Structural skeleton. What are the different shapes of bones? Features of the structure of bone tissue

Everyone needs to know the human skeleton with the names of the bones. This is important not only for doctors, but also ordinary people, because information about his skeleton and muscles will help him strengthen, feel healthy, and at some point they can help out in emergency situations.

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Types of bones in the adult body

The skeleton and muscles together make up the human locomotor system. The human skeleton is a whole complex of bones different types and cartilages, interconnected by continuous joints, synarthrosis, symphyses. Bones are divided according to their composition into:

• tubular, forming the upper (shoulder, forearm) and lower (thigh, lower leg) limbs;
• spongy, foot (in particular, tarsus) and human hand (wrist);
• mixed - vertebrae, sacrum;
• flat, this includes the pelvic and cranial bones.

Important! Bone tissue, despite its increased strength, is capable of growing and regenerating. Metabolic processes occur in it, and blood is even formed in the red bone marrow. With age, bone tissue is rebuilt and becomes able to adapt to various loads.

Types of bones

How many bones are there in the human body?

The structure of the human skeleton undergoes many changes throughout life. On initial stage During development, the fetus consists of fragile cartilaginous tissue, which over time is gradually replaced by bone tissue. A newborn baby has more than 270 small bones. With age, some of them can grow together, for example, the cranial and pelvic ones, as well as some vertebrae.

It is very difficult to say exactly how many bones are in the body of an adult. Sometimes people have extra ribs or bones in their feet. There may be growths on the fingers, slightly smaller or large quantity vertebrae in any part of the spine. The structure of the human skeleton is purely individual. On average for an adult have from 200 to 208 bones.

Functions of the human skeleton

Each department performs its own highly specialized tasks, but the human skeleton as a whole has several common functions:

1. Support. The axial skeleton is the support for all the soft tissues of the body and a system of levers for the muscles.
2. Motor. Movable joints between bones allow a person to make millions of precise movements using muscles, tendons, and ligaments.
3. Protective. The axial skeleton protects the brain and internal organs from injuries, acts as a shock absorber during impacts.
4. Metabolic. Part bone tissue included a large number of phosphorus and iron involved in the exchange of minerals.
5. Hematopoietic. Red brain tubular bones is the place where hematopoiesis takes place - the formation of red blood cells (red blood cells) blood cells) and leukocytes (cells immune system).

If certain skeletal functions are impaired, diseases may occur varying degrees gravity.

Functions of the human skeleton

Skeletal departments

The human skeleton is divided into two large sections: axial (central) and accessory (or skeleton of the limbs). Each department performs its own tasks. The axial skeleton protects the abdominal organs from damage. Skeleton upper limb connects the arm to the body. Due to increased mobility hand bones, it helps to perform many precise movements with the fingers. The functions of the skeleton of the lower extremities are to connect the legs to the body, move the body, and provide shock absorption when walking.

Axial skeleton. This section forms the basis of the body. It includes: the skeleton of the head and torso.

Skeleton of the head. The cranial bones are flat, motionlessly connected (with the exception of the movable lower jaw). They protect the brain and sense organs (hearing, vision and smell) from concussions. The skull is divided into the facial (visceral), cerebral and middle ear sections.

Skeleton of the torso. Bones chest. By appearance this subsection resembles a compressed truncated cone or pyramid. The rib cage includes paired ribs (out of 12, only 7 are articulated with the sternum), vertebrae of the thoracic spine and the sternum - the unpaired breastbone.

Depending on the connection of the ribs with the sternum, true (upper 7 pairs), false (next 3 pairs), floating (last 2 pairs) are distinguished. The sternum itself is considered the central bone included in the axial skeleton.

The body is isolated in it, top part- the handle, and the lower part - xiphoid process. The bones of the chest have compound increased strength with vertebrae. Each vertebra has a special articular fossa designed for attachment to the ribs. This method of articulation is necessary to perform the main function of the body skeleton - protecting the human life support organs: lungs, parts digestive system.

