corresponding to the vascular canals. They are usually located obliquely: in the long tubular bones of the upper limb - closer and towards the elbow joint; in the long tubular bones of the lower limb - further and in the direction from the knee joint; in short tubular bones of the hand and foot - closer and towards the end that does not have a true epiphysis.
Spongy substance on x-ray has the appearance of a looped network consisting of bone crossbars with enlightenments between them. The nature of this network depends on the location of the bone plates in a given area, according to the compression and tension lines.
Bone development. X-ray examination of the skeletal system becomes possible from the 2nd month of uterine life, when ossification points appear on the basis of cartilage or connective tissue.
Appearance ossification points easily identified on radiographs, and these points, separated by cartilage tissue, look like separate bone fragments. They can give rise to erroneous diagnoses of fracture, fracture or necrosis (death) of the bone. Because of this, knowledge of the location of bone nuclei, the timing and order of their appearance is extremely important in practical terms.
Therefore, we present ossification in all relevant places on the basis of data not from an anatomical study of corpses, but from x-ray anatomy (study of a living person).
In cases of non-fusion of accessory nuclei with the main part of the bone, they can remain for life in the form of independent, unstable or accessory bones. Their detection on an x-ray may lead to diagnostic errors.
All major ossification nuclei appear in the bones of the skeleton before the onset of puberty, called puberty. WITH the onset of puberty the fusion of the epiphyses with the metaphyses begins, i.e., the transformation of synchondrosis connecting the bone epiphysis with the bone metaphysis into synostosis. This is radiographically expressed in the gradual disappearance of clearing at the site of the metaepiphyseal zone, corresponding to the metaepiphyseal cartilage separating the epiphysis from the metaphysis. Upon the onset of complete synostosis, traces of the former synchondrosis cannot be determined (Fig. 1).
Aging of the skeletal system. In old age, the skeletal system undergoes significant changes. On the one hand, there is a decrease in the number of bone plates and bone loss (osteoporosis); on the other hand, excessive bone formation occurs in the form of bone growths (o s t e f i t o v) and calcification of articular cartilage, ligaments and tendons at the site of their attachment to the bone.
Accordingly, the X-ray picture of aging of the osteoarticular apparatus consists of the following changes, which should not be interpreted as symptoms of pathology (degeneration).
I. Changes caused by atrophy of bone substance:
1) osteoporosis (on the x-ray the bone becomes more transparent);
2) deformation of the articular heads (disappearance of their round shape, “grinding down” of the edges, appearance of “corners”).
II. Changes caused by excessive deposition of lime in the connective tissue and cartilaginous formations adjacent to the bone:
1) narrowing of the joint “X-ray” gap due to calcification of articular cartilage;
2) strengthening of the diaphysis relief due to calcification at the site of attachment of tendons and their fibrous sheaths;
3) bone growths - osteophytes , formed as a result of calcification of ligaments at the site of their attachment to the bone.
The described changes are especially clearly visible in the spine and hand. In the remaining parts of the skeleton, three main radiological symptoms of aging are observed: osteoporosis, increased bone relief and narrowing of joint spaces. For some people, these signs of aging are noticed early (30-40 years), for others - late (60-70 years) or not at all.
Summarizing the presentation of general data on the ontogenesis of the skeletal system, we can say that x-ray examination makes it possible to more accurately and deeply study the development of the skeleton in its functioning state than the study of only cadaveric material.
In this case, a number of normal morphological changes are noted:
1) the appearance of ossification points - main and additional;
2) the process of their synostosis with each other;
3) senile involution of bone.
The described changes are normal manifestations of age-related variability of the skeletal system. Consequently, the concept of “norm” cannot be limited only to an adult and considered as a single type. This concept must be extended to all other ages.
DEPENDENCE OF BONE DEVELOPMENT ON INTERNAL AND EXTERNAL FACTORS
The skeleton, like any organ system, is a part of the body that reflects various processes occurring in it. Therefore, many factors influence the development of the skeletal system.
Influence of internal factors. X-ray examination reveals a number of morphological changes in bones, depending on the activity of other organs. It is especially clearly determined by radiography connection between the skeletal system and the endocrine glands. The active activation of the gonads entails the onset of puberty, puberty . Before this, in the prepubertal period, the activity of other endocrine glands, the appendage of the brain - the pituitary gland, increases, the function of which is associated with the appearance of ossification nuclei. By the beginning of the prepubertal period, all the main ossification points appear, and there is a gender difference in the timing of their appearance: in girls 1-4 years earlier than in boys. The onset of the prepubertal period, associated with the function of the pituitary gland, coincides with the appearance of an ossification nucleus in the pisiform bone, which belongs to the category of sesamoid bones.
