Phase 1a revision - Bone Anatomy & Phsyiology Flashcards
What are osteogenic stem cells?
- Cells derived from mesenchymal stem cells and have the capacity to differentiate into osteoblasts and chondroblasts
What are the 5 types of bone?
- Flat bones
- Long bones
- Irregular bones
- Short bones
- Sesamoid bones
Where does red marrow reside in?
- Cancellous bone
What are osteocytes?
- Osteocytes are mature osteoblasts that have been enveloped within the bone matrix
Where do osteocytes reside?
- Osteocytes reside within the lacuna and communicates with surroundings by canaliculi
What are the main functions of osteocytes (3)?
- Capable of bone deposition and resorption involved in bone deformation caused by muscular activity
- Strengthens bone in response to additional stresses
- Continue to form bone to an extent (maintain strength of the bone matrix)
What is the function of the osteoblasts?
- Responsible for the catalysing and synthesising the mineralisation of osteoid during bone formation and remodelling
Which cells do osteoblasts arise from?
- Arise from the differentiation of osteogenic cells in the periosteum – the tissue that covers the superficial surface of bone and in the endosteum (marrow cavity)
- Differentiation requires constant supply of blood
What is the periosteum?
- The tissue that covers the superficial surface of bone
What do osteoblasts secrete (5)?
- Alkaline phosphatase
- Colleganase
- Growth factors
- Collagen
- Osteocalcin
What are osteoclasts?
- Osteoclasts are large multinucleated cells responsible for the dissolution and absorption of bone – mediators of bone destruction by phagocytosis
Where do osteoclasts reside?
- Within Howship Lacunae - caused by their erosion of bone by osteoclast derived enzymes
What are the 2 main types of bone?
- Immature woven (primary) bone
- Mature lamellar (secondary) bone
How are the collagen fibres organised within woven bone?
- In a haphazard organisation
What is the first type of bone formed in embryonic development and fracture healing?
- Primary bone - immature woven bone
What are the two forms of mature bone?
- Cortical (compact) bone
- Cancellous (cancellous) bone
Which type of bone ensheathes the bony medulla?
- Cortical bone
How is cortical bone organised?
-
Lamellar configuration
- Densely arranged osteons (Haversian systems)
What is an osteon?
- The chief structural unit of compact (cortical) bone consisting of:
- Contain a central canal that is surrounded by concentric rings (lamella) of the matrix
- Osteocytes located between lamellae within the small cavities - lacunae
- Canaliculi radiate from the launcae to the Haversian canal to provide passageways through the hard matrix
How do the blood vessels interconnect within bone?
- By Volkmann’s canal
Which cells mediate bone resorption through phagocytosis?
- Osteoclasts
How do osteoclasts mediate bone resorption (3 steps)?
- Ruffled border (invaginations of the plasma membrane) is formed by osteoclasts, which define the active region where acid phosphatase enzymes are secreted to dissolve the organic collagen and inorganic calcium & phosphate of the bone
- Attach to the bone by osteopontin and sialoprotein forming a sealing zone between the osteoclast and bone
- Calcium hydroxyapatite crystals are removed from the bone by acidification – the osteoid is protected against osteoclastic resorption
How is calcium stored within bone?
- Calcium hydroxyapetite crystals
Which cells are predominantly found within immature woven bone?
- Osteocytes
What type of bone is the humerus?
- Long bone
What type of bone is patella?
- Sesamoid bone
Which type of collagen forms the bone?
- Type I bone (90%) + Type V bone
How is cancellous bone organised?
- Cancellous bone is characterised by a trabecular structure that is comparatively less dense, softer, weaker and less stiff than cortical bone
Where does cancellous bone reside?
- Within the epiphysis of the bone and within the medullary canal
What is the function of cancellous bone (2)?
- Greater surface area is ideal for metabolic activity - exchange of calcium ions
- High vascular and red bone marrow support haemopoiesis
What is the function of flat bones?
- Protects internal organs
What type of bone is the cranial cavity?
- Flat bone
What is the function of long bones?
- Support & facilitate movement
What is the function of irregular bones?
- Vary in shape and structure
What is the function of short bones?
- No diaphysis, as wide as they are long, provide stability and some movement
What is the function of sesamoid bones?
- Embedded within the tendons potentially protects tendons from stress or wear
What is the diaphysis?
- A tubular shaft that traverses between the proximal and distal ends of the bone
- The hollow region within the diaphysis is considered to be the medullary cavity
What does the medullary cavity encapsulate?
- Yellow marrow
What are the walls of the diaphysis composed of?
- Dense and hard compact bone
What is the membranous lining of the medullary cavity?
- Endosteum
What is the outer surface of the medullary cavity?
- Periosteum
Where does the red marrow occupy?
- The cavities of the trabeculae within the epiphysis
What is the epiphysis?
- Wider terminal ends of bone that are filled with cancellous bone
What is the point at which the epiphysis meets the diaphysis?
- Metaphysis
What is the metaphysis?
- Narrow segments that contain the epiphyseal growth plates - a layer of hyaline in a growing bone
What is intramembranous ossification (8 steps)?
-
Mesenchymal cells undergo differentiation and specialises into osteogenic cells and ultimately osteoblasts
- Clusters of osteoblasts form an ossification centre
- Osteoblasts secrete osteoid, uncalcified matrix consists of collagen precursors and organic proteins which calcifies due to mineralisation - therefore entrapping osteoblasts
- Osteoblasts that are entrapped within the matrix become osteocytes
- As osteoblasts transform into osteocytes, osteogenic cells in the surrounding connective tissue differentiate into osteoblasts at the edges of growing bone
- Clusters of osteoid unite around capillaries → Forms a trabecular matrix
- Osteoblasts on the surface of newly formed spongy bone become the cellular layer of the periosteum
- The periosteum secretes compact bone superficial to the cancellous bone
- Cancellous bone aggregates near blood vessels condensing into red bone marrow
What is endochondral ossification?
- The bone develops through hyaline cartilage replacement - Behaving as a template to be completely replaced by new bone
Compare the rate at which intramembranous and endochondral ossification occur.
- Endochondral ossification is longer than intramembranous ossification
What is the process of endochondral ossification (7 steps)?
- Formation of matrix increases cartilaginous model size - blood vessels in the perichondrium brings osteoblasts to the edges of the structure
- Arriving osteoblasts deposit osteoid in concentric formation around the diaphysis
- Bony edges of the developing structure prevent nutrients from diffusing into the centre of the hyaline cartilage → Chondrocyte death
-
Periosteal bud invasion: Without cartilage inhibiting blood vessel invasion, blood vessels penetrate the resulting space - enlarging the cavities and transferring osteogenic cells with them - forming osteoblasts
- The enlarged spaces become the medullary cavity
- Chondrocytes and cartilage continue to grow at the epiphyses, increasing length
- Continued growth is accompanied by remodelling inside the medullary cavity, and overall lengthening of the diaphysis
- Cartilage remains at the epiphyses and at joint surfaces as articulate cartilage
- Secondary ossification centre forms
