Histo Specialized CT Study Guide

Samantha Blum

Cartilage: Hyaline• Notice that the cartilage has no blood vessels, lymphatics or nerves supplying it from within.

Nutrients and waste products are exchanged by diffusion to and from blood vessels in the perichondrium.

• Notice that the highest degree of basophilia is in the immediate vicinity of the lacunae• Identify the perichondrium (schematic; 10X, 50X). In these sections, the fibrous layer

predominates. The cellular layer is present, but is probably only one cell layer thick.

Cartilage: Hyaline• Identify the perichondrium (schematic; 10X, 50X). In these sections, the fibrous layer

predominates. The cellular layer is present, but is probably only one cell layer thick.

Cartilage: Hyaline

Bone-cartilage interfaceIsogenous groups visible

Cartilage: Hyaline• In these sections, the cartilage present was in the process of being replaced by bone at the

time of tissue preparation. Study those areas in which cartilage and bone can be seen together (1X, 5X) for comparison.

• Locate and examine the perichondrium (20X). Identify both fibrous and cellular layers. The cellular layer contains progenitor (stem) cells that give rise to new chondroblasts.

Cartilage: Elastic• Note that only elastic fibers are visible here, although collagenous fibers are also present. • Identify perichondrium (20X, 40X). Notice that some elastic fibers of matrix intermingle (40X,

50X) with collagenous fibers of the perichondrium.

Cartilage: Fibrocartilage• Look for alternating layers (100X) of dense collagenous fibers (20X) and scattered

chondrocytes in lacunae surrounded by hyaline cartilage matrix. (BLACK ARROWS, LEFT)• Identify basophilic regions (hyaline cartilage matrix, 40X) and acidophilic regions (collagenous

fibers, 40X). (RIGHT)

Cartilage: Fibrocartilage

Compact Bone• Examine an osteon and identify the Haversian (central) canal, lacunae, and lamellae around

the osteon (20X). Note that osteocytes are not present in sections prepared by grinding.• Identify the lacunae, which are small cavities that once contained osteocytes (schematic; 20X

). Each osteocyte resides in its own lacuna, connected to its neighbours by cellular processes that run through small tunnels called canaliculi.

Compact Bone• In this decalcified section, the mineral component (calcium phosphate) has been removed,

leaving only the organic component (osteoid) and the cells. Removal of the mineral portion of the matrix makes the lamellae much less distinct. Osteocytes are visible within lacunae, although the method of preparation has caused most of them to shrink.

• Note that the bone matrix (4X) is quite acidophilic• Endosteum consists of a single layer of osteoblasts that line the inside of the bone marrow

cavity and Haversian canals

Compact Bone: Sharpey’s Fibers• Ligaments and tendons attach to the periosteum of bone, and these points of attachment are

subject to great stress. To prevent separation of the periosteum from the bone, connective tissue fibers (Sharpey's fibers) extend from the periosteum into the bone, at right-angles to the bone surface (special stain). These fibers serve to firmly anchor the periosteum.

Compact Bone: Sharpey’s Fibers• The root of the tooth has a bone-like covering called cementum; this cementum is anchored

to the bone of the tooth socket by fibers of the periodontal ligament (0.5X). Identify connective tissue fibers of the ligament extending deep into the bone of the jaw (3X, 20X). This arrangement permits the tooth to move slightly during chewing, but to remain firmly attached within the socket.

Sharpey’s Fibers

Trabecular Bone• Osteocytes found within trabeculae• Identify osteoblasts (40X) lining the surface of the trabeculae. • Locate osteoclasts (schematic; 100X). These large, multinucleated cells can be found

adjacent to the bone surface often within resorption cavities (Howship's lacunae). • Bony trabeculae are continually remodeled through the action of osteoclasts.

Trabecular Bone

Osteoclast (white arrow)

Intramembranous Ossification• In intramembranous ossification, bone forms directly within a layer of condensed

mesenchymal tissue, forming as tiny, needle-like spicules radiating from the ossification center and expanding toward the periphery.

• Identify trabecular bone (4X), osteoblasts, and osteocytes (40X). Remember that cartilage is not involved in this type of osteogenesis.

Find examples of intramembranous osteogenesis (10X). Look for fibrous connective tissue, osteoblasts at the periphery of bone trabeculae, osteoid, and calcified bone with osteocytes (40X).

Intramembranous Ossification

Endochondral Osteogenesis• In endochondral ossification, bone tissue is deposited upon a cartilaginous "model" that

serves as a template. Long bones (humerus, radius, ulna, femur, tibia, fibula, etc.) develop and grow by this process, which also produces the principal marrow cavities (although the bony collar of these bones forms by imtramembranous ossification).

Endochondral Osteogenesis• Note that the calcified matrix forms the core of the trabeculae upon which new bone is laid

by osteoblasts. The calcified cartilage (40X) cores are basophilic (lavender). The new bone matrix (40X) is acidophilic (pink), and is present at the edges of the trabeculae.

• Look for sites of intramembranous osteogenesis (40X) occurring in the bony collar surrounding the shaft of the long bone. Even in bones that form by endochondral ossification, the bony collar forms intramembranously. (RIGHT, black arrows)

• Eventually, the spaces and layers of matrix will be remodelled into Haversian canals at the centers of the Haversian systems of the compact bone making up the shaft.

Endochondral Osteogenesis• Note that a secondary center of ossification (4X) is present within the epiphysis. The process

of endochondrial ossfication is proceeding radially from the center of the epiphysis. At the articular end of the epiphysis, the hyaline cartilage will remain as articular cartilage (schematic).

• The epiphyseal plate is now completely formed between the epiphysis and the diaphysis. Identify the following zones (20X; schematic): zone of reserve cartilage, zone of proliferation/maturation, zone of hypertrophy, zone of calcification, and zone of ossification.

Endochondral Ossification• In the knee slide (low mag.), development has not proceeded as far, so the secondary

ossification centers are just beginning to form around ingrowing blood vessels (1X, 10X).• Identify the growth plate (2X), as well as the zone of resting cartilage (5X, "1"), zone of

proliferation ("2"), zone of hypertrophy ("3"), and the zone of calcified cartilage ("4"). (RIGHT)

Growth plate (zoomed at right)

Endochondral Ossification• Calcified cartilage and newly-formed bone are easily distinguished in the developing vertebra

of slide E-25 (low mag., 2X). Identify calcified cartilage, which is blue (horizontal arrows, 10X), and bone, which is red (vertical arrows, 10X).

Endochondral Ossification

Ultrastructure: Osteocyte

Clinical Correlation• Chondroma of bone is a benign tumor in which cartilage replaces bone.

Osteoarthritis involves the destruction of a joint due to damage of its articular surfaces.

Paget's Disease involves increased bone remodeling and disruption of normal, lamellar bone structure.

Bone fracture callus. A callus develops at the site of a bone fracture, and represents one of the earliest steps in bone repair.

Rheumatoid arthritis is an autoimmune disease in which the lining of the joint (the synovium) is severely damaged, leading ultimately to joint destruction.