Bone as an organ: structure, properties, functions

Bone as an organ enters the system of organs of motion and support, and at the same time is characterized by an absolutely unique form and structure, a rather characteristic architectonics of nerves and vessels. It is built mainly of special bone tissue, which is covered externally with the periosteum, and inside contains the bone marrow.

Key Features

Each bone as an organ has a certain amount, shape and location in the human body. All this is significantly influenced by the various conditions in which they develop, as well as all the various functional loads experienced by the bones during the life of the human body.

Any bone is inherent in a number of sources of blood supply, the presence of specific locations, as well as a fairly characteristic architectonics of blood vessels. All these features just the same apply to the nerves that innervate this bone.

Structure

Bone as an organ includes several tissues that are in certain proportions, but, of course, the most important among them is bone lamellar tissue, the structure of which can be considered as an example of a diaphysis (central part, 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 intercalary 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 that are directly under the periosteum. Through these layers pass specialized perforating canals, which contain the same blood vessels. On the border with the medullary cavity, the tubular bones also contain an additional layer with internal surrounding plates, which are permeated with a variety of different channels that expand into cells.

The cavity is entirely lined with a so-called endostom, which is an extremely thin layer of connective tissue, which includes flattened osteogenic inactive cells.

Osteons

Osteon is represented by concentrically placed bone plates that look like cylinders of different diameters, nested into each other and surrounding the Havers channel, through which various nerves and blood vessels pass . In the predominant majority of cases, the osteons are placed parallel to the long bone, while anostomosing multiple times.

The total number of osteons is individual for each particular bone. So, for example, the femur as an organ includes them in an amount of 1.8 for each 1 mm², and the Havers channel in this case is 0.2-0.3 mm².

Between the osteons are intermediate or intercalary plates, which run in all directions and represent the remaining parts of the old osteons that have already disintegrated. The structure of the bone as an organ provides for a continuous flow of processes of destruction and neoplasm of osteons.

The bony plates are in the form of cylinders, and the ossein fibrils adjoin each other in them densely and in parallel. Between concentrically lying plates are located osteocytes. The processes of bone cells, gradually spreading along numerous tubules, move towards the processes of neighboring osteocytes and participate in intercellular connections. Thus, they form a spatially oriented lacunar-tubular system, taking direct part in various metabolic processes.

The osteon composition includes more than 20 different concentric bone plates. Human bones pass one or two vessels of the microcirculatory channel through the osteon channel, as well as various mothless nerve fibers and special lymphatic capillaries, which are accompanied by interlayers of connective loose tissue, including various osteogenic elements such as osteoblasts, perivascular cells and many others.

The channels of osteons have a sufficiently dense connection between themselves, as well as with the medullary cavity and periostium due to the presence of special perforating channels, which contributes to the general anastomosis of the bone vessels.

Periosteum

The structure of the bone as an organ implies that it is covered from the outside by a special periosteum, which is formed from the 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 regeneration, as well as providing a protective and trophic function, which is achieved through the passage here of various blood vessels. Thus, the blood and bone interact with each other.

What are the functions of the periosteum

The pustule almost completely covers the outer part of the bone, and the only exception here is the place where the articular cartilage is located, and the ligaments or tendons of the muscles are attached. It should be noted that with the help of the periosteum, blood and bone are limited from surrounding tissues.

In itself, it represents an extremely thin, but at the same time, strong film, which consists of an 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 bone substance from the periosteum. Regardless of whether the nasal bone or some other one is being considered, the periosteum has a rather 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, eventually it ceases to be viable and completely deadens. When performing any surgical interventions on the bones, for example in fractures, the periosteum must be preserved without fail to ensure their normal further growth and healthy state.

Other structural features

Virtually any bones (with the exception of the predominant majority of cranial regions, including the nasal bone) have articular surfaces that ensure their articulation with others. Such surfaces instead of the periosteum have specialized articular cartilage, which in its structure is fibrous or hyaline.

Inside the majority of the bones, the bone marrow is located, which is located between the plates of the spongy substance or is located directly in the medullary cavity, and it can be yellow or red.

In newborns, as well as in fetuses, only the red bone marrow is present in the bones, which is hematopoietic and represents a homogeneous mass saturated with uniform elements of blood, vessels, and a special reticular tissue. Red bone marrow includes a large number of osteocytes, bone cells. The volume of red bone mozag is about 1500 cm³.

In an adult who has already had bone growth, the red bone marrow is gradually replaced with yellow, represented mainly by special fat cells, and it is immediately worth noting the fact that only the bone marrow that is located in the medullary cavity is replaced.