On the eve of puberty, other sesamoid bones also ossify, namely at the metacarpophalangeal joint of the first finger. The beginning of the pubertal period, when, in the words of the famous endocrine researcher Beadle, “the sex glands begin to play the main melody in the endocrine concert,” is manifested in the skeletal system by the onset of synostoses between the epiphyses and metaphyses, with the very first such synostosis observed in the first metacarpal bone. Therefore, based on its comparison with other data on sexual development (the appearance of terminal vegetation, the onset of menstruation, etc.), synostosis of the 1st metacarpal bone is considered an indicator of incipient puberty, i.e., an indicator of the onset of puberty; among St. Petersburg residents, synostosis of the first metacarpal bone occurs at the age of 15-19 years in boys and at 13-18 years in girls.
Full puberty, also receives a well-known reflection in the skeleton: at this time, synostoses of the epiphyses with metaphyses in all tubular bones end, which is observed in women aged 17-21 years, and in men - at 19-23 years. Since the end of the process of synostosis ends the growth of bones in length, it becomes clear why men, whose puberty ends later than women, are generally taller than women.
Taking into account this connection of the skeletal system with the endocrine system and comparing data on the age-related characteristics of the skeleton with data on puberty and general development of the body, we can talk about the so-called “bone age”. Thanks to this, from the X-ray picture of some parts of the skeleton, especially the hand, it is possible to determine the age of a given individual or judge the correctness of his ossification process, which is of practical importance for diagnosis, forensic medicine, etc. Moreover, if the “passport” age indicates the number of years lived years (i.e. on the quantitative side), then the “bone” age to a certain extent indicates their qualitative side.
X-ray examination also reveals dependence of bone structure on the state of the nervous system, which, regulating all processes in the body, carries out, in particular, the trophic function of bone. At enhanced trophic function of the nervous system More bone tissue is deposited in the bone, and it becomes denser and more compact (osteosclerosis). On the contrary, when weakening of trophism bone loss is observed - osteoporosis. The nervous system also influences the bone through the muscles, the contraction of which it controls (as will be discussed below). Finally, the various parts of the central and peripheral nervous system determine the shape of the surrounding and adjacent bones. Thus, all vertebrae form the spinal canal around the spinal cord. The bones of the skull form a bony box around the brain and take on the shape of the latter. In general, bone tissue develops around elements of the peripheral nervous system, resulting in the formation of bone canals, grooves and pits that serve for the passage of nerves and other nerve formations (nodes).
Bone development is also in very close depending on the circulatory system. The entire process of ossification from the moment the first bone nucleus appears until the end of synostosis takes place with the direct participation of vessels, which, penetrating into the cartilage, contribute to its destruction and replacement with bone tissue. In this case, bone plates (Haversian) are deposited in a certain order around the blood vessels, forming Haversian systems with a central canal for the corresponding vessel. Consequently, when bone arises, it is built around blood vessels. This also explains the formation of vascular canals and grooves in the bones at the places where arteries and veins pass and adjoin them.
Ossification and bone growth after birth also occurs in close dependence on blood supply. It is possible to outline a number of stages of age-related variability in bone associated with corresponding changes in the bloodstream (Fig. 2).
1. Neonatal stage , characteristic of the fetus (the last months of intrauterine development) and the newborn; the vascular bed of the bone is divided into a number of vascular regions (epiphysis, diaphysis, metaphysis, apophysis), which do not communicate with each other (closedness, isolation) and within which the vessels do not connect to each other, do not anastomose (terminal nature of the vessels, “limb”) .
2. Infantile stage , characteristic of children before the onset of synostosis; the vascular regions are still separated, but within each of them the vessels anastomose with each other and their terminal character disappears (“closedness” in the absence of a “limb”).
3. Juvenile stage , characteristic of young men, begins with the establishment of connections between the vessels of the epiphysis and metaphysis through the metaepiphyseal cartilage, due to which the closedness of the epiphyseal begins to disappear. metaphyseal and diaphyseal vessels.
4. Mature stage , characteristic of adults; synostosis occurs, and all intraosseous vessels form a single system: they are not “closed” and not “finite”.
5. Senile stage , characteristic of old people; the vessels become thinner and the entire vascular network becomes poorer.
On the shape and position of the bones affect to the inside, for which they form bone receptacles, beds, pits, etc.
