BONE SYSTEM: FUNCTIONS, PARTS, TYPES, REGIONS AND CARE - ANATOMY AND PHYSIOLOGY - 2025

The bone system, more commonly known as the skeleton, is the set of specialized structures made up of living tissue (cells) and minerals (calcium). This system is in charge of supporting the body of vertebrate animals, including man.

It is such a specialized structure and that marks such a clear difference between living beings that possess it and those that do not, that it divides the animal kingdom into two large groups: invertebrates (animals that do not have bones) and vertebrates (those who do have a skeleton).

As a member of the group of higher mammals and therefore being a vertebrate, the human being has a complex skeleton that protects the internal organs in certain parts of the body and allows locomotion by serving as an anchor for the muscles of the extremities.

Functions of bones

Bones have multiple functions, some common to all bones in the body and others more specialized depending on their location.

In these structures it is clearly shown that the structure and shape are conditioned by the function, to the point that to classify the bones their function is taken into account. In general it can be said that there are common functions and specific functions.

Common functions

These are the functions that all bones of the skeleton have, regardless of their location or size. In this sense, there are two main main functions:

- Model the area where they are.

- Serve as an anchor to muscles and ligaments.

- Anatomy modeling

The anatomy and shape of each region of the body depends largely on the bones that support it, so the external appearance depends on the bones that are inside, beyond our sight.

This function is so important that, when the bones present malformations or problems in their structure that do not allow them to perform this function adequately, structural alterations and severe deformities of the affected anatomical areas occur that require several surgeries to be corrected.

- Anchoring of muscles and ligaments

There is practically no bone structure that is not firmly attached to one or more muscles, as well as to different ligaments.

This function is directly related to the modeling of the anatomy. The skeleton is the foundation on which the rest of the body is built, both inside and out.

Muscles are largely responsible for the shape of the vertebral contour, and these need to be anchored to a fixed point in order to perform their function; therefore, there is practically no bone that does not receive muscle insertions.

The bone-muscle junction is called the osteo-muscular system, since they act together to be able to perform such specialized functions as locomotion.

Specialized functions

Just as there are common functions, bones have specialized functions according to their anatomical location, this being the basis for the classification of the different components of the bone system.

In this sense, it can be said that the main specialized functions of bones are:

- Protection.

- Support and locomotion.

- Super specialized functions.

Depending on its location and shape, each bone in the body fulfills some of these functions.

- Protection

The bones whose main function is to protect the internal organs are generally wide, flat, light and at the same time very resistant; most have a curved, hemispherical shape or comprise a circumferential section of some kind.

This characteristic allows them to increase their resistance to impact, making them stronger and capable of dissipating the energy of external trauma without the need for the bone to be much denser.

In addition, this particular shape makes it possible to increase the interior space available to house the organs found in the body. The bones that provide protection are found in three areas: head, thorax, and pelvis.

Skull

The bones of the skull are perhaps the most specialized of all, as failure could lead to instant death since the organ they protect, the brain, is extremely sensitive to external trauma.

Thus, the bones of the skull function as an impregnable vault that keeps the brain isolated from any contact with the outside.

Ribs

In the second place of this group of bones are the ribs, which as an individual bone do not represent a great mass or a lot of strength, but forming a system of interconnected arches they provide great protection to the structures of the rib cage (heart, lungs and great vessels).

Unlike the skull that provides a solid shell, the ribs have open spaces (boneless) between them, functioning as a kind of protective "cage".

This is because they protect organs that change in size and shape: the lungs increase in size with each inspiration and shrink when they expire; likewise, the chambers of the heart change in volume according to the phase of the cardiac cycle.

For this reason it is necessary that the "shield" of these organs can be made larger or smaller depending on the case.

Pelvis

Finally, there is the pelvis, made up of several fused bones and inside which are quite delicate organs, such as the female reproductive system and the end of the great vessels.

Due to its position in the lower part of the body, the pelvis functions as a bone with a dual function: it provides protection to the lower abdominal structures (bladder, rectum, uterus, etc.) and allows the transfer of body weight to the lower extremities; hence they are the strongest protective bones in the entire body.

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Although it provides some support, the pelvis is a bone with no movable joints; that is, it functions as a weight-bearing point, but by itself it is not capable of providing mobility, unlike the bones of the extremities.

In this sense, both arms and legs have a series of interconnected bones through the joints, whose main characteristic is that they are quite long, receiving insertions from multiple muscle groups.