Osteology

What is the skeleton of a person, how the fusion of bones is carried out, and any other processes associated with them take place, osteology is involved. The exact number of organs described in man can not be precisely determined, because it changes in the course of aging. Few people realize that from childhood to the elderly, people constantly suffer damage to bones, tissue deaths and many other processes. In general, throughout life can develop more than 800 different bone elements, 270 of which - even in the prenatal period.

It should be noted that most of them predominate among themselves, while the person is in childhood and adolescence. In an adult human skeleton contains only 206 bones, and besides permanent in adulthood can also appear unstable bones, the occurrence of which is determined by various individual characteristics and functions of the body.

Skeleton

The bones of limbs and other parts of the body, together with their compounds, form the skeleton of a man, which is a complex of dense anatomical formations, which in the vital activity of the organism are assumed mainly by purely mechanical functions. In this modern science stands out a solid skeleton, which is represented by bones, and soft, which includes all kinds of ligaments, membranes and special cartilaginous joints.

Individual bones and joints, as well as the human skeleton as a whole, can perform a variety of functions in the body. So, the bones of the lower extremities and the trunk basically serve as the support of soft tissues, while most of the bones are levers, since muscles are attached to them that provide the locomotor function. Both of these functions allow us to correctly call the skeleton a completely passive element of the human musculoskeletal system.

The human skeleton is an anti-gravity construction, counteracting the force of gravity. While under its influence, the human body must be pressed to the ground, but due to the functions that carry the individual cells of the bone and the skeleton as a whole, the body shape does not change.

Functions of bones

The bones of the skull, pelvis and trunk provide a protective function against various injuries to vital organs, nerve trunks or large vessels:

• The skull is a complete container for the organs of balance, vision, hearing and brain;
• The vertebral canal includes the spinal cord;
• The thorax provides protection of the lungs, heart, as well as large nerve trunks and vessels;
• Pelvic bones are protected from damage to the bladder, rectum, as well as various internal genital organs.

The predominant majority of the bones inside itself contains the red bone marrow, which is the special organs of the hematopoiesis and the immune system of the human body. It should be noted that the bones provide protection from damage, as well as create favorable conditions for the maturation of various elements of blood and its trophic.

In addition, special attention should be paid to the fact that the bones take a direct part in the mineral metabolism, because they contain a lot of chemical elements, among which calcium and phosphorus salts occupy a special place. Thus, if radioactive calcium is introduced into the body, in 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 there are several types of ossification:

• Endless. It is carried out directly in the connective tissue of integumentary, primary bones. From various points of ossification to the embryo of connective tissues, the ossification procedure begins to spread out radially on all sides. The superficial layers of connective tissue remain in the form of the periosteum, from which the bone begins to grow in thickness.
• Perichondral. Occurs on the outer surface of the cartilaginous rudiments with the direct participation of the perichondrium. Due to the activity of osteoblasts located under the perichondrium, bone tissue gradually replacing the cartilaginous and forming an extremely compact bone substance is gradually deposited.
• Periodic. Occurs at the expense of the periosteum, into which the perichondrium transforms. Previous and this type of osteogenesis go one after another.
• Endochondral. It is carried out inside the cartilaginous rudiments with the direct participation of the perichondrium, which provides the supply to the cartilage of processes containing special vessels. This bone-forming tissue gradually destroys the dilated cartilage and forms a point of ossification right in the center of the cartilaginous bone model. With the further spread of endochondral ossification from the center to the periphery, formation of a spongy bone substance takes place.

How does it happen?

In each person, ossification is functionally conditioned and begins with the most loaded central parts of the bone. Approximately in the second month of life, the primary points begin to appear in the womb, from which the development of diaphyses, metaphyses and tubular bones are carried out. Later they ossified by endochondral and perichondral osteogenesis, and immediately before birth or in the first few years after birth, secondary points begin to appear, from which epiphyses develop.

In children, as well as people in adolescence and adulthood, additional islets of ossification may appear, from which the development of apophyses begins. Different bones and their separate parts, consisting of a special spongy substance, eventually endochondrally ossified, while those elements that include spongy and compact substances in their composition ossify peri- and endochondral. The ossification of each individual bone completely reflects its functionally conditioned processes of phylogenesis.

Growth

During the course of the reconstruction, a slight shift in bone is carried out. New osteons begin to form, and in parallel, resorption is carried out, which is a resorption of all old osteons, which is produced by osteoclasts. Due to their active work, almost completely the entire endochondral bone of the diaphysis eventually dissipates, and instead a full bone marrow cavity is formed. It is also worth noting that the layers of the perichondral bone also dissolve, and instead of the missing bone tissue additional layers are deposited from the periosteum. As a result, the bone begins to grow in thickness.

The growth of bones in length is ensured by epiphyseal cartilage, a special layer between the metaphysis and the epiphysis, which persists throughout adolescence and childhood.