4 Types of Bone Cells

1. Osteoprogenitor Cells

- found within the endosteum membrane

- can differentiate into Osteoblasts

2.Osteoblasts

-use mineral salts and calcium to produce new bone

-can differentiate into Osteocytes

3.Osteocytes

-mature bone cells that maintain bone

4. Osteoclasts

-thought to develop from leukocytes

-functions in breaking down or resorption of bone

-releases calcium

          “Too many Osteoclasts can cause the release of too much

            calcium resulting in Osteoporosis.”

                                   differentiate into                        differentiate into

Osteoprogenitor Cells    =     Osteoblasts     =      Osteocytes

                                               (produce new bone)     (maintain bone)

                         differentiate into

Leukocytes     =     Osteoclasts           

                                 (break down bone)

.

The Epiphyseal Plate

The Epiphyseal Plate

A cartilaginous “growth” plate located between the ends of bones

(the epiphysis and the metaphysis) which allows for lengthwise bone growth

4 Zones of the Epiphyseal Plate

1. Zone of Resting Cartilage

-toward Diaphysis

               -small, scattered chrondrocytes that anchor or glue the epiphyseal plate

                to the epiphysis

2. Zone of Proliferating Cartilage

               -dividing chrondrocytes, scattered and stacked

3. Zone of Hydrotrophic (growing) Cartilage

               -chrondrocytes growing

               -stacked in columns for lengthwise growing

4. Zone of Calcified Cartilage (adjacent to Diaphysis)

            -mineral salts deposited in cartilage matrix which changes it to bone

There are 2 Different ways that bone forms:

1. Intamembranous Ossification

-future bone begins as a fibrous connective tissue membrane and  changes into a bone.  Example:  Skull

2. Endochondral Ossification

               -future bone begins as a hyline cartilage model

               - the most common way bones are formed

               -Example: Epiphyseal Plate

Bones

Bones -- Terminology
Canaliculi		The canaliculi connect all bone cells to the nutrient supply, keeping them well-supplied in spite of their hard matrix material
Cartilage		Tough connective tissue covering the ends of the bone. The cartilage reduces friction and acts as a shock absorber.
Haversian canals		central canals carrying the blood vessels and nerves. The Haversian canals run lengthwise through the bone
Haversian system		each complex of a Haversian canal and it's matrix rings
Lacunae		tiny cavities arranged in concentric circles, called lamellae
Lamellae		circles of lacunae and Osteocytes about the central Haversian canal
Ligament		Fibrous tissue that connects bones or cartilage to strengthen and support joints.
Ossification		the gradual conversion of cartilage or other tissue into bone
Osteoblasts		build bone and secrete matrix, located on the surface
Osteoclasts		break down bone and secrete alkaline phosphates, located on the surface of the bone
Osteocytes		the mature bone cells, found in tiny cavities within the matrix called lacunae
Osteocytes		mature bone cells found in the lacunae
Compact bone		Compact bone is dense and hard, especially the outer layer of the bone.
Spongy bone		Made up of a lattice work of bone, the spaces are filled with red marrow which produces blood cells.
cuboidal		box shaped
Flat bones		Plate like and highly PROTECTIVE e.g. bones of the skull protect the brain.
Irregular bones		e.g. vertebrae (spine)
Long bones		Slightly curved for STRENGTH with long narrow shafts with knobbly ends (especially found in arms and legs e.g. femur).
Short bones		Tend to be spongy e.g. wrists, fingers, toes and ankles.
Parts of Bones
diaphysis	The shaft of a long bone.
Epiphysis	The knob like end of the bone, often contains red marrow (blood cells).
epiphyseal plate	growth plate - cartilaginous area where a majority of bone growth occurs - Metaphysis
Metaphysis	Region where the diaphysis joins the epiphysis, important in bone growth - epiphyseal plate
medullary cavity	Marrow cavity inside the bone. Contains yellow marrow (fat cells).
periosteum	The dense fibrous membrane covering the surface of bones except at the joints and serving as an attachment for muscles and tendons
Articular cartilage	cartilage that lines the joints
hyaline	cartilage that forms most of the fetal skeleton and is found in the trachea, larynx, and joint surfaces of the adult.

BONE FORMATION

A.   Bone formation is termed osteogenesis or ossification.

Two types of ossification:

1.     Intramembranous ossification is the formation of bone directly from or within fibrous connective tissue membranes.

2.     Endochondrial ossification is the formation of bone from hyaline cartilage models.

B.    Intramembranous ossification forms the flat bones of the skull and the mandible

A typical long bone consists of numerous parts.

1.     The diaphysis is the shaft of the long bone.

2.     The epiphyses are the ends of the bone

3.     The metaphyses are the areas between the epiphysis and diaphysis and include the epiphyseal plate in growing bones.

4.     Hyaline cartilage (articular cartilage) at the ends of the bones reduces friction and absorbs shock at freely moveable joints.

5.     The periosteum is a connective tissue covering of the surface of the bone which contains osteogenic cells, protects bone, assists in fracture repair, helps nourish bone tissue, and serves as an attachment point for ligaments and tendons.

6.     The space within the diaphysis is the marrow cavity.

7.     The endosteum is the lining of the medullary cavity.

Compact Bone

a.     Compact bone is arranged in units called osteons or Haversian systems

b.     Osteons contain blood vessels, lymphatic vessels, nerves, and osteocytes along with the calcified matrix.

c.     Osteons are aligned in the same direction along lines of stress. These lines can change as the stresses on the bone changes.

Spongy Bone

a.     Spongy bone does not contain osteons.

b.      It consists of trabeculae. (a lattice work of bone containing red marrow in certain regions)

c.     It forms most of the structure of short, flat, and irregular bones, and the epiphyses of long bones.