Generality
The skeleton is the internal scaffolding of the human body. At its constitution, the bones and, secondly, the cartilages and the joints are mainly involved.
The man has a slightly different skeleton from the woman: the diversities are subtle, yet an expert eye (eg a doctor) is able to catch them and understand the sex of an individual from the mere observation of the skeletal framework (when, of course, no other information is available).
The skeleton covers various functions, including: support of the human body, protection of underlying organs and soft tissues, assistance to balance and movement, production of blood cells, release of the osteocalcin hormone and storage department for mineral salts such as calcium and iron.
The skeleton can be the victim of injuries (eg: bone fractures or joint distortions) and pathologies, such as osteoporosis or arthritis.
What is the skeleton?
The skeleton is the internal scaffold of the human body, in which the bones (main component), the cartilaginous tissues and the joints participate .
Anatomy
The skeleton of an adult human being constitutes 30-40% of the total body mass ( body mass) and includes as many as 206 bones, different in shape and function, and present in equal modalities (eg: the two femurs) or uneven (eg : hyoid bone).
ANATOMICAL DIVISIONS: SKILLETRO ASSILE AND APPENDICULAR
According to the classical anatomical view, the skeleton of the human being can be subdivided into: an axial skeleton and an appendicular skeleton .
The axial skeleton is the set of bones that make up the skull, the vertebral column and the thoracic cage, plus the hyoid bone and the three ossicles of each ear (hammer, anvil and stirrup). In all, it includes 80 bone elements:
- The 22 bones of the skull;
- The 26 bones of the vertebral column, provided that we consider the bones of the sacral tract (or sacral vertebrae) as a whole and constituting the so-called sacrum (otherwise, the bones of the spine would be 33-34);
- The 25 bones of the rib cage (12 pairs of ribs plus the sternum).
- The aforementioned hyoid bone and 3 ossicles of each ear;
The appendicular skeleton, on the other hand, represents the set of bones that form the scapular belt (or shoulder girdle ), upper limbs, pelvis and lower limbs . Overall, it includes 126 bone elements:
- The 4 bones of the scapular girdle, which are the 2 scapulae and the 2 clavicles ;
- The 3 bones of each upper limb without hand, which are humerus, radius and ulna ;
- The 27 bones of each hand, which are the carpal bones, the metacarpals and the phalanges of the fingers . The two hands, therefore, contain the beauty of 54 bones;
- The 2 bones of the pelvis, which are the iliac bones ;
- The 4 bones of each lower limb excluding the foot, which are the femur, the patella, the tibia and the fibula ;
- The 26 bones of each foot, which are the tarsal bones, the metatarsals and the phalanges of the fingers . The two feet therefore contribute to the total number of skeletal bones with 52 elements.
COMPOSITION OF BONES
The bones of the skeleton are the result of a cellular component and a non-living component, called the bone matrix .
- The cellular component of skeletal bones comprises three types of cells, which are: osteoblasts, osteoclasts and osteocytes . The contribution of the cells just mentioned, to the total mass of the skeleton, is small; however, this does not mean that they are of fundamental importance for bone health and skeletal health in general.
- Moving on to the bone matrix, this is, half, water and, half, collagen mixed with calcium phosphate (83-85%), calcium carbonate (9-11%), magnesium phosphate (1-2%) and calcium fluoride (0.7-3%). It is important to point out that, often, calcium phosphate, calcium carbonate and calcium fluoride, present in bones, are known by a more general term, corresponding to hydroxyapatite .
To learn more about the cellular component of skeletal bones, readers can consult the article here.
TYPES OF SKELETON BONES
Based on shape and size, anatomists distinguish the bones of the human skeleton in at least 6 different types, which are:
- The typology of long bones . All bones in which the length prevails over width and thickness belong to this category. The long bones are distinguished by a narrow central part, called diaphysis or body, and by two bulky ends, called epiphyses.
Inside the long bones, to be precise inside the diaphysis, resides the bone marrow, whose function will be taken into consideration in the chapter dedicated to the functions of the skeleton.
The bone tissue that makes up the long bones is generally very compact.
Typical examples of long bones are: the humerus, the ulna, the radium, the femur, the tibia, the fibula and the clavicle.
- The typology of short (or short) bones . Bones in which length and diameter are equivalent belong to this category.
The short (or short) bones have a particular composition: spongy bone, internally, and compact bone, externally.
Typical examples of short (or short) bones are: wrist bones, calcaneus, and vertebrae.
- The typology of flat bones . All bones of limited thickness and laminar appearance fall into this category.
