The structure of spongy and flat bones. Spongy types of bones Human short bones examples
Classification of bones
There are various classifications that cover all types of bones of the human skeleton depending on their location, structure and functions.
1. By location : cranial bones; trunk bones; limb bones.
2. Development The following types of bones are distinguished : primary (appears from connective tissue); secondary (formed from cartilage); mixed.
3. The following types of human bones are distinguished by structure: tubular; spongy; flat; mixed.
Tubular bones
Tubular long bones consist of both dense and spongy substance. They can be divided into several parts. The middle of the bone is formed by a compact substance and has an elongated tubular shape. This area is called the diaphysis. Its cavities first contain red bone marrow, which is gradually replaced by yellow bone marrow containing fat cells. At the ends of the tubular bone there is an epiphysis - this is an area formed by spongy substance. Red bone marrow is placed inside it. The area between the diaphysis and the epiphysis is called the metaphysis. During the period of active growth of children and adolescents, it contains cartilage, due to which the bone grows. Over time, the anatomy of the bone changes, the metaphysis completely turns into bone tissue. Long tubular bones include the femur, shoulder, and forearm bones. Tubular small bones have a slightly different structure. They have only one true epiphysis and, accordingly, one metaphysis. These bones include the phalanges of the fingers and metatarsal bones. They function as short movement levers.
Spongy types of bones
The name of the bones often indicates their structure. For example, cancellous bones are formed from spongy substance covered with a thin layer of compact. They do not have developed cavities, so the red bone marrow is placed in small cells. Spongy bones are also long and short. The first include, for example, the sternum and ribs. Short spongy bones are involved in the work of muscles and are a kind of auxiliary mechanism. These include the wrist bones and vertebrae.
Flat Bones
These types of human bones, depending on their location, have different structures and perform certain functions. The bones of the skull are, first of all, protection for the brain. They are formed by two thin plates of dense substance, between which there is a spongy substance. It contains holes for veins. The flat bones of the skull develop from connective tissue. The scapula and pelvic bones are also a type of flat bone. They are formed almost entirely from spongy substance, which develops from cartilage tissue. These types of bones serve not only as protection, but also as support.
Mixed dice
Mixed bones are a combination of flat and short spongy or tubular bones. They develop in different ways and perform those functions that are necessary in a particular area of the human skeleton. These types of bones, such as mixed ones, are found in the body of the temporal bone and vertebrae. These include, for example, the collarbone.
Cartilage tissue
Cartilage tissue has an elastic structure. It forms the ears, nose, and some parts of the ribs. Cartilage tissue is also located between the vertebrae, as it perfectly resists the deforming force of loads. It has high strength, excellent resistance to abrasion and compression.
· Internally filled with spongy bone substance and covered with a thin layer of compact substance
The structure of the tubular bone 1. diaphysis 2. epiphyses 3. medullary cavity 4. periosteum 5. perichondrium 6. articular hyaline cartilage 7. spongy substance of the epiphyses filled with red bone marrow 8. compact substance of the diaphysis 9. yellow bone marrow 10. metaphysis (bone growth plates in length)
Bone connections
· Each bone occupies a specific place in the body and is connected to other bones by different types of connections
· There are three groups of joints of skeletal bones: continuous, semi-joints (symphyses) And intermittent joints
I. Continuous connections
o Forms fixed connections bones
ü the bones in the joint grow together and are connected to each other using a thin lining of bone, cartilage or connective tissue
ü movements between bones are very limited or absent
ü very durable, have protective value
v Fixed joints with connective tissue joint
– bones of the brain and facial skull (strength and immobility are achieved by numerous protrusions of one bone, which fit into the corresponding depressions of the other – seams) - strengthening the roots of teeth in the cells of the jaw bones - alveoli
- ulna and radius bones of the forearm
- tibia and fibula of the leg
v Fixed joints with bone connection
Connections of the iliac, ischial and pubic bones during their fusion into single pelvic bones
II. Half-joints
o Form semi-movable joints
ü The bones are connected using a relatively thick cartilaginous layer, in which there is an underdeveloped gap (cavity) with a small amount of fluid
ü More movable connection, less durable than fixed ones
Connection of vertebrae by intervertebral discs (when walking, jumping, running, cartilage acts as protective shock absorbers of shocks and shocks); junction of ribs and sternum
Joint of the pubic bones (symphysis pubis)
III. Joints (discontinuous joints)
o Form movable joints (provides a wide variety of movements)
o Between the bones there is a joint cavity filled with joint fluid
o Relatively weak
o Each joint has:
ü Articular fossa and articular head– articular surfaces of articulating bones (covered with smooth, slippery, springy protective hyaline articular cartilage); fit tightly to each other
ü Joint space (cavity)- cavity between the glenoid fossa and the head
ü Articular ligaments in the outer layer of the articular capsule ( connect bones, strengthen the joint)
