Ultrastructure of Bone Flashcards
What is haematopoiesis?
Formation of blood cells from haematopoietic stem cells in bone marrow
What are the main functions of bone?
Haematopoiesis
Lipid and mineral storage
Support
Protection
Where in the bone is adipose tissue stored?
Bone marrow
Where in the bone is calcium stored?
Hydroxyapatite crystals
What are the cellular components of bone?
Osteoblasts
Osteocytes
Osteoclasts
What is the function of osteoblasts?
Synthesise osteoid
What is osteoid?
Uncalcified/unmineralised extracellular matrix
What is the function of osteocytes?
Monitor minerals and proteins to regulate bone mass
How do osteocytes form?
Osteoblasts become entombed between lamellae in lacunae of mineralising osteoid > mature into osteocytes
From what are osteoclasts derived?
Monocytes
What is the function of osteoclasts?
Resorb bone by releasing H+ ions and lysosomal enzymes
What is the extracellular matrix?
Molecules that provide biochemical and structural support to cells
What is the main mineral salt found in the extracellular matrix of bone?
Ca hydroxyapatite
What is woven bone?
Primary bone Appears in - Embryonic development - Fracture repair Made of - Osteoid - Collagen fibres arranged randomly Temporary structure
What is lamellar bone?
Secondary bone Bone of adult skeleton Made of - Highly organised sheets of mineralised osteoid Stronger than woven bone
What are the two types of lamellar bone?
Compact
Spongy
What are the two layers of connective tissue lining the external and internal surfaces of bone, respectively?
Periosteum
Endosteum
Where is compact bone found?
Outer part of lamellar bone
Where is spongy bone found?
Inner part of lamellar bone
What is the structure of compact bone?
Lamellae organised into concentric circles surrounding vertical Haversian canal
What does the Haversian canal transmit?
Small neurovascular and lymphatic vessels
What is the functional unit of bone, and of what is it comprised?
Osteon = set of concentric circles of lamellae around Haversian canal + neurovascular and lymphatic vessels inside canal
What are Volkmann’s canals?
Horizontal canals within compact bone
Connect Haversian canals
Contain small vessels that anastomose with arteries of Haversian canals
Carry vessels from periosteum
What are trabeculae?
Made up of 3D network of fine columns that crosslink in irregular way
What fills trabeculae?
Bone marrow
What are the two types of bone marrow?
Yellow - contains adipocytes
Red - contains haematopoietic stem cells
What are the two types of ossification?
Endochondral
Intramembranous
What is endochondral ossification?
Hyaline cartilage replaced by osteoblasts secreting osteoid
What is intramembranous ossification?
Mesenchymal/embryonic tissue condensed into bone
Where does bone remodelling primarily occur?
At sites of stress and damage