Important! The bones of the chest are susceptible external influences, are prone to modification. Physical activity and proper seating at the table contribute proper development chest. Sedentary image life and stooping lead to tightness of the chest organs and scoliosis. An improperly developed skeleton threatens serious problems with health.

Spine. The department is central axis and main support the entire human skeleton. The spinal column is formed from 32-34 individual vertebrae that protect spinal canal with nerves. The first 7 vertebrae are called the cervical, the next 12 are called the thoracic, then there are the lumbar (5), 5 fused to form the sacrum, and the last 2-5 to form the coccyx.

The spine supports the back and torso, provides spinal nerves motor activity the entire body and the connection of the lower body with the brain. The vertebrae are connected to each other semi-movably (in addition to the sacral ones). This connection is made through intervertebral discs. These cartilaginous formations soften shocks and shocks during any human movement and provide flexibility to the spine.

Limb skeleton

Skeleton of the upper limb. Skeleton of the upper limb represented by the shoulder girdle and the skeleton of the free limb. The shoulder girdle connects the arm to the body and includes two paired bones:

1. The collarbone, which has an S-shaped bend. At one end it is attached to the sternum, and at the other it is connected to the scapula.
2. A spatula. In appearance it is a triangle adjacent to the body from the back.

The skeleton of the free limb (arm) is more mobile, since the bones are connected in it large joints(shoulder, wrist, elbow). Skeleton represented by three subdivisions:

1. The shoulder, which consists of one long tubular bone - the humerus. One of its ends (epiphysis) is attached to the scapula, and the other, passing into the condyle, to the forearm bones.
2. Forearm: (two bones) the ulna, located in line with the little finger and the radius - in line with the first finger. Both bones on the lower epiphyses form a radiocarpal articulation with the carpal bones.
3. A hand that includes three parts: the bones of the wrist, metacarpus and digital phalanges. The wrist is represented by two rows of four spongy bones each. The first row (pisiform, triangular, lunate, scaphoid) is used for attachment to the forearm. In the second row there are the hamate, trapezium, capitate and trapezoid bones, facing towards the palm. The metacarpus consists of five tubular bones, with their proximal part they are motionlessly connected to the wrist. Finger bones. Each finger consists of three phalanges connected to each other, in addition thumb, which is opposed to the others, and has only two phalanges.

Skeleton lower limb. The skeleton of the leg, as well as the arm, consists of a limb girdle and its free part.

Limb skeleton

The girdle of the lower extremities is formed by the paired bones of the pelvis. They grow together from paired pubic, ilium and ischial bones. This occurs by the age of 15-17, when the cartilaginous connection is replaced by a fixed bone one. Such strong articulation is necessary to support the organs. Three bones to the left and right of the body axis, forming acetabulum, necessary for the articulation of the pelvis with the head of the femur.

The bones of the free lower limb are divided into:

• Femoral. The proximal (upper) epiphysis connects to the pelvis, and the distal (lower) epiphysis connects to the tibia.
• Patella (or knee cap) covers, formed at the junction of the femur and tibia.
• The lower leg is represented by the tibia, located closer to the pelvis, and the fibula.
• Bones of the foot. The tarsus is represented by seven bones, making up 2 rows. One of the largest and most well developed is calcaneus. The metatarsus is the middle section of the foot; the number of bones included in it is equal to the number of toes. They are connected to the phalanges using joints. Fingers. Each finger consists of 3 phalanges, except the first, which has two.

Important! Throughout life, the foot is subject to changes; calluses and growths may form on it, and there is a possible risk of developing flat feet. This is often due to the wrong choice of shoes.

Sex differences

Structure of a woman and a man no fundamental differences. Only certain parts of some bones or their sizes undergo changes. Among the most obvious are narrower breasts and wide pelvis in a woman, which is associated with labor. Men's bones, as a rule, are longer, more powerful than women's, and have more traces of muscle attachment. It is much more difficult to distinguish a female skull from a male one. The male skull is slightly thicker than the female, it has a more pronounced contour brow ridges and occipital protuberance.