ü Joint capsule (capsule), covering the articular surfaces and limiting the articular cavity
- consists of two sheets:
external (fibrous) - dense, thick, strengthened by ligaments and passes into the periosteum ( holds articulating bones and protects the joint)
internal (synovial)– thin, fuses with the outer one, forms joint fluid(facilitates the sliding of articular surfaces, reduces friction and nourishes cartilage)
o There is always negative pressure in the sealed joint cavity (increases the strength of the bone connection)
o Auxiliary elements of the joint – ligaments, tendons(strengthen the wall of the capsule, direct the movement of the joint in a certain direction, and prevent the joint from bending in the other direction)
o Joints are simple (two bones are connected - phalanges of the fingers, hip) and complex (three or more bones are connected - knee, ankle)
o The strength of the joint is ensured by the articular ligaments, a dense joint capsule, and negative pressure inside the joint
o Greater mobility is ensured by the coincidence of the articular head and fossa, slippery cartilage, articular lubricating fluid and is limited by the depth of the articular fossa (eg hip)
Joints of the body: mandibular, shoulder, elbow, wrist, hip, knee, ankle, phalangeal joints
Rice. 1 Fig. 2 Fig. 3
Rice. 1 A. Fixed joint B. Semi-movable joint (half-joint) C. Movable joint (joint) Fig. 1 Joint structure: 1. Articulating bones 2. Articular cartilage 3. Articular ligaments 4. Outer (fibrous) layer of the articular capsule 5. Internal (synovial) layer of the articular capsule 6. Articular cavity (cleft) filled with articular fluid
Rice. 3 Spine structure
Human skeleton
| Skeletal departments | Skeleton bones | Types of bones | Types of bone connections |
| Scull Brain department | Paired dice: parietal, temporal Unpaired bones: frontal, occipital, main (sphenoid) | Flat | Fixed (sutures) |
| Scull Facial department | Paired dice: maxillary, zygomatic, nasal, palatal Unpaired bones: lower jaw, sublingual | Flat | Fixed, except for the lower jaw (movable, real joint) |
| Spine 5 sections (33 – 34 vertebrae) | Cervical– 7 vertebrae (1 - atlas) Chest- 12 vertebrae with ribs Lumbar– 5 vertebrae Sacral– 5 fused vertebrae Coccygeal– 4-5 underdeveloped vertebrae | Short | Semi-moving connection |
| Upper limb girdle (shoulder girdle) | - Two shoulder blades- Two collarbone | Flat (shoulder blades) Long tubular (clavicles) | Semi-movable Functions: attachment of upper limbs |
| Free upper limb | - Shoulder - Forearm (ulna and radius bones), - Hand (wrist, metacarpus, phalanges) | Long, tubular; wrist bones - short | Movable joint (real joints) |
| Lower limb girdle (pelvic girdle) | Paired dice: pelvic bones (iliac, ischial, pubic)– grow together by 12–14 years of age) | Flat | Immobile (pelvis) Functions: attachment of lower limbs |
| Free lower limb | - Hip - Shin (tibia, fibula) - Foot (tarsus, metatarsus, phalanges) | Long, tubular (thigh, tibia), short (foot bones) | Movable joint (real joints); foot - semi-movable |
| Rib cage | - 12 thoracic vertebrae, - 12 pairs of ribs (7 pairs – true ribs, 3 pairs – false ribs, 2 pairs – oscillating ribs) - Sternum (manubrium, body, xiphoid process) | Flat (ribs, sternum); short (vertebrae) | Semi-movable Functions: breathing, organ protection (lungs, heart, aorta, esophagus) |
Bones, hard, durable parts of the skeleton of various sizes and shapes, form the support of our body, perform the function of protecting vital organs, and also provide motor activity, since they are the basis of the musculoskeletal system.
- Bones are the skeleton of the body and vary in shape and size.
- Bones are connected by muscles and tendons, thanks to which a person can make movements, maintain and change the position of the body in space.
- Protect internal organs, including the spinal cord and brain.
- Bones are an organic storehouse of minerals such as calcium and phosphorus.
- Contains bone marrow, which produces blood cells.
Bones are made of bone tissue; Throughout human life, bone tissue is constantly modified. Bone tissue consists of a cellular matrix, collagen fibers and an amorphous substance, which is covered with calcium and phosphorus, which ensure the strength of bones. Bone tissue contains special cells that, under the influence of hormones, form the internal structure of bones throughout human life: some destroy old bone tissue, while others create new one.
The interior of the bone under a microscope: spongy tissue is represented by more or less densely located trabeculae.
The osteoid substance consists of an osteoblast, on top of which minerals are located. On the outer side of the bone, consisting of strong periosteum tissue, there are numerous bony membranes located around the central canal, where a blood vessel passes, from which many capillaries extend. Clusters in which the bone membranes are located close to each other without gaps form a solid substance that provides bone strength and is called compact bone tissue, or compact substance. Conversely, in the inner part of the bone, called cancellous tissue, the bony membranes are not as close and dense, this part of the bone is less strong and more porous - spongy substance.
Despite the fact that all bones consist of bone tissue, each of them has its own shape and size, and according to these characteristics they are conventionally classified as three types of bones:
;Long Bones: tubular bones with an elongated central part - the diaphysis (body) and two ends called the epiphysis. The latter are covered with articular cartilage and participate in the formation of joints. Compact substance(endosteum) has an outer layer several millimeters thick - the most dense, a cortical plate, which is covered with a dense membrane - the periosteum (with the exception of the articular surfaces covered with cartilage).
