Book 4 - Self Instructional Manual for Cancer Registrars - SEER ...

Structure of BoneEach long bone of the body is made up of several parts (Figure 62). The main shaft is calledthe diaphysis. It provides strong support without undue weight, and consists mainly of compactbone, 1 although the innermost portion is composed of cancellous2, or spongy, bone. At the endsof a bone are structures known as epiphyses which are bulbous in shape, allowing ample space formuscle attachments near joints.• Short bones consist of a core of cancellous bone encased in a thin layer of compact bone.• Flat bones are made up of a layer of cancellous bone containing red marrow between twoplates of compact bone.• Irregular bones are similar in structure to short bones in that they are composed of a thinlayer of compact bone forming a casing over cancellous bone.• Round (or sesamoid) bones are made of dense fibrous tissue, cartilage, and bone in varyingproportions. They are found embedded in tendons in close relation to articulating surfaceswhere they modify pressure and reduce friction.The outside of the bone is covered by a fibrous membrane, the periosteum. Blood vessels,lymphatic vessels, and nerves are present in the periosteum and enter the Haversian 3 canals ofthe compact bone to become vessels of the Haversian system permeating the entire bone.The Haversian system is a series of small canals containing blood vessels which bring oxygenand nutrients to the bone and remove waste products such as carbon dioxide.Bone MarrowIn the adult there are two types of bone marrow: yellow and red. In the center of thediaphysis there is a large space called the medullary cavity which is filled with yellow or fatty bonemarrow. Red marrow fills the cancellous spaces in the upper (proximal) epiphyses of thehumerus and femur, the iliac crest, body of the vertebra, bones of the skull (diploe), ribs, sternum,clavicle, and scapula. Red bone marrow is the source of red cells and granular leukocytes as wellas platelets and monocytes. Marrow is changed from red to yellow by the replacement of myeloidcells by fat cells, a process which begins soon after birth.Special lymphocytes, B cells, are formed in the bone marrow. Mature B cells are responsiblefor the manufacture of antibodies which circulate in blood or other body fluids and respond toantigens found on the surface of viruses and bacteria, thus preventing the spread of infection.1compact bone--continuousthe aid of a microscopedense, hard structure in which spaces can only be distinguished with2cancellous bone--spongy or lattice-like structure surrounding intercommunicatingwith bone marrow.spaces filled3Haversian--the canal or system named after Clopton Havers (1650-1702) an English anatomist,who first described the structure of osseous tissue.356