Human anatomy. Skeleton bones!

What bones does the human skeleton consist of, a detailed story

Conclusion

The human structure is extremely complex, but a minimal amount of information about the functions of the skeleton, the growth of bones and their location in the body can help in maintaining one’s health.

Children are interested in how the world works and everything in it. Their curiosity makes no exception for humans. They are interested in how a person works, how he sees and hears, runs and jumps. Modern children learn about the human skeleton, which cannot be seen with the naked eye like skin or eyes, from cartoons and comics. This makes the skeleton even more interesting in the eyes of a child.

But you won’t see a human skeleton with the names of bones and muscles in cartoons and comics, and it won’t hurt children to memorize them little by little.

Knowledge of how complex and fascinating it is human body, will awaken in the child an interest in biology and medicine, and will encourage a more conscious approach to their health and the health of others. Finally, this knowledge will be useful to him at school, where he is already primary school become familiar with the human structure.

The skeleton and muscles are the framework that determines the shape of a person, protects his internal organs and allows him to move. If it were not for the skeleton, then the person would be like a shapeless jellyfish. Muscles are attached to the skeleton and enable any of our movements - from fluttering eyelashes to lifting weights.

Bones consist of organic and inorganic substances, the first of which provide them with flexibility, and the second with strength. Thanks to this, the bones are unusually elastic and strong. Their complex structure adds strength and flexibility at the same time. Any bone consists of several layers.

• The outer layer is made up of strong bone tissue.
• The next connective layer covers the outside of the bone.
• Loose connective tissue that contains blood vessels.
• At the ends there is cartilage tissue, due to which bone growth occurs.
• Another layer - nerve endings, through which signals are transmitted from the brain and back.

Contained inside a bone tube Bone marrow, which also comes in two types. Red is involved in hematopoiesis and bone formation. It is full of blood vessels and nerves. Yellow is responsible for the growth and strength of bones. We see that the skeleton, among other things, contributes to the renewal of blood. This is where they are born blood cells. If, due to illness, it ceases to perform this task, the organism dies.

In the organization of the skeleton, several groups of bones are distinguished. One of them is the main supporting structure of our body, which includes the spine, bones of the head and neck, chest and ribs. Together they form the axial skeleton. The second part is called accessory skeleton and it includes the bones that form our arms and legs, and the groups of bones that provide their connection with the axial skeleton.

Skeletal structure

The bones of the head include the skull and bones of the middle ear. The skull houses and protects the brain. It consists of two sections: the brain and the facial. The first of which includes eight dice. There are fifteen of them in the front section.

Torso bones

This part of the skeleton includes the chest and spine, starting from the neck. We combine them because they are closely connected both literally (the chest is attached to the spine), and by location, and by the tasks they solve. These are some of the largest human bones. Their function is to provide protection to the heart, lungs, etc. Among them are spinal column and chest.

Spinal column

The human spine is the main support of the entire body, its main axis. It is he who ensures our upright posture. Thanks to spinal cord provides a connection between the upper and lower parts bodies. It contains five sections, consisting of 32-34 vertebrae. They are called according to their location - cervical, thoracic, lumbar, sacral and coccygeal.

Rib cage

The chest really looks like a cage, where 12 pairs of ribs play the role of a lattice behind which the heart, lungs, vital important organs. It ends with a flat, wide bone called the sternum. In total, the rib cage includes 37 bones.

Bones of the upper limb

This is what scientists and doctors call our hands. I don’t think it’s necessary to explain how much it means to a person to be able to do both lifting weights and cross-stitching with them. But think about how different problems they are designed to solve. This explains their rather complex structure. The bones of the upper limb (EL) include the EL girdle and the free part of the EL.