Despite their small thickness, the flat bones consist of two layers of bone tissue: an inner layer, which includes spongy bone and bone marrow, and an outer layer, which includes compact bone tissue.
Classic examples of flat bones are: skull, pelvis, and sternum bones and shoulder blades.
- The typology of irregular bones . Bones of irregular shape belong to this category, and it is difficult to describe them.
Two examples of irregular bones are the ethmoid and the sphenoid, two bones of the splancnocranium.
- The type of sesamoid bones . This category includes all the small, roundish and flattened bones.
Sesamoid bones are important for the relationship they establish with tendons.
The most classic example of sesamoid bone is the knee patella.
- The typology of wormian or sutural bones . The flat and indefinite bones that lie between the sutures of the skull bones belong to this category.
CARTILAGINEI FABRICS
Cartilaginous tissues, better known as cartilage or cartilage (in the singular), are supporting connective tissues, endowed with extreme flexibility and resistance.
Without blood vessels, cartilages are tissues that result from the union of particular cells, called chondrocytes .
In the human skeleton, cartilaginous tissues can have different peculiarities, depending on the functions they must fulfill. To understand what has just been said, the reader thinks of the cartilage of the auricles and the cartilage of the meniscus: although belonging to the same category of tissue and resulting from the union of chondrocytes, these two examples of cartilage differ considerably in consistency and specific properties.
The human skeleton includes three types of cartilage:
- Hyaline cartilage ;
- Elastic cartilage ;
- The fibrous cartilage .
| Types of cartilage in the human body | Location (examples) | Features |
| Hyaline cartilage | Ribs, nose, trachea, bronchi and larynx | Bluish white in color, it is the most common type of cartilage in the human body. It is not present in the joints. |
| Elastic cartilage | Auricles, Eustachian tube and epiglottis | Matt yellow in color, it has remarkable elasticity. |
| Fibrous cartilage | Intervertebral discs, knee menisci and pubic symphysis | Of whitish color, it is particularly resistant to mechanical stress. It is richly present in the joints. |
JOINTS
The joints are anatomical structures, sometimes complex, which put two or more bones in mutual contact. In the human skeleton, they are 360 and perform functions of support, mobility and protection.
According to the most common anatomical view, there would be three main categories of joints:
- Fibrous joints (or synarthrosis ). They generally lack mobility and the constituent bones are held together by fibrous tissue. Typical examples of synarthrosis are the joints between the bones of the skull.
- Cartilaginous joints (or amphiarthrosis ). They have poor mobility and the constituent bones are joined by cartilage. Classic examples of amphiarthrosis are the joints that connect the vertebrae of the spine.
- Synovial joints (or diarthrosis ). They are highly mobile and include various components, including: the articular surfaces and the cartilage that covers them, the joint capsule, the synovial membrane, the synovial bags and a series of ligaments and tendons.
Typical examples of diarthrosis are the joints of the shoulder, knee, hip and ankle.
DIFFERENCES BETWEEN THE TWO SEXES
The skeleton of the man has some differences compared to the skeleton of the woman.
These differences are subtle (only one expert eye can understand them) and concern:
- The skull. Between the male skull and the female skull there is a gross difference at the level of: midline nuchal, mastoid processes, supraorbital margins, superciliary arches and chin.
- The long bones and the musculature that concerns them. Man's long bones are wider than the woman's long bones. Furthermore, the muscle insertion zones, on the long bones, are much wider and more resistant in men, rather than in women, demonstrating the greater muscular strength of the male sex, compared to the female sex.
- The pelvis. The female pelvis differs from the male pelvis in shape and size. It is in fact wider and more spacious, to allow the growth of the fetus, during a possible pregnancy, and to favor the escape of the same fetus, at the moment of birth. Therefore, the pelvic level differences between the two sexes are linked to reproduction.
In the presence of a skeletal remnant of which gender belonging is ignored (is it man or woman?), The observation of the pelvis represents one of the most accurate and reliable methods of investigation, to establish sex.
- The general robustness of the skeletal scaffold. Female skeletal elements have a tendency to be less robust and smaller than equivalent male skeletal elements.
Skeletal differences between men and women are an example of sexual dimorphism .
By sexual dimorphism, we mean the morphological difference between individuals belonging to the same species, but of different sex.
Perhaps readers don't know that ...
In the human skeleton, a long bone that allows to establish, with a certain degree of security, the sex of an individual is the clavicle.
