Where is spongy bone in a typical long bone

Arms: The humerus, radius, and ulna. The clavicles or collar bones. Metacarpals, metarsals, phalanges. Growth occurs by a lengthening of the diaphysis. Short Bones Short bones are about as wide as they are long. Inside the interior of the bone is the trabecular bone tissue, an open cell, porous network that is also called cancellous or spongy bone. Flat Bones Flat bones are broad bones that provide protection or muscle attachment.

Sesamoid Bone Sesamoid bones are smaller bones that are fixed in tendons to protect them. Irregular Bone The irregular bones are named for their nonuniform shape. Key Points Long bones are those that are longer than they are wide. The end of the long bone is the epiphysis and the shaft is the diaphysis. When a human finishes growing these parts fuse together. The outside of the flat bone consists of a layer of connective tissue called the periosteum.

The interior part of the long bone is the medullary cavity with the inner core of the bone cavity being composed of marrow. Flat bones have broad surfaces for protection or muscular attachment. Flat bones are composed of two thin layers of compact bone that surround a layer of cancellous spongy bone.

In an adult, most red blood cells are formed in the marrow in flat bones. Key Terms endosteum : A thin vascular membrane of connective tissue that lines the surface of the bone tissue that forms the medullary cavity of long bones. You can thank artistic conditioning in kindergarten for that one.

The thing is, bones may be hard on the outside, but on the inside they're a smorgasbord of vessels, nerves, and other things. I may just blow your mind with this post. Compact bone is dense bone tissue found on the outside of a bone. Basically, in kindergarten when you drew skeletons, you were drawing compact bone. Compact bone is enclosed, except where it's covered by articular cartilage, and is covered by the periosteum.

The periosteum is a thick fibrous membrane covering the entire surface of a bone and serving as an attachment for muscles and tendons. Vessels pass from the periosteum through pores into the compact bone and run through canals found throughout the tissue. Spongy bone is on the interior of a bone and consists of slender fibers and lamellae—layers of bony tissue—that join to form a reticular structure.

Spongy bone is supplied by fewer and larger vessels than compact bone. These vessels perforate the outer compact layer and are distributed into the spongy portion of bone, which is filled with marrow. Bone marrow is tissue found in long bones, like the femur, that contains stem cells. Osteons are interesting little things.

Osteons are structural units of compact bone. Each osteon consists of a central canal, which contains nerve filaments and one or two blood vessels, surrounded by lamellae. Lacunae, small chambers containing osteocytes, are arranged concentrically around the central canal. Bone marrow fills the cavities of long bones and occupies the spaces of spongy bone. Yellow marrow, consisting mostly of fat, is found in the central cavities of long bones.

Red marrow is found in the medullary cavities of flat and short bones, articular ends of long bones, vertebral bodies, spongy bone of the cranium, sternum, ribs, and scapulae. The femur is famous for being the longest bone in the body, as well as one of the strongest. Your femurs support a great deal of weight—your entire upper body, in fact! The femur is also known for its marrow-filled medullary cavity, which is present in all of the long bones of the limbs.

The sternum and hip bone are the sites from which marrow is usually extracted, however the femur is also used. Red bone marrow fills the spaces between the spongy bone in some long bones. Each epiphysis meets the diaphysis at the metaphysis. During growth, the metaphysis contains the epiphyseal plate, the site of long bone elongation described later in the chapter. When the bone stops growing in early adulthood approximately 18—21 years , the epiphyseal plate becomes an epiphyseal line seen in the figure.

These bone cells described later cause the bone to grow, repair, and remodel throughout life. On the outside of bones there is another layer of cells that grow, repair and remodel bone as well. The cellular layer is adjacent to the cortical bone and is covered by an outer fibrous layer of dense irregular connective tissue see Figure 6.

The periosteum also contains blood vessels, nerves, and lymphatic vessels that nourish compact bone. Tendons and ligaments attach to bones at the periosteum.

The periosteum covers the entire outer surface except where the epiphyses meet other bones to form joints Figure 6. In this region, the epiphyses are covered with articular cartilage , a thin layer of hyaline cartilage that reduces friction and acts as a shock absorber. The two layers of compact bone and the interior spongy bone work together to protect the internal organs.

If the outer layer of a cranial bone fractures, the brain is still protected by the intact inner layer. Four types of cells are found within bone tissue: osteoblasts, osteocytes, osteogenic cells, and osteoclasts Figure 6. The osteoblast is the bone cell responsible for forming new bone and is found in the growing portions of bone, including the endosteum and the cellular layer of the periosteum.

Osteoblasts, which do not divide, synthesize and secrete the collagen matrix and other proteins. As the secreted matrix surrounding the osteoblast calcifies, the osteoblast become trapped within it; as a result, it changes in structure and becomes an osteocyte , the primary cell of mature bone and the most common type of bone cell. Each osteocyte is located in a small cavity in the bone tissue called a lacuna lacunae for plural.

Osteocytes maintain the mineral concentration of the matrix via the secretion of enzymes. Like osteoblasts, osteocytes lack mitotic activity. Osteocytes are connected to one another within the canaliculi via gap junctions. If osteoblasts and osteocytes are incapable of mitosis, then how are they replenished when old ones die? The answer lies in the properties of a third category of bone cells—the osteogenic osteoprogenitor cell. These osteogenic cells are undifferentiated with high mitotic activity and they are the only bone cells that divide.

Immature osteogenic cells are found in the cellular layer of the periosteum and the endosteum. They differentiate and develop into osteoblasts. The dynamic nature of bone means that new tissue is constantly formed, and old, injured, or unnecessary bone is dissolved for repair or for calcium release. The cells responsible for bone resorption, or breakdown, are the osteoclasts. These multinucleated cells originate from monocytes and macrophages, two types of white blood cells, not from osteogenic cells.

Osteoclasts are continually breaking down old bone while osteoblasts are continually forming new bone. The ongoing balance between osteoblasts and osteoclasts is responsible for the constant but subtle reshaping of bone. Table 6. Although compact and spongy bone are made of the same matrix materials and cells, they are different in how they are organized. Compact bone is dense so that it can withstand compressive forces, while spongy bone also called cancellous bone has open spaces and is supportive, but also lightweight and can be readily remodeled to accommodate changing body needs.

Compact bone is the denser, stronger of the two types of osseous tissue Figure 6. It makes up the outer cortex of all bones and is in immediate contact with the periosteum.

In long bones, as you move from the outer cortical compact bone to the inner medullary cavity, the bone transitions to spongy bone.