Skeletal System Chapter 6

Bone Growth-Length

Epiphyseal cartilage (close to the epiphysis) of the epiphyseal plate divides to create more cartilage, while the diaphyseal cartilage (close to the diaphysis) of the epiphyseal plate is transformed into bone. This increases the length of the shaft.

Structure of Long Bones pt.2

The external surface of the entire bone except for the joint surfaces of the epiphyses is covered by a double-layered membrane known as the periosteum. Outer fibrous layer is dense irregular connective tissue. Inner cellular layer contains osteoprogenitor cells and osteoblasts. Periosteum is richly supplied with nerve fibers, lymphatic vessels and blood vessels. These enter the bone of the shaft via a nutrient foramen. Periosteum is connected to the bone matrix via strong strands of collagen.

Step 5 of Endochondral Ossification

Around birth, most long bones have a bony diaphysis surrounding remnants of spongy bone, a widening medullary cavity, and 2 cartilaginous epiphyses. At this time, capillaries and osteoblasts will migrate into the epiphyses and create secondary ossification centers. The epiphysis will be transformed into spongy bone. However, a small cartilaginous plate, known as the epiphyseal plate, will remain at the juncture between the epiphysis and the diaphysis.

Step 3 of Endochondral Ossification

Blood supply to the periosteum, and capillaries and fibroblasts migrate into the heart of the cartilage, invading the spaces left by the disintegrating chondrocytes. The calcified cartilaginous matrix breaks down; the fibroblasts differentiate into osteoblasts that replace it with spongy bone. Bone development begins at this primary center of ossification and spreads toward both ends of the cartilaginous model. While the diameter is small, the entire diaphysis is filled with spongy bone.

Step 2 of Endochondral Ossification

Blood vessels grow into the perichondrium surrounding the shaft of the cartilage. The cells of the inner layer of the perichondrium in this region then differentiate into osteoblasts. The perichondrium is now a periosteum and the inner osteogenic layer soon produces a thin layer of bone around the shaft of the cartilage. This bony collar provides support.

Osteoblasts

Bone-building cells. Synthesize and secrete collagen fibers and other organic components of bone matrix. Initiate the process of calcification. Found in both the periosteum and the endosteum

Step 1 of Endochondral Ossification

Chondrocytes near the center of the shaft of the hyaline cartilage model increase greatly in size. As these cells enlarge, their lacunae expand, and the matrix is reduced to a series of thin struts. These struts soon begin to calcify. The enlarged chondrocytes are now deprived of nutrients (diffusion cannot occur through calcified cartilage) and they soon die and disintegrate.

Osteoclasts

Huge cells derived from the fusion of as many as 50 monocytes (a type of white blood cell). Cells that digest bone matrix - this process is called bone resorption and is part of normal bone growth, development, maintenance, and repair. Concentrated in the endosteum. On the side of the cell that faces the bone surface, the PM is deeply folded into a ruffled border. Here, the osteoclast secretes digestive enzymes (how might this occur?) to digest the bone matrix. It also pumps out hydrogen ions (how might this occur?) to create an acid environment that eats away at the matrix. What advantage might a ruffled border confer? Why do we want a cell that eats away at bone? (Hint: bone is a very dynamic tissue.)

Structure of Long Bone pt.3

Internal bone surfaces are covered with a delicate connective tissue membrane known as the endosteum. Covers the trabeculae of spongy bone in the marrow cavities and lines the canals that pass through compact bone. Contains both osteoblasts and osteoclasts.

What are the 4 types of bones?

Long bone,short bone, flat bone, irregular bone

Osteocytes

Mature bone cells. Osteoblasts that have become trapped by the secretion of matrix. No longer secrete matrix. Responsible for maintaining the bone tissue.

Structure of Compact Bone

Mature compact bone is lamellar, or layered, in structure. It is permeated by an elaborate system of interconnecting vascular canals, the haversian systems, which contain the blood supply for the osteocytes; the bone is arranged in concentric layers around those canals, forming structural units called osteons.

Bone Growth- Thickness

Osteoblasts beneath the periosteum secrete bone matrix on the external surface of the bone. This obviously makes the bone thicker. At the same time, osteoclasts on the endosteum break down bone and thus widen the medullary cavity. This results in an increase in shaft diameter even though the actual amount of bone in the shaft is relatively unchanged.

What are the 3 typed of bone Cells?

Osteoblasts, osteocytes, and osteoclasts

Structure of Long Bones pt.1

Shaft is known as the diaphysis. Consists of a thick collar of compact bone surrounding a central marrow cavity. Ends are epiphyses Thin layer of compact bone covering an interior of spongy bone. Joint surface of each epiphysis is covered w/ a type of hyaline cartilage known as articular cartilage. It cushions the bone ends and reduces friction during movement.

Step 4 of Endochondral Ossification

The primary ossification center enlarges proximally and distally, while osteoclasts break down the newly formed spongy bone and open up a medullary cavity in the center of the shaft. As the osteoblasts move towards the epiphyses, the epiphyseal cartilage is growing as well. Thus, even though the shaft is getting longer, the epiphyses have yet to be transformed into bone.

Structure of Short, Flat, and Irregular Bones

Thin plates of periosteum-covered compact bone on the outside and endosteum-covered spongy bone within. Have no diaphysis or epiphysis because they are not cylindrical. Contain bone marrow between their trabeculae, but no marrow cavity. In flat bones, the internal spongy bone layer is known as the diploë, and the whole arrangement resembles a stiffened sandwich.