The formation of the skeleton and organs refers to the beginning of embryonic life; during their development, they influence each other, which is why there is a correspondence between organs and their bone containers, for example, the chest and lungs, the pelvis and its organs, the skull and the brain, etc.
The development of the entire skeleton must be considered in the light of these relationships.
Influence of external (social) factors on the structure and development of the skeleton. Unity of form and function in the structure of bones. Influencing nature in the process of labor activity, a person sets in motion his natural tools - arms, legs, fingers, etc. In the tools of labor, he acquires new artificial organs that complement and lengthen the natural organs of the body, changing their structure. And the man himself “...at the same time changes his own
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nature." Hence, labor processes have a significant impact on the human body as a whole, on its movement apparatus, including the skeletal system.
Reflects especially clearly on the skeleton muscle work. As experimental studies by P.F. Lesgaft have shown, the stronger the muscle work, the better the bone develops, and vice versa. At the sites of tendon attachment, protrusions (tubercles, processes,
roughness), and locally
Rice. 3. Radiographs of the metatarsal bones.
places of attachment of the muscles of the ballerina (a) and sedentary workers (b).
attachments of muscle bundles - smooth or concave surfaces (pits).
RELATIONSHIP OF THE ACTIVE AND PASSIVE PART OF THE MUSCULOCAL SYSTEM
The more developed the muscles, the better the places of muscle attachment on the bones are expressed. This is why the bone relief, caused by the attachment of muscles, is more pronounced in an adult than in a child, and more pronounced in men than in women.
Long-term and systematic muscle contractions, as occurs during physical exercise and professional work, gradually cause, through the reflex mechanisms of the nervous system, a change in metabolism in the bone, resulting in an increase in bone matter, called working hypertrophy (Fig. 3). This working hypertrophy causes changes in the size, shape and structure of bones, which are easily determined radiographically in living people.
Different professions require different physical work, which is associated with different degrees of participation of certain bones in this work.
Increased physical stress on the movement apparatus causes working hypertrophy of the bones, as a result of which their shape, width and length change, as well as the thickness of the compact substance and the size of the medullary space; The structure of the spongy substance also changes.
Width of bones. Thus, for loaders, the width of their bones, as their professional experience increases, reaches significantly larger sizes than for representatives of office work.
Research by P.F. Lesgaft identified a number of patterns in the relationship between the active and passive parts of the musculoskeletal system. They established:
1. Bones develop more strongly, the greater the activity of the surrounding muscles; with less load on the organs, they become thinner, longer, narrower and weaker.
2. The shape of the bones changes depending on the pressure of the surrounding organs (muscles, skin, eyes, teeth, etc.), they thicken and are directed towards the least resistance.
3. The shape of the bone also changes due to the pressure of the external parts; the bone grows more slowly due to increased external pressure, bending under the influence of one-sided action.
4. Fascia - thin membranes that cover and separate the muscles and are directly influenced by them, also exert lateral pressure on the bones.
5. Bones are active in relation to the shape of their structure (architecture), playing the role of racks or supports for surrounding organs.
RELATIONSHIP OF SOCIAL AND BIOLOGICAL IN BONE STRUCTURE
Bone is not a frozen model that does not change after its formation, as previously thought. Such a metaphysical view has been overcome by modern anatomy, which considers the vital activity of bone, even in an adult, as a continuous exchange of substances with other tissues of the body, as a dialectical unity and struggle of two opposing processes - bone formation and bone destruction (resorption; resorptio - resorption). As a result of this struggle, there is a constant change in bone structure and its chemical composition; so, for example, the femur is completely renewed within 50 days. In this case, the bone is subject to a number of biological laws: adaptation (adaptation) to new living conditions, the unity of the organism and the environment, the unity of form and function, variability as a result of exercise or lack of exercise, the effect of mechanical compression of one part on another, etc. The morphological expression of these laws in relation to the skeleton is the restructuring of the bone structure (bone remodeling) in accordance with changing functional needs, as mentioned above.
This, in brief, is the “biological side” of the relationship between the social and the biological. As for the “social side”, the following must be kept in mind.
Various social factors (profession, lifestyle, diet, etc.) are associated with different physical activity, which determines the different degrees of participation of certain bones in a given work. The work of a professional worker requires the body to remain in one position or another for a long time (for example, a bent position over a machine or a desk) or a constant change in body position in one direction or another (for example, bending the torso forward and throwing it back in carpenters). Therefore, the nature of the professional load and its volume determine the greater or lesser participation in the work of a given part of the skeleton and each bone separately and determine the different nature and degree of restructuring of its structure. When changing profession, bone restructuring is observed in the direction of increasing or weakening working hypertrophy, depending on the nature of the professional load. The growth of bones in length increases with favorable physical activity.
