The framework of the human body: the structure, function and composition of the skeleton

**The framework and skeleton of the human body**

Skeletal development is congenital and cannot be changed later in life. Therefore, people with larger bones and higher bone density tend to weigh more than those with smaller bones and lower bone density. Skeletal structures are composed of various shapes and have complex internal and external structures, allowing the skeleton to maintain strength while reducing weight. The human body has 206 bones, divided into three main parts: the skull, trunk, and limbs. The skull has 29 bones, the trunk 51, and the limbs 126. Children actually have 217-218 bones, while newborns have as many as 305. This is because: children have 5 sacral bones, which fuse into 1 in adulthood; children have 4-5 coccyx bones, which also fuse into 1; and children have 2 iliac bones, 2 ischial bones, and 2 pubic bones, which fuse into 2 hip bones in adulthood. In total, children have 11-12 more bones than adults. Adults have 206 bones, but Chinese and Japanese people only have 204 bones each. This is because the fifth toe bone in Chinese people has only two phalanges, while Europeans and Americans have three. Therefore, Chinese people have two fewer bones than Europeans and Americans. Bones are generally connected by joints and ligaments. Apart from the six auditory ossicles which are sensory organs, the bones can be divided into 23 skull bones, 51 trunk bones, and 126 limb bones according to their location.

Skeletalization is the foundation of the increasing complexity of biological structures, and the skeletal system is also a limiting factor in the evolution of biological morphology. Human bones contain water, organic matter (bony collagen), and inorganic salts. The water content is lower than other tissues, averaging 20% ​​to 25%. Of the remaining solid matter, approximately 40% is organic matter, and over 60% is inorganic salts. Inorganic salts determine bone hardness, while organic matter determines bone elasticity and toughness. The inorganic salt portion of bone is called bone salt, which is a chemical compound primarily composed of calcium and phosphorus. Human bones consist of 25.6% calcium (Ca), 12.3% phosphorus (P), and sodium (Na), magnesium (Mg), potassium (K), etc. The functions of the skeleton are movement, support and protection of the body, production of red and white blood cells, and mineral storage. One component of the skeleton is mineralized bone tissue, which has a hard, honeycomb-like three-dimensional structure; other tissues include bone marrow, periosteum, nerves, blood vessels, and cartilage. The tissues of the skeleton include: connective tissue, bone, cartilage, fibrous connective tissue, blood vessels, blood, and nerve tissue.

The human skeleton plays a vital role in supporting the body and is an integral part of the human musculoskeletal system. First, it provides support. Different bones in the human body are connected by joints, muscles, ligaments, and other tissues to form a unified whole, supporting the body. Without a skeleton, humans would simply be a mass of soft tissue lying on the ground, unable to stand, much less walk. Second, it provides protection. The human skeleton acts as a framework, protecting vital organs and minimizing the impact and damage from external forces. For example, the skull protects the brain, the spine and ribs protect the heart and lungs, and the pelvic bones protect the bladder and uterus. Without skeletal protection, external impacts can easily damage internal organs. Third, it facilitates movement. The skeleton works in conjunction with muscles, tendons, and ligaments to perform motor functions. Bones provide the necessary support for movement, muscles and tendons provide the power, and ligaments maintain the stability of the skeleton, allowing movement to continue. Therefore, we say that the skeleton is the foundation of movement. Fourth, it facilitates metabolism. Bones are closely related to the body's metabolism. We know that bones contain large amounts of calcium, phosphorus, and various organic and inorganic substances, participating in and regulating the body's inorganic salt metabolism. Bones also participate in the regulation of the body's endocrine system, affecting hormone secretion and metabolism, and are related to electrolyte balance. Fifthly, they have hematopoietic function. The hematopoietic function of bones is mainly manifested in childhood, when the bone marrow cavity contains a large number of hematopoietic cells that participate in blood formation. Even in adulthood, some cancellous bone still contains red bone marrow with hematopoietic function.

To avoid skeletal deformities in our daily lives, which are generally related to prolonged incorrect posture, such as sitting, standing, and sleeping positions, it's important to cultivate correct posture habits from a young age. This helps prevent skeletal deformities and slows down bone aging.