Histo 2.1

Flashcards covering bone remodeling, types of bone, ossification processes (endochondral and intramembranous), bone fracture repair, and synovial joint structure and cells.

What are Haversian systems also called?

Osteons

How are osteons produced?

Via bony remodeling; removal of existing bone by osteoclasts and redeposition of new bone by osteoblasts.

What is the outer margin of an osteon delimited by?

A cement line

What are the histological characteristics of woven bone?

Cells and collagen that are irregularly arranged

What are the histological characteristics of lamellar bone?

Collagen arranged in parallel bundles or lamellae, cells are regularly spaced, and matrix is mineralized.

What percentage of lamellar bone is compact bone?

80%

What percentage of lamellar bone is cancellous bone?

20%

What are the three consecutive phases of the bone remodeling cycle?

Resorption, reversal, and formation

Which cells digest old bone during the resorption phase of bone remodeling?

Osteoclasts

Which cells lay down new bone during the formation phase of bone remodeling?

Osteoblasts

What are the primary functions of bone remodeling?

To adjust bone architecture to meet changing mechanical needs, repair microdamage, and maintain plasma calcium homeostasis

What are the major systemic regulators of bone remodeling?

PTH, calcitonin, growth hormone, glucocorticoids, thyroid hormones, and sex hormones

What determines the pattern of bone modeling?

Local mechanical stresses

What is endochondral ossification?

The replacement of a cartilage precursor by bone

What is intramembranous ossification?

The direct replacement of mesenchyme by bone; no cartilage precursor

What is characteristic of primary or woven bone?

Less mineralized and more cellular (more osteocytes).

In endochondral ossification, where does the primary center of ossification occur?

The mid-diaphysis

What occurs during the proliferation stage of endochondral ossification?

Blood vessels penetrate the periosteum bringing osteoprogenitor cells, and chondrocytes increase and form isogenous groups.

What happens when chondrocytes in the midsection hypertrophy during endochondral ossification?

They mature and form superlacunae

What happens as the midsection of the cartilage model becomes heavily calcified?

Calcification affects the viability of chondrocytes, causing them to die due to lack of diffusion for oxygen and nutrients.

Where do the secondary centers of ossification occur in endochondral ossification?

The epiphyses

What is the epiphyseal plate?

The region of the metaphysis that remains 'open' (unmineralized) allowing continuous longitudinal growth

What does 'closure of epiphysis' refer to?

The complete ossification of the epiphyseal plate, which occurs at 18-20 years.

What are the distinct zones of the epiphyseal growth plate from cartilage to bone?

Zone of Reserve Cartilage, Zone of Proliferation, Zone of Maturation, Zone of Hypertrophy (& Calcification), Zone of (Cartilage) Degeneration/Calcification, and Zone of Ossification.

In which zone of the epiphyseal growth plate do chondrocytes undergo successive mitotic division to form columns?

Zone of Proliferation

In which zone of the epiphyseal growth plate do chondrocytes greatly enlarge, become vacuolated, and calcify?

Zone of Hypertrophy (& Calcification)

In which zone of the epiphyseal growth plate do osteogenic cells differentiate into osteoblasts to form bony trabeculae?

Zone of Ossification

What is the first step in intramembranous ossification?

Mesenchymal cells differentiate into osteoblasts and group into ossification centers.

During intramembranous ossification, what do osteoblasts become when they are entrapped by the osteoid they secrete?

Osteocytes

What is the difference between a simple (closed) and a compound (open) fracture?

A simple fracture has no break in the skin, while a compound fracture involves damage to the skin exposing the bone.

What is the initial event at a bone fracture site?

Blood fills the fracture site, forming a hematoma.

What is granulation tissue in the context of bone repair?

Vascular collagenous tissue that forms post-fracture, which later becomes progressively more fibrous and is replaced by hyaline cartilage.

What is a bony callous and how is it formed?

Formed by osteoprogenitor cells and osteoblasts producing a meshwork of woven bone within the provisional callous, which helps stabilize and bind the fracture.

What type of bone is the bony callous progressively remodeled into?

Mature lamellar bone

What are synovial joints also known as?

Diarthroses

What secretes synovial fluid in a synovial joint?

The synovium

What are the two types of synovial cells and what do they resemble?

Type A resemble macrophages, and Type B resemble fibroblasts.

What is the function of Type A synoviocytes?

Non-fixed cells that phagocytose cell debris and wastes and have antigen-presenting ability

What do Type B synoviocytes produce?

Hyaluronan, collagens, fibronectin, and lubricin for the intimal interstitium and synovial fluid.

What is the role of lubricin in healthy joints?

It coats the cartilage surface, providing boundary lubrication and preventing cell and protein adhesion