Bone aging occurs later in workers who have properly organized long-term physical labor, which does not cause premature wear of bone tissue.
The stated facts of individual variability of the skeletal system are due to both biological and social factors. Environmental irritants are perceived biologically by the body and lead to skeletal restructuring. The ability of bone tissue to adapt to changing functional needs through bone restructuring is the biological cause of bone variability, and the nature of the profession, the volume of professional workload, the intensity of work, the lifestyle of a given person and other social factors are the social reasons for this variability.
This is the relationship between the social and the biological in the structure of the skeleton. Knowing this relationship, it is possible to specifically influence the structure of the skeletal system by selecting appropriate physical exercises in work and sports and by changing social conditions of life.
Test questions for the lecture:
1. X-ray anatomy of bones.
2. Dependence of bone development on internal and external factors.
3. Structural and functional relationships between the active and passive parts of the musculoskeletal system.
4. The role of the Russian scientist P.F. Lesgaft in the study of the interdependence of the muscular and skeletal systems.
5. The relationship between social and biological factors in the formation of the human skeleton.
Lecture No. 6
General arthrosyndesmology.
Purpose of the lecture. Consider the functional and anatomical features of various types of bone connections.
lecture plan:
1. Consider the development of bone joints in phylogeny.
2. Consider the classification of bone connections.
3. Reveal the functional anatomy of syndesmoses.
4. Reveal the functional anatomy of synchrodrosis, synostosis, and semi-joints.
5. Consider the classification of joints according to the number of articular surfaces and the shape of the articular surfaces.
6. Consider the classification of joints according to the number of axes of motion.
7. Consider the general characteristics of combined joints and complex joints.
8. Consider the structure of the main and auxiliary elements of the joints.
9. Reveal the basic principles of joint biomechanics.
10. Reveal the functional and morphological features of the spinal column as a whole.
11. Reveal the functional and morphological features of the pelvis as a whole.
12. Reveal the functional and morphological features of the foot as a whole.
DEVELOPMENT OF BONE JOINTS IN PHYLOGENESIS
The initial form of bone connection is their fusion with the help of connective or (later) cartilaginous tissue. However, this continuous method of connecting the bones limits the range of movement. With the formation of bone levers of movement, cracks and cavities appear in the tissue intermediate between the bones due to the resorption of the latter, as a result of which a new type of bone connection has arisen - discontinuous articulation. The bones began not only to connect, but also to articulate, joints were formed that allowed the bone levers to produce extensive movements. Thus, in the process of phylogenesis, 2 types of bone connections developed: the initial one was continuous, continuous with a limited range of movements, and the later one was discontinuous, allowing extensive movements. Reflecting this phylogenetic process in human embryogenesis, the development of bone joints goes through these 2 stages. Initially, the skeletal rudiments are continuously interconnected by layers of mesenchyme. The latter turns into connective tissue, from which the apparatus that connects the bones is formed. If the areas of connective tissue located between the bones turn out to be solid, then a continuous continuous connection of bones will result - fusion, or synarthrosis. If a cavity is formed inside them by resorption of connective tissue, then another type of connection occurs - cavitary, or discontinuous - diarthrosis.
Thus, according to development, structure and function, all bone joints can be divided into 2 large groups:
1. Continuous connections - synarthrosis(BNA) - earlier in development, immobile or sedentary in function.
2. Discontinuous connections - diarthrosis(BNA) - later in development and more mobile in function.
There is a transition between these forms - from continuous to discontinuous or vice versa. It is characterized by the presence of a small gap that does not have the structure of a real articular cavity, as a result of which this form is called semi-joint - symphysis, symphysis (BNA).
bone, os, ossis, As an organ of a living organism, it consists of several tissues, the most important of which is bone.
Chemical composition of bone and its physical properties.
Bone substance consists of two types of chemical substances: organic (1/3), mainly ossein, and inorganic (2/3), mainly calcium salts, especially lime phosphate (more than half - 51.04%). If the bone is exposed to a solution of acids (hydrochloric, nitric, etc.), then the lime salts dissolve (decalcinatio), and the organic matter remains and retains the shape of the bone, being, however, soft and elastic. If the bone is fired, the organic substance burns out, and the inorganic substance remains, also retaining the shape of the bone and its hardness, but being very fragile. Consequently, the elasticity of bone depends on ossein, and its hardness on mineral salts. The combination of inorganic and organic substances in living bone gives it extraordinary strength and elasticity. This is also confirmed by age-related changes in bones. In young children, who have relatively more ossein, the bones are highly flexible and therefore rarely break. On the contrary, in old age, when the ratio of organic and inorganic substances changes in favor of the latter, bones become less elastic and more fragile, as a result of which bone fractures are most often observed in old people.