The belt includes the scapula and clavicle, connected by a ball joint to humerus. This is where the muscles are attached. In the free part of the upper limb there are three sections - the shoulder (humerus), forearm (radius and ulna) and brush. The most bones in this area of ​​the arm are twenty-seven; they are noticeably smaller than the bones of the forearm and differ from them in shape.

Pelvic girdle

This belt provides connection between the spine and lower extremities, and also accommodates and protects the organs of the digestive, urinary and reproductive systems. The pelvis consists of three fused bones.

Bones of the lower limb

The skeleton of the leg resembles the structure of the arm. They are fundamentally designed the same, differing in size and some other details. Since it is the legs that bear the main weight of our body when moving, they are more powerful and stronger than the bones of the arm.

What are the different shapes of bones?

Depending on their functions in the human body, bones differ in shape. There are four types of bone shapes:

1. Wide or flat (for example, near the skull);
2. Long or tubular (mainly in the limbs);
3. Short, such as the bones of the wrist;
4. Asymmetrical, having a composite shape. These are the pelvic bones, vertebrae, etc.

Muscles of the head and face

Previously, only specialists could know the structure of a person, his skeleton and the list of muscles. Today, anyone interested in this topic can find detailed information on the Internet. anatomical atlas, where given detailed description movements of our body and all its parts that provide this. The most important role in ensuring movement is played by muscles, organs consisting of special elastic tissue that can

contract under influence nerve impulses. There are more than 640 different muscles in the human body. Among them are different kinds according to different parameters:

• By the functions they provide;
• In the direction of the fibers of which they are composed;
• According to the form;
• In relation to the joints.

It’s not so easy to understand all this, so let’s look at the muscles depending on where they are located on our body.

When we talk about movement, we first of all imagine how our arms and legs work. Meanwhile, the muscles of the head and face also work hard, providing breathing, facial expressions, speech, and our nutrition. The strongest muscles in our body are the chewing muscles.

The muscles of facial expression and the muscles of the eye, unlike all others, are not attached to the bones. This allows them to be especially sensitive and guarantee the implementation of even micro movements. Thanks to this, we can convey both joy and sadness, the slightest change in emotions.

Neck muscles

This group of muscles allows us to turn around, bow, swallow something and speak, even breathe.

Muscles of the trunk

Muscles are attached to bones by tendons and perform different tasks. – provide mobility and the ability to maintain balance, fix joints. According to their functions and modes of action, there are those that contract synchronously during work or synergists, and muscles that perform opposite actions (antagonists). Most often, actions occur due to the fact that some muscles contract and other muscles relax at the same time.

The muscles of the body include the superficial and deep muscles of the back and chest, oblique, rectus and other abdominal muscles.

Pelvic muscles

These muscles begin on the bones of the pelvis and spine, are attached to the upper edge of the thigh and surround hip joint. Among them there are two groups: internal and external.

Muscles of the upper limbs

Among this group of muscles, the same parts stand out as in the bones of the arm:

1. Muscles of the VK belt;
2. Shoulder;
3. The forearms provide flexion and extension of the forearm, hand and each finger.

Muscles of the lower extremities

Thanks to these muscles, a person walks and runs, swims or jumps. In order to provide such different actions no group required various muscles. These include the muscles of the thigh, leg and foot. It's pretty a complex system, including muscles that are different in shape, direction of fibers, in relation to joints, etc., mutually complementing each other.

Muscle anatomy Muscle physiology How muscles work

The human skeleton, while being similar to the skeleton of animals, has some features due to upright walking and labor activity. The human skeleton is divided into the skeleton of the torso, the skeleton of the upper and lower extremities, and the skeleton of the head - the skull.

Skeleton of the torso

Consists of the spinal column and chest bones. The spinal column includes five sections: cervical, consisting of 7 vertebrae, thoracic - of 12, lumbar - of 5, sacral (or sacrum) - of 5 and coccygeal (or tailbone) - of 4-5 vertebrae. Consequently, the human spinal column consists of 33-34 vertebrae.

