the main
about the project
Medicine news
To authors
Licensed books on medicine
<< Ahead Next >>

General information

In accordance with the prevailing frequency and importance of diseases of the skeletal system as compared with lesions of muscles and soft tissues, most of this chapter is devoted to bone pathology.

The skeleton consists of 206 bones, differing in size and shape (tubular, flat, cuboid). Bones play an important role in mineral homeostasis, are the site of hematopoiesis, provide mechanical support for movement and protection, determine the size and shape of the human body. They are connected by many joints that are involved in providing movement and stability.

Bone tissue is one of the types of connective tissue that is calcified (mineralized) under normal conditions. Using biochemical methods, it was established that bone tissue consists of an organic matrix (35%) and inorganic elements (65%). One of the inorganic components is calcium hydroxyapatite [Ca10 (PO4) 6 (OH) 2], a mineral that not only provides strength and hardness, but is also a “storage” of 99% of calcium ions, 80% of phosphorus, 65% of sodium and magnesium. The formation of hydroxyapatite crystals in the bones occurs by converting a liquid material into a dense material (by analogy with the crystallization of water upon freezing). This process is caused by the organic matrix and is governed by many factors, many of which are not yet known. The level of mineralization can vary, but its duration, as a rule, is 12–15 days. The bone that remains unmineralized is called the osteoid. Organic components of bone tissue include matrix proteins and cells. Most of the bone matrix proteins are represented by type I collagen and a small amount of non-collagen proteins. Cellular elements make up only 2% of bone mass. They provide renewal and maintenance of this tissue throughout life. The bone-forming elements are precursor cells, osteoblasts and osteoclasts.

Progenitor cells are pluripotent (totipotent, polypotent; I mean their different possibilities with respect to the directions of differentiation) mesenchymal stem cells. They are located near the bone surfaces and, with appropriate stimulation, are capable of producing offspring by dividing, differentiating into osteoblasts, which is extremely important for physiological growth, renewal and restoration of bone.

Osteoblasts are located on the surface of the bone. They synthesize, transport and distribute many matrix proteins. These cells also initiate the mineralization process. At certain times, osteoblasts are collected in groups of up to 400 cells. The functional activity of these groups is coordinated, since by this time the bone already consists of structural units, giving it greater strength and stability. Osteoblasts have receptors for hormones (parathyroid hormone, estrogen), vitamin D, cytokines, and growth factors that regulate the differentiation, growth, and metabolism of bone cells. Once the osteoblasts are surrounded by the matrix, they become osteocytes. They have long cytoplasmic processes that give the cells a spider-like appearance.

Osteocytes are not involved in metabolism, but they play an important role in controlling daily fluctuations in serum levels of calcium and phosphorus. Being imprisoned in the bone tissue, osteocytes communicate with superficial cells and between themselves using a complex network of tubules passing through the matrix. The processes of osteocytes cross the canaliculi, and the contacts of these cells in the zones of slit-like joints (nexus) provide for the transfer of substrates and potentials of the surface membrane (plasmolemma).

Osteoclasts are cells responsible for bone resorption (resorption). These are cell derivatives - precursors of granulocyte monocytes, localized in the hematopoietic part of the bone marrow. They contain 6–12 nuclei and are closely related to the bone surface. Resorption pits, which are created and often populated by these cells, appear in the morphological literature under the name of Gaussian lacunae (J.Howship). They usually have scalloped edges. On that part of the osteoclast plasmolemma, which is located on the resorptive surface, a number of villous processes appear. So you create an i-corrugated border that serves to increase the surface membrane area. The plasmolemma, which surrounds this area along the entire edge, forms a zone of hermetic closure with the underlying bone, preventing the “expansion” of the osteolytic action of enzymes and other substances performing resorption. Self-sustaining extracellular resorption space, hermetically limited on all sides, resembles a secondary lysosome. Osteoclasts oxidize the environment of this space by “pumping” hydrogen ions into it, which contributes to the dissolution of minerals. In addition, osteoclasts secrete into the space of many enzymes that catalyze the splitting of the protein matrix into amino acids, as well as the release and activation of growth factors and enzymes. Among the latter, we call collagenase, which at the time of release is deposited and is associated with the matrix with the help of osteoblasts. Thus, as soon as the bone breaks down into elementary units, certain substances are released, which initiate its renewal (regeneration).

Collagen type I forms the core of the matrix and makes up 90% of its organic component. Osteoblasts are capable of depositing collagen, either as a disordered plexus, forming a coarse-fibered bone, or as a connected and complex complex, forming a lamellar bone. The coarse fibrous bone is found in the skeleton of embryos and fetuses. In an adult, it can be found in the zones of bone growth (Fig. 24.1, A). The advantages of coarse-fiber bones are expressed in the speed of formation and equal strength in all directions. The presence of areas of such bone in adults always indicates a pathological process, but is not a diagnostic marker. For example, in circumstances that require rapid reparative stabilization, such as a fracture, coarse fibrous bone is primarily formed. It also forms around the sites of infection and forms the matrix of bone-forming tumors.