Bone structure
The structural unit of bone, visible through a magnifying glass or at low magnification of a microscope, is an osteon, i.e., a system of bone plates concentrically located around a central canal containing blood vessels and nerves.
Osteons do not adhere closely to each other, and the spaces between them are filled with interstitial bone plates. Osteons are not located randomly, but according to the functional load on the bone: in tubular bones parallel to the length of the bone, in spongy bones - perpendicular to the vertical axis, in flat bones of the skull - parallel to the surface of the bone and radially.
Together with the interstitial plates, osteons form the main middle layer of bone substance, covered from the inside (from the endosteum) by the inner layer of bone plates, and from the outside (from the periosteum) by the outer layer of the surrounding plates. The latter is penetrated by blood vessels coming from the periosteum into the bone substance in special perforating canals. The beginning of these canals is visible on the macerated bone in the form of numerous nutrient holes (foramina nutricia). The blood vessels passing through the canals ensure metabolism in the bone. Osteons consist of larger elements of bone, visible to the naked eye on a cut or on an x-ray - the crossbars of the bone substance, or trabeculae. These trabeculae make up two types of bone substance: if the trabeculae lie tightly, then a dense compact substance, substantia compacta, is obtained. If the trabeculae lie loosely, forming bone cells between themselves like a sponge, then the result is a spongy, trabecular substance, substantia spongiosa, trabecularis (spongia, Greek - sponge).
The distribution of compact and cancellous substance depends on the functional conditions of the bone. The compact substance is found in those bones and in those parts of them that primarily perform the function of support (rack) and movement (levers), for example, in the diaphysis of tubular bones.
In places where, with a large volume, it is necessary to maintain lightness and at the same time strength, a spongy substance is formed, for example, in the epiphyses of tubular bones.
The crossbars of the spongy substance are not arranged randomly, but regularly, also in accordance with the functional conditions in which a given bone or part of it is located. Since the bones experience a double action - pressure and muscle traction, the bone crossbars are located along the lines of compression and tension forces. According to the different directions of these forces, different bones or even parts of them have different structures. In the integumentary bones of the cranial vault, which primarily perform a protective function, the spongy substance has a special character that distinguishes it from other bones that carry all 3 skeletal functions. This spongy substance is called diploe, diploe (double), since it consists of irregularly shaped bone cells located between two bone plates - the outer, lamina externa, and the inner, lamina interna. The latter is also called vitreous, lamina vftrea, since it breaks when the skull is damaged more easily than the outer one.
Bone cells contain bone marrow - an organ of hematopoiesis and biological defense of the body. It is also involved in nutrition, development and bone growth. In tubular bones, the bone marrow is also located in the canal of these bones, therefore called the medullary cavity, cavitas medullaris.
Thus, all the internal spaces of the bone are filled with bone marrow, which forms an integral part of the bone as an organ.
![](https://i1.wp.com/meduniver.com/Medical/Anatom/Img/stroenie_trubchatoi_kosti-a.jpg)
There are two types of bone marrow: red and yellow.
Red bone marrow, medulla ossium rubra(for structural details, see the histology course), has the appearance of a tender red mass consisting of reticular tissue, in the loops of which there are cellular elements that are directly related to hematopoiesis (stem cells) and bone formation (bone builders - osteoblasts and bone destroyers - osteoclasts) . It is penetrated by nerves and blood vessels that, in addition to the bone marrow, supply the inner layers of the bone. Blood vessels and blood elements give bone marrow its red color.
Yellow bone marrow, medulla ossium flava, owes its color to the fat cells of which it is mainly composed.
During the period of development and growth of the body, when greater hematopoietic and bone-forming functions are required, red bone marrow predominates (fetuses and newborns have only red marrow). As the child grows, the red marrow is gradually replaced by yellow marrow, which in adults completely fills the medullary cavity of the tubular bones.
The outside of the bone, with the exception of the articular surfaces, is covered with periosteum, periosteum.
Periosteum- this is a thin, strong connective tissue film of pale pink color, surrounding the bone from the outside and attached to it with the help of connective tissue bundles - perforating fibers that penetrate the bone through special tubules. It consists of two layers: outer fibrous (fibrous) and inner bone-forming (osteogenic, or cambial). It is rich in nerves and blood vessels, due to which it participates in the nutrition and growth of bone thickness. Nutrition is carried out by blood vessels penetrating in large numbers from the periosteum into the outer compact substance of the bone through numerous nutrient openings (foramina nutricia), and bone growth is carried out by osteoblasts located in the inner layer adjacent to the bone (cambium). The articular surfaces of the bone, free from periosteum, are covered by articular cartilage, cartilage articularis.
