Human joints: structure, classification, function

Consider the types and structure of joints

The joints of a person are the basis of every movement of the body. They are found in all bones of the body (the only exception is the hyoid bone).

Their structure resembles a hinge, due to which there is a smooth sliding of bones, preventing their friction and destruction.

The joint is a mobile joint of several bones, and in the body there are more than 180 in all parts of the body.

They are immovable, partially mobile, and the main part is represented by moving joints.

The degree of mobility depends on such conditions:

• volume of connecting material;
• the type of material inside the bag;
• forms of bones at the point of contact;
• level of muscle tension, as well as ligaments within the joint;
• their location in the bag.

How is the joint? It looks like a bag of two layers that surrounds the connection of several bones. The bag provides a tightness of the cavity and contributes to the development of synovial fluid.

It, in turn, is a shock absorber of the movements of bones.

Together, they perform the three main functions of the joints: they help stabilize the position of the body, are part of the process of movement in space, ensure the movement of parts of the body in relation to each other. friend.

Basic elements of the joint

The structure of the human joints is not simple and is divided into such basic elements as cavity, capsule, surface, synovial fluid, cartilaginous tissue, ligaments and muscles. Briefly about each we'll talk further.

1. The joint cavity is a slotted space, which is hermetically sealed and filled with synovial fluid.
2. Joint Capsule - consists of a connective tissue that envelops the connecting ends of bones. The capsule is formed from the outside of the fibrous membrane, but inside it has a thin synovial membrane (source of synovial fluid).
3. Joint surfaces - have a special shape, one of them convex (also called the head), and the second is pitted.
4. Synovial fluid. its function is to lubricate and moisten the surfaces, and also plays an important role in the exchange of fluids. It is a buffer zone for various movements (shocks, jerks, squeezing). Provides both slip and discrepancy of bones in the cavity. Reducing the number of synovia leads to a number of diseases, deformation of bones, loss of a person's ability to normal physical activity and, as a consequence, even to disability.
5. Cartilage tissue (thickness, mm). The surfaces of the bones are covered with cartilaginous tissue, the main function of which is amortization during walking, playing sports. The anatomy of the cartilage is represented by connective tissue fibers that are filled with fluid. It in turn nourishes cartilage in a calm state, and during movements it releases a liquid for greasing bones.
6. Ligaments and muscles are auxiliary parts of the structure, but without them the normal functionality of the whole organism is impossible. With the help of ligaments, bones are fixed, without interfering with the movements of any amplitude due to their elasticity.

Also important is the role of stubby projections around the joints. Their main function is to limit the amplitude of the movements. As an example, consider the shoulder. In the humerus there is a bony tubercle. Due to the location next to the scion blade, it reduces the range of the arm movement.

Classification and types

In the development of the human body, the way of life, the mechanisms of human interaction and external environment, the need to perform various physical actions and obtained a variety of types joints. The classification of joints and its basic principles are divided into three groups: the number of surfaces, the shape of the end of bones, functional capabilities. We'll talk about them a little later.

The main type in the human body is the synovial joint. Its main feature is the combination of bones in the bag. This type includes the shoulder, knee, hip and others.

There is also a so-called facet joint. Its main characteristic is a rotation limitation of 5 degrees and a slope of 12 degrees.

The function also consists in limiting the mobility of the spine, which helps maintain the balance of the human body.

By structure

In this group, the classification of joints occurs depending on the number of bones that connect:

• A simple joint is the union of two bones (interphalangeal).
• Complicated - the connection of more than two bones (elbow). The characteristic of such a connection implies the presence of several simple bones, and the functions can be realized separately from each other.
• Complex joint - or two-chambered, in which there is a cartilage that connects several simple joints (lower jaw, radiolucent). The cartilage can separate the joints completely (the shape of the disc) and partially (meniscus in the knee).
• Combined - combines isolated joints, which are placed independently of each other.

By the shape of the surfaces

The forms of the joints and the end of the bones have the form of various geometric shapes (cylinder, ellipse, ball).

Depending on this, movements are made around one, two, or three axes. Also seen is a direct relationship between the type of rotation and the shape of the surfaces.

