Identify some key pathological examples relevant to bone histology. Keywords bone osteoblast osteocyte osteoclast ruffled border Howship's lacuna osteoid type I collagen glycosaminoglycan GAG calcium hydroxyapatite compact bone cortical bone trabecular bone cancellous bone spongy bone bone marrow epiphyses diaphysis epiphyseal growth plate metaphysis articular cartilage periosteum endosteum Haversian system lamellae Haversian canal Volkmann's canal lacunae canaliculi woven bone lamellar bone endochondral ossification intramembranous ossification activation resorption reversal formation cement line.
Pre-Lab Reading Introduction The skeletal system, which is made up of bone and cartilage, serves three primary functions:. Bone is a tissue in which the extracellular matrix has been hardened to accommodate a supporting function. The fundamental components of bone, like all connective tissues, are cells and matrix.
There are three key cells of bone tissue. They each have unique functions and are derived from two different cell lines. The balance between osteoblast and osteoclast activity governs bone turnover and ensures that bone is neither overproduced nor overdegraded.
These cells build up and break down bone matrix, which is composed of:. Bone is divided into two types that are different structurally and functionally. Most bones of the body consist of both types of bone tissue:.
Long bones are composed of both cortical and cancellous bone tissue. They consist of several areas:. Different areas of the bone are covered by different tissue:. Compact bone is organized as parallel columns, known as Haversian systems, which run lengthwise down the axis of long bones.
These columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or Haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone.
The lamellae are the concentric circles around the Haversian canal; they are a bone matrix formed from calcium , phosphorus salts and fibres.
The lacunae are small spaces in the lamellae which provide an area for bone cells or osteocytes. This is the key difference between lamellae and lacunae. Overview and Key Difference 2. What are Lamellae 3. What are Lacunae 4. Similarities Between Lamellae and Lacunae 5.
The lamella of a bone provides the fibrillar matrix of the bone. A lamella is composed of a number of bundles of fibrils. These fibrils are arranged in concentric circles in the same plane around the Haversian canal. Lamellae receive a good supply of blood via the Haversian canal. Lamellae are arranged parallel to each other and have different angles. They are rich in collagen fibres. The fibre density of the lamellae is lower at the borders, and the tissue appears as a lamellar structure under the microscope.
The thickness of the lamellae is greatly varied from point to point. Lamellae are arranged into inner circumferential, outer circumferential and interstitial lamellae. Lamellae can be mainly divided as homogenous lamellae or striated lamellae.
Giant multinucleated osteoclasts , which break down bone, are occasionally found in lacunae termed Howship's lacunae. These are readily found in the ossification zone of the growth plate.
The compact bone in this slide surrounds the marrow cavity and spongy bone. Locate the periosteum external and endosteum internal linings of the bone.
Note the separation of these linings is artifact of slide preparation. Slide 74 Bone, ground preparation.
Observe the Haversian sytems or osteons of compact bone in this slide. The lamellae are concentrically located around a central canal haversian canal which contained blood vessels, nerves, and loose connective tissue. Volkmann's canals may be seen connecting haversian canals. The other lamellae of compact bone are organized into inner circumferential, outer circumferential, and interstitial lamellae.
Only interstitial lamellae are seen in this slide. The osteonic canals contain blood vessels that are parallel to the long axis of the bone. These blood vessels interconnect, by way of perforating canals, with vessels on the surface of the bone.
Spongy cancellous bone is lighter and less dense than compact bone. Spongy bone consists of plates trabeculae and bars of bone adjacent to small, irregular cavities that contain red bone marrow.
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