Thus, the concept of bone as an organ includes bone tissue, which forms the main mass of the bone, as well as bone marrow, periosteum, articular cartilage and numerous nerves and vessels.
Video lesson: Bone as an organ. Development and growth of bones. Classification of bones according to M.G. I'll gain weight
Other video lessons on this topic are:A person knows a lot about his body, for example, where the organs are located, what function they perform. Why not penetrate deep into the bone and find out its structure and composition? This is very interesting, because the chemical composition of bones is very diverse. It helps to understand why each bone element is very important and what function it has.
basic information
Living bone in adults has:
- 50% - water;
- 21.85% - substances of inorganic type;
- 15.75% - fat;
- 12.4% - collagen fibers.
Inorganic substances are different salts. Most of them are represented by lime phosphate (sixty percent). Calcium carbonate and magnesium sulfate are present in smaller quantities (5.9 and 1.4%, respectively). Interestingly, all earthly elements are represented in the bones. Mineral salts can be dissolved. To do this, you need a weak solution of nitric or hydrochloric acid. The process of dissolution in these substances has its own name - decalcification. After it, only organic matter remains, which retains its bone form.
Organic matter is porous and elastic. It can be compared to a sponge. What happens when this substance is removed through combustion? The shape of the bone remains the same, but now it becomes brittle.
It is clear that only the interaction of inorganic and organic substances makes the bone element strong and elastic. The bone becomes even stronger due to the composition of the spongy and compact substance.
Inorganic composition
About a century ago, it was suggested that human bone tissue, or rather its crystals, are similar in structure to apatites. Over time this has been proven. Bone crystals are hydroxylapatites, and their shape is similar to rods and plates. But the crystals are only a fraction of the mineral phase of the tissue, the other fraction is amorphous calcium phosphate. Its content depends on the age of the person. Young people, teenagers and children have a lot of it, more than crystals. Subsequently, the ratio changes, so at an older age there are more crystals.
Every day, the bones of the human skeleton lose and gain again about eight hundred milligrams of calcium
The adult human body has more than one kilogram of calcium. It is found mainly in dental and bone elements. When combined with phosphate, hydroxyapatite is formed, which does not dissolve. The peculiarity is that in the bones the main part of calcium is regularly renewed. Every day, the bones of the human skeleton lose and gain again about eight hundred milligrams of calcium.
The mineral lobe has many ions, but pure hydroxyapatite does not contain them. There are ions of chlorine, magnesium and other elements.
Organic composition
95% of the organic type matrix is collagen. If we talk about its significance, then, together with mineral elements, it is the main factor on which the mechanical properties of bone depend. Bone tissue collagen has the following features:
- it contains more hydroxyproline compared to skin collagen;
- it contains many free ε-amino groups of oxylysine and lysine residues;
- it contains more phosphate, the main part of which is associated with serine residues.
Dry demineralized bone matrix contains almost twenty percent non-collagenous proteins. Among them there are parts of proteoglycans, but they are few. The organic matrix contains glycosaminoglycans. They are believed to be directly related to ossification. In addition, if they change, ossification occurs. The bone matrix contains lipids, a direct component of bone tissue. They are involved in mineralization. The bone matrix has another feature - it contains a lot of citrate. Almost ninety percent of it is the share of bone tissue. Citrate is believed to be important for the mineralization process.
Substances of bone
Most of the bones of an adult human contain lamellar bone tissue, from which two types of substance are formed: spongy and compact. Their distribution depends on the functional loads placed on the bone.
If we consider the structure of bones, then the compact substance plays an important role in the formation of the diaphysis of tubular bone elements. It, like a thin plate, covers the outside of their epiphyses, flat, spongy bones, which are built from spongy substance. The compact substance contains a lot of thin tubules, which consist of blood vessels and nerve fibers. Some canals are essentially parallel to the bony surface.
The walls of the channels located in the center are formed by plates whose thickness ranges from four to fifteen microns. They seem to be inserted into each other. One channel near itself can have twenty similar records. The composition of the bone includes an osteon, that is, the union of a canal located in the center with plates near it. Between the osteons there are spaces that are filled with intercalary plates.