This characteristic allows them to act as levers that increase the force generated by the muscle, so that by working in unison, the bones and the muscular system, a great amount of force can be generated in the extremities. This force serves for locomotion (lower extremities) and for support and mobility (upper extremities).

Another characteristic of supporting bones is that they are highly resistant to vertical loads and torsion, which allows them to act as "pillars" to support the weight of the body and, at the same time, as levers with mobility in different planes.

If they were not resistant to twisting, stresses in the wrong plane could easily break these bones.

Super specialized functions

In this group are bones with very specialized and specific functions that determine very particular shapes and sizes.

- Spine

When seen in isolation, these small bones are not very impressive, but when placed together, working in unison, they are capable of creating a structure so wonderful and complex that it has not been able to be reproduced until now by any mechanical system.

The spinal column functions as a rigid pillar that supports the body's weight, taking it towards the extremities (load-bearing function), but at the same time it is flexible enough to allow angulations of up to 90º, giving it great mobility (locomotion). To realize this, it is enough to see a routine of a gymnast.

Its functions do not end there. In addition to serving as a support and helping with locomotion; The vertebrae also protect extremely delicate structures - such as the spinal cord - and important blood vessels found within the chest and abdomen.

Thus, the vertebrae are also capable of providing protection, functioning as a kind of "articulated medieval armor." The versatility of the vertebrae is fascinating, especially when seen working together.

- Sternum

On the other hand is the sternum. It is a flat, modest and not very striking bone; It does not move or carry cargo, but its function is vital to preserve life.

The sternum is a sheet of solid bone that sits in the front of the rib cage and functions as a dense, hard shield that sits in front of the heart.

Until then, it could be considered as a bone with a protective function, but its mission goes beyond that since the ribs are inserted in this bone.

Although their mobility is limited, the set of costo-chondral joints (between cartilage and ribs) that take their point of support in the sternum are a fine clockwork mechanism that allows the rib cage to expand and contract as necessary without the ribs "jump" out of position.

- Middle ear

Finally, there are some bones that are almost invisible, small and unknown to most people. They are the smallest bones in the body and their function is neither protective nor supportive; in fact, there are only 6 (3 on each side) and without them we could not have a perception of the world like we do.

These are the bones of the middle ear. Three highly specialized structures whose sole function is to transmit the vibration produced by sound waves in the eardrum to the inner ear where they will be transformed into nerve impulses that our brain will interpret as sounds.

They are tiny and super specialized, to the point that when they get sick (otosclerosis) people lose their hearing. The bones of the middle ear are the epitome of super specialized bones.

Classification of bones

Knowing their function, bones can be divided into two large groups:

- Flat bones.

- Long bones.

In these cases the form depends on the function. Also, both flat bones and long bones inside are made up of two different types of bone tissue:

- Spongy bone.

- Cortical bone.

The ratio of one to the other varies depending on the type of bone. In flat bones, spongy bone predominates, making them lighter but highly resistant to impact.

On the other hand, in long bones the cortical bone predominates, whose particular characteristics make it very resistant to loads and torsion, although this implies an added weight.

Flat bones

They are bones in which width and length are the predominant measurements, while thickness is usually very small. Thus, they can be considered two-dimensional bones.

This characteristic allows them to take almost any shape, to the point that in certain areas of the organism they fuse together like puzzle pieces, forming a single and indivisible whole.

All bones that provide protection are flat, so the skull, ribs, and pelvis are in this group.

Long bones

Unlike flat bones, in long bones a single measure predominates over all others: length, limiting the thickness and width to the minimum necessary.

They are very hard and resistant bones, since they tend to function as a lever and are exposed to great mechanical stress. They also support the weight of the body, so they need to be very resistant.

In this group of bones are all those of the extremities: from the longest of the leg (such as the femur) to the smallest of the hands and feet (phalanges).

All of these bones are made up primarily of cortical bone, which is very dense and strong. To limit weight, its interior is hollow and is occupied by the bone marrow, that is, soft tissue.

Long bones can be compared to structural tubing, as they provide an excellent strength-to-weight ratio.

Spongy bone

The interior of flat bones is made up of cancellous bone. The structure of this bone resembles a honeycomb, so they have a very large internal area (which houses the marrow) and is capable of absorbing impacts very effectively.

This is because the energy is dissipated over hundreds of thousands of tiny bony sheets that act as individual buffers.

Since its structure is porous, the cancellous bone is covered by small layers of cortical bone both on its inner side (which faces the organs it protects) and on its outer side (the one that faces outside the body), so that the cortical bone provides a hard covering to the whiter cancellous bone.