Next, a detailed classification of joints in the shape of its surfaces:

1. Cylindrical joint - the surface has the shape of a cylinder, rotates around one vertical axis (parallel to the axis of the connected bones and the vertical axis of the body). This species can have a rotational name.
2. Block-shaped joint - inherent form of the cylinder (transverse), one axis of rotation, but in the frontal plane, perpendicular to the direction of the connected bones. The movements of flexion and extension are characteristic.
3. Screw-like - a type of the previous type, but the axis of rotation of this shape is located at an angle different from 90 degrees, forming a helical rotation.
4. Ellipsoidal - the ends of the bones have the shape of an ellipse, one of them is oval, convex, and the second concave. Movements occur in the direction of the two axes: bend-unbend, withdraw-lead. The bundles are perpendicular to the axes of rotation.
5. Ushchelkovy - a kind of ellipsoid. The main characteristic - the condyles (rounded process on one of the bones), the second bone in the form of a hollow, between themselves can vary greatly in size. the axis of rotation is represented by the front. The main difference from the block-like one is the strong difference in the dimensions of the surfaces, from the ellipsoidal one - the number of heads of the connecting bones. This type has two condyles, which can be found in one capsule (similar to a cylinder, similar in function to block-like), and in different (similar to ellipsoidal).
6. Saddle-shaped - is formed due to the joining of two surfaces as if "sitting" on each other. One bone moves along, while the second is across. Anatomy involves rotation around perpendicular axes: flexion-extension and lead-out.
7. Ball-shaped joint - the surfaces have the form of balls (one convex, the second concave), due to which people can make circular motions. In general, the rotation occurs along three perpendicular axes, the point of intersection is the center of the head. A feature in a very small number of ligaments, which does not prevent circular rotation.
8. The cup-like anatomical view suggests a deep hollow of one bone that covers most of the area of ​​the head of the second surface. As a result, less free mobility compared with spherical. It is necessary for a greater degree of joint stability.
9. Flat joint - flat endings of bones of approximately the same size, interaction in three axes, the main characteristic - a small amount of movements and surrounding bundles.
10. Taut (amphiarthrosis) - consists of different in size and shape bones, which are closely connected to each other. Anatomy - inactive, surfaces are tight capsules, not elastic short ligaments.

By the nature of the movement

In view of their physiological characteristics, joints perform many movements along their axes.

There are three types in this group:

• Uniaxial - which rotate around one axis.
• Biaxial - rotation around two axes.
• Multi-axis - mainly around three axes.

The following table shows the correspondence of forms and types of human joints.

Classification by axes	Kinds	Examples
Uniaxial	Cylindrical	Atlanto-axial median
Block-shaped	Interphalangeal joints of fingers
Screw-like	Plecheliteal
Biaxial	Ellipsoidal	Wrist Band
Ushchelkovy	Knee
Saddle-shaped	Carpometacarpal joint of thumb
Multi-axis	Globular	Brachial
Cup-shaped	Hip
Flat	Intervertebral discs
Tight	Sacred-pandemonium

In addition, there are also different types of movements in the joints:

• Flexion and extension.
• Rotation inside and out.
• Leading and casting.
• Circular motions (the surfaces move between the axes, the end of the bone prescribes a circle, and the entire surface is the shape of a cone).
• Sliding movements.
• Removal one from another (example, peripheral joints, finger separation).

The degree of mobility depends on the difference in the magnitude of the surfaces: the larger the area of ​​one bone over the other, the greater the volume of motion.

Braking the volume of motion can also ligament and muscle.

Their presence in each type is determined by the need to increase or decrease the range of motion of a certain part of the body.

"Demonstrative review of anatomy"

In the next video you can visually study the anatomy and see how the joints work on the skeleton.

A source: https://prospinu.com/anatomija/stroenie-sustava.html

Structure and function of joints

JointIs the movable articulation of two or more bones of the skeleton.

The joints unite the bones of the skeleton into a single whole. Move to a person helping more than 180 different joints. Together with bones and ligaments they are referred to the passive part of the motor apparatus.

Joints can be compared to hinges, the task of which is to ensure smooth sliding of bones relative to each other.

In their absence, the bones will simply rub against each other, gradually breaking down, which is a very painful and dangerous process.

The main elements that exist in all the so-called true joints are:

• articular surfaces (ends) of connecting bones;
• articular capsule;
• articular cavity.

The joint cavity fills the synovial fluid, which is a kind of lubricant and promotes free movement of the articular ends.

