14. Osteogenesis (ossification). Types and structural characteristics.

Osteogenesis is the __________ of bone.

formation

The process of laying down new bone material is done by __________.

osteoblasts

Development of the skeleton begins in the __________ and foetus.

early embryo

Growth continues after birth and up to __________.

adolescence

Bones are formed by either intra-membranous or __________ ossification.

endochondral

Intra-membranous ossification occurs in areas of ordinary __________.

mesenchyme

Flat bones of the cranium, part of the mandible, and __________ develop via Intra-membranous ossification.

clavicles

Endochondral ossification is when __________ differentiate into cartilage.

mesenchymal cells

Most long bones, vertebral column, ribs, and __________ develop via endochondral ossification.

pelvis

Both types of osteogenesis have the same mechanism of __________ and mineralization.

bone matrix deposition

Intramembranous bone formation begins when mesenchymal cells aggregate at sites of __________.

richly-vascularised connective tissue

Hydroxyapatite is the __________ mineral of the bony matrix.

dominant

During ossification, osteoblasts become __________ which reside in lacunae.

osteocytes

Trabeculae of newly formed bone are initially laid down, then they __________ and merge.

thicken

In fracture healing, endochondral osteogenesis is the __________ occurring process.

most common

The first site of ossification occurs in the __________ of ossification.

primary centre

The outer layer of the cartilage model becomes __________.

periosteum

The osteoblasts secrete __________ against the shaft of the cartilage model.

osteoid

The calcification of the matrix causes chondrocytes in the centre of ossification to __________ and die.

grow

Toward the end of foetal life and continuing into __________, ossification centres appear in the epiphyses.

puberty

After adolescence, __________ close and growth is ceased.

growth plates

when development begins

early embryo and fetus till adolescence

intra-membranous ossification

in areas of ordinary mesenchyme where the osteoblasts differentiate directly from rich-vascularised mesenchymal CT

how flat bones of cranium, mandible, clavicles are developed

during development when mesenchymal cells aggregate at rich CT then differentiate into osteoblasts

secrete collagen, osteoid, alkaline phosphate inducing mineralization of osteoid

endochondral ossifciation

mesenchymal cells differentiate into cartilage and the cartilage is replaced by bone

how long bones like vertebral column, ribs, pelvis is developed

hydroxyapatite

dominant mineral in the bony matrix

how do mesenchymal stem cells change

body becomes larger and rounder the long.thin processes are no longer present, golgi and RER increase

what happens at the lacunae?

where the osteocytes are residing the trabeculae of newly formed bone is initially laid down to which they thicken and merge to produce a 3D spongy bone

what happens in fractures?

endochondral osteogenesis which is the formation of cartilage tissue from mesenchymal cells adn the replacement of cartilage tissue by bone

stages of endochrondral ossification and where it starts

begins at the primary centre of ossification which is the middle of diaphysis

1. Formation of periosteum: The perichondrium becomes periosteum. The periosteum contains a layer of osteoprogenitor cells, which later become osteoblasts.

2. Formation of bone collar: The osteoblasts secrete osteoid against the shaft of the cartilage model, this serves as support for the new bone

3. Calcification of the matrix: The chondrocytes in the centre of ossification begin to grow and die. From the periosteum, blood vessels invade the diaphysis and bring in mesenchymal and osteoprogenitor cells. 

Incoming blood vessels carry in bone marrow cells. Proliferation of remaining chondrocytes causes the epiphyses to increase in length. They eventually form the epiphyseal plate.