10.2

The Functions of the Skeletal System

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Bones are the primary components of the skeletal system that provide support, structure, and movement to the body.

While seemingly static, they are dynamic organs that also perform other physiological functions.

They are rich in minerals, particularly calcium and phosphate, and serve as storage reservoirs that help maintain mineral homeostasis in the body.

In addition to minerals, bones also store fat as an energy reserve. The yellow marrow found in the cavities of certain bones comprises adipocytes, or fat cells, that store lipids.

The yellow marrow also contains mesenchymal stem cells, which can differentiate into specialized cells of the bones and cartilage.

Another type, the red marrow, is present in the spongy bone cavities and in the center of flat bones, such as the pelvic girdle.

Red marrow contains hematopoietic stem cells, or HSCs, that can differentiate to produce different blood cells, including red blood cells, white blood cells, and platelets.

Towards the bone surface, cells called osteoblasts secrete the hormone osteocalcin, which regulates glucose homeostasis, cognitive functioning, and muscle exercise capacity.

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The most apparent functions of the skeletal system are support, protection, and movement. However, bone tissue also performs several other critical metabolic functions. For one, the bone matrix acts as a reservoir for a number of minerals important to the functioning of the body, especially calcium and phosphorus. These minerals, present in the bone tissue, can be released back into the bloodstream when required. Calcium ions, for example, are essential for muscle contractions and controlling the flow of other ions involved in the transmission of nerve impulses.

Bone also serves as a site for fat storage and blood cell production. The softer connective tissue that fills the interior of most bones is referred to as bone marrow. There are two types of bone marrow — yellow marrow and red marrow. Yellow marrow contains adipose tissue, which stores triglycerides as a source of energy. Red marrow is where hematopoiesis — the production of blood cells — takes place. Red blood cells, white blood cells, and platelets are all produced in the red marrow.

Skeletal System Disorders

Some common skeletal system disorders include osteoporosis, arthritis, Paget's disease, and Rickets. Osteoporosis is the loss of bone mass and density, making the bones easily susceptible to breaks or fractures. It is an age-related disorder that tends to progress rapidly in post-menopausal women. In contrast, arthritis is the loss or breakdown of cartilage, such as at the joints. Commonly affected joints are the knee, hip, and hand. Other disorders are a result of dysregulation of bone development and growth. Rickets, for example, is a condition that affects bone development in children resulting in weak or deformed bones. In adults, especially the elderly, a disruption of the normal cycle of bone remodeling results in a condition called Paget's disease.

Part of this text is adapted from Openstax, Anatomy and Physiology 2e, Section 6.1: The Functions of the Skeletal System

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