Doesn't this remind you of the structure of a compound bow? For nature developed that principle long before man discovered it.

Cortical bone

Unlike cancellous bone, cortical bone is composed of superimposed layers of bone, close together, forming concentric rings of extremely dense and resistant material.

Cortical bone has no pores, it is compact and, due to the action of the muscles throughout growth, it has a certain degree of torsion in its structure, a characteristic that makes it very strong.

This is the type of bone that makes up long bones. As a consequence of their function (load) and mechanical demands, they are bones with a higher mineral density; that is, most of the calcium in bones is in the cortical bone, while flat bones have a lower mineral density.

Regions of the bone system

At this point, knowing the function and shape, the different regions of the bone system can be deduced:

- Skull.

- Trunk.

- Extremities.

Skull

Made up entirely of flat bones, its structure is divided into two parts: the cranial vault (which contains the brain), which is made up of 8 bones; and the frontal-facial massif, made up of 14 bones that make up the face, all of them flat.

Articulated with the skull is the first cervical vertebra (atlas). Through its articulation with the second (axis), this allows the head to be attached to the rest of the body through the neck, whose bone structure is made up of only 7 cervical vertebrae (back) and a specialized bone, hyoid, for in front.

The latter serves as an anchor and reflection point (they bend) to the muscles that connect the head to the trunk.

Trunk

Unlike the skull, the trunk is not a solid bony structure. Instead, they are different groups of bones linked together by muscles.

In this area of ​​the body, the vertebral column is located behind (from the thoracic segment to the coccyx). The sternum is in front and in the superior part (thorax), and is united to the column by means of the arches that form each one of the ribs, which together form the «thoracic cage».

Downwards, the spine joins the pelvis, forming a sort of inverted dome that provides support and protection to the internal organs of the body and allows the transmission of weight to the extremities.

Extremities

Divided into superior and inferior, they are constituted by long bones articulated with each other. The upper extremities (which go from the scapula - formerly called the shoulder blade - to the fingers of the hand) have 32 bones each, while the lower extremities (from the hip to the toes) consist of 30 bones.

Bone system care

Despite being resistant, the skeletal system is subjected to a lot of stress, so it is necessary to take proper care of it to prevent it from deteriorating. In this sense, there are three basic measures to take into account:

- Food.

- Mechanical measurements.

- Pharmacological measures.

Each of these is important and cannot be separated from each other, although at certain stages of life one may be more relevant than the others.

Feeding

Bone is a living structure with a very intense metabolic activity. For its formation it is essential to have enough calcium, as well as collagen and proteins that allow the formation of the bone matrix. Thus, it is necessary that the diet has a sufficient supply of calcium, as well as protein.

This is particularly important during childhood and adolescence, when the bone is growing and metabolically more active.

A diet rich in dairy derivatives (milk, yogurt, cheese) and green vegetables such as spinach is important to ensure a sufficient supply of calcium; otherwise, the bones will not develop the necessary strength.

It is very important to emphasize that exposure to sunlight is essential for vitamin D to be synthesized in the body and allows the calcium in the diet to be fixed, so that exercises and walks outdoors, especially on sunny days, are a a good way to keep your bones healthy, even if the sun's rays never touch them.

Mechanical measurements

They can be divided into two groups: those aimed at strengthening the bone and those aimed at protecting it.

In the first group, the best thing to do is exercise. When training, the muscles exert tension on the bones, triggering a series of chemical and mechanical stimuli that induce the formation of more bone, which is usually stronger.

Thus, the more exercise you do, the more robust the bone system will be, making it more resistant and strong.

On the other hand, there are measures aimed at protecting the bone. It includes all those strategies aimed at protecting the skeleton from blows and trauma.

From the use of helmets and knee pads to avoid bumps, bruises and fractures when playing sports, to the use of a seat belt in the car and protective harnesses when working at height to avoid falls. The idea is to protect the bones from impacts that can break them.

Pharmacological measures

This group of measures becomes important already at the end of life, when bone metabolism begins to decline and the body needs help to keep bone healthy and strong.

In this sense, the most important thing is to avoid osteopenia / osteoporosis (decrease in bone mineral density), for which oral calcium supplements are used, as well as drugs that help fix said calcium in the bones.

It is a very useful treatment that reduces the risk of fractures in the elderly, improving their quality of life and avoiding major orthopedic surgeries derived from fractures such as the hip, very common in people with osteoporosis.

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