Ch. 6 - Bone Tissue Flashcards
What is the main function of the skeletal system?
support and protection of the body
What are 5 functions of bones?
- support and protection of soft tissues
- attachment site for muscles, making movement possible
- storage of minerals (Ca, PO4)
- blood cell production in red bone marrow
- triglyceride storage in yellow bone marrow
What do long bones consist of?
Diaphysis (shaft) Epiphysis (ends) Metaphysis (includes plate, where shaft grows) Articular cartilage Periosteum Endosteum Medullary cavity
What is the articular cartilage?
thin layer of hyaline C that absorbs shocks & reduces friction at joints
How does the periosteum differ from the endosteum in terms of structure and function?
P - tough layer of dense CT that covers all bones; contains osteogenic cells BV; allows bone to grow in thickness; attch point for lig and tendons
E - single osteoblast layer with CT (thin membrane) that lines medullary cavity; active during repair & remodelling
What does the medullary cavity contain?
fatty yellow bone marrow; reduces bone weight
What does the osseous matrix comprise of?
15% water
30% collage fibers (strength)
55% crystallized mineral salts (hardness)
What occurs during calcification? When does it occur?
- calcium phosphate combines w calcium hydroxide to form hydroxyapatite
- salts and ions are deposited on framework of collagen fibres
- only in presence of collagen fibres!
What are osteogenic cells and what do they do?
- undifferentiated stem cells from mesenchyme (embryonic CT)
- divide to replace themselves and can differentiate into osteoblasts
What are osteoblasts and what do they do?
- form matrix by secreting collagen fibres and depositing mineral salts (responsible for bone calc)
- become osteocytes
*cannot divide
What are osteocytes and what do they do?
- mature cells that no longer secrete matrix
- maintain bone metabolism
*cannot divide
What are osteoclasts and what do they do?
- formed by monocytes
- function in bone resorption
- secrete enz that breakdown ENZ, releasing min/ions into blood
Where are compact bones found?
diaphysis of long bones and beneath periosteum of all bones
Where are spongy bones found?
in the epiphysis of long bones and in flat bones
What are the functions of compact bone?
- provides protection and support (strongest form of BT)
- resists stresses bt weight/movement
How are compact bones arranged?
in parallel units called osteons (concentric rings of matrix of lamellae)
What are osteons?
- rings of calcified matrix (lamellae) surrounding vertically oriented central canal that contains BV and nerves
- aligned parallel along lines of stress
What are lacunae?
concentric lamellae; osteocytes are found in small spaces between lacunae
What are canaliculi? What are found inside them?
channels filled with EC fluid that connect one lacuna to the next to the central canal
inside are extensions of osteocytes
What are the 3 types of lamellae?
concentric, circumferential, interstitial
What does spongy bone consist of?
network of trabeculae; no osteons
What are trabeculae?
lattice of thin plates of bone oriented along lines of stress; space in bt are filled with red bone marrow; consist of lamellae with osteocytes and canaliculi
What are the functions of spongy bone?
support and protects red bone marrow, handles stress from multiple directions
What do nutrient arteries help supply? How?
inner parts of compact bone, spongy bone, red bone marrow
enter through nutrient foramen in center of diaphysis
What do metaphyseal and epiphyseal arteries supply?
ends of bones (red bone marrow and tissue of meta/epiph)
What do periosteal arteries supply? How?
periosteum and outer part of compact bone
enter through diaphysis via perforating canals
What part of the bone are rich in sensory nerves?
periosteum; particularly pain receptors
What are the 4 types of bone formation?
- ossification in utero
- growth of bones from infancy to adolescence
- remodelling throughout life
- repair of fractures
What are the 2 types of ossification in utero and how do they differ?
intramembranous and endochondral
I - from mesenchymal CT (flat/spongy)
E - from hyaline cartilage (long)
Describe the process of intramembranous ossification
- Formation of ossification centers: mesenchymal cells differentiate into osteogenic cells then into osteoblasts that deposit osteoid (non-calcified matrix)
- Calcification: osteoblasts diff into osteocytes that lie w/i lacunae; osteoid calcifies (hardens)
- Formation of trabeculae (in spongy bone): as oss centers move towards each other, trabeculae is formed around BV
- Formation of periosteum: osteoblasts + CT along bone surface; BV w/i bone matrix eventually become bone marrow
What are the steps of endochondral ossification
- Development of cartilage model
- Growth of cartilage model
- Dev of primary oss center
- Dev of medullary cavity
- Dev of secondary oss center
- Formation of articular cartilage and epiphyseal plate
What occurs during the development and growth of the cartilage model? (steps 1 & 2 in endoch oss)
- mesenchymal cells differentiate into chondroblasts, forming cartilage model of bone made of hyaline C; perichondrium develops around this model
- chondroblasts become buried in cartilage ECM; become chondrocytes
- Ccytes divide and C model grows in length
- Ccytes in centre die and cartilage becomes calcified; spaces left from dead Ccytes form lacunae
What occurs in the development of primary oss centre? (step 3)
- nutrient artery penetrates center of C model
- osteogenic cells from periosteum differentiate into osteoblasts
- osteoblasts deposit bone matrix over calcified cartilage –> forming spongy bone trabeculae
What occurs in the development of medullary cavity? (step 4)
- osteoclasts break down newly formed trabeculae and form medullary cavity
- eventually most of wall is replaced by compact bone
What occurs in the development of the secondary oss centre? (step 5)
- epiphyseal arteries enter epiphyses and trigger differentiation of osteogenic cells into osteoblasts from periosteum
- spongy bone is formed at epiphyses; NOT destroyed by osteoclasts
How are the articular cartilage and epiphyseal plate formed? (step 6)
- cartilage on ends of bone remain as articular cartilage
- cartilage at epiphyseal plate remains for future growth
What is the difference between interstitial growth and appositional growth?