Compared to the female clavicle, the male clavicle is thicker, forms a more pronounced S, lacks symmetry (in the sense that the right clavicle is different from the left clavicle) and, finally, has insertion zones for the wider muscles.
SKELETON IN NEWBORNS
The skeleton of a newborn human being comprises about 300 bones, so almost a hundred more than the skeleton of an adult human being.
This difference depends on the fact that, with growth, many distinct adjacent bones fuse together, forming a single bone.
Typical examples of bones that melt, during growth, are the bones of the skull (process of fusion of the cranial sutures).
Development
In the course of life, the human skeleton undergoes various changes.
As stated, it changes in the number of bones, due to fusion processes; it also changes in the composition, which passes from predominantly cartilaginous, during fetal life and in the first years of existence, to predominantly bone, in adult life; finally, it changes in size, due to the growth of bones in length and diameter.
Functions
The skeleton fulfills a variety of functions, including:
- Support . The bony elements of the so-called axile skeleton are indispensable for the maintenance of the erect posture and for the correct discharge of the weight from the upper part of the body (head, trunk and upper limbs) to the lower part of the body (also and lower limbs).
- Protection of delicate organs and soft tissues . This is the case of the skull (or skull bones) with respect to the brain, the thoracic cage with respect to the organs located in the thorax (heart, lungs, aorta, etc.), vertebrae with respect to the spinal cord and pelvic bones towards the abdominal organs.
- Balance and movement, along with muscles and nerves . The bones of the appendicular skeleton provide mainly balance and movement.
- Production of blood cells ( red blood cells, white blood cells and platelets ). The process of producing blood cells is the responsibility of the bone marrow, present inside the long bones, and is called hematopoiesis.
- Plastic . The skeleton of each individual gives a precise shape to the body of the latter.
- Storage of mineral salts . The bones of the skeleton are fundamental for the storage and metabolism of calcium, for the metabolism of iron and for the accumulation of iron in the form of ferritin.
This should not come as a surprise if one thinks of the so-called bone matrix, rich in calcium phosphate, calcium carbonate, etc.
- Release of the osteocalcin hormone . The main tasks of osteocalcin are: to increase insulin secretion by acting directly on the pancreas, and to increase insulin sensitivity by acting on fat cells.
clinic
The skeleton can be the victim of injuries and various pathologies .
Among the skeletal injuries, first of all, there are bone fractures and, secondly, articular distortions / dislocations .
Among the skeletal pathologies, on the other hand, the following are certainly worth mentioning: osteoporosis, osteopenia and arthritis .
BONE FRACTURES AND JOINT DISTORSIONS
Bone fractures and joint distortions / dislocations are injuries to the skeleton, which, in general, have a traumatic origin . The first concern the bones, while the second concern the joints.
The typical symptoms of bone fractures and joint distortions / dislocations are: pain, limitation of movements (eg, lameness, if the lower limbs are involved), swelling and hematoma.
Treatment depends on the severity of the injury: minor injuries heal with rest, a cast (in case of fracture) and physiotherapy, while serious injuries require surgery by the surgeon (in addition to rest, plastering and physiotherapy ).
OSTEOPOROSIS AND OSTEOPENIA
Osteoporosis is a common systemic disease of the skeleton, which causes a strong weakening of the bones. This weakening originates from the deterioration of the microarchitecture of the bone tissue and from the consequent reduction of the bone mineral mass (eg: reduction in calcium and / or iron levels, etc.). Due to the aforementioned bone weakening, the bones of people with osteoporosis are more fragile and prone to fractures.
Osteopenia is a condition very similar to osteoporosis; to distinguish it from the latter are the lower degree of reduction in bone mineral density and the consequent lower risk of skeletal fractures. In other words, osteopenia is mild osteoporosis .
Osteopenia and osteoporosis are two typical conditions of advanced age: in the female population, it is particularly widespread from the age of 65 and up, but in the male population, it is particularly common starting from the age of 70 and up.
ARTHRITIS
The term arthritis indicates any inflammatory condition that affects one or more joints of the skeleton.
There are different types (or forms) of arthritis, each with unique causes and characteristics.
Among the most well-known and widespread types of arthritis, it is certainly worth mentioning: osteoarthritis (or arthrosis ), rheumatoid arthritis, gouty arthritis (or gout ) and ankylosing spondylitis .
The classic symptoms of arthritis are: pain, joint stiffness, joint swelling, redness and a sense of heat at the joint in question and, finally, reduced ability to move by the joint involved.
Arthritis is a widespread morbid condition of the skeleton, which, in its various forms, can affect individuals of all ages.
