Osteology: what is it and what does this branch of anatomy study?

A summary of the characteristics of osteology as a branch of anatomy.

Anatomy is a science that studies the structure of the different living beings that inhabit the planet Earth. A specialist in anatomical studies investigates the topography, shape, location, arrangement and relationship between the organs and systems that make up a living entity.

Although anatomy is based on an objective description of the structures analyzed, each of them must also be contrasted with their function, so it is closely linked to the physiological study of systems.

There are many types of anatomyDescriptive, comparative, topographic, surgical, clinical, radiological, pathological and many other terms. Some branches of anatomy focus on the clinical peculiarities of human organs, while other branches study the tissues and systems of plants, for example. From a plant to a mammal there are thousands of years of distance, but anatomists, specialized in their field, describe with equal thoroughness the structures of each of them.

Since the human body is so complex, it is not enough to specialize in "human anatomy" to describe each and every one of its particularities. Based on this premise, osteology arises.or, in other words, the study of bones. We tell you all about this exciting discipline.

What is osteology?

As we have hinted in previous lines, osteology can be defined as a branch of descriptive anatomy that studies the shape, structure and arrangement of bones. It is a variant of the systematic or descriptive anatomyIt is a variant of systematic or descriptive anatomy, in that it investigates one of the multiple subsystems into which the body is divided and is in charge of its study exclusively.

Belonging to the phylum of chordates (Chordata), the human species Homo sapiens sapiens is characterized by an osteocartilaginous skeleton, meaning the set of bones and joints that make up the skeletal system. All this bone conglomerate represents about 12% of the human body: if an adult person weighs 75 kilograms, 9 of them will be pure bone tissue.

Below we present a series of particularities about the human skeleton and the composition and function of bone tissue. The knowledge of all these data is possible thanks to the work of anatomists specialized in osteology.It should be remembered that this branch of descriptive anatomy has historically focused on the study of the human skeletal system.

The peculiarities of the human skeleton

As we have said, approximately 12% of our weight is pure bone. From an anatomical (or now that we have learned the term, osteological) point of view, our skeleton is divided into 2 parts, our skeleton is divided into 2 main sections: axial and appendicular..

The axial skeleton is made up of 80 bones that define the central axis of the human being, i.e., it includes the bony structures that form the skull, the auditory bones, the hyoid, the rib cage, the sternum and the spine. The main function of the axial skeleton is to give us shape, to allow us to interact in an upright three-dimensional environment and, above all, to serve as protection for the vital organs (brain, heart and lungs, among others).

On the other hand, the appendicular skeleton the appendicular skeleton comprises the 126 bones that form the upper and lower limbs (arms and legs), as well as the bony girdles.. Some of them will ring a bell: the femur, the humerus, the radius, the ulna, the phalanges of the fingers and many others. The main function of the appendicular skeleton is movement and, therefore, here we also find a great diversity of muscles and tendons.

Human skeleton (206 bones): axial skeleton (80 bones) + appendicular skeleton (126 bones)

The bones

Bones are defined as hard and resistant parts of the vertebrate skeletons, white/yellowish in color, that are composed of organic substances, mineral salts and a fibrous sheath.. Bone tissue stands out above all for its hardness, since 98% of it is composed of mineralized extracellular matter, while only 2% are living cells per se.

The extracellular matrix of bone (what we perceive as the hard white material) is made up of 70% hydroxyapatite, an extremely resistant substance rich in calcium and phosphorus. Without going any further, our body stores 1-1.2 kilograms of pure calcium, 99% of which is found forming the structure of the bones. The remaining 1% of calcium is performing its relevant tasks in the bloodstream and target tissues. Returning to the "non-living" structure of bone, the other 30% of the bone matrix corresponds to organic matter, mainly collagen fibers.

Bone tissue is notable for a low representation of cell bodies.. However, here is a quick list of the main cells found in bone:

• Osteogenic cells: unspecialized stem cells derived from mesenchyme that specialize and give rise to other cell types.
• Osteoblasts: synthesize bone matrix, so they are responsible for bone hardness, normal development and growth throughout an individual's life.
• Osteocytes: derived from osteoblasts. They make up 95% of bone cells and are responsible for secreting surrounding matrix or resorbing it.
• Osteoclasts: their function is bone resorption, i.e. the digestion and dissolution of the hard bone matrix.

Thanks to this cellular diversity, bone tissue is not watertight and unchanging over time.. Bone is continuously formed and destroyed, and normally both processes are balanced throughout the individual's life. Osteoblasts and osteoclasts are regulated by the hormonal action of calcitonin, estrogens, vitamin D, cytokines and many other substances.

Peak bone mass in men and women is at 30 years of age. Once this peak is reached, the bone mass remains stable for 10 years, to begin to lose bone by resorption processes in the order of 0.3-0.5% annually. After menopause, this loss accelerates in women by 3 to 5%, which makes them much more prone to suffer osteoporosis.

The functionality of the skeleton

As you can imagine the main function of the skeleton is to provide vertebrates with support and protection.. The human skeletal system is a sort of "framework" that supports all the soft tissues of the body and keeps vital organisms safe from shocks and mechanical stress. However, this is not its only task from an anatomical and physiological point of view.

For example, bones are the sites of hematopoiesis, i.e. the formation of all the cell bodies that circulate in the Blood (white, red and other blood cells). Certain types of bones contain within them a substance called bone marrow, which houses the multipotent hematopoietic stem cells, which in turn differentiate into the various circulating elements. Hematopoiesis occurs mainly in the skull, pelvis, ribs, sternum and the ends of the femur and humerus.

Finally, the bones are also an excellent reservoir site. In addition to harboring large amounts of calcium and phosphate with structural functions, bone tissue can be reabsorbed depending on the physiological needs of the individual. For example, in the face of prolonged hypocalcemia, some of the bone material is digested to release circulating calcium into the bloodstream. As you can imagine, this is counterproductive in the long term, but it can get the body out of more than a few tight spots.

Summary

Osteology is a branch of descriptive anatomy that has allowed us, as a society, to know all the data we have presented here. In any case, you should not see this scientific discipline as isolated from the rest.Osteology must rely on physiology, cellular biology, histology and many other aspects to fully understand the human skeleton and its relationship with the rest of the systems.

Nothing in the human being is watertight. After all, we are nothing more than a network of intricate connected systems: if one piece falls, the domino effect may be greater or lesser, but nothing acts on its own. The relationship of the skeletal system with the rest of the organs and physiological processes is clear proof of this.

Bibliographic references:

• Blazquez, C. Skeletal system: functions. Bones: structure and classification. Histology of bone tissue: cells, compact bone tissue and spongy bone tissue. Bone formation and growth. Divisions of the skeletal system. Main bones of the different regions of the skeleton. Mexico: Universidad Veracruzana; 2012.[Accessed May 19, 2017].
• Estrada, C., Paz, A. C., & López, L. E. (2006). Bone tissue engineering: basic considerations. Revista EIA, (5), 93-100.
• Osteology, Universidad de los Andes. Retrieved February 24 from https://www.uandes.cl/macroscopico/osteologia/.
• Osteology and arthrology: functional anatomy. Recogido a 24 de febrero en https://www.berri.es/pdf/ANATOMIA%20FUNCIONAL%E2%80%9A%20Estructura%E2%80%9A%20funci%C3%B3n%20y%20palpaci%C3%B3n%20del%20aparato%20locomotor%20para%20terapeutas%20manuales/9789500602815