Vertebral structure

A vertebra consists of a vertebral body and an arch from which several processes extend. The vertebral body and arch form the vertebral foramen. The vertebral foramina, when vertebrae overlap each other, form spinal canal where the spinal cord is located.

The dimensions of the vertebral bodies depend on the magnitude of the load on them: the smallest are located in cervical spine, and the largest are in the lumbar.

In an adult, the vertebrae of the sacrum and coccyx are fused. The vertebrae, connecting to each other with the help of cartilage and ligaments, form a flexible and elastic column with significant mobility.

Spinal column

The human spinal column is characterized by curves. In the cervical and lumbar regions they are convexly facing forward, in the thoracic and sacral areas - backward. The shape of the spinal column changes with age. In a newborn it is straight. When the child begins to hold his head, a cervical curve is formed; when he begins to sit, there is a thoracic curve.

The lumbar and sacral curves are formed when the child begins to stand and walk, which is associated with maintaining balance in an upright body position. The curves of the spinal column increase the size of the thoracic and pelvic cavities, make it easier for the body to maintain balance, and soften shocks and shocks of the body when jumping and running.

Rib cage

Formed by the unpaired sternum, 12 pairs of ribs and thoracic vertebrae. The ribs are connected movably to the vertebrae and semi-movably (using cartilage) to the sternum. The breastbone, or breastbone, is a flat bone. 7 pairs of upper ribs articulate with it at the anterior ends. The next 3 pairs are connected to each other by their cartilages: the underlying ones with the overlying ones, forming a costal arch. The anterior ends of the 11th and 12th pairs of ribs lie freely in the soft lateral parts abdominal wall. The posterior ends of all 12 pairs are connected to the vertebrae.

The chest limits chest cavity, which serves as a container for the heart, lungs, esophagus, trachea, blood vessels and nerves. She takes part in breathing movements due to the rhythmic contraction of the intercostal muscles. The shape of a person’s chest depends on gender, age, build and physical development. It can be wide and short, long and narrow. But, due to upright posture, the anterior-posterior size of the chest, unlike animals, is smaller than the transverse one.

Skeleton of the upper limbs

Consists of a skeleton shoulder girdle, with the help of which the limbs are connected to the body (scapula, collarbone), and the skeleton of the free upper limbs.

Spatula- flat triangular shape bone adjacent to the anterior surface back wall chest. Its outer angle forms the glenoid cavity for articulation with the humerus.

Collarbone has an S-shape. Its contours are clearly visible under the skin, it can always be felt. The sternal end of the clavicle is connected to the sternum, the outer end is connected to the process of the scapula. The function of the clavicle is that it extends shoulder joint from the chest, providing greater freedom of movement of the upper limbs.

Skeleton of the free upper limb form the humerus, two bones of the forearm - the ulna and radius and the bones of the hand (bones of the wrist, metacarpus and phalanges of the fingers).

Skeleton of the lower limbs

Formed by the pelvic girdle and the skeleton of the free lower extremities.

Composed of the pelvic girdle includes two pelvic bones, articulated at the back with the sacrum. In children, the pelvic bone is represented by separate bones - the ilium, ischium and pubis, or pubis. Only after 16 years do they merge into one. At the site of their fusion there is an acetabulum, into which the head of the femur enters.

Complex structure pelvic bone due to its function. Connecting to the thigh and sacrum, transferring the weight of the body to the lower limbs, the pelvic bone performs the function of movement and support, as well as a protective function. Due to vertical position In the human body, the pelvis is wider and more massive than that of animals.

Sex differences are revealed in the structure of the pelvis. You can easily notice that a woman’s pelvis is wider and shorter than a man’s. This is due to the meaning female pelvis like the birth canal.

To the bones of the free lower limb include the femur, patella, tibia, fibula and foot bones. The tibia and fibula form the lower leg. The bones of the foot consist of the tarsus, metatarsus and phalanges. The foot as a whole performs a supporting function when standing and walking. Connecting with each other, the bones of the foot form an elastic arch, convexly facing upward. This structure is associated with the vertical position of the human body, with an increase in the load on the foot when walking upright.

