B Appendicular skeleton

The appendicular skeleton is one of the two primary bone groups in the body, the other being the axial skeleton, and it is responsible for the movement of the limbs. The appendicular skeleton is made up of the upper and lower extremities, which include the shoulder girdle and pelvis, as well as the thoracic and abdominal cavities. It is through the shoulder girdle and pelvis that mechanical loads are transferred between the appendicular skeleton and the axial skeleton, which is why they are so important. The appendicular skeleton is made up of a total of 126 bones and is comprised of 206 bones in the mature human body. The bones of the hands, foot, upper extremity, lower extremity, shoulder girdle, and pelvic bones are among the bones that make up the appendicular skeleton, as are the bones of the upper and lower extremities.

B Appendicular skeleton in brief

When it comes to vertebrates, the appendicular skeleton is the section of the skeleton that contains the bones that provide support for the appendages. There are a total of 126 bones. The appendicular skeleton is comprised of the skeletal elements found within the limbs, as well as the shoulder girdle and pelvic girdle that provide support. The adjective appendicular is derived from the term appendage, which itself refers to a part of something larger that is connected to another part.

The organization of the appendicular system
It is critical to understand that, due to anatomical variance, it is usual for the skeleton to contain a large number of auxiliary bones (sutural bones in the skull, cervical ribs, lumbar ribs and even extra lumbar vertebrae).

The appendicular skeleton, which consists of 126 bones, and the axial skeleton, which consists of 80 bones, combine to produce the complete skeleton, which consists of 206 bones in the human body. The appendicular skeleton, in contrast to the axial skeleton, is not fused, allowing for a far larger range of motion.

The appendicular skeleton is made up of the bones of the limbs as well as the girdles that support the limbs. Between the axial and appendicular skeletons, there are significant distinctions in the organisation and developmental control of the skeletons. Anterior soft internal structures (such as the brain, spinal cord, and pharynx) are protected by the axial skeleton, which is formed by mesenchyme that is induced by the organs that are protected by the axial skeleton. The bones of the appendicular skeleton, on the other hand, serve as a focal support for the limbs’ movements. When it comes to limb development, interaction with an epithelium (such as the apical ectodermal layer of the limb bud is essential. However, morphogenetic regulation of the limb is inherent in the mesoderm, with the epithelium serving solely as a stimulatory factor. All of the components of the appendicular skeleton begin as cartilaginous models, which later transform into genuine bone through the process of endochondral ossification later in the embryonic development.

Several well-defined genetic mutations cause significant disruptions in the development of the appendicular skeleton in mice and rats. achondroplasia, the most frequent form of dwarfism, is caused by mutations in the FGF receptor 3 gene, which is located on chromosome 3. (FGFR3). This syndrome is characterised by short height as a result of limb shortening, hypoplasia of the midface, a disproportionately big head, and a severe lumbar lordosis (curvature of the spine). Thanatophoric dysplasia is a more severe result of the same gene, and it is characterised by much more severe shortening of the extremities than the previous condition. Because of the narrowness of the thorax, death from respiratory insufficiency frequently occurs during infancy or childhood. Campomelic dysplasia is caused by a SOX-9 mutation, which is characterised by significant bowing of the limbs, a variety of other skeletal deformities, and sex reversal in XY males, as a result of a disruption of SOX-9 in the process of sexual differentiation in XY males.

Appendicular Skeleton Function

• The fundamental roles of the appendicular skeleton are to allow us to move freely and to give shape to our limbs, which are our arms and legs in this instance. The bones of the appendicular skeleton, like the bones of the axial skeleton, provide a variety of additional purposes as well. For example, red blood cell synthesis takes place in the bone marrow, as do aspects of our immune system such as leukocytes, or white blood cells, which are produced in the bone marrow.
• Additionally, the bones of the appendicular skeleton play a role in maintaining mineral homeostasis. Many minerals are kept in our bones, and when minerals are required by other organ systems, minerals can be released from our bones and used by other organ systems. In a similar vein, when the body has an excess of minerals, our bones have the ability to absorb any excess minerals.

Conclusion

The appendicular skeleton of the human body is made up of the bones of the upper limbs, the bones of the lower limbs, the pectoral girdle, and the bones of the pelvic girdle. The upper limbs, which include the arm, forearm, wrist, and hand, are attached to the body through the pectoral girdle. The pelvic girdle is responsible for bearing the weight of the body and for locomotion, and it is also responsible for attaching the lower limbs to the body. The lower limbs, which include the thighs, legs, and feet, support the entire weight of the body and absorb the resulting forces from locomotion.