Cell and Molecular Biology Lecture 7: Histogenesis of Bone

What to mesenchymal stem cells in bone differentiate into?

Osteoprogenitors

What do osteoprogenitors differentiate into?

Osteoblasts

What do osteoblaststurn into?

Osteocytes

What do hematopoietic stem cells in bone differentiate into?

Osteoclasts

What attaches bone to periosteum but does not cover the articular surface?

Sharpey's Fibers

What are the two types of ossifications?

Intramembranous and endochondral

Embryonic skeleton consists of _____ and _____, which are replaced by _____

Fibrous Membranes, Hyaline Cartilage, and Bone Matrix

Which ossification begins in the uterus as well as forms the clavicle, cranium, sternum, scapulae, ribs, and flat bones?

Intramembranous

Which ossification is involved in the replacement of cartilage with bone and forms long and short bones

Endochondral

In intramembranous ossification, _____ group up, form different _____. MSCs then differentiate into _____ and form _____. Formation of _____ occurs, then a random network of _____ or _____ forms. Blood transports _____ cells and fills trabecular bone area. Mesenchyme is replaced by _____ and a thin layer of compact bone.

Mesenchymal stem cells (MSCs), ossification centers, osteoblasts, organic matrix (osteoid), osteocytes, bone spicules, trabeculae, marrow cells, periosteum

What is bone growth that occurs within an area of hyaline cartilage?

Endochondral ossification

Which parts of long bones are formed by the primary center of ossification which starts in the middle of the hyaline cartilage?

Diaphysis and medullary cavity

What are the four steps in the formation of the primary center of ossification?

1. Bone collar formation 2. Enlargement, calcification, and cavitation 3. Periosteal bud invasion 4. Diaphysis elongation

What are the key differences in the events of the secondary center of ossification and the first?

1. No bony collar formation 2. Osteoprogenitors invade epiphyseal cartilage and differentiate into osteoblasts 3. Osteoclasts resorb spongy bone and produce cavities

What does hyaline cartilage covering the epiphyses on the end of a long bone become?

Articular cartilage

Articular cartilage does not contribute to bone growth in _____

Length

The epiphyseal plate is the site of what?

Bone elongation

What lengthens long bones?

Growth of cartilage in the epiphyseal plate

What type of growth is lengthening of bones?

Interstitial

Resting zone in growth plate

Zone 1: Reserve Cartilage

What type of growth is the increase in width of a bone?

Appositional

How is the width of bone increased?

Deposition of bone in the periosteal region

Matrix production and division occurs here, resulting in longitudinal growth

Zone 2: Proliferation

Cell size increases here; glycogen and lipids are contained here; secretion of alkaline phosphatase

Zone 3: Maturation and Hypertrophy

Matrix calcification occurs here; traditionally cells here are metabolically very inactive; increasing vacuolation indicated death by hypoxia

Zone 4: Calcification

Transition from cartilage to bone occurs here

Zone 5: Ossification

_____ at the top of stacks divide quickly by mitosis

Chondroblasts

The bone grows in _____ when the rate of mitosis at the zone of _____ equals the rate of ossification in the zone of _____

Length, Proliferation, Ossification

As adolescence draws to an end, _____ divide less often and long bones stop lengthening when the _____ and _____ fuse

Chondroblasts, Diaphysis, Epiphysis

_____ growth occurs in the diaphysis

Appositional

What bone type is newly formed bone matrix containing only organic matrix?

Osteoid

What is bone type is immature, incompletely mineralized, randomly and rapidly organized, and seen in Paget's Disease?

Woven bone

What bone type is mineralized bone?

Mature lamellar none

Hematoma formation is what stage of bone fracture healing?

1st

Soft callous formation is what stage of bone fracture healing?

2nd

Hard callous formation is what stage of bone fracture healing?

3rd

Bone remodeling is what stage of bone fracture healing?

4th

_____ collagen is produced early in fracture healing, and then followed by _____ collagen formation and calcification

Type II, Type I

Matrix vesicles are produced by _____ in osteoblasts

Mitochondria

What inhibits the calcification process by binding to the surface of calcium PO4 ions and blocking further crystal growth of CaPO4 ions?

Pyrophosphate inhibitors

What is an initial biomarker for bone formation by osteoblasts?

Expression of alkaline phosphatase

Tissue nonspecific ______________ increases phosphate concentration by cleaving PP-I, which is essential for regulating bone mineralization

Alkaline Phosphatase

Organic phosphates and calcium form _____ by the crystallization process.

CaPO4 (Hydroxyapatite)

What are the regulatory factor(s) that control the differentiation of osteoblasts?

RUNX2 (cbfa1), BMPs, TGFbeta

What are the regulatory factor(s) that control differentiation of osteoclasts?

mCSF1, RANKL, TNFalpha

What are the regulatory factor(s) that inhibits differentiation of osteoclasts?

Osteoprotegerin

What are the regulatory factor(s) that increases apoptosis of osteoblasts and osteocytes, which leads to increased bone resorption

Steroids (Glucocorticoids)

What are the regulatory factor(s) that stimulates osteoblasts to secrete osteoclast differentiation/stimulation factor, which increases osteoclast function. This activity leads to the liberation of calcium into the blood.

PTH

What are the regulatory factor(s) that inhibits bone resorption by osteoclasts

Calcitonin