Head bones

They are firmly connected to each other with seams. The exception is lower jaw. The skull is the seat of the brain, as well as the sense organs (vision, smell, hearing). The bones of the skull also perform a supporting function for respiratory tract(nasal cavity) and digestive system (oral cavity, pharynx). The skeleton of the head is divided into the brain and facial sections.

Brain department The skull consists of paired temporal and parietal bones and unpaired ones - frontal, ethmoid, sphenoid, occipital. The occipital bone has a foramen magnum that connects the cranial cavity with the spinal canal.

Facial bones skulls include six paired bones - upper jaw, nasal, lacrimal, zygomatic, palatal, inferior turbinate and three unpaired bones - the lower jaw, vomer, hyoid bone.

The bones of the skull are pierced by many holes and canals through which blood vessels and nerves pass. Some of them have cavities filled with air. The shape of the human skull is very different from the shape of the animal skull. In humans brain section the skull significantly predominates over the facial, which is associated with greater development of the brain and less load on the masticatory apparatus.

Skeleton(from the Greek skeleton - dried) of a person is a collection of bones connected to each other in a certain way. The adult human skeleton consists of approximately 205 bones. The skeleton (Fig. 12) has three sections: the skeleton of the body, the skeleton of the skull and the skeleton of the limbs (Table 2).

Rice. 12. Human skeleton (front view):

1 – brain skull, 2 - facial skull, 3 - bones of the upper limb girdle, 4 - humerus, 5 - bones of the forearm, 6 - bones of the hand, 7 - chest 8 - spinal column, 9 - bones of the lower limb girdle, 10 - femur, 11 - bones shin, 12 – foot bones

The skeleton of the body consists of the vertebrae that form the spine and the bones of the chest. Each segment of the human body skeleton is formed by a vertebra, and in the thoracic region also by a pair of ribs and a section of the sternum.

The skeleton of the head, the skull, protects the brain, sensory organs and serves as a support for the initial sections of the digestive and respiratory organs. The skull is conventionally divided into two sections - the brain and the facial.

The skeleton of the upper and lower extremities is divided into the skeleton of the free limb and the skeleton of the belt. The skeleton of the upper limb girdle (shoulder girdle) consists of two paired bones - the scapula and the clavicle, and the skeleton of the free upper limb - of three sections: humerus, bones of the forearm and bones of the hand.

The skeleton of the lower limb girdle (pelvic girdle) consists of a paired pelvic bone, and the skeleton of the free lower limb is divided into three sections: the femur, the bones of the lower leg and the bones of the foot. Every bone independent body, performing a specific function.

The bones of the skeleton differ in shape and structure. Distinguish tubular, spongy, flat, mixed And air bones(Fig. 13).

Rice. 13. Types of bones:

1 – long (tubular) bone, 2 – flat bone, 3 – spongy (short) bones, 4 – mixed bone

Tubular bones are divided into long (humerus, femur, bones of the forearm and tibia) and short (tarsal and metatarsal bones, phalanges of the fingers). Except for the bones articular surfaces, covered with a connective tissue membrane - periosteum, which performs bone-forming and protective functions. The periosteum is firmly fused to the bone with the help of connective tissue fibers that penetrate deep into the bone. The outer layer of the periosteum is coarsely fibrous, consisting of complexly intertwined fibers and connective tissue cells. This layer contains many blood vessels and lymphatic vessels, nerve fibers that provide vital activity to the bone. The inner layer of the periosteum is thin and contains cells from which osteoblasts are formed - young bone cells. Due to the bone-forming function of the periosteum, the bone grows in thickness and heals during fractures.

Inside the bones there are medullary cavity(in tubular bones) and cells of spongy substance, which contains bone marrow. In a newborn child and in childhood, the bone marrow cavities are filled with red bone marrow, which performs blood-forming and protective functions. Red bone marrow stem cells form blood cells (erythrocytes, leukocytes) and immune system cells (lymphocytes). In an adult, red bone marrow is stored only in the cells of spongy bone. Other bone cavities contain obese yellow bone marrow that has lost its functions.

