Hist Lab 4 - Bone

1. Osteoprogenitor cells – osteogenic stem cell
a. mesenchymal stem cell hiding in periosteum and endosteum
b. can undergo mitosis (that’s why it is called a stem cell)
c. differentiate into osteoblasts

2. Osteoblasts – primary producer of bone matrix
a. basophilic cells with round euchromatic nucleus (typical protein secreting cell, RER)
b. lined up in one-cell thick rows on surfaces of bone (appositional growth)
c. secrete organic unmineralized components of bone matrix called osteoid (collagen & ground substance) and matrix vesicles that initiate bone mineralization.
d. terminally differentiated, can NOT undergo mitosis
e. when trapped in mineralizing matrix, becomes an osteocyte

Osteocytes – trapped in lacunae (appears like a clear space)
a. trapped in lacunae, with long, thin cell processes extending into tiny channels called canaliculi
b. communicate with each other via gap junctions at the tips of their processes
c. maintain bone matrix (some synthetic and resorptive ability)
d. osteocytes can NOT divide and are terminally differentiated.

Osteoclasts – bone resorbing cell
a. phagocytic, derived from monocytes in blood
b. large multinucleated cell with acidophilic cytoplasm (abundant mitochondria) and a ruffled or high folded cell membrane, in a shallow depression on the bone surface (Howship’s lacunae).
c. contain many lysosomes, secretes acid, collagenase, and other lytic enzymes, that break down bone matrix (resorption), releasing calcium & phosphate into blood. Cell membrane is highly folded into a ruffled border.

Haversian system inside a osteon
-google - Haversian canals are a series of tubes around narrow channels formed by lamellae. The Haversian canals surround blood vessels and nerve fibers throughout the bone and communicate with osteocytes. The canals and the surrounding lamellae are called a Haversian system (or an osteon).

arrows - tiny canaliculi
rectangle - lacunae - dark stain

Haversian canal in compact bone (white structure)

(like the image says) interstitial lamallae that is inbetween osteons

Volkmann's canal entering the bone from the periosteum

periosteum that is continuous with dense CT of tendon of skeletal muscl

osteoblasts (secretes bone matrix), eventually a haversian canal will be left

periosteum

Haversian canals are parallel to bone surface

dense regular connective tissue

Spongy bone

hyaline cartilage

osteocyte

chondrocyte

osteoclasts - multinucleated, phagocytic cells breaking down bone

Osteoblasts lined up in rows against spongy bone. Newly formed osteocyte is indicated in red rectangle.

Hyaline

spongy bone surrounding a developing tooth

uneven staining in spongy bone

This is a unmineralized matrix called osteoid (appears as a light region between the osteoblasts and the red calcified bone matrix). This is secreted by osteoblasts

Hyaline cartilage. Explaining this picture: start with all cartilage and then begin to form bone bc more oxygen and blood vessels. The cartilage then begins to die (center).

Osteocyte in red bone matrix

Calcified cartilage matrix

Hypertrophied chondrocytes in enlarged lacunae

Hypertrophied chondrocytes and lacunae

Osteoclasts in zone of resorption

zone of proliferation

Growth of epiphyseal plate

Hypertrophied chondrocyte

fibrocartilage

fibroblast

chondrocytes
-a cell which has secreted the matrix of cartilage and become embedded in it.

osteoclast

spongy bone

It is woven or primary bone

spongy

osteoblasts

ollagen fiber (Type I)

osteoid

zone of hypertrophy

chondrocytes

calcified cartilage matrix

osteoclast

aversian canal in an osteon

volkmann’s canal

Compact bone in cross section

– longitudinal section of compact
bone