;Flat Bones: come in different shapes and sizes and consist of two layers compact substance; between them is spongy tissue, called diploe in flat bones, the trabeculae of which also contain bone marrow
.
;Short Bones: These are usually small bones that are cylindrical or cubic in shape. Although they differ in shape, they consist of a thin layer compact bone substance and are usually filled with spongy substance, the trabeculae of which contain bone marrow.
The structure of the human bone.
Bones begin their formation even before a person is born, in the embryonic stage, and are completed by the end of adolescence. Bone mass increases as you get older, especially during adolescence. Starting from the age of thirty, bone mass gradually decreases, although under normal conditions the bones remain strong until old age.
Name
Spongy bones (short bones) - skeletal bones that combine strength and compactness with limited mobility. Unlike tubular (long) bones, the width of spongy bones is approximately equal to their length.
Structure
Spongy bones are formed primarily by spongy tissue surrounded by a thin layer of compact substance.
Examples of cancellous bones
Spongy bones include the carpal and tarsal bones. Spongy bones sometimes include sesamoid bones (including the patella), some flat bones (ribs and sternum), and mixed bones (including vertebrae).
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Excerpt characterizing spongy bones
Nikolai Rostov, meanwhile, stood in his place, waiting for the beast. By the approach and distance of the rut, by the sounds of the voices of dogs known to him, by the approach, distance and elevation of the voices of those arriving, he felt what was happening on the island. He knew that there were arrived (young) and seasoned (old) wolves on the island; he knew that the hounds had split into two packs, that they were poisoning somewhere, and that something untoward had happened. Every second he waited for the beast to come to his side. He made thousands of different assumptions about how and from which side the animal would run and how it would poison it. Hope gave way to despair. Several times he turned to God with a prayer that the wolf would come out to him; he prayed with that passionate and conscientious feeling with which people pray in moments of great excitement, depending on an insignificant reason. “Well, what does it cost you,” he said to God, “to do this for me! I know that You are great, and that it is a sin to ask You for this; but for the sake of God, make sure that the seasoned one comes out on me, and that Karai, in front of the “uncle” who is watching from there, slams into his throat with a death grip.” A thousand times during these half-hours, with a persistent, tense and restless gaze, Rostov looked around the edge of the forest with two sparse oak trees over an aspen underhang, and the ravine with a worn edge, and the uncle’s hat, barely visible from behind a bush to the right.CLASSIFICATION OF BONES
The skeleton is divided into the following parts: the bones of the torso (vertebrae, ribs, sternum), the bones of the skull (cerebral and facial), the bones of the limb girdles - the shoulder (scapula, clavicle) and pelvic (ilium, pubis, ischium) and the bones of the free limbs - the upper ( shoulder, bones of the forearm and hand) and lower (thigh, bones of the leg and foot).
The number of individual bones that make up the skeleton of an adult is more than 200, of which 36-40 are located along the midline of the body and are unpaired, the rest are paired bones.
Based on their external shape, bones are distinguished between long, short, wide and mixed.
However, such a division, established back in the time of Galen, based only on one characteristic (external form) turns out to be one-sided and serves as an example of the formalism of the old descriptive anatomy, as a result of which bones that are completely heterogeneous in their structure, function and origin fall into one group. Thus, the group of flat bones includes the parietal bone, which is a typical integumentary bone that ossifies endesmally, and the scapula, which serves for support and movement, ossifies on the basis of cartilage and is built from ordinary spongy substance.
Pathological processes also occur completely differently in the phalanges and bones of the wrist, although both belong to short bones, or in the femur and rib, which are included in the same group of long bones.
Therefore, it is more correct to distinguish bones on the basis of 3 principles on which any anatomical classification should be built: form (structure), function and development.
From this point of view, the following classification of bones can be outlined:
I. Tubular bones: 1. Long; 2. Short
II. Spongy bones: 1. Long; 2. Short; 3. Sesamoids;
III. Flat bones: 1. Bones of the skull; 2. Bones of belts
I. Tubular bones. They are built from a spongy and compact substance that forms a tube with a medullary cavity: they perform all 3 functions of the skeleton (support, protection and movement). Of these, the long tubular bones (the shoulder and bones of the forearm, the femur and the bones of the leg) are the pillars and long levers of movement and, in addition to the diaphysis, have enchondral foci of ossification in both epiphyses (biepiphyseal bones); short tubular bones (metacarpus, metatarsus, phalanges) represent short levers of movement; Of the epiphyses, the enchondral focus of ossification is present only in one (true) epiphysis (monoepiphyseal bones).
II. Spongy bones. Constructed primarily of a spongy substance covered with a thin layer of compact. Among them, there are long spongy bones (ribs and sternum) and short ones (vertebrae, carpus, tarsus). Spongy bones include sesamoid bones, i.e., similar to the sesamoid grains of the sesame plant, which is where their name comes from (patella, pisiform bone, sesamoid bones of the fingers and toes); their function is auxiliary devices for muscle work; development is enchondral in the thickness of the tendons, which they strengthen. Sesamoid bones are located near the joints, participating in their formation and facilitating their movements, but are not directly connected to the bones of the skeleton.