The lamellar bone, which gradually in the process of growth replaces the coarse-fiber bone, is formed much slower, but it has greater strength.
This tissue is represented in the adult body by two main types: compact and spongy bone. The compact bone forms a cortical (surface) layer of tubular bones. This layer is built from three systems. A system of osteons is located under the external bony plates (haversian system; S.Havers). Osteons are formed by concentric bone plates and contain in the center the vascular channels of osteon (gaversovy channels). Between osteons there are intercalated bone plates. Under the system of osteons is a system of internal common plates. In addition to the vascular canals of osteon, compact bone permeates the nutritional canals (Folkmann channels; AW Volkmann), through which blood vessels and nerves pass (Fig. 24.1, B, C).

Below the system of osteons are bone trabeculae, which are a spongy bone. In the long tubular bones of the skeleton, the spongy bone fills the inner part of the epiphysis (the widest articular end of these bones) and the metaphysis (the part of the diaphysis adjacent to the epiphyseal cartilage). Diaphases of such tubular bones contain spongy bone in the base

Fig. 24.1.

Bone structure


And - coarse fibrous bone; B - compact bone.

Fig. 24.1. Continued.

AT -

two osteons of compact bone

in the center of which bone canals are visible (haversian channels), and in the concentric plates there are process osteocytes.

on the margins of the bone marrow cavities, i.e. closer to the metaphysics. 13 flat bones (for example, in the parietal bone or scapula) the space between two plates of a compact substance is entirely occupied by a spongy bone.

Non-collagen bone proteins are associated with the matrix and are grouped according to their functions as adhesive, calcium-bound, mineralized, enzymes, cytokines, and growth factors. Only osteocalcin is specific for bone tissue. It is determined in serum and serves as a reliable marker of osteoblastic activity. Cytokines and growth factors control the proliferation of bone cells, their differentiation and metabolism. They play an important role in the transmission (translation) of mechanical and metabolic signals to ensure local bone cell activity and adaptation processes.

Formation (modeling) and renewal (remodeling) of bone tissue. Osteoblasts and osteoclasts interact in a coordinated manner and are now regarded as a single functional bone system, known as the “basic multicellular unit”. The processes of bone formation and resorption are closely related to each other, and their balance determines the skeletal mass in different periods of life. During growth and growth of the skeleton (modeling), bone formation prevails. When the skeleton matures, the processes of destruction and renewal (remodeling) equalize. It happens like this. The peak of bone mass is achieved in a young adult body, and 5–10% of the total skeleton mass is updated annually. At the same time, the amount of bone substance that is absorbed and newly created by the main multicellular units becomes approximately equal. However, from the third decade of life, resorption begins to prevail over osteogenesis, which results in a gradual decrease in skeletal mass.

Osteoblasts provide the largest part of local control in the formation and maintenance of the skeleton system, since they not only produce the bone matrix, but also play an important role in the mediation of osteoclast activity. Many of the primary bone resorption stimulants - parathyroid hormone or parathyroid hormone with an associated protein, interleukin-1, interleukin-6, and tumor necrosis factor-p (TNF-p) - have minimal effect or do not have a direct effect on osteoclasts. Indeed, osteoblasts possess receptors for these substances, and as soon as they receive the appropriate signal, they release a soluble mediator that induces bone resorption by osteoclasts. Cytokines and growth factors [especially transforming growth factor-p (TGF-p)], released from the matrix during osteoid cleavage, on the principle of feedback, trigger the activation of osteoblasts for synthesis and deposition in the resorptive gaps of an equivalent amount of new bone [by Cotran RS, Kumar V., Collins T., 1998]. Bone tissue renewal and resorption, carried out in the order described, are not only related to each other in time and space, but also subject to control by local and systemic factors.

Growth and development of bones. Bone tissue is created by osteoblasts. After its creation, a further increase in bone mass is achieved only due to the deposition of new bone on the pre-existing matrix. Such a mechanism of approximate growth of bone mass is the key to understanding the various mechanisms of skeletal development.

The forerunner of the early skeleton is the primitive mesenchyme. Bones such as the cranial and some parts of the clavicles originate from an intramembrane formation and are formed by osteoblasts directly from the mesenchyme. On the contrary, in the process of creating an enchondral bone, the mesenchyme first forms the cartilage model, or the germ of the future bone. Subsequently, at about the 8th week of pregnancy, the cartilage in the center of the fetal bone undergoes degenerative changes, is mineralized and removed by osteoclast-type cells. This process, which progresses towards both future epiphyses, is accompanied by the growth of blood vessels and precursors of osteogenic elements, which ensure the creation of osteogenic cells.