I - long bones lengthen via addition of material on diap side of ep plate via endochondral oss
A - bones grow in thickness
What are the different stages of interstitial growth?
- zone of resting cartilage
- zone of proliferating C
- zone of hypertrophic cartilage
- zone of calcified cartilage
What are happening to the chondrocytes in each stage of interstitial growth?
- Ccytes are small and scattered
- Ccytes undergo rapid cell division to replace dying Ccytes
- Ccytes are enlarged and remain in columns
- Ccytes are dead; matrix is calcified
What occurs in the zone of calcified cartilage?
Oblasts and capillaries move in to create bone
Cartilage replaced with bone
This zone becomes the new diaphysis
How does appositional growth occur?
osteoblasts deposit bone on outer surface; osteoclasts widen medullary cavity from inside
What are the steps in appositional growth?
- ridges in periosteum create groove for periosteal BV
- periosteal ridges fuse, form endosteum-lined tunnel
- osteoblasts in endosteum form an osteon by building new concentric lamellae toward tunnel center
- bone grows outward as Oblasts in periosteum build new circumferential lamellae
- osteon formation repeats as new periosteal ridges fold over BV
What is bone resorption?
removal of minerals and collagen by osteoclasts; releases Ca and P into interstitial fluid
What is bone deposition?
addition of minerals and collagen by osteoblasts
What can trigger bone remodelling?
exercise and lifestyle (diet)
i.e. active vs. sedentary
How does nutrition affect bone growth and remodelling?
Ca and P: needed in large amounts for growth and remodelling
Vit. D: needed for proper Ca absorption in small intestine
Vit. C: required for collagen formation
Vit. K and B12: needed for protein synthesis
Vit. A: stimulate osteoblast activity
How do hormones affect bone growth and remodelling?
- insulin-like growth factors (IGFs) stimulate osteoblasts, promote cell division at epip plate + periosteum
- thyroid hormones stimulate osteoblasts
- estrogens and testosterone trigger sudden growth at puberty to form M + F forms; stimulate osteoblasts
In both sexes, how does estrogen affect bone growth?
contributes to closing of epiphyseal plates; close sooner in women bc higher levels of E; induce apoptosis in osteoclasts
How does exercise affect bone tissue?
BT becomes stronger under stress via increased deposition of mineral salts and collagen fibre prod
Weight- bearing activities help build and retain bone mass
How does aging affect bone tissue?
As sex hormone levels decrease with age, bone resorption occurs more rapidly than bone deposition
What are 2 major effect of aging on bone tissue?
- decreased rate of prot synthesis (collagen production that gives its tensile strength; becomes brittle and more susceptible to fracture)
- loss of bone mass via demineralization (loss of calcium); can lead to osteoporosis
What can cause osteoporosis?
lack of calcium, changes is hormone levels
Why is healing faster in bone than cartilage?
because bone is well-vascularized; but still slow process due to vessel damage
What is the difference between closed and open reduction?
C - restore pieces to normal position via manipulation
O - realignment during surgery
What are the 3 steps in clinical treatment of bone repair?
realignment, immobilization, restoration of functions
What are the 4 steps in repair of bone fractures?
- reactive phase: formation of fracture hematoma
2a. reparative phase: fibrocartilaginous callus formation
2b. reparative phase: bony callus formation - bone remodelling phase
What occurs in the reactive phase?
- blood from damaged BV forms a clot around fracture site (fracture hematoma w/i 6-8 hours of injury)
- nearby bone cells die
- swelling and inflammation occur; phagocytic cells clear debris
- new capillaries grow into damaged area
What occurs in the formation of fibrocartilaginous callus?
- cells from periosteum invade fracture site and start producing collagen and fibrocartilage
- mass of collagen fibres and cartilage (repair tissue) bridges broken ends of bone
*lasts ~3 weeks
What occurs during the formation of bony callus?
- osteoblasts secrete spongy bone that replaces fibrocartilage
- joints the broken ends of bones
*lasts 3-4 months
What occurs during the bone remodelling phase of bone repair?
- compact bone replaces spongy bone in bony callus
- surface is remodeled back to normal shape
