Bone Tissue

Bones are taken into consideration organs due to the fact that they save various varieties of tissue, such together blood, connective tissue, nerves, and bone tissue. Osteocytes, the living cell of bone tissue, form the mineral procession of bones. There are two varieties of bone tissue: compact and also spongy.

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Compact Bone Tissue

Compact bone (or cortical bone) develops the hard outside layer of every bones and also surrounds the medullary cavity, or bone marrow. It provides protection and strength come bones. Compact bone tissue consists of units referred to as osteons or Haversian systems. Osteons room cylindrical structures that save a mineral matrix and living osteocytes associated by canaliculi, which deliver blood. They space aligned parallel to the lengthy axis of the bone. Every osteon is composed of lamellae, which space layers of compact procession that surround a main canal referred to as the Haversian canal. The Haversian canal (osteonic canal) includes the bone’s blood vessels and also nerve fibers (Figure 1). Osteons in compact bone tissue room aligned in the very same direction follow me lines of stress and anxiety and aid the bone resist bending or fracturing. Therefore, compact bone tissue is influential in locations of bone in ~ which stresses are used in only a couple of directions.


Figure 1. Compact bone tissue consists of osteons that room aligned parallel come the long axis the the bone, and also the Haversian canal that has the bone’s blood vessels and also nerve fibers. The inner great of bones consists of spongy bone tissue. The small dark ovals in the osteon stand for the life osteocytes. (credit: change of work-related by NCI, NIH)


Practice Question

Which that the complying with statements around bone tissue is false?

Compact bone tissue is made of cylindrical osteons that room aligned such the they travel the length of the bone.Haversian canals contain blood ship only.Haversian canals save blood vessels and nerve fibers.Spongy tissue is uncovered on the inner of the bone, and compact bone organization is uncovered on the exterior.

Spongy Bone Tissue

Whereas compact bone tissue develops the outer layer of all bones, spongy bone or cancellous bone forms the inner layer of all bones. Spongy bone tissue does not contain osteons that constitute compact bone tissue. Instead, it is composed of trabeculae, which space lamellae that are arranged as rods or plates. Red bone marrow is found between the trabuculae. Blood vessels in ~ this tissue provide nutrients to osteocytes and also remove waste. The red bone marrow of the femur and the internal of other large bones, such together the ilium, develops blood cells.


Figure 2. Trabeculae in spongy bone space arranged such the one next of the bone bear tension and the other withstands compression.


Spongy bone reduces the density of bone and allows the ends of long bones come compress as the result of stresses applied to the bone. Spongy bone is influential in locations of skeletal that space not heavily stressed or wherein stresses arrive from numerous directions. The epiphyses that bones, such as the neck the the femur, room subject to stress and anxiety from many directions. Imagine laying a heavy framed photo flat top top the floor. You might hold increase one next of the snapshot with a toothpick if the toothpick was perpendicular to the floor and also the picture. Now drill a hole and stick the toothpick right into the wall surface to cave up the picture. In this case, the function of the toothpick is come transmit the downward press of the snapshot to the wall. The pressure on the snapshot is straight down come the floor, but the force on the toothpick is both the picture wire pulling down and also the bottom of the hole in the wall pushing up. The toothpick will break off best at the wall.

The neck of the femur is horizontal favor the toothpick in the wall. The weight of the body pushes it down near the joint, yet the vertical diaphysis that the femur pushes it up in ~ the various other end. The neck the the femur have to be strong enough to carry the downward pressure of the body weight horizontally to the vertical pillar of the femur (Figure 2).


Cell types in Bones

Bone consists of four species of cells: osteoblasts, osteoclasts, osteocytes, and osteoprogenitor cells. Osteoblasts are bone cells that room responsible for bone formation. Osteoblasts synthesize and secrete the organic component and inorganic component of the extracellular matrix of bone tissue, and collagen fibers. Osteoblasts end up being trapped in this secretions and differentiate into less active osteocytes. Osteoclasts are huge bone cells with up come 50 nuclei. They eliminate bone structure by release lysosomal enzymes and acids that dissolve the bony matrix. These minerals, released from bones into the blood, assist regulate calcium concentration in body fluids. Bone may also be resorbed because that remodeling, if the applied stresses have changed. Osteocytes room mature bone cells and are the main cells in bony connective tissue; this cells can not divide. Osteocytes preserve normal bone framework by recycling the mineral salt in the bony matrix. Osteoprogenitor cells are squamous stem cells that division to create daughter cells that identify into osteoblasts. Osteoprogenitor cells are important in the fix of fractures.

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In Summary: structure of Bones

Compact bone organization is written of osteons and forms the outside layer of all bones. Spongy bone organization is created of trabeculae and also forms the inner part of every bones. Four varieties of cells write bony tissue: osteocytes, osteoclasts, osteoprogenitor cells, and also osteoblasts.