The osteoblast, or bone-forming cell, is approximately 20 µm in diameter and contains a single eccentric nucleus. Under the direction of RUNX2 and Osterix transcription factors, osteoblasts arise from osteoprogenitor…

Mature lamellar bone has the same chemical composition and material properties throughout the skeleton, regardless of its mechanism of formation—intramembranous or endochondral—or its structural organization—cortical (compact) or trabecular bone. Skeletal…

Metaphysis. The three functions of the metaphysis are vascular invasion of the transverse septa at the bottom of the cartilaginous portion of the growth plate, bone formation, and bone remodeling…

Regardless of its specialized function, all cartilage consists of cells—chondrocytes and chondroblasts. These cells synthesize and deposit around them an elaborate matrix of macromolecules that are some of the largest…

Hypertrophic Zone. The functions of this zone are preparation of the matrix for expansion, degradation, and matrix calcification. Chondrocytes in this zone progressively become more spherical and greatly enlarged along…

Muscle fibers that must remain active over a long time (type I or slow-twitch fibers) are rich in mitochondria, whose iron-containing cytochrome oxidase enzymes and abundant myoglobin content give the…

In glycolysis, glucose-6-phosphate, derived either from the degradative phosphorylation of glycogen or from the phosphorylation of glucose in serum, is broken down into two molecules of acetyl coenzyme A (CoA)….

The tension of the twitch can be measured under conditions in which the muscle is not allowed to shorten (isometric contraction). Because all the sarcomeres are activated, the single-twitch strength…

The voltage-dependent sodium channel, which mediates the muscle action potential, is also time dependent: prolonged depolarization inactivates the action potential. This can be reversed only by a repolarization of the…

The membrane of the nerve terminal has a different assortment of ion channels: fewer sodium channels, several types of potassium channels, and, most important, voltage-dependent calcium channels. When an action…