III. Flat bones:
a) flat bones of the skull (frontal and parietal). Function - mainly protection (integumentary bones); structure - diploe; ossification - based on connective tissue;
b) flat bones of the belts (scapula, pelvic bones), function - support and protection; structure - predominantly made of spongy substance; ossification - on the basis of cartilaginous tissue.
IV. Mixed bones (bones of the base of the skull) - these include bones that merge from several parts that have different functions, structure and development. Mixed bones include the clavicle, which develops partly endesmally and partly enchondrally.
IN skeleton The following parts are distinguished: the skeleton of the body (vertebrae, ribs, sternum), the skeleton of the head (bones of the skull and face), the bones of the limb girdles - upper (scapula, clavicle) and lower (pelvic) and the bones of the free limbs - upper (shoulder, forearm bones and hand) and lower (thigh, leg bones and foot).
Number of individual bones There are more than 200 bones that make up the skeleton of an adult, of which 36 - 40 are located along the midline of the body and are unpaired, the rest are paired bones.
According to external form There are long, short, flat and mixed bones.
However, this division, established back in the time of Galen, is only one attribute(external form) turns out to be one-sided and serves as an example of the formalism of the old descriptive anatomy, as a result of which bones that are completely different in their structure, function and origin fall into one group. Thus, the group of flat bones includes the parietal bone, which is a typical integumentary bone that ossifies endesmally, and the scapula, which serves for support and movement, ossifies on the basis of cartilage and is built from ordinary spongy substance.
Pathological processes also occur completely differently in the phalanges and bones the wrists, although both belong to the short bones, or in the femur and rib, classified in the same group of long bones.
Therefore it is more correct distinguish bones based on 3 principles on which any anatomical classification should be built: form (structure), function and development.
From this point of view, we can outline the following bone classification(M. G. Gain):
I. Tubular bones. They are built of a spongy and compact substance that forms a tube with a medullary cavity; perform all 3 functions of the skeleton (support, protection and movement).
Of these, the long tubular bones (the shoulder and bones of the forearm, the femur and the bones of the leg) are struts and long levers of movement and, in addition to the diaphysis, have endochondral foci of ossification in both epiphyses (biepiphyseal bones); short tubular bones (carpal bones, metatarsals, phalanges) represent short levers of movement; Of the epiphyses, the endochondral focus of ossification is present only in one (true) epiphysis (monoepiphyseal bones).
II. Spongy bones. Constructed primarily of a spongy substance covered with a thin layer of compact. Among them, there are long spongy bones (ribs and sternum) and short ones (vertebrae, carpal bones, tarsus). Spongy bones include sesamoid bones, i.e., similar to the sesamoid grains of the sesame plant, which is where their name comes from (patella, pisiform bone, sesamoid bones of the fingers and toes); their function is auxiliary devices for muscle work; development is endochondral in the thickness of the tendons. Sesamoid bones are located near the joints, participating in their formation and facilitating movements in them, but are not directly connected to the bones of the skeleton.
III. Flat bones:
A) flat bones of the skull(frontal and parietal) perform a predominantly protective function. They are built from 2 thin plates of a compact substance, between which there is diploe, diploe, is a spongy substance containing channels for veins. These bones develop on the basis of connective tissue (integumentary bones);
b) flat bones belts(scapula, pelvic bones) perform the functions of support and protection, built mainly from spongy substance; develop on the basis of cartilage tissue.
IV. Mixed bones (bones of the base of the skull). These include bones that merge from several parts that have different functions, structure and development. Mixed bones also include the clavicle, which develops partly endesmally and partly endochondrally.
The bones form a solid skeleton, which consists of the vertebral column (spine), the sternum and ribs (bones of the torso), the skull, and the bones of the upper and lower extremities (Fig. 1). Skeleton (skeleton) performs the functions of support, movement, protection, and is also a depot of various salts (minerals). Red bone marrow, located inside the bones, produces blood cells (red blood cells, white blood cells, etc.) and immune system cells (lymphocytes).
The human skeleton consists of 206 bones. Of these: 36 unpaired and 85 paired.
Classification of bones
Taking into account the shape and structure, long (tubular) bones, short (spongy), flat (wide), mixed and pneumatic bones are distinguished (Fig. 2).
Long Bones have an elongated bone body - the diaphysis, and thickened ends - the epiphyses. The epiphyses contain articular surfaces for connection with adjacent bones. The part of the long bone located between the diaphysis and the epiphysis is called the metaphysis. Among the tubular bones, long tubular bones (humerus, femur, etc.) and short tubular bones (metacarpals, metatarsals, etc.) are distinguished.
short bones, or spongy, have a cubic or polygonal shape. Such bones are located in those parts of the body where greater mobility is combined with increased mechanical load (carpal and tarsal bones).
Flat Bones form the walls of cavities and perform protective functions (bones of the roof of the skull, pelvis, sternum, ribs, scapula).
Rice. 1. Human skeleton. Front view.