A similar sequence of events occurs in the epiphysis. The plate of the cartilage model is immured between the expanding zones of ossification and is known as physis, or the growth plate. Chondrocytes within growth plates undergo a number of changes: proliferation, growth, degradation and mineralization. Cartilage salinity becomes a signal for a physiological counterweight — resorption of mineralized cartilage. The remains of mineralized cartilage are the basis for the deposition of bone on their surfaces. These structures form the primary spongy bone. The process of enchondral ossification is also found at the base of the articular cartilage. Through these mechanisms, the bones increase the length and the articular surfaces the diameter.

<< Ahead Next >>
= Go to tutorial content =

General information

    The emergence and spread of various microbial diseases is due to the fact that some microbes under certain conditions can acquire pathogenic properties. These are so-called pathogenic microorganisms. Pathogenic microorganisms can cause various diseases, including infectious ones. It is known that strict specificity is characteristic of pathogenic microorganisms, i.e.
    Saveliev Vladimir Petrovich 2. 50 years 3. KAPO them. Gorbunova 4. Technological engineer 5. G. Kazan, st. Zoryanskaya, 12, ap. 46. 6. November 20, 1999
    Yalovy Alexey Ivanovich 2. 42 years 3. Kazan Optical-Mechanical Plant 4. Locksmith 5. Kazan, Mira St., 6, apt. 67 6. April 24, 1999
    In the basins of rivers, lakes, seas and other bodies of water in Russia, there are about 1,350 different types of fish, about 250 of them are commercial. The largest commercial basins are the Northern, Baltic, Azov-Chernomorsky, Volga-Caspian and Far Eastern. Depending on the habitat and spawning grounds, fish are subdivided into marine, freshwater, migratory and semi-migratory. TO
  5. General information
    Fracture is a complete or partial violation of the integrity of the bone, which arose during an external mechanical effect. Fractures are closed when the bone fragments do not extend beyond the skin, and open when the bone fragments rupture the muscles, subcutaneous tissue, skin and go outside. When injuries can also form bone cracks and tears of bone bumps, which are attached
  6. General information
    Superficial skin burns up to 15% and deep to 7-10% of the body surface in young and middle-aged people do not cause gross disturbances of homeostasis, as well as the functions of internal organs and systems. With more extensive thermal lesions develops both local and clinically pronounced general reaction of the body, which begins immediately after injury and lasts not only the entire period
  7. General information
    Anesthetic machines are multifunctional, which is provided by various components (Fig. 4-1 and 4-2), such as: • Inlet openings (input ports) for medical gases: medical gases come from cylinders or through a stationary gas distribution system. • Pressure regulators (reducers) that reduce gas pressure. • A safety mechanism for reducing oxygen pressure,
  8. General information
    All entering the maternity ward are potential candidates for planned or emergency anesthesia. It follows from this that the anesthesiologist should know the following minimum about each patient of the department: age, number of pregnancies and deliveries, gestational age, concomitant diseases, PI complicating factors. If it is known in advance that anesthesia is unavoidable, then it is necessary to conduct a detailed
  9. General information
    Prevalence The prevalence of anesthesia complications is difficult to accurately assess for a number of objective reasons. First of all, in many cases it is impossible to establish exactly what caused the adverse outcome - concomitant diseases, the severity of the operation or anesthesia, because all three factors can be combined. In addition, it is difficult to formulate what exactly falls under the definition
  10. General information
    For many patients, the awakening after general anesthesia and the resolution of the effects of regional anesthesia is a strong physiological stress. Ideally, waking up after general anesthesia should be smooth, gradual and manageable. Unfortunately, patients often wake up in the operating room or on the way to the wake-up ward, which may be accompanied by airway obstruction, tremor, agitation,
  11. General information
    In 80% of cases, stroke is caused by insufficient blood flow through the cerebral arteries, and in 20% by hemorrhage (ch. 27). Ischemic stroke is caused by thrombosis or embolism of one of the cerebral arteries, or its spasm (ch. 26). Stroke is called neurological deficit, persisting for> 24 hours; its patho-morphological correlate is a focal brain infarction. Transient violations
  12. General information
    A. Pathogenesis. In the blood of HIV-infected patients, the number of CD4 lymphocytes and the ratio of CD4 / CD8 gradually decreases. In the early stages of HIV infection, 1,000–10,000 CD4 lymphocytes account for only 1 infected with HIV. As the disease progresses, the proportion and absolute number of infected CD4 lymphocytes increases, which is accompanied by an increase in the concentration of viral RNA in the plasma. Established
    The cerebrospinal fluid (liguor cerebrospinalis) is located in the subarachnoid space, the ventricles and the canals of the brain and spinal cord, which are connected with the venous and lymphatic pathways, perineural, perivascular and pericellular spaces. Thanks to this system, the cerebrospinal fluid washes away the nerve elements. The formation, circulation and composition of the cerebrospinal fluid depend on
    Among the diseases of the peripheral nervous system primarily distinguish neuritis and neuralgia. Neuritis is talked about in the presence of motor, sensory and vegetative disorders caused by pathological changes in the nerve, plexus or root. Neuralgia is defined as a symptom complex characterized by bouts of pain spreading along the nerve, plexus or root without
Medical portal "MedguideBook" © 2014-2016