Skeletal system: what it is, parts and characteristics

These are the distinctive characteristics of the skeletal system in humans.

At the biological level, the skeletal system, bony system or skeleton comprises a series of structures that provide support, support and protection to the soft tissues and muscles of living beings. When you think of a skeleton, the first thing that comes to mind are bones, right? In reality, this complex system reports much more variability than it first appears in the animal kingdom.

In addition to the vertebrate endoskeleton, in nature there are the exoskeletons of arthropods, which support proportionally less weight than ours. These are usually composed mainly of chitin, calcium carbonate, silica or other minerals. Its main function is to protect, but it also allows these "simpler" living beings from an evolutionary point of view to breathe and move in the environment.

Even further down the evolutionary scale we have the hydroskeleton, which consists of a fluid-filled cavity (coelom) surrounded by muscles that gives the animal shape and locomotion capacity. Annelids, nematodes and other invertebrates present this type of skeleton. With this express class we reach what is perhaps the evolutionary pinnacle of biomechanics: here we will see everything you need to know about the skeleton. we will see everything you need to know about the human skeleton or skeletal system..

What is the skeletal system?

Osteology is a branch of descriptive anatomy that has been dedicated to answering this question over the years. After centuries of research and study, we have arrived at the simplest possible definition, but at the same time full of secrets and nuances that we will see in later lines: the skeletal system is defined as the set of bones that give the human body its structure.

Barring pathologies and mutations, all individuals of our species have a total of 206 bones.. This represents approximately 12% of the total weight of the human body, so a person weighing 75 kilograms will have a bone mass of 9 kilos. As a consequence of this figure, you will not be surprised to learn the following curious fact: an adult individual contains 1-1.2 kilos of pure calcium.

Parts of the skeleton

The human skeleton is divided into two major planes based on bone physiology and anatomy. These are briefly described below.

1. Axial skeleton

Axis in Latin means axis, so you can imagine what we are referring to. The axial skeleton is the axis of the body, the bony section that allows us to stand upright in a three-dimensional environment and gives us the "human form" that characterizes our species. and gives us the "human form" that characterizes our species. This bony conglomerate includes the bones that form the bony structure of the head, the auditory bones, the hyoid bone, the vertebral column and the rib cage.

The main function of the axial skeleton is protection, since both the thoracic cage and the skull house and guard what are probably the three most important organs in the entire human body: the brain, the heart and the lungs. In total, in this section we count a total of 80 bones.

2. Appendicular skeleton

Of the total of 206 bones that we present human beings, the appendicular skeleton includes all those that form the lower limbs, the upper limbs and the bony girdles (shoulder girdle and pelvic girdle). (shoulder girdle and pelvic girdle). From the femur to the metacarpus, these 126 bones allow us to move our limbs at will.

It should be noted that all these bones included here are bilateral, i.e. they are repeated on each side of the body. We have two femurs, two humeri, two ulnae, two radii, etc. You must keep in mind that our organism is based on the physical premise of bilateral symmetryThe body is divided in a single plane (sagittal), giving rise to two specularly identical halves.

Bones and bone tissue

Bones are the real protagonists of osteology. They could be defined as extraordinarily hard organs that are made up of bone tissue, itself composed of a cellular and a matrix portion. We will tell you about the particularities of bone tissue in the following sections.

1. Extracellular bone matrix

It is the portion of the bone that does not correspond to living cells and occupies 98% of the total tissue.. The secret of its hardness lies in its mineralization, since 65% of this matrix is composed of hydroxyapatite crystals (calcium phosphate). These crystals have the shape of hexagonal prisms, generally short and tabular, with a whitish-yellowish color.

The other 35% of the matrix is made up of organic substances, 90% of which are collagen, a fiber-forming protein.a fiber-forming protein of a primarily structural nature. In addition to this compound, there are other protein substances that vary from structural to hormonal action: osteonectin, osteopontin, thrombospondin and alkaline phosphatase are some examples.