1 - skull, 2 - spinal column, 3 - clavicle, 4 - scapula, 5 - humerus, 6 - forearm bones, 7 - wrist bones, 8 - metacarpal bones, 9 - phalanges of the fingers, 10 - femur, 11 - patella, 12 - fibula, 13 - tibia, 14 - tarsal bones, 15 - phalanges of the toes, 16 - metatarsal bones, 17 - tibia bones, 18 - sacrum, 19 - pelvic bone, 20 - radius, 21 - ulna bone, 22 - ribs, 23 - sternum.
Rice. 2. Bones of various shapes.
1 - pneumatic bone, 2 - long (tubular) bone, 3 - flat bone, 4 - spongy (short) bones, 5 - mixed bone.
Mixed dice have a complex shape, their parts look like flat, spongy bones (for example, vertebrae, sphenoid bone of the skull).
Air bones contain cavities lined with mucous membrane and filled with air. Some bones of the skull have such cavities (frontal, sphenoid, ethmoid, temporal, maxillary bones). The presence of cavities in the bones lightens the weight of the head. These cavities also serve as voice resonators.
On the surface of each bone there are elevations (processes, tubercles), which are called apophyses. These places are the places of attachment of muscles, fascia, and ligaments. In places where blood vessels and nerves meet, there are grooves and notches on the surface of the bones. On the surface of each bone there are small nutrient openings(foramina nutritia), through which blood vessels and nerve fibers pass.
Bone structure
In the structure of bone, a distinction is made between compact and spongy substance (Fig. 3).
Compact substance (substantia compacta) forms the diaphysis of tubular bones, covers the outside of their epiphyses, as well as short (spongy) and flat bones. The compact substance of the bone is penetrated by thin canals, the walls of which are formed by concentric plates (from 4 to 20). Each central channel, together with the plates surrounding it, was named osteona, or the Haversian system (Fig. 4). Osteon is a structural and functional unit of bone. Between the osteons there are intercalary, intermediate plates. The outer layer of the compact substance is formed by the outer surrounding plates (Fig. 5). The inner layer delimiting the bone marrow cavity is formed
Rice. 3. Compact and spongy bone. 1 - spongy (trabecular) substance, 2 - compact substance, 3 - nutrient canal, 4 - nutrient opening.
Rice. 4. The structure of osteon.
1 - osteon plates, 2 - osteocytes (bone cells), 3 - central canal.
Rice. 5. Microscopic structure of bone (low magnification).
1 - periosteum, 2 - outer surrounding plates, 3 - osteon plates, 4 - central canals (osteon canals), 5 - bone cells, 6 - intercalary plates.
Rice. 6. Bone cell (osteocyte) in a bone lacuna.
1 - bone cell, 2 - bone lacuna, 3 - wall of the bone lacuna.
inner surrounding plates. Bone plates are built from bone cells (osteocytes) and intercellular substance impregnated with salts of calcium, phosphorus, magnesium and other chemical elements. The bone contains connective tissue fibers that have different orientations in adjacent plates. Processed bone cells are located in miniature lacunae containing bone (tissue) fluid (Fig. 6).
Due to the presence in bone tissue of a significant amount of salts of various chemical elements that block x-rays, the bone is clearly visible on x-rays.
Spongy substance (substantia spongiosa) built from bone plates (beams) with cells between them (Fig. 7). The bone beams are directed towards pressure forces and tensile forces (Fig. 8). This arrangement of the bone beams promotes uniform transfer of pressure to the bone, which gives the bone greater strength.
Rice. 7. Spongy substance of the body and alveolar part of the lower jaw in a longitudinal section. Right view. 1 - dental alveoli, 2 - spongy substance of the alveolar part of the lower jaw, 3 - compact substance of the dental alveoli, 4 - spongy substance of the body of the lower jaw, 5 - compact substance of the body of the lower jaw, 6 - angle of the lower jaw, 7 - ramus of the lower jaw, 8 - condylar process, 9 - head of the mandible, 10 - notch of the mandible, 11 - coronoid process of the mandible.
Rice. 8. Diagram of the location of the bone crossbars in the cancellous substance of the tubular bone. 1 - compression line (pressure), 2 - tension line.
All bones, except their articular surfaces, are covered with a connective tissue membrane - periosteum(periosteum), which is firmly fused with the bone (Fig. 9). The walls of the bone marrow cavities, as well as the cells of the spongy substance, are lined with a thin connective tissue plate - endostome, which, like the periosteum, performs a bone-forming function. The internal surrounding plates of compact bone substance are formed from osteogenic endosteal cells.
Skeletal structure
Taking into account the structure of bones and their functions, the axial skeleton and the accessory skeleton are distinguished. The axial skeleton includes the trunk skeleton (vertebral column and chest bones) and the head skeleton (skull). The accessory skeleton includes the bones of the upper and lower extremities.
One of the most important acts of adaptation of the body to the environment is movement. It is carried out by a system of organs, which include bones, their joints and muscles, which together make up the movement apparatus. All the bones, connected to each other by connective, cartilage and bone tissue, together make up the skeleton. The skeleton and its connections are the passive part of the movement apparatus, and the skeletal muscles attached to the bones are its active part.
