21 julio, 2024

Classification of bones: according to shape, size, structure, function

The bone classification It is a practical method to simplify the study and better understand the functioning of these anatomical structures typical of vertebrates.

Bones are rigid organs that make up the skeleton. They fulfill mechanical and protective functions, in addition to having a fundamental role in the formation of blood cells and serving as a storage site for essential minerals.

The set formed by the bones, muscles, ligaments and damping elements, forms the locomotor skeletal system, which guarantees the movement, balance, plasticity and elasticity of the body. All types of bone are distributed in the body without a specific order, rather shaping a functional and practical system.

Bone cells differentiate early in the fetus, forming primitive bones that remain in their final position during the first trimester of gestation. However, as the individual continues to increase in size into adulthood, bones have the ability to lengthen through a hormone-mediated process.

Regardless of their size and shape, all bones are made of a type of bone tissue that can be completely solid (compact bone) or have sponge-like hollow spaces (cancellous or trabecular bone) or both.

Bone cells have a particular characteristic that is to remove and replace bone tissue throughout life. This process is known as bone remodeling. Thus, under normal conditions, the complete skeleton of an adult is replaced every 10 years through bone cell activity.


bone classification

To achieve the harmonious composition of the skeleton, there are several types of bone that differ both in size and shape, as well as in the distribution of bone cell tissue.

Therefore, we recognize different types of bones depending on where they are located.

According to their size they are classified into long and short; according to its shape in planes, sesamoid and irregular; and according to its structure in compact and spongy.

– Types of bone according to its size


Long bones are all those that are taller than they are wide, regardless of their size. Some examples are the femur, tibia, and clavicle. The bones that make up the fingers are also considered long since they are taller than they are wide.

These types of bones are essential to balance the body, although they are also part of the joints providing movement. Many of them support a significant load of weight, such as the bones of the legs.

During the growth stage they elongate by a process mediated by the growth hormone It is secreted by the pituitary gland, which is located in the brain. Anatomically, several parts are distinguished in the long bone, these are:

– Epiphysis: the ends.

– Diaphysis: the body.

– Metaphysis: junction area between the epiphysis and the diaphysis.

– Articular cartilage: it is the portion of soft tissue that joins two bones, forming a joint.

– Periosteum: external sheet that covers the bone, very fibrous and resistant with a high content of blood vessels and neurological endings.

– Endosteum: surface that covers the internal part of the bone.

– Artery: called feeding artery, constitutes the blood supply for the metabolic activities of bone cells. Each bone has an artery that feeds it.

– Medullary cavity: space containing a tissue rich in triglycerides and which constitutes an important energy reservoir.


Short bones are those whose dimensions, in height and width, are the same or almost the same, adopting a cuboid shape. They provide stability, cushioning and support to the skeleton, but not mobility.

Examples of these are some bones of the hand and foot, specifically those that form the carpus and tarsus.

– Types of bone according to its shape


They are those that have a flattened shape and where their height and extension predominate over their thickness.

Its main function is to protect organs, such as the ribs, the sternum, the bones of the pelvis and those of the skull. They also provide a sufficient surface area for the attachment of some muscles.

They are composed mainly of spongy bone tissue, which contains the bone marrow, which is the organ responsible for the formation of blood cells.

Due to their content, rich in marrow tissue, they are preferred when performing bone marrow biopsies or extracting this material for transplantation. One of the most used bones for these procedures is the ischium or pelvic bone.


They are small bones that are embedded within a tendon or muscle.

Its function is to act as a pulley, providing a smooth surface on which soft structures, such as tendons, can slide without encountering friction.

They are present in several locations, but they are easy to show by radiography, next to the joint of the big toe. Calcification of the sesamoid bones is an important finding as it indicates that the patient has reached puberty.


Irregular bones are those that, by size or shape, do not fall into any of the above categories. They are peculiar in shape and fulfill different functions depending on the site in which they are located.

The vertebrae of the spinal column are an example of irregular bones that are responsible for protecting the spinal cord; The hyoid bone, which is located in the neck, is an attachment surface for the muscles of mastication and swallowing.

– Types of bone according to its structure

The structure of bone refers to the type of tissue that makes it up. It can be compact or spongy. These tissues are arranged in all the bones of the body to a greater or lesser extent, depending on the shape and function of each one.

Therefore, the terms compact bone either spongy bone they refer specifically to the internal structural part of the anatomy of each bone and not to an additional type to those previously described.

compact bone

Also called cortical, is a strong, dense and hard tissue that represents about 80% of the total bone mass of the body. It is very resistant to torsion and compression.

It is made up of firm layers of lamellae that are arranged in the form of a column, giving the high density characteristic of this fabric. Within the compact bone are the most important bone cells, the osteocytes.

It is located mainly in the body of the long bones, diaphysis, and on the outside of the flat bones. There is also compact tissue in the short bones depending on their location.

This type of tissue contains the feeding vessels of the bone, and forms canaliculi through which the bone cells receive their blood supply.

The metabolic activity of compact bone is low but it has a great capacity to form new bone, therefore it is an essential tissue when injuries such as fractures occur. This process is known as bone remodeling.

spongy bone

Also Known As trabecularis a type of very porous tissue that is located at the ends of the long bones, epiphysisin the vertebrae and inside the flat bones.

It is composed of trabeculae or hard septa that form empty spaces, within which the red bone marrow is distributed.

During movement, it is in charge of cushioning the force that the bone receives, transmitting it to the compact tissue surface, which is more resistant.

Within this tissue, the bone marrow carries out the formation and release of blood cells into the bloodstream. This process is called hematopoiesis.

bone anatomy

The bone is the main anatomical unit of the skeleton. The adult body has 213 bones. They are composed of a specialized tissue that contains various types of collagen and a large amount of calcium, which gives it its characteristic rigidity.

Together with the ligaments and muscles they form the skeletal systeman apparatus for supporting and protecting the body.

Bones contain living tissue called bone marrow, which is responsible for the creation and release of blood cells into the circulation. This process is called hematopoiesis.

The main function of the bones is to support the soft tissues and protect the organs and vital elements. In addition to this, they are storage sites for mineral salts, such as calcium and phosphate, which is why they play a fundamental role in maintaining the balance of the organism.

In the bone, a complex process of formation and reabsorption of bone mass occurs, directly mediated by the cells that are found inside it.

Bone-forming cells are called osteoblasts and those that reabsorb it are the osteoclasts. These are specialized cells that have the ability to recognize states of stress and trauma, making it possible to remove non-functional tissue and form new bone.

During growth, bone cells are activated to make tissue that lengthens the bone. This happens in a specific part of the bones which is not fully solidified during childhood and adolescence.


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