mechanisms of bone. growth and deveopment Flashcards

Question

where does IMO occur

Answer 1

neurocranium visercocranium clavicle

Answer 2

Mesenchymal stem cells condense, differentiate into osteoblasts and secrete extracellular matrix (osteoid) in long strands - osteoblasts lay down bone mineral on the strands of osteoid (osteoid is the organic part of the ECM) - slowly increase in size and length by laying down more bone on the outside of the little spinicles - once the spinicles are mineralised and a little larger they are called trabeculae (don’t necessarily form trabeculae bone though) - consecutive growth rings of osteoid (lamella) added onto the trabecula to increase thickness - further bone growth by cycles of osteoid secretion and mineralisation (appositional growth – width growth) - multiple trabecula within the developing bone contact one another to form a lattice structure - areas of bones may completely fill in with mineralised osteoid (eventually ends up with cortical bone by remodelling) - bones containing lattice structures are called primary trabecular bones - most bones are mixtures of cortical bone outer surface and trabecular bone interior

Answer 3

ECO is three phase process 1) A miniature cartilage replica of a bone is formed by differentiation of mesenchymal or ectomesenchyme cells into chondroblasts which mature into chondrocytes 2) Cartilage grows in a specific direction – by interstitial (length) and appositional (width) growth 3) cartilage is converted into bone - cartilage mineralisation draws in blood vessels which bring the stem cells in(mesenchymal cells) - they then mature into the osteoblasts - as the blood supplys it brings in the precursors of osteoclasts - this leads to the remodelling, giving cortical bone on the outside and trabecular on the inside - as the bone grows you get secondary ossification at the ends of the long bones until the same process caries on, giving mature bone with bone marrow in the centre

Answer 4

- Epiphyseal bone at the top | - Metaphyseal bone underneath

Answer 5

- Chondrocytes are found in the reserve zone, quiescent - when given appropriate signals the start to divide, giving proliferative zones - they then get very big, and are called hypertrophic chondrocytes - these cells undergo metabolic changes, start to resorb away some of the ECM - deposit mineral on the cartilage surface - release factors drawing in the blood supply

Answer 6

- collagen X is being laid down so they can lay down the mineral on the matrix - also produce factors such as vascular and endothelial growth factor, stimulates ingrowth of blood vessels

Answer 7

parallel colums of dividing chondrocytes formation of the ECM

Answer 8

- Chondrocytes undergo apoptosis - then get bone production in the mineralised matrix (cartilage matrix mineralisation)

Answer 9

prolifertion zone hypertrophic zone cartilage/bone interface

Answer 10

release calcium alter architecture of cancellous one to meet new stresses or bone thats going to become cortical bone during bone growth so that it meets new stresses

Answer 11

1) Bone resorption phase - bone ECM destroyed and removed - This phase takes approx. 3 weeks 2) bone formation - new ECM formed and mineralised - 3-4 months

Answer 12

1) bone resorption is initiated by recruitment of osteoclasts precursors (hemopoietic cells) to remodelling site 2) osteoclast precursors mature into osteoclasts by fusing together 3) bone lining cells erode a little ECM and leave the remodelling site 4) Osteoclasts bind to the ECM exposed by bone lining cells and digest the bone matrix with enzymes to form a resorption pit 5) osteoclasts release hydrochloric acid and also release proteinase (enzyme), which digests the organic phase away in the acidic environment, the acid dissolves the calcium phosphate 6) Calcium chloride is produced which is soluble and that can be removed into the ECM and flushed away by the interstitial fluids 7) Osteoclasts then stop digesting the matrix and die by apoptosis 8) osteoblast precursors recruited to the remodelling site 9) osteoblast precursors develop into mature osteoblasts 10) osteoblasts make new ECM to fill the resorption pit made by the osteoclasts 11) synthesis of matrix is complete the new bone surface becomes covered in bone lining cells

Answer 13

- Clot formation - inflammatory cells which release chemokines - new angiogenesis and the soft tissues - migration and proliferation of those mesenchymal stem cells - laying down of the new ECM stem cells will then differentiate directly into osteoblasts, then start to lay down bone by IMO

Answer 14

- rare genetic disorder that interferes with intramembranous ossification (skeletal dysplasia) - Autosomal dominant defect in the RUNX2 gene (important in the differentiation of chondrocytes and osteoblasts

Answer 15

Achondroplasia | - recessive genetic condition affecting bone formation via ECO