The doctrine of bones is called osteology, the doctrine of bone joints - arthrology, about muscles - myology.
The skeleton of an adult human consists of more than 200 interconnected bones (Fig. 23); it forms the solid base of the body.
The importance of the skeleton is great. Not only the shape of the entire body, but also the internal structure of the body depends on the features of its structure. The skeleton has two main functions: mechanical And biological. Manifestations of mechanical function are support, protection, movement. The supporting function is carried out by the attachment of soft tissues and organs to different parts of the skeleton. The protective function is achieved by the formation of cavities by some parts of the skeleton in which vital organs are located. Thus, the brain is located in the cranial cavity, the lungs and heart are located in the chest cavity, and the genitourinary organs are located in the pelvic cavity.
The function of movement is due to the movable connection of most bones, which act as levers and are driven by muscles.
A manifestation of the biological function of the skeleton is its participation in metabolism, especially mineral salts (mainly calcium and phosphorus), and participation in hematopoiesis.
The human skeleton is divided into four main sections: the trunk skeleton, the skeleton of the upper limbs, the skeleton of the lower limbs and the skeleton of the head - the skull.
Bone structure
Each bone (os) is an independent organ with a complex structure. The basis of bone is a compact and spongy (trabecular) substance. The outside of the bone is covered with periosteum (periosteum). The exception is the articular surfaces of bones, which do not have periosteum, but are covered with cartilage. Inside the bone contains bone marrow. Bones, like all organs, are equipped with blood vessels and nerves.
Compact substance(substantia compacta) makes up the outer layer of all bones (Fig. 24) and is a dense formation. It consists of strictly oriented, usually parallel, bone plates. In the compact substance of many bones, bone plates form osteons. Each osteon (see Fig. 8) includes from 5 to 20 concentrically located bone plates. They resemble cylinders inserted into each other. The bone plate consists of calcified intercellular substance and cells (osteocytes). In the center of the osteon there is a canal through which blood vessels pass. Intercalated bone plates are located between adjacent osteons. In the superficial layer of the compact substance, under the periosteum, there are external general, or common, bone plates, and in its inner layer on the side of the medullary cavity there are internal general bone plates. Intercalary and general plates are not part of osteons. In the outer common plates there are channels that perforate them, through which vessels pass from the periosteum into the bone. In different bones and even in different parts of the same bone, the thickness of the compact substance is not the same.
Spongy substance(substantia spongiosa) is located under the compact substance and has the appearance of thin bone crossbars that intertwine in different directions and form a kind of network. The basis of these crossbars is lamellar bone tissue. The crossbars of the spongy substance are arranged in a certain order. Their direction corresponds to the action of compression and tension forces on the bone. The compressive force is determined by the pressure exerted on the bone by the weight of the human body. The tensile force depends on the active pull of the muscles acting on the bone. Since both forces act on 1 bone simultaneously, the cancellous crossbars form a single beam system that ensures that these forces are distributed evenly across the entire bone.
Perioste(periosteum) (periosteum) is a thin but fairly strong connective tissue plate (Fig. 25). It consists of two layers: internal and external (fibrous). The inner (cambial) layer is represented by loose fibrous connective tissue with a large number of collagen and elastic fibers. It contains blood vessels and nerves, and also contains bone-forming cells - osteoblasts. The outer (fibrous) layer consists of dense connective tissue. The periosteum is involved in the nutrition of the bone: vessels penetrate from it through holes in the compact substance. Due to the periosteum, the developing bone grows in thickness. When a bone is fractured, osteoblasts of the periosteum are activated and participate in the formation of new bone tissue (a callus is formed at the site of the fracture). The periosteum is tightly fused to the bone through bundles of collagen fibers penetrating from the periosteum into the bone.
Bone marrow(medulla ossium) is a hematopoietic organ, as well as a nutrient depot. It is located in the bone cells of the spongy substance of all bones (between the bone crossbars) and in the canals of the tubular bones. There are two types of bone marrow: red and yellow.
Red bone marrow- delicate reticular tissue, horned with blood vessels and nerves, in the loops of which there are hematopoietic elements and mature blood cells, as well as bone cells involved in the process of bone formation. Mature blood cells, as they form, penetrate into the bloodstream through the walls of relatively wide blood capillaries with slit-like pores located in the bone marrow (they are called sinusoidal capillaries).
Yellow bone marrow consists mainly of adipose tissue, which determines its color. During the period of growth and development of the body, red bone marrow predominates in the bones; with age, it is partially replaced by yellow. In an adult, red bone marrow is located in the spongy substance, and yellow bone marrow is in the canals of the tubular bones.
According to modern concepts, the red bone marrow, as well as the thymus gland, are considered the central organs of hematopoiesis (and immunological defense). In the red bone marrow, red blood cells, granulocytes (granular leukocytes), blood platelets (platelets), as well as B lymphocytes and T lymphocyte precursors are formed from hematopoietic cells. T-lymphocyte precursors travel through the bloodstream to the thymus gland, where they transform into T-lymphocytes. B and T lymphocytes from the red bone marrow and thymus gland enter the peripheral hematopoietic organs (lymph nodes, spleen), where they multiply and transform under the influence of antigens into active cells involved in protective reactions.
