Skeletal System Flashcards
What’s Endosteum?
Thin inner layer membrane of single cells (osteoblasts) lining the inner layer of the medullary cavity.
What’s Periosteum?
Tough outer connective sheath which surround the surface of bone where there is no articular cartilage.
Where are Osteogenic cells found?
Found within the periosteum, endosteum and along the channels which contain blood vessels.
What do Osteogenic cells divide into?
Osteoblasts
Where are Osteoclast cells found?
Endosteum
Whats another name for compact bone?
Cortical bone
Cancellous (spongy) bone makes up what majority of bone types?
Short bones, flat bones, sesamoid and irrgular bones
Where’s bone marrow mainly found?
Within the medullary cavity and spaces within trabeculae
What types of bones are formed through Endochondral ossification?
Long, Short, Irregular and Sesamoid bones
What types of bones are formed through Intramembranous ossification?
Flat bones
What bones develop within tendons?
Sesamoid bones
Describe Intramembranous ossification
Mesenchyme cells cluster together at the primary ossification centre and differentiate into osteogenic cells which divide into osteoblasts.
The osteoblasts secretions form the extracellular matrix. The osteocytes lay within the lacunae and connect via the canaliculi.
As the extracellular matrix develops it fuses to one another to form the trabeculae of cancellous bone.
Simultaneous with the development of the trabeculae the mesenchyme at the periphery of the bone condenses and develops into periosteum.
Describe Endochondral ossification
Mesenchyme cells cluster together in the general shape of a bone
These develope into chondroblasts which secrete collagen forming the extracellular matrix of the cartilage model.
Chondroblasts surrounded by the collagen become chondrocytes. The cartilage model grows in size with the development of new chondroblasts into chondrocytes.
Tiny arteries penetrate the cartilage model supplying nutrients. This stimulates the production of osteogenic cells forming the periosteum.
Periosteal capillaries grow into the cartilage model providing nutrients to the centre of the model and initiating the growth of the primary ossification centre – here cartilage begins to be replaced by bone tissue.
The primary ossification centre continues to grow replacing cartilage tissue with bone from the centre of the model outwards. Osteoclast cells now begin to resorb bone tissue creating a cavity in the middle of the diaphysis.
The epiphyseal artery penetrates the end of the cartilage model supplying nutrients and initiating the growth of the secondary ossification centre
Eventually all cartilage is replaced by bone tissue except for a layer of cartilage covering the articular surface and a layer separating the epiphysis from the diaphysis – known as the epiphyseal growth plate.
Describe stages of Fracture Repair
Blood vessels at the fracture site break and bleed eventually clotting and causing a haematoma to develop.
New blood vessels grow into the fracture haematoma restoring blood and nutrient supply. This allows phagocytes to remove bacteria cells and for osteoclasts to resorb dead bone tissue.
The intact periosteum produces fibroblasts and chondroblasts which secrete collagen fibres forming a fibrocartilaginous (soft) callous around the fracture site.
Periosteum osteogenic layer produces osteoblast cells which begin to produce new bony extracellular matrix within the callous.
Osteoclasts continue to remove bone extracellular matrix
Eventually the cartilage is replaced by new cancellous bone and calcification begins.
Cancellous bone is replaced by compact bone at the periphery.
What’s the FOUR zones of growth?
- Zone of resting cartilage
- Zone of proliferating cartilage
- Zone of hypertrophic cartilage
- Zone of calcified cartilage
Whats the two types of bone growth?
- Interstitial growth
- Appositional growth
What’s Interstitial growth?
The lengthening of the bone
What’s Appositional growth?
The increase in the diameter of bone
Describe Interstitial growth
Chondrocytes develop on the epiphyseal side of the growth plate (in the proliferation zone), old cartilage is replaced by bone on the diaphyseal side of the plate (calcification zone), as this process continues the thickness of the epiphyseal plate remains relatively constant however the length of the diaphysis is increasing with each new layer of bone replacing old cartilage.
Describe Appositional growth
Within the periosteum cells differentiate into osteoblasts which secrete collagen forming new extracellular matrix. The osteoblasts are surrounded by the matrix and become osteocytes. This forms a ridge around the periosteal blood vessels (lining the outside of the periosteum) which eventually fuse and encapsulate the vessel. The old periosteum is now endosteum surrounding that vessel. Osteoblasts in the new endosteum continue to deposit extracellular matrix and develop concentric lamellae.
Which vitamins influence bone growth?
- Vitamin A – stimulate osteoblasts
- Vitamin C – synthesis of collagen
- Vitamin D – increases absorption of calcium from food
Which hormones influence the rate of bone growth?
Parathormone – controls calcium levels and indirectly, phosphate levels
Thyroxine – influences normal physical development
Testosterone/oestrogen –influences skeletal growth
What two hormones regulate calcium levels?
Parathyroid (PTH) hormone
Calcitonin (CT) hormone
What hormone detects a decrease in blood calcium?
Parathyroid hormone