In the structure of bone, spongy substance is no less important. Its name suggests that it is similar to a sponge. The way it is. It is built with beams, between which there are cells. Human bone is constantly under stress in the form of compression and tension. They determine the dimensions of the beams and their location.
The bone structure includes the periosteum, that is, the connective tissue membrane. It is firmly connected to the bone element with the help of fibers that extend into its depth. The bone has two layers:
- External, fibrous. It is formed by collagen fibers, thanks to which the shell is durable. This layer contains nerves and blood vessels.
- Internal, sprout. Its structure contains osteogenic cells, thanks to which the bone expands and recovers after injury.
It turns out that the periosteum performs three main functions: trophic, protective, bone-forming. Speaking about the structure of bone, we should also mention the endosteum. The bone is covered from the inside with it. It looks like a thin plate and has an osteogenic function.
A little more about bones
Due to their amazing structure and composition, bones have unique characteristics. They are very flexible. When a person performs physical activity and trains, the bones become flexible and adapt to changing circumstances. That is, depending on the load, the number of osteons increases or decreases, and the thickness of the plates of substances changes.
Every person can contribute to optimal bone development. To do this, you need to exercise regularly and moderately. If your life is dominated by sedentary activities, your bones will begin to weaken and become thinner. There are bone diseases that weaken them, for example, osteoporosis, osteomyelitis. Bone structure can be influenced by occupation. Of course, heredity plays an important role.
So, a person is not able to influence some features of the bone structure. Still, some factors depend on it. If, from childhood, parents ensure that the child eats properly and engages in moderate physical activity, his bones will be in excellent condition. This will significantly affect his future, because the child will grow up to be a strong, healthy, that is, successful person.
First of all, our bones consist of bone substance, which contains calcium salts. In general, bone as an organ also consists of soft tissues such as articular cartilage and periosteum (in the language of specialists, periosteum), bone marrow inside the bones, as well as blood vessels and nerves that pass through the periosteum and .
Bone substance
Bone matter makes up the bulk of our bones. It is very strong, as it contains calcium (experts talk about calcium salts), its weight can reach up to 70% of the weight of the bones. Bone matter occurs in bones mainly in two forms: compact bone substance And cancellous bone substance.
Compact bone substance is a hard, dense, whitish mass. First of all, it seems to envelop (cover) with a thick layer the bone marrow cavities inside long tubular bones (for example, femurs or humeri). But cancellous bone substance consists of fairly thin plates/bars. It can be found in our short, flat bones, such as the vertebrae.
Bone substance consists of mature bone cells called osteocytes. Osteocytes have processes and with the help of these processes they connect with each other. Working together with young osteoblast cells, which are responsible for bone formation, new bone begins to grow. Bone tissue is destroyed by cells called osteoclasts.
Articular cartilage
Articular cartilage is found in almost all bones, with the exception of the skull bones. They cover the articular surfaces and are the last remaining part of the skeleton from embryonic development.
Periosteum
The periosteum (which experts call the periosteum) covers the outside of all our bones. Therefore, the bone substance itself is nowhere to be seen. It is covered by either periosteum or articular cartilage.
Bone marrow
Bone marrow is the soft mass that is found in cavities inside bones. Bone marrow is red and yellow. Red bone marrow is responsible for hematopoiesis in the body. And yellow bone marrow is mostly adipose tissue.
Yellow bone marrow does not appear in a person immediately, but gradually during human development, red bone marrow is replaced by yellow one. Therefore, the older a person gets, the more yellow bone marrow he has. In adults, yellow bone marrow fills the central part of long tubular bones (this could be, for example, the humerus), which experts call the diaphysis. Red bone marrow is found primarily inside short, flat bones (such as inside the vertebrae).
Blood vessels and nerves
Blood vessels and nerves are found in the bone substance, in the periosteum, and in the bone marrow. They transmit information, nutrients and oxygen to bone cells. Through tiny holes on the surface of the bones, they enter the bone, and from the bone they exit into the circulatory system or, respectively, into the nerves that connect them to the nervous system.
Bone tissue is distinguished by a number of very unique qualities that sharply distinguish it from all other tissues and systems of the human body and place it in a separate place. The main and main feature of bone tissue is its richness in mineral salts.
If we take the body weight of an adult as an average of 70 kg, then the bone skeleton weighs 7 kg, and together with the bone marrow - 10 kg (muscles - “meat” - weigh 30 kg). The bones themselves, by weight, are 25% water, 30% organic matter and 45% minerals. The water content and therefore the relative content of other ingredients varies. The amount of water is comparatively very large in embryonic life, it decreases in childhood and gradually decreases with the growth and development of the child, adolescent and mature person, reaching in old age the smallest ratio to total weight. With age, bones literally dry out.