Chemical composition of bones. The composition of bones includes water, organic and inorganic substances. Organic substances (ossein, etc.) determine the elasticity of the bone, and inorganic substances (mainly calcium salts) determine its hardness. The combination of these two types of substances determines the strength and elasticity of bones. The ratio of organic and inorganic substances in bones changes with age, which affects their properties. Thus, in old age, the content of organic substances in the bones decreases, and inorganic substances increase. As a result, bones become more fragile and more susceptible to fractures.
Bone development
Bones develop from embryonic connective tissue - mesenchyme, which is a derivative of the middle germ layer - Mesoderm. In their development, they go through three stages: 1) connective tissue (membranous), 2) cartilaginous, 3) bone. The exceptions are the clavicle, the bones of the roof of the skull and most of the bones of the facial part of the skull, which in their development bypass the cartilaginous stage. Bones that go through two stages of development are called primary, and three stages are called secondary.
The process of ossification (Fig. 26) can occur in different ways: endesmal, enchondral, perichondral, periosteal.
Endesmal ossification occurs in the connective tissue of the future bone due to the action of osteoblasts. An ossification nucleus appears in the center of the anlage, from which the ossification process spreads radially throughout the entire plane of the bone. In this case, the superficial layers of connective tissue are preserved in the form of periosteum (periosteum). In such a bone, one can detect the location of this primary ossification nucleus in the form of a tubercle (for example, the tubercle of the parietal bone).
Enchondral ossification occurs in the thickness of the cartilaginous anlage of the future bone in the form of a focus of ossification, and the cartilaginous tissue is preliminarily calcified and is not replaced by bone, but is destroyed. The process spreads from the center to the periphery and leads to the formation of a spongy substance. If a similar process occurs in reverse, from the outer surface of the cartilaginous bone rudiment to the center, then it is called perichondral ossification, with the active role played by the osteoblasts of the perichondrium.
As soon as the process of ossification of the cartilaginous bone anlage is completed, further deposition of bone tissue along the periphery and its growth in thickness are carried out due to the periosteum (periosteal ossification).
The process of ossification of the cartilaginous anlagen of some bones begins at the end of the 2nd month of intrauterine life, and in all bones it is completely completed only by the end of the second decade of human life. It should be noted that different parts of the bones do not ossify at the same time. Later than others, cartilage tissue is replaced by bone in the area of the metaphyses of tubular bones, where bone growth occurs in length, as well as in the places of attachment of muscles and ligaments.
Bone Shape
Based on their shape, there are long, short, flat and mixed bones. Long and short bones, depending on the internal structure, as well as developmental characteristics (ossification process), can be divided into tubular (long and short) and spongy (long, short and sesamoid).
Tubular bones built from a compact and spongy substance and have a medullary cavity (canal). Of these, the long ones are the levers of movement and make up the skeleton of the proximal and middle parts of the limbs (shoulder, forearm, thigh, lower leg). In each long tubular bone there is a middle part - diaphysis, or body, and two ends - epiphyses(the areas of bone between the diaphysis and epiphyses are called metaphyses). Short tubular bones are also levers of movement, making up the skeleton of the distal parts of the limbs (metacarpus, metatarsus, fingers). Unlike long tubular bones, they are monoepiphyseal bones - only one of the epiphyses has its own ossification nucleus, and the second epiphysis (bone base) ossifies due to the spread of this process from the bone body.
Spongy bones They have a predominantly spongy structure and are covered on the outside with a thin layer of compact substance (they do not have a channel inside). Long spongy bones include the ribs and sternum, and short ones include the vertebrae, carpal bones, etc. This group may also include sesamoid bones, which develop in the tendons of muscles near some joints.
Flat Bones consist of a thin layer of spongy substance located between two plates of compact substance. These include part of the skull bones, as well as the shoulder blades and pelvic bones.
Mixed dice- these are bones that consist of several parts, having different shapes and development (bones of the base of the skull).
Bone connections
Bone connections are divided into two main groups: continuous connections - synarthrosis and discontinuous connections - diarthrosis (Fig. 27).
Synarthrosis- these are connections of bones through a continuous layer of tissue that completely occupies the spaces between the bones or their parts. These joints, as a rule, are inactive and occur where the angle of displacement of one bone relative to another is small. In some synarthrosis there is no mobility. Depending on the tissue connecting the bones, all synarthrosis is divided into three types: syndesmosis, synchondrosis and synostosis.
Syndesmoses, or fibrous junctions, are continuous connections using fibrous connective tissue. The most common type of syndesmosis is ligaments. Syndesmoses also include membranes (membranes) and sutures. Ligaments and membranes are usually built of dense connective tissue and are strong fibrous formations. Sutures are relatively thin layers of connective tissue through which almost all the bones of the skull are connected to each other.
Synchondroses, or cartilaginous joints, are connections between bones using cartilage. These are elastic fusions, which, on the one hand, allow mobility, and on the other, absorb shocks during movements.
Synostosis- fixed joints with the help of bone tissue. An example of such a connection is the fusion of the sacral vertebrae into a monolithic bone - the sacrum.