On the side of the medullary cavity and cells, the bone is covered with a thin connective tissue plate - endostome, also producing bone tissue.

The bones of the skeleton and the skeleton in the whole body perform supporting, motor and protective functions. Bones are also a depot for minerals - phosphorus, calcium, iron, copper and other trace elements.

Bone Strength is ensured by the presence of organic and inorganic substances in them, as well as the structure of bone tissue. In terms of hardness and elasticity, bones can be compared with bronze and cast iron. The compact and spongy substance of bones is built from bone tissue. Compact (dense) bone substance forms the outer layer of each bone. spongy substance, formed by bone crossbars (beams), is located under the compact substance. In tubular bones, in the area of ​​their body (diaphysis), the compact bone substance is thick (up to 1 cm). At the ends of tubular bones and flat bones and other bones, this layer is thin. The compact bone substance is penetrated by a system of bone canals in which blood vessels and nerve fibers(Fig. 14).

Rice. 14. Scheme of the structure of the tubular bone:

1 - periosteum, 2 - compact bone substance, 3 - layer of outer surrounding plates, 4 - osteons, 5 - layer of internal surrounding plates, 6 - medullary cavity, 7 - bone crossbars of cancellous bone substance.

Each bone canal (osteon canal) is surrounded by concentric plates in the form of 4 to 20 thin tubes inserted into one another. The system of such tubes together with the tubule is called osteona, or Haversian system(Fig. 15). The spaces between osteons are occupied by intermediate, or intercalary, plates, which, during bone restructuring due to changing physical load, serve as material for the formation of new osteons. The surface layer of compact bone substance is represented by the outer surrounding plates, which are a product of the bone-forming function of the periosteum.

Rice. 15. Structure of osteon in a section: 1 – osteon plates, 2 – bone cells(osteocytes), 3 – central canal (osteon channel)

The inner layer of bone, bordering the medullary cavity, is formed by internal surrounding plates and covered with fibrous connective tissue - endosteum.

Spongy bone substance located under the compact, is located at the ends of the tubular bones - the epiphyses, in the bodies of spongy, mixed bones, in flat and pneumatic bones. Spongy bone substance consists of bone crossbars intersecting each other in different directions. Their distribution corresponds to the direction of the main lines of compression (pressure) and tension acting on the bone (Fig. 16).

Rice. 16. Diagram of the location of bone crossbars in the spongy substance of bones (cut top end femur): 1 – compression (pressure) lines, 2 – tension lines

This arrangement of the bone crossbars at an angle to each other ensures uniform distribution of pressure and muscle force on the skeletal bones.

Bone is highly plastic. Depending on the load on the bones, the number of osteons increases or decreases, and their location in the compact substance changes. With constant muscle load, sports, and physical labor, the number of osteons and their sizes increase, the layer of compact bone substance in tubular and other bones thickens, and the bone marrow cavities narrow. The bone crossbars (beams) of the spongy substance also thicken and acquire a more complex structure (branch). At the same time, the bones become thicker and stronger. With a decrease in physical (muscle) activity, a sedentary lifestyle, and prolonged bed rest during illness, the bones become thinner and weaker.

Organic and inorganic substances also provide bone strength. Organic substances give bones flexibility and elasticity.

Inorganic substances (calcium phosphate, calcium carbonate and other salts) give bones hardness. In living bone, organic substances account for about 60% of its mass, the rest belongs to inorganic compounds.

The influence of organic and inorganic substances on the strength properties of bones can be tested experimentally. Once the organic matter is removed by roasting the bone over a fire, it becomes brittle. Removing inorganic substances (salts) from the bone by keeping the bone in acid makes the bone soft and flexible. The combination of the hardness of inorganic compounds with the elasticity of organic compounds ensures the strength of bones.

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