Skeletal System Foundations Flashcards
Bone is a dynamic organ
dynamic → changes throughout life
osseous tissue
mineralized connective tissue
- 1 of the 5 major types of mature CT
- cells and extracellular matrix (CT → large amount of extracellular matrix, widely dispersed cells)
different components of extracellular matrix: organic
collagen → tensile strength
- not stiff → flexible to withstand force
different components of extracellular matrix: inorganic
calcified minerals/salts
- hardness → support/protection
organic/inorganic are hard → unique compared to other connective tissues
tensile strength
maximum strength that a structure can withstand while being stretched or pulled
- collagen - cartilage, tendons, ligaments
compression strength
maximum strength that a structure can withstand while being crushed/compressed/squeezed
shear(ing) strength
maximum strength that a structure can withstand while being pushed in opposite directions
cartilage
mostly hyaline cartilage
huge role in MSK:
- bone ossification: bone formation – cartilage model first
- joints: cartilage = connective tissue joining bones
- cartilage will cover ends of long bones → shock absorption, protection
- synovial joints: shoulder, elbow, hip, knee, …
cartilage → mostly AVASCULAR
- no/poor blood supply
- compared to most of skeletal system which has rich vascular supply
- healing implication: cartilage doesn’t heal as well as bony tissue - no O2 or nutrients reaching
dense connective tissue
microscopically appear denser → higher frequency of tightly packed fibers
Dense CT: periosteum, ligaments, tendons
periosteum: surrounds bone → tethered by fibers
* dense irregular CT
ligaments: bone to bone/tendons: muscle to bone
- send fibers into matrix of bone - close connections
- dense regular CT
marrow
soft pulpy tissue, housed in hollow spaces within bony tissue
2 types:
1) red marrow → found throughout skeleton in fetus + first year
- hemopoietic - blood forming
2) yellow marrow → framework of CT - supports numerous blood vessels and cells
- hollow portions of shafts/bodies of long bones
- adipocytes: fat forming
Yellow marrow gradually replaces most red marrow
-EXCEPT: vertebrae, sternum, ribs, clavicles, scapula, hip bones, proximal ends (epiphysis) of long bones - humerus/femur
neurovasculature
** vital to function of body
arteries
– blood vessel → carry (OXYGENATED) blood away from the heart to tissues
veins
– blood vessel → conveys (DEOXYGENATED) blood from tissues back to the heart
nerves
– bundle of axons bundled together outside of CNS
– communication with CNS
axial skeleton
80 bones associated
bones that lie around longitudinal axis
appendicular skeleton
126 bones associated
appendages
– girdles, upper limb, hands, lower limb, feet
parts of a long bone
diaphysis, epiphyses, metaphyses, epiphyseal plate, articular cartilage, periosteum, medullary cavity, endosteum
diaphysis
shaft, body
epiphyses
typically, proximal/distal ends of bones
metaphyses
meta = between
regions between epiphyses & diaphysis
composition differs widely between age in terms of individuals
epiphyseal plate (growth plate)
hyaline cartilage – attaching epiphysis to diaphysis
synchondrosis → cartilaginous joint
allows diaphysis to grow in length – cartilage grows and is replaced by bone
replaced with epiphyseal line
articular cartilage
– thin layer of hyaline cartilage
– located on epiphysis (formation of synovial joints)
** not associated with bone growth → associated with synovial joints - added layer of shock absorption/protection
– lacks blood