Bone Tissue

Bones are considered organs due to the fact that they save on computer various species of tissue, such as blood, connective tissue, nerves, and also bone tissue. Osteocytes, the living cell of bone tissue, form the mineral procession of bones. There are two types of bone tissue: compact and spongy.

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Compact Bone Tissue

Compact bone (or cortical bone) forms the hard external layer of all bones and surrounds the medullary cavity, or bone marrow. It gives protection and strength to bones. Compact bone tissue consists of units called osteons or Haversian systems. Osteons space cylindrical structures that contain a mineral matrix and also living osteocytes linked by canaliculi, which move blood. They room aligned parallel to the long axis the the bone. Each osteon consists of lamellae, which are layers that compact matrix that surround a main canal called the Haversian canal. The Haversian canal (osteonic canal) contains the bone’s blood vessels and also nerve yarn (Figure 1). Osteons in compact bone tissue space aligned in the same direction along lines of tension and help the bone resist bending or fracturing. Therefore, compact bone organization is significant in locations of bone in ~ which stresses are applied in only a couple of directions.


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


Practice Question

Which the the adhering to statements about bone organization is false?

Compact bone organization is make of cylindrical osteons that are aligned such that they take trip the length of the bone.Haversian canals save on computer blood vessels only.Haversian canals save on computer blood vessels and nerve fibers.Spongy organization is found on the inner of the bone, and compact bone organization is found on the exterior.

Spongy Bone Tissue

Whereas compact bone tissue creates the outer layer of every bones, spongy bone or cancellous bone develops the inner great of all bones. Spongy bone tissue does no contain osteons that constitute compact bone tissue. Instead, it consists of trabeculae, which room lamellae that room arranged together rods or plates. Red bone marrow is found in between the trabuculae. Blood vessels in ~ this tissue deliver nutrients to osteocytes and also remove waste. The red bone marrow of the femur and the internal of other big bones, such as the ilium, forms blood cells.


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


Spongy bone reduce the thickness of bone and enables the end of long bones come compress together the an outcome of stresses used to the bone. Spongy bone is prominent in locations of bones that room not heavily stressed or where stresses arrive from numerous directions. The epiphyses that bones, such as the neck that the femur, space subject to tension from numerous directions. Imagine laying a hefty framed snapshot flat top top the floor. You can hold increase one side of the picture with a toothpick if the toothpick to be perpendicular come the floor and the picture. Now drill a hole and also stick the toothpick right into the wall surface to hang up the picture. In this case, the duty of the toothpick is to transmit the downward press of the snapshot to the wall. The pressure on the photo is right down to the floor, yet the force on the toothpick is both the picture wire pulling down and the bottom of the hole in the wall pushing up. The toothpick will certainly break off best at the wall.

The neck of the femur is horizontal like the toothpick in the wall. The load of the body pushes that down near the joint, but the vertical diaphysis that the femur pushes the up at the various other end. The neck that the femur must be solid enough to transfer the downward force of the body load horizontally come the vertical tower of the femur (Figure 2).


Cell varieties in Bones

Bone is composed of four varieties of cells: osteoblasts, osteoclasts, osteocytes, and also osteoprogenitor cells. Osteoblasts room bone cell that room responsible because that bone formation. Osteoblasts synthesize and secrete the organic part and inorganic component of the extracellular procession of bone tissue, and also collagen fibers. Osteoblasts come to be trapped in these secretions and also differentiate right into less energetic osteocytes. Osteoclasts are huge bone cells through up to 50 nuclei. They remove bone structure by publication lysosomal enzymes and acids that dissolve the bony matrix. These minerals, released from bones into the blood, help regulate calcium concentration in human body fluids. Bone may also be resorbed for remodeling, if the applied stresses have actually changed. Osteocytes room mature bone cells and also are the key cells in bony connective tissue; this cells cannot divide. Osteocytes keep normal bone framework by recycling the mineral salts in the bony matrix. Osteoprogenitor cells are squamous stem cell that divide to develop daughter cell that differentiate into osteoblasts. Osteoprogenitor cell are essential in the fix of fractures.

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In Summary: structure of Bones

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