The number of articular surfaces distinguishes:

1. a simple joint with only 2 articular surfaces, for example interphalangeal joints;
2. A complex joint with more than two articulating surfaces, for example an elbow joint. A complex joint consists of several simple joints in which movements can be made separately;
3. complex joint containing intraarticular cartilage, which divides the joint into 2 chambers (a two-chamber joint).

The classification of joints is carried out according to the following principles:

• on the number of articular surfaces;
• by the form of articular surfaces;
• by function.

The articular surface of the bone is formed by hyaline (rarely fibrous) articular cartilage. Articular cartilage is a tissue filled with liquid.

The surface of the cartilage is even, strong and elastic, capable of absorbing well and secreting the liquid.

The thickness of the articular cartilage is, on average, millimeter.

The joint capsule is formed by a connective tissue. It surrounds the articulating ends of bones and on the articular surfaces passes into the periosteum.

The capsule has a thick outer fibrous fibrinous membrane and an internal thin synovial membrane that secures a synovial fluid into the joint cavity.

The ligaments and tendons of the muscles strengthen the capsule and promote the movement of the joint in certain directions.

To the auxiliary joint formations include intraarticular cartilages, disks, menisci, lips and intracapsular ligaments.

Blood supply of the joint is carried out from a widely anastomosing (branched) articular arterial network, formed by 3-8 arteries.

They show significant amounts of nerve endings that carry pain, and as a result, they can become a source of pain.

Joints are usually divided into 3 groups:

1. synarthrosis - fixed (fixed);
2. amphiarthroses (semi-joints) - partially mobile;
3. diartrozy (true joints) - mobile. Most joints refer to moving joints.

According to the World Health Organization, every 7th inhabitant of the planet suffers from joint pain. At the age of 40 to 70 years, joint diseases are observed in 50% of people and in 90% of people over 70 years old.

The synovial joint is a joint in which the ends of the bones converge in the joint bag. These include most of the human joints, including the carriers - knee and hip joints.

The joints are divided into simple and complex. In the formation of simple participate 2 bones, complex - more than 2 bones. If several independent joints participate in the movement, as in the lower jaw during chewing, these joints are called combined joints.

The combined joint is a combination of several joints isolated from each other, located separately, but functioning together.

These are, for example, both temporomandibular joints, proximal and distal ray-elbow joints, and others.

In shape, the articular surfaces resemble segments of surfaces of geometric bodies: a cylinder, an ellipse, a sphere. Depending on this, cylindrical, ellipsoid and spherical joints are distinguished.

The shape of the articular surfaces determines the volume and direction of movements around the 3 axes: sagittal (passes through front-to-back direction), frontal (parallel to the support plane) and vertical (perpendicular to plane of support).

Sliding movements of articular surfaces are possible, as well as their removal from each other, as, for example, it is observed when the fingers are stretched.

The joint function is determined by the number of axes around which movements are made.

Distinguish the following main types of movements in the joints:

• movement around the front axis - flexion and extension;
• movements around the sagittal axis - reduction and retraction of movement around the vertical axis, that is, rotation: inside (pronation) and outward (supination).

The human brush contains: 27 bones, 29 joints, 123 ligaments, 48 ​​nerves and 30 named arteries. Throughout life, we make finger movements millions of times. Movement of the hand and fingers provide 34 muscles, only when the thumb moves 9 different muscles are involved.

Shoulder joint

He is the most mobile in man and is formed by the head of the humerus and the articular cavity of the scapula.

The articular surface of the scapula is surrounded by a ring of fibrous cartilage - the so-called articular lip. Through the joint cavity, the tendon of the long head of the biceps arm muscle passes.

The shoulder joint is strengthened by a powerful beak-brachial ligament and surrounding muscles-deltoid, subscapular, supra- and subacute, large and small round.

In the movements of the shoulder, the large thoracic and widest muscles of the back are also involved.

The synovial membrane of the thin articular capsule forms two extraarticular twists - the tendons of the biceps arm muscle and the subscapular muscle.

In the blood supply of this joint, the anterior and posterior arteries, surrounding the humerus, and the pectoral artery, the venous outflow take place in the axillary vein.

Outflow of lymph occurs in the lymph nodes of the axillary region. The humerus is innervated by the branches of the axillary nerve.

1. brachial bone;
2. scapula;
3. collarbone;
4. articular capsule;
5. folds of the joint capsule;
6. acromioclavicular joint.

