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

Anatomy is a science that studies the structure of the different living beings that inhabit 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 the anatomy is based on an objective description of the analyzed structures, it must also be each of them has been contrasted with its function, so it is closely linked to the physiological study of systems.

There are many types of anatomy: descriptive, comparative, topographic, surgical, clinical, radiological, pathological and many more terms. Some branches of anatomy focus on the clinical peculiarities of the organs of beings humans, while other aspects study the tissues and systems of plants, for example. From a plant to a mammal there are thousands of years apart, but anatomists, specialized in their field, describe the structures of each one with equal detail.

As the human body is so complex, it is not enough to specialize in "human anatomy" to describe each and every one of its peculiarities.

Based on this premise, osteology arises, or what is the same, the study of bones. We will tell you everything about this exciting discipline.

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What is osteology?

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

Belonging to the phylum of the chordates (Chordata), the human species Homo sapiens sapiens is characterized by presenting a osteocartilaginous skeleton, understood as the set of bones and joints that constitute the system skeletal. 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.

Here we present a series of peculiarities 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 osteologyAs we recall 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 point of view (or now that we have learned the term, osteological), our skeleton is divided into 2 large sections: axial and appendicular.

The axial skeleton is made up of 80 bones that define the central axis of the human being, that is, it encompasses the bony structures that make up the skull, auditory bones, hyoid, rib cage, sternum, and spine vertebral. The main function of the axial skeleton is to give us shape, to allow us to relate in a three-dimensional environment upright and, above all, to protect vital organs (brain, heart and lungs, among others).

On the other hand, the appendicular skeleton comprises the 126 bones that make up the lower and upper limbs (arms and legs), as well as the bony girdles. You will hear some of them: the femur, the humerus, the radius, the ulna, the phalanges of the fingers and many more. 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, tough pieces of vertebrate skeletons, white / yellowish in color, that they consist of organic substances, mineral salts and a fibrous envelope. Bone tissue stands out above all for its hardness, since 98% of it is made up of mineralized extracellular matter, while only 2% are living cells per se.

The extracellular matrix of bones (what we perceive as hard white material) is 70% made up of hydroxyapatite, an extremely resistant substance rich in calcium and match. Without going any further, our body stores 1-1.2 kilograms of pure calcium, which is 99% forming the structure of bones. The remaining 1% of calcium is performing its pertinent 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 stands out for a low representation of cell bodies. Anyway, we present you in a list, in a quick way, the main cells found in the bones:

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

Thanks to this cellular diversity, bone tissue is not watertight and invariable over time. Bone is formed and destroyed continuously, and both processes are normally 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, bone mass remains stable for 10 years, to begin to lose bone through resorption processes in the order of 0.3-0.5% annually. After menopause, this loss accelerates in women by 3 to 5%, making them much more likely to suffer from osteoporosis.

• You may be interested in: "Axial skeleton: what is it, parts and characteristics"

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 kind of "framework" that supports all the soft tissues of the body and keeps vital organisms safe from shock and mechanical stress. However, this is not his only job from an anatomical and physiological point of view.

For example, bones are the places where hematopoiesis occurs, that is, the formation of all cell bodies that circulate in the blood (white, red blood cells and others). 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 elements circulating. Hematopoiesis occurs primarily in the skull, pelvis, ribs, sternum, and the ends of the femur and humerus.

By last, bones are also an excellent reserve place. 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 prolonged hypocalcemia, part of the bone matter is digested to release circulating calcium into the bloodstream. As you can imagine, this is counterproductive in the long run, but it can get the body out of more than one spot.

Resume

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

Nothing in the human being is watertight. At the end of the day, we are nothing more than a network of intricate connected systems: if a piece falls, the domino effect may be greater or less, but nothing works by itself. The relationship of the bone 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. Formation and growth of bones. Skeletal system divisions. Main bones of the different regions of the skeleton. Mexico: Veracruzana University; 2012. [Accessed on May 19, 2017].
• Estrada, C., Paz, A. C., & López, L. AND. (2006). Bone tissue engineering: basic considerations. EIA Magazine, (5), 93-100.
• Osteology, Universidad de los Andes. Picked up on February 24 at https://www.uandes.cl/macroscopico/osteologia/
• Osteology and Arthrology: Functional Anatomy. Picked up on February 24 at 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