2. Bone cells

Although they only represent 2% of bone matter, bone cells are truly interesting, as they perform tasks that are very difficult to imagine in such an apparently "watertight" and "immovable" type of tissue. They perform tasks that are very difficult to imagine in a type of tissue as apparently "watertight" and "immovable" as that which characterizes bones.. We list them briefly:

• Osteoprogenitor cells: they are found in the periosteum, endosteum and in the bone canals containing the Blood vessels. They give rise to osteoblasts.
• Osteoblasts: these are the bone matrix-forming cells, i.e. they synthesize the mineral component already described. Curiously, these are "trapped" in the solid matrix they create.
• Osteocytes: represent 95% of bone cells. They derive from osteoblasts and their function is to synthesize and resorb bone matrix.
• Osteoclasts: cell type responsible for resorbing and remodeling the surrounding bone matter.

Functions of the skeletal system

We have already explored the parts into which the skeleton is divided and the type of tissue that makes it up, so all that remains is to know the functionality of this system in order to draw a complete picture of this true work of art of biomechanics.

Support, protection and movement are functionalities of the bones that we take for granted.. Bones are the anchor point for muscles, so when the latter contract, the bone tissue functions as a lever to allow us to perform movements. For this reason, the striated musculature, bones, joints and tendons make up what we know as the "human locomotor apparatus".

On the other hand, it is really interesting to know that the bone system is a perfect place for mineral storage. Without going any further, 99% of calcium is found in the bones and only 1% is circulating in our body, in order to carry out its relevant functions.. In the event of a calcium and mineral deficit, the cellular bodies described above can digest bone matrix, thus releasing these compounds into the bloodstream. This mechanism is very negative in the long term: pathologies such as osteoporosis develop as a result.

In addition to all this, bones are the site of production of all blood cells. Red bone marrow is a type of flexible biological tissue that is found inside the long bones (such as the femur). (such as the femur), vertebrae, ribs and others, whose function is to give rise to leukocytes, red blood cells and platelets.

This task is assigned to hematopoietic stem cells, which, when differentiated, give rise to red and white blood cells, among others. The hematopoietic component of the bone marrow plays an invaluable role in human physiology, synthesizing approximately 500 billion red blood cells per day. Can you imagine what the human anatomy would be like without this key tissue?

Summary

As you may have noticed, we are not exaggerating when we say that the human skeletal system is the pinnacle of biomechanics. Bones go far beyond the protection of vital organs.Bones allow us to move, maintain homeostatic balance at the mineral level, store substances and, in addition, all circulating cell bodies are synthesized within them. Without the bone marrow, neither the immune system nor the blood would exist, so life as we know it would not be possible.

If we want to make a clear concept beyond all that has been described, it is the following: it is necessary to conceive each system of our organism as a series of dynamic, changing tissues and structures in absolute harmony with the rest of the "gears". Even bone tissue, apparently hard and inflexible, undergoes substantial changes over time and interacts with the rest of the organs.

Bibliographic references:

• Atlas of animal and plant histology: bone tissue. Retrieved February 26 at https://mmegias.webs.uvigo.es/guiada_a_oseo.php.
• Axial skeleton, visible Body. Retrieved February 26 from https://www.visiblebody.com/es/learn/skeleton/axial-skeleton#:~:text=The%20axial%20skeleton%20includes%20all%20skeletons,vertebral%20and%20the%20cage%20tor%20C3%A1cic.
• Skeletal system: functions. Bones: structure and classification. Histology of bone tissue: cells, compact bone tissue and cancellous bone tissue. Bone formation and growth. Divisions of the skeletal system. Main bones of the different regions of the skeleton. UV.mx. Retrieved February 26 at https://www.uv.mx/personal/cblazquez/files/2012/01/Sistema-Oseo.pdf.
• Osteoporosis, medlineplus.gov. Retrieved February 26 from https://medlineplus.gov/spanish/osteoporosis.html.