In the shoulder joint movements around 3 axes are possible. Flexion is limited to the acromial and coracoid processes of the scapula, as well as the coracoid-brachial ligament, extension-acromion, coracoid-brachial ligament and joint capsule.

Retraction in the joint is possible up to 90 °, and with the participation of the upper extremity belt (with the inclusion of the sternoclavicular joint) - up to 180 °. The abduction of the large tuberosus of humerus in the coracoid-acromial ligament is stopped at the moment of abutment.

The humeral girdle and the shoulder joint function in most cases as a single functional formation.

Hip Joint

He is the most powerful and heavily loaded joint in the human body and is formed by the acetabulum of the pelvic bone and the head of the femur.

The hip joint is strengthened by the intraarticular ligament of the head of the femoral brush, as well as by the transverse ligament of the acetabulum, which surrounds the femoral neck.

From the outside, a powerful iliac-femoral, pubic-femoral and sciatic-femoral ligament are weaved into the capsule.

The blood supply of this joint is carried out through the arteries that round the femur, the branches of the locking and (non-permanent) branches of the upper perforating, gluteal and internal genital arteries.

The outflow of blood occurs through the veins surrounding the femur, into the femoral vein and through the veins of the veins into the iliac vein. Lymph outflow is carried out in the lymph nodes located around the external and internal iliac vessels.

The hip joint is innervated by the femoral, blocking, ischial, upper and lower gluteal and sexual nerves.
The hip joint is a kind of globular joint.

This joint is under great stress, so it is not surprising that its lesions take first place in the common pathology of the joint apparatus.

Knee-joint

One of the large and complex joints of man. It consists of 3 bones: femoral, tibial and fibular. Stability to the knee joint is provided by intra-and extra-articular ligaments.

The extraarticular joints of the joint are the peroneal and tibial collateral ligaments, oblique and arched popliteal ligaments, patellar ligament, medial and lateral supporting ligament patella.

Intra-articular ligaments include the anterior and posterior cruciate ligaments.

The joint has many auxiliary elements, such as meniscuses, intraarticular ligaments, synovial folds, synovial bags. In each knee joint there are 2 meniscus - external and internal.

Menisci have the form of semi-moons and perform an amortization role. The auxiliary elements of this joint are synovial folds, which are formed by the synovial membrane of the capsule.

The knee joint also has several synovial bags, some of which communicate with the joint cavity.

Everyone had to admire the performances of gymnasts and circus performers. About people who are able to climb into small boxes and unnaturally bend, they say that they have gutta-percha joints.

Of course, this is not so. Authors of the Oxford Handbook of Body Organs assure readers that "in such people the joints are phenomenally flexible" - in medicine this is called the joint hypermobility syndrome.

• femur
• tibia
• cartilage
• synovial fluid
• inner and outer meniscuses
• medial ligament
• lateral ligament
• cruciate ligament
• patella

In form, the joint is a condylar joint. It can move around 2 axes: frontal and vertical (with a bent position in the joint). Around the front axis is flexion and extension, around the vertical axis - rotation.

The knee joint is very important for human movement. At each step, due to flexion, it allows the leg to step forward without hitting the ground. Otherwise, the leg would be carried forward by raising the hip.

A source: http://meddoc.com.ua/stroenie-i-funkcii-sustavov/

Joints in man

The basis of the structure of a living organism is the skeleton, which includes mobile connections, as well as bone and cartilaginous tissue.

Man's joints are important and necessary for walking, performing complex and coordinated movements in daily work and professional activities.

Arthrology is a complex science that studies all kinds of anastomoses with bones, a brief general explanation of which is mandatory for everyone.

Species, their anatomy and structure

A clear example of studying the structure of bone anastomoses in the human body is the synovial joint. The clinical anatomy of a person divides all the structural components into two types:

• Essential elements:
  • articular surfaces - areas on the bones to which they are in contact (head and hollow);
  • articular cartilage - protects against fracture as a result of friction;
  • capsule - is a defense, responsible for the production of synovia;
  • cavity - gap between surfaces, filled with liquid;
  • synovia - softens the friction of the bones, nourishes the cartilage, supporting the metabolism.
• Auxiliary formations:
  • cartilaginous disk - a plate that divides the cavity into two halves.
  • menisci - play the role of shock absorber, are in the knee;
  • joint lip - a border of cartilage around the joint cavity;
  • ligamentous connecting device - controls movements;
  • large and minor muscles.

