Bone Tissue Chapter 4

Bone Tissue Chapter 4 -- A&P Textbook

Ossification (osteogenesis)

-process of bone development
-2 pathways -- Intramembranous Ossification and Endochondral Ossification

Cartilage Template

-acts as a template for bones
-template designed & laid out during fetal development
-template made of chondroblasts

Chondrocytes

-cartilage cells
-made of chondroblasts that are surrounded by cartilage matrix
-made of collagen fibers and water and other minerals
-form the cartilaginous skeletal precursor of bones

Intramembranous Ossification Overview

-compact & spongy bone develop directly from sheets of mesenchymal connective tissue
-forms flat bones of face, cranial bone, and clavicles

Intramembranous Ossification Steps

1) mesenchymal cells gather and differentiate to capillaries, osteogenic, and osteoblasts
2) cells spread out when bone tissue forms and ossification center appears
3) osteoblasts secrete osteoid to trap osteoblasts
4) osteogenic cells in connective tissue become osteoblasts
5) osteoid around capillaries create trabecular matrix
6) osteoblasts on spongy bone surface become periosteum
7) periosteum creates a layer of compact bone over trabecular bone
8) trabecular bone crowds blood vessels to condense into red marrow

Osteoid

uncalcified matrix which hardens

Endochondral Ossification Overview

-bone develops by replacing hyaline cartilage
-more time then intramembranous ossification
-used for bone as at base of skull & long bones

Endochondral Ossification Steps

1) some mesenchymal cells differentiate into chondrocytes
2) Perichondrium appears
3) More matrix produced and chondrocytes in center grow in size
4) Cartilage dies because matrix calcifies so nutrients cannot reach chondrocytes
5) Blood vessels fill cavities & make them bigger & bring osteogenic cells to become osteoblast
6) capillaries penetrate cartilage which turns perichondrium into periosteum
7) bone cell development & ossification ramps up & creates the primary ossification center

Perichondrium

membrane that covers cartilage

Primary Ossification Center

region deep in periosteal collar where ossification beings

Secondary Ossification Center

-centers of activity that occur in epiphyseal region
-where matrix mineralization, death of chondrocytes, invasion of blood vessels from periosteum, & seeding with osteogenic cells that become osteoblasts

Reserve Zone

-region closest to epiphyseal end of plate
-has small chondrocytes in matrix
-chondrocytes secure epiphyseal plate to bone of epiphysis

Proliferative Zone

-has stacks of chondrocytes
-make new chondrocytes via mitosis to replace dead ones at diaphyseal end of plate
-cell division here contributes to longitudinal growth of bone

Zone of Maturation and Hypertrophy

-has older and larger chondrocytes
-cells mature here; contributes to longitudinal growth of bone

Zone of Calcified Matrix

-zone closest to diaphysis
-most chondrocytes dead due to calcified matrix
-osteoblasts secrete bone tissue on calcified cartilage

Epiphyseal Line

appears when chondrocytes in epiphyseal plate stops proliferating

Modeling

-process of incresing diameter of diaphysis and medullary cavity
-osteoclasts resorb bone in one place and osteoblasts deposit new bone somewhere else

Remodeling

-destroying old or damaged bone on same surface where osteoblasts will lay new bone to replace it

Osteogenesis Imperfecta (OI) (brittle bone disease)

-bones do not properly form so they break easily
-affects production of collagen for bone matrix
-bone deformities and fractures follow