The organic composition of bones is formed mainly from proteins - proteins, mainly ossein, but the complex organic part of bone tissue also includes some albumins, mucoids and other substances of a very complex chemical structure.
What is the mineral composition of bone matter that interests us most? 85% of the salts are lime phosphate, 10.5% calcium carbonate, 1.5% magnesium phosphate, and the remaining 3% are sodium, potassium, chlorine and some elements rare for the human body. Calcium phosphate, therefore constituting 19/20 of the contents of the total salty bone matter, forms 58% of the total weight of the bones.
Phosphoric acid salts have a crystalline structure, and the crystals are located in the bone correctly and naturally. A very thorough study of the mineral skeleton of bone matter, carried out in the 30s using the most advanced methods, primarily through x-ray structural analysis, showed that inorganic human bone matter has the structure of phosphatite-apatite, namely hydroxyl-apatite. It is interesting that the apatite in human bones (and teeth) is close or even similar to the natural mineral apatite in dead nature. This identity of apatite of human bone and mining origin is also indicated by their comparative study in polarized light. Human bone apatite is also distinguished by the content of a small amount of chlorine or fluorine halogen. Some structural analysis specialists are of the opinion that in human bones apatite is still associated with other chemical compounds, i.e. that crystals of inorganic bone substance are a mixture of two inorganic chemicals, one of which is close to apatite. It is believed that the most correct physical and chemical structure of bone apatite was deciphered by the Hungarian scientist St. Naray-Szabo. The most probable formula for the structure of the inorganic composition of bone is: ZSA 3 (PO 4) 2. CaX 2, where X is either Cl, F, OH, V2O, 1/2 SO 4, 1/2 CO 3, etc. There are also indications that apatite consists of two molecules - CaF. Ca 4 (PO 4) 3 or CaC1. Ca 4 (PO 4) 3.
Extremely interesting are the indications of Reynolds et al. that during certain pathological processes bones lose their normal chemical apatite structure. This occurs, for example, in hyperparathyroid osteodystrophy (Recklinghausen's disease), while in Paget's disease the apatite crystal structure is completely preserved.
Bone tissue is, albeit very ancient in phylogeny, but at the same time highly developed and extremely finely and in detail differentiated, extremely complex in all its life manifestations mesenchymal connective tissue.
Changes in bones during various pathological processes are infinitely diverse; for each individual disease, in each individual bone, in each individual case, the pathoanatomical and pathophysiological, and therefore the x-ray picture, has its own characteristics. All this enormous variety of painful phenomena is reduced, however, in the end only to some not so numerous elementary qualitative and quantitative processes.
A disease, as is known, is not only a perverted arithmetic sum of individual normal phenomena; under pathological conditions, specific qualitative changes arise in the whole organism and in individual organs and tissues, for which there are no normal prototypes. Painfully altered bone also undergoes deep qualitative metamorphosis. The periosteum, for example, forming a callus at the site of a diaphyseal fracture, begins to perform a new function that is not normally characteristic of it, it produces cartilage tissue. A bone tumor is associated with the development, for example, of epithelial, myxomatous, giant cell and other formations that are as foreign to normal bone histologically as deposits of cholesterol in xanthomatosis or kerasin in Gaucher disease are chemically unusual for it. The bone apparatus during rickets or Paget's restructuring acquires completely new physical, chemical, biological and other qualities for which in normal bone we are not able to find quantitative criteria for comparison.
But these qualitative properties, specific to pathological processes in the bone substance, unfortunately, cannot themselves be directly determined radiographically; they appear on radiographs only in the form of indirect, secondary symptoms. The power of radiology does not lie in recognizing and studying them. Only when the qualitatively changed tissue in its quantitative definition has reached the level of possible detection does the x-ray method of research come into its own. With the help of impeccable experimental studies, Pauline Mack (Mack) proved that of the various components of bone tissue, the absorption of X-rays occurs by 95% due to the mineral composition (80% of the rays are retained by calcium and 15% by phosphorus), and only up to 5%. The shadow image of bones is caused by the organic “soft” ingredient of bone tissue. Therefore, due to the very nature of X-ray examination, in the X-ray diagnosis of diseases of bones and joints, the assessment of quantitative changes in bone tissue comes to the fore. You cannot measure distance with scales. The radiologist, using his extremely valuable, but still one-sided method, is currently still forced to limit himself to the analysis of mainly two main quantitative processes of bone activity, namely the creation of bone and its destruction.