Functions and tasks

Articulations create depreciation during the motor activity of a person.

Different types of human joints, their diverse anatomical design are of fundamental importance for a number of functional duties performed by bone connections. All actions are divided into the following functions:

• The combination of bones, teeth and cartilage with each other, makes them a durable shock absorber of movements.
• Prevention of bone tissue destruction.
• Performing axial movements, among which are:
  • frontal - flexion, extension;
  • sagittal - reduction, diversion;
  • vertical - supination (movement outside), pronation (inside);
  • Circular motion - moving the stroke from axis to axis.
• Physical activity of a person, which ensures the correct structure of the joint.
• Preservation of the position of the skeleton.
• Influence on growth and development of the body.

Classification, its principles

Compounds in the body are many, each has its own characteristics and performs specific functions.

The most convenient in clinical practice is the classification of joints in species and types, which is well represented by the table.

It does not include continuous interchilar connections of the ribs, starting from the 6th to the 9th.

View	Characteristic	A type	Location Features
Fibrous	Connective tissue with collagen	Suture	Stitches of the skull
SYNDESMOZIS	Connects the radial and ulnar bone of the forearm
Nails	Teeth
Cartilaginous	In structure there is a hyaline cartilage or a disk	Synchronous	Stem and sternum joint
Symphysis or semi-joints	Pubic symphysis, intervertebral articulations
Synovial	The joint connects the cavity, capsule, additional ligaments, synovial fluid, bag, tendon sheaths	Flat (sliding)	Sacral-iliac
Block-shaped	Elbow, knee, plechelitevoy (spiral joint)
Ball	Breast-rib (cup-like)
Hinged (cylindrical joint)	Connects the tooth of the epistope and the atlas
Ushchelkovy	Metacarpophalangeal fingers
Saddle-shaped	Metacarpal thumb
Ellipsoidal	Wrist Band

Connection types

Other joints are divided by such criteria:

The joints can be classified according to the degree of mobility.

• Mobility:
  • sinarthrosis - immovable;
  • amphiarthrosis - inactive;
  • diarthroses are mobile.
• Motion axes:
  • uniaxial joints;
  • biaxial;
  • three-axis.
• Biomechanical properties:
  • plain;
  • complicated;
  • complex.

Basic joints in the human body

Hip

The joint connects the femur to the pelvic bone.

Connects parts of the pelvic to the femoral head, which are covered with cartilage and synovial membrane. Spherical, paired, multi-axis joint of lower extremities.

The axes of movement are frontal, sagittal, vertical, circular rotations. The joint capsule is attached in such a way that the acetabulum and the femoral neck are located in the joint cavity.

The connecting component is represented by a bundle of the femoral head, pubic-femoral, iliac-femoral, ischial-femoral and circular zone.

Knee design diagram

The complex, condylar, the largest joint on the extremities of the lower belt is arranged with the involvement of the patella, the proximal margin of the tibia and the distal - the femur. Anatomical ligaments of the knee joint are represented by three groups:

• Lateral - collateral small and tibial.
• Extra-capsular (posterior) - patellar patella, arcuate, supporting lateral-medial, popliteal.
• Intracapsular - transverse knee ligament and cruciform.

Provides rotations and movements in the front axle. Has a number of synovial bags, the number and size of which are individual.

The folds of the synovial membrane accumulate adipose tissue. The surfaces of the joint are covered with a cartilaginous layer.

A distinctive feature is the presence of the external and internal sickle-shaped cartilage parts, which have the names of menisci.

Ankle

The joint is more often injured in people actively engaged in sports.

The mobile joint, in which the distal epiphyses (bottoms) of the small and tibia bones are joined to the human foot, namely the talus bone.

Block-shaped, is involved in the movements of the frontal and sagittal axes. Ligaments are represented by two groups: lateral, which includes the talus-peroneal and heel-fibular ligaments and the medial, or deltoid ligament.

Ankle joint is the main area of ​​trauma in athletes who move continuously.

Saddle-shaped

A variety of synovial anastomoses, reminiscent of a rider on a horse, corresponds to the name. On bone, similar in shape to the saddle, another bone is planted. Are flexible in comparison with others.

A vivid example of the joint, which has the human musculoskeletal system, is the metacarpal joint of the thumb. Here the saddle is the bone of the trapezoid, and on it is placed the first metacarpal bone.

The opposing thumb on the upper limbs is the distinguishing feature of a person, which distinguishes him from the world of animals, and thanks to which there is an opportunity to do work, including mastering new professions.

Double elbow

A complex, movable articulation of the humerus with radial and ulna bones, which consists of three joints surrounded by a single capsule. Among them:

1. the humerus is a globose joint, responsible for the movement in two axes along with the elbow;
2. shoulder-block - block-shaped, helical;
3. proximal lucheloid - a rotational joint of the 1st type.

The junction has a complex structure and has the largest size in the upper limbs.

The largest joint of the upper half of the body, which provides movement of the upper limbs and corresponds to their number.

Anatomically it is considered block-like with screw-like slides, lateral movements in it are impossible.

Auxiliary elements are represented by two collateral ligaments - radial and ulnar.

Globular

This includes the hip and shoulder joint of bones (multiaxial structures), which have the greatest mobility. The name of this group identified the obligatory bone element resembling a ball: in the first example it is the head of the humerus, in the 2nd - the head of the thigh.

Common elements of the structure are represented by a globular head on the end of one bone and a cup-shaped depression on the second. The shoulder joint has the largest range of free movements in the skeleton, it is simple in structure, and the hip joint is less mobile, but stronger and sturdier.

Block-shaped

Types of joints that are synovial. This includes the knee, elbow, ankle and less complex departments, which have good mobility - interphalangeal joints of the hands and feet.

These joints, to the best of their characteristics, are endowed with lesser work and keep a small mass, which is standard to their structure - small ligaments, hyaline cartilage, capsule with synovial membrane.

Ellipsoidal

The wrist joint is elliptical.

The type of joints, also known as flat, is formed by bones with an almost smooth surface.

In the joint space constantly functions synovia, which produces a membrane. These movable joints contribute to a limited amplitude in all directions.

Representatives of the group are intervertebral, carpal, carpometacarpal joints in the human body.

Ushchelkovye

A separate subspecies of ellipsoid class. It is considered a transitional type from block-shaped.

A distinctive feature from the 1st is the discrepancy between the shape and dimensions of the connecting surfaces, from the ellipsoid - by the number of heads of the structure.

In the body, there are two examples of such joints - temporomandibular and knee, the latter moving around 2 axes.

Diagnosis of joint diseases

It is based on the following methods and techniques:

Goniometry allows you to determine how much a person can move the joint.

• Complaints.
• Anamnesis of the disease.
• General examination, palpation.
• Goniometry is a characteristic of the free amplitude of movements.
• Mandatory laboratory tests:
  • general blood analysis;
  • biochemistry of blood, especially C-reactive protein, erythrocyte sedimentation reaction, antinuclear antibodies, uric acid;
  • the analysis of urine the general or common.
• Radiation methods of research:
  • X-ray;
  • arthrography;
  • CT.
• Radionuclide.
• MRI.
• USD.

Treatment of ailments

Therapy is effective only with a correctly diagnosed diagnosis and, if the diagnosis is not late. Table of major diseases identifies the cause, which should be treated. When there are foci of infection, antibiotics are prescribed.

In the autoimmune process, immunosuppressors - monoclonal antibodies, corticosteroids, cytostatics - are used. The degenerative states are corrected by chondroprotectors.

Accept non-steroidal anti-inflammatory drugs that affect the level of calcium and bone strength. Rehabilitation is provided by physiotherapy and physiotherapy.

Surgical treatment is used after the exhaustion of conservative methods, but it does not guarantee complete blockage of any pathological process.

A source: https://OsteoKeen.ru/fiziologia/sustavy-cheloveka.html

Structure and function of joints

Joints of our body - this is a true masterpiece of engineering thought. They combine sufficient simplicity and compact design with high strength. However, many aspects of their function are not fully understood.

In the human body, there are more than 230 joints. They are represented in the skeleton wherever there are distinct movements of parts of the body: flexion and extension, retraction and reduction, rotation ...

The joints of the bones must be a priori mobile, so that a person can realize the motor function, and at the same time reliably fastened together. The role of such "fastenings" is performed by joints.

And despite the fact that the size and shape of the joints are extremely diverse, in the design of any of them there are mandatory elements.

For example, the bones of the skull, the body of the vertebrae are connected).

Intermittent joint allows joints bones to move relative to each other, of course, with the help of muscles. The joint surfaces of the bones are not the same.

In their form they can resemble a ball, an ellipse, a cylinder and other geometric shapes.

A material of high strength, cartilage, is applied to both articulating surfaces, the thickness of which varies from up to 6 millimeters in different joints.

In appearance, a uniform, smooth and shiny cartilage under an electron microscope resembles a sponge with very thin pores.

Cartilage tissue is formed by cells-chondrocytes and intercellular substance, through which the supply of chondrocytes is supplied with nutrients, water, oxygen.

Observations showed that the fibers of the intercellular substance can change their direction, adapting to long-acting loads. This dynamic fiber increases the wear resistance of cartilaginous tissue.

The junction of the bones is surrounded by an articular capsule. The outer layer of the capsule is strong, fibrous: its inner surface is covered with a layer of endothelial cells, which produce a viscous, transparent, yellowish liquid - synovia.

Simultaneously, the synovium strengthens the joint, creating a force of adhesion between the articular surfaces. It, like a buffer, softens the tremors that bones experience when walking, jumping, various movements.

Synovial fluid also has a significant role in providing nutrition to cartilaginous tissue.

It is established that in each joint the level of synovia characteristic for him is maintained. But its composition is not always the same. For example, with an increase in the speed of movement in the joint, the viscosity of the synovium decreases, thereby further reducing the friction between the articular surfaces of the bones.

Investigating the function of the synovial membrane, scientists came to the conclusion that it functions as a biological pump. The experimenters found in this shell narrowly differentiated cells of type A and B.

Cells of type B specialize in the production of hyacuronic acid, which informs synovia of the miraculous property of facilitating the realization of "motion without friction".

Cells of type A are kind of cleaners: they suck out the waste products of the vital activity of cells from the synovial fluid.

However, only a general scheme of the device and the action of this living pump is known to those skilled in the art. Its main "nodes" and features of its work have yet to be studied.

The function of the biological pump is closely related to maintaining a constant negative pressure inside the joint cavity.

This pressure is always lower than the atmospheric pressure (which increases the adhesion force between the articular surfaces, they are closer to each other), but the person does not feel it.

The design of most joints is not limited to mandatory elements and includes various disks, meniscuses, bundles and other "technical improvements" that nature created in the process evolution. In the knee joint, for example, two meniscus: external and internal.

Due to these crescent cartilage, rotational and flexion-extension movements are performed in the joint, they also serve as buffers that protect the joint surfaces from sudden tremors.

Their role in the physiology and mechanics of the knee joint is so great that the meniscus is sometimes called the joint in the joint.

The function assigned to the joint dictates the design. The most convincing proof of this is the joints of the hand.

In the process of human labor, the joint and ligament apparatus of the brush reached constructive perfection.

Various combinations of joints - and there are more than twenty of them in the hand, including block-shaped ones. ellipsoid, spherical, saddle-shaped, - allow to make differentiated movements.

Or, for example, such joints as the shoulder and hip. Both are spherical, both simple, as each is composed of two bones.

Try to raise your hand across the side up. Easily! Now lift your leg.

Its capacity increases the fibrous-cartilaginous ring, the so-called articular lip, which joins the edge of the cavity. This structure allows you to make movements in the shoulder joint movement in almost all directions.

In the hip joint, such a volume of movements is not provided. Here the main thing is another - the strength of the design: after all, the joint constantly has to experience significant and dynamic and static loads.

In this joint, the cavity of the pelvic bone covers the head of the thigh almost completely, which, naturally, limits the volume of movements.

But not only is the hip joint less mobile than the shoulder joint.

If in the shoulder joint the capsule is very spacious and slightly stretched, then in the hip it is less bulky and very durable, in some places even reinforced with additional ligaments.

And why do gymnasts, acrobats, ballet dancers, circus not only need to raise their legs vertically upwards, but also do more complex movements? This is another proof of the plasticity of the musculoskeletal system, its enormous potential.

What are the secrets of this plasticity, high performance joints? Experts conduct research that will help answer this and other questions.

The results of scientific research are not only of theoretical interest. Practical medicine is interested in them: surgery, orthopedics, transplantology.

A source: https://krasgmu.net/publ/anatomija/stroenie_i_funkcii_sustavov/95-1-0-1066