Bone as an organ enters the system of organs of movement and support, and at the same time it differs in an absolutely unique shape and structure, rather characteristic architectonics of nerves and vessels. It is built mainly from special bone tissue, which is externally covered with the periosteum and inside contains bone marrow.
Key Features
Each bone as an organ has a specific size, shape and location in the human body. All this is significantly influenced by the various conditions in which they develop, as well as all sorts of functional loads experienced by the bones during the life of the human body.
Any bone is characterized by a certain number of sources of blood supply, the presence of specific places of their location, as well as the rather characteristic architectonics of blood vessels. All these features apply in the same way to the nerves that innervate this bone.
Structure
Bone as an organ includes several tissues, which are in certain proportions, but, of course, the most important among them is bone plate tissue, the structure of which can be seen in the example of the diaphysis (central section, body) of a tubular long bone.
The main part of it is located between the inner and outer surrounding plates and is a complex of insert plates and osteons. The latter is a structural and functional unit of bone and is considered on specialized histological preparations or thin sections.
Outside, any bone is surrounded by several layers of common or general plates, which are located directly under the periosteum. Through these layers pass specialized perforating channels, which contain the same blood vessels. At the border with the bone marrow cavity, the tubular bones also contain an additional layer with internal surrounding plates pierced by many different channels, expanding into cells.
The bone marrow cavity is completely lined with the so-called endostomy, which is an extremely thin layer of connective tissue, which includes flattened osteogenic inactive cells.
Osteons
Osteon is represented by concentrically placed bone plates, which look like cylinders of different diameters, nested into each other and surrounding the Haversian canal through which various nerves and blood vessels pass . In the predominant majority of cases, osteons are placed parallel to the bone length, while repeatedly anostomosing among themselves.
The total number of osteons is individual for each specific bone. So, for example, the femur as an organ includes them in the amount of 1.8 for each 1 mm², and the Haversian canal in this case accounts for 0.2-0.3 mm².
Between the osteons are intermediate or insertion plates extending in all directions and representing the remaining parts of the old osteons that have already collapsed. The structure of the bone as an organ provides for the continuous occurrence of processes of destruction and neoplasm of osteons.
Bone plates are cylindrical in shape, and the ossein fibrils fit tightly and parallel to each other. Osteocytes are located between concentrically lying plates. The processes of bone cells, gradually spreading along the numerous tubules, move towards the processes of neighboring osteocytes and participate in intercellular connections. Thus, they form a spatially oriented lacunar-tubular system, which is directly involved in various metabolic processes.
The composition of osteon includes more than 20 different concentric bone plates. Human bones pass one or two vessels of the microvasculature through the osteon canal, as well as various bezmyelinovy nerve fibers and special lymphatic capillaries, which are accompanied by layers of connective loose tissue, including various osteogenic elements, such as osteoblasts, perivascular cells and many others.
Osteon canals have a fairly tight connection between each other, as well as with the bone marrow cavity and periosteum due to the presence of special probating channels, which contributes to the general anastomosis of bone vessels.
Periosteum
The structure of the bone as an organ implies that it is externally covered with a special periosteum, which is formed from connective fibrous tissue and has an outer and inner layer. The latter includes cambial progenitor cells.
The main functions of the periosteum include participation in the regeneration, as well as the provision of protective and trophic functions, which is achieved through the passage of various blood vessels here. Thus, blood and bone interact with each other.
What are the functions of the periosteum
The periosteum almost completely covers the outer part of the bone, and the places where the articular cartilage is located are the only exception, as well as the ligaments or tendons of the muscles. It should be noted that with the help of the periosteum, blood and bone are limited from the surrounding tissues.
In itself, it is an extremely thin, but at the same time strong film, which consists of extremely dense connective tissue, in which the lymphatic and blood vessels and nerves are located. It is worth noting that the latter penetrate into the substance of the bone precisely from the periosteum. Regardless of whether the nasal bone or some other one is considered, the periosteum has a fairly large influence on the processes of its development in thickness and nutrition.
The inner osteogenic layer of this coating is the main place in which bone tissue is formed, and in itself it is richly innervated, which affects its high sensitivity. If the bone loses the periosteum, it eventually ceases to be viable and completely dead. When carrying out any surgical interventions on the bones, for example, during fractures, the periosteum must be preserved without fail in order to ensure their normal further growth and healthy state.
Other design features
Almost any bones (with the exception of the predominant majority of the cranial, which includes the nasal bone) have articular surfaces, which ensures their articulation with others. Such surfaces, instead of the periosteum, have specialized articular cartilage, which in its structure is fibrous or hyaline.
Inside the predominant majority of bones is the bone marrow, which is located between the plates of the spongy substance or is located directly in the bone marrow cavity, and it can be yellow or red.
In newborns, as well as in fetuses in the bones, there is exclusively red bone marrow, which is hematopoietic and represents a homogeneous mass, saturated with formed elements of the blood, vessels, and also a special reticular tissue. Red bone marrow includes a large number of osteocytes, bone cells. The volume of red bone marrow is approximately 1500 cm³.