Throughout a person's life, one type of continuous connection can be replaced by another. Thus, some syndesmoses and synchondroses undergo ossification. With age, for example, ossification of the sutures between the bones of the skull occurs; synchondroses present in childhood between the sacral vertebrae transform into synostoses, etc.
Between synarthrosis and diarthrosis there is a transitional form - hemiarthrosis (half-joint). In this case, there is a narrow gap in the center of the cartilage connecting the bones. Hemiarthrosis includes the pubic symphysis - the connection between the pubic bones.
Diarthrosis, or joints(solid, or synovial joints) are discontinuous movable joints, which are characterized by the presence of four main elements: the articular capsule, the articular cavity, synovial fluid and articular surfaces (Fig. 28). Joints (articulationes) are the most common type of joint in the human skeleton; They carry out precise, measured movements in certain directions.
Joint capsule surrounds the joint cavity and ensures its tightness. It consists of outer - fibrous and inner - synovial membranes. The fibrous membrane fuses with the periosteum (periosteum) of the articulating bones, and the synovial membrane fuses with the edges of the articular cartilage. The inside of the synovial membrane is lined with endothelial cells, which makes it smooth and shiny.
In some joints, the fibrous membrane of the capsule becomes thinner in places, and the synovial membrane forms protrusions in these places, which are called synovial bursae, or bursae. They are usually located near the joints under the muscles or their tendons.
Articular cavity- this is a gap limited by the articular surfaces and synovial membrane, hermetically isolated from the tissues surrounding the joint. The pressure in the joint cavity is negative, which helps bring the articular surfaces closer together.
Synovial fluid(synovia) is a product of the exchange of synovial membrane and articular cartilage. It is a clear, sticky liquid, its composition reminiscent of blood plasma. It fills the joint cavity, moisturizes and lubricates the articular surfaces of the bones, which reduces friction between them and promotes their better adhesion.
Articular surfaces of bones covered with cartilage. Thanks to the presence of articular cartilage, the articulating surfaces are smoother, which promotes better gliding, and the elasticity of the cartilage softens possible shocks during movements.
Articular surfaces are compared in shape to geometric figures and are considered as surfaces obtained from the rotation of a straight or curved line around a conventional axis. When a straight line is rotated around a parallel axis, a cylinder is obtained, and when a curved line is rotated, depending on the shape of the curvature, a ball, ellipse or block, etc. is formed. Based on the shape of the articular surfaces, spherical, ellipsoidal, cylindrical, block-shaped, saddle-shaped, flat and other joints are distinguished (Fig. 29). In many joints, one articular surface is shaped like a head and the other is shaped like a socket. The range of movements in the joint depends on the difference in the length of the arch of the head and the arch of the socket: the greater the difference, the greater the range of movements. Articular surfaces corresponding to each other are called congruent.
In some joints, in addition to the main elements, there are additional ones: articular lips, articular discs and menisci, articular ligaments.
Articular labrum consists of cartilage, is located in the form of a rim around the articular cavity, thereby increasing its size. The shoulder and hip joints have a labrum.
Articular discs And menisci constructed from fibrous cartilage. Located in the duplication of the synovial membrane, they penetrate into the joint cavity. The articular disc divides the joint cavity into two sections that do not communicate with each other; The meniscus does not completely separate the joint cavity. Along their outer circumference, the discs and menisci are fused with the fibrous membrane of the capsule. The disc is present in the temporomandibular joint, and the meniscus is present in the knee joint. Thanks to the articular disc, the volume and direction of movement in the joint changes.
Articular ligaments are divided into intracapsular and extracapsular. Intracapsular ligaments, covered with synovial membrane, are located inside the joint and are attached to the articulating bones. Extracapsular ligaments strengthen the joint capsule. At the same time, they influence the nature of movements in the joint: they promote the movement of the bone in a certain direction and can limit the range of movements. In addition to ligaments, muscles are involved in strengthening joints.
In the ligaments and capsules of the joints there are a large number of sensitive nerve endings (proprioceptors) that perceive irritations caused by changes in the tension of the ligaments and capsules during joint movement.
To determine the nature of movements in the joints, three mutually perpendicular axes are drawn: frontal, sagittal and vertical. Around the frontal axis flexion (flexio) and extension (extensio) are performed, around the sagittal axis - abduction (abductio) and adduction (adductio), and around the vertical axis - rotation (rotatio). In some joints, circular motion (circumductio) is also possible, in which the bone describes a cone.
Depending on the number of axes around which movement can occur, joints are divided into uniaxial, biaxial and triaxial. Uniaxial joints include cylindrical and block-shaped, biaxial joints include ellipsoidal and saddle-shaped, and triaxial joints include spherical joints. In triaxial joints, as a rule, a large range of movements is possible.
Flat joints are characterized by low mobility, having the nature of sliding. The articular surfaces of flat joints are considered as segments of a ball with a large radius.
Depending on the number of articulating bones, joints are divided into simple, in which two bones are connected, and complex, in which more than two bones are connected. Joints that are anatomically separate from each other, but in which movements can only occur simultaneously, are called combined. An example of such joints are the two temporomandibular joints.