In an adult who already has bone growth, the red bone marrow is gradually replaced by yellow, which is mainly represented by special fat cells, while it is immediately worth noting that it replaces only the bone marrow located in the bone marrow cavity.
Osteology
Osteology is involved in what the human skeleton is, how bone fusion is performed, and any other processes associated with them occur. The exact number of organs described in humans cannot be precisely determined, because it changes during aging. Few people realize that from childhood to old age, people constantly experience bone damage, tissue death, and many more other processes. In general, over 800 different bone elements can develop throughout life, 270 of which are still in the prenatal period.
It should be noted that the vast majority of them grow together, while a person is in childhood and adolescence. In an adult, the skeleton contains only 206 bones, and in addition to the permanent bones in adulthood, unstable bones may also appear, the appearance of which is caused by various individual characteristics and functions of the body.
Skeleton
The bones of the limbs and other parts of the body, together with their joints, form the human skeleton, which is a complex of dense anatomical formations that, in the vital activity of the body, take on exclusively mechanical functions. At the same time, modern science distinguishes the solid skeleton, which appears to be bones, and the soft one, which includes all kinds of ligaments, membranes, and special cartilage joints.
Individual bones and joints, as well as the skeleton of a person as a whole, can perform a variety of functions in the body. So, the bones of the lower extremities and the body mainly serve as a support for soft tissues, while most of the bones are levers, since muscles that provide locomotor function are attached to them. Both of these functions allow us to rightly call the skeleton a completely passive element of the musculoskeletal system of a person.
The human skeleton is an anti-gravity structure that counteracts the force of gravity. Staying under its influence, the human body should be pressed to the ground, but due to the functions carried by individual bone cells and the skeleton as a whole, the change in body shape does not occur.
Bone function
The bones of the skull, pelvis and trunk provide a protective function against various injuries of vital organs, nerve trunks or large vessels:
- the skull is a full-fledged container for the organs of balance, vision, hearing and the brain;
- the spinal canal includes the spinal cord;
- the chest provides protection for the lungs, heart, and also large nerve trunks and vessels;
- The pelvic bones protect the bladder, rectum, and various internal genital organs from damage.
The predominant majority of bones within themselves contain red bone marrow, which is a special organ of blood formation and the immune system of the human body. It should be noted that the bones protect it from damage, and also create favorable conditions for the maturation of various blood cells and its trophism.
Among other things, special attention should be paid to the fact that bones are directly involved in mineral metabolism, since many chemical elements are deposited in them, among which calcium and phosphorus salts occupy a special place. Thus, if radioactive calcium is introduced into the body, after about 24 hours more than 50% of this substance will be accumulated in the bones.
Development
The formation of bone is carried out due to osteoblasts, and several types of ossifications are distinguished:
- Endesmal. It is carried out directly in the connective tissue of the integumentary, primary bones. From various ossification points on the connective tissue embryo, the ossification procedure begins to spread radially on all sides. The surface layers of connective tissue remain in the form of a periosteum, from which the bone begins to grow in thickness.
- Perichondral. It occurs on the outer surface of the cartilaginous primordia with the direct participation of the perichondrium. Due to the activity of osteoblasts located under the perichondrium, bone tissue is gradually deposited, replacing cartilage and forming an extremely compact bone substance.
- Periosteal. It occurs due to the periosteum, into which the perichondrium is transformed. The previous and this types of osteogenesis go one after another.
- Endochondral. It is carried out inside the cartilaginous primordia with the direct participation of the perichondrium, providing the supply into the cartilage of processes containing special vessels. This bone-forming tissue gradually destroys the dilapidated cartilage and forms an ossification point right in the center of the cartilage bone model. With the further spread of endochondral ossification from the center to the periphery, spongy bone is formed.
How is it going?
In each person, ossification is functionally determined and begins with the most stressed central parts of the bone. Approximately in the second month of life, primary points begin to appear in the womb, from which the development of diaphysis, metaphysis and tubular bone bodies occurs. Subsequently, they become ossified by endochondral and perichondral osteogenesis, and right before birth or in the first few years after birth secondary points begin to appear, from which the development of the pineal glands is carried out.
In children, as well as people in adolescence and adulthood, additional islands of ossification can appear, from where the development of apophyses begins. Various bones and their individual parts, consisting of a special spongy substance, become ossified endochondrally over time, while those elements that include spongy and compact substances ossify peri- and endochondral. The ossification of each individual bone fully reflects its functionally determined processes of phylogenesis.
Height
Throughout growth, rearrangement and a slight bone displacement are carried out. New osteons begin to form, and parallel to this, resorption is also carried out, which is the resorption of all old osteons, which is due to osteoclasts. Due to their active work, almost completely the entire endochondral bone of the diaphysis dissolves in the end, and instead a full bone marrow cavity is formed. It is also worth noting that the layers of the perichondral bone are absorbed, and instead of the missing bone tissue, additional layers from the periosteum are deposited. As a result, the bone begins to grow in thickness.
Bone growth in length is ensured by the pineal cartilage, a special layer between the metaphysis and pineal gland, which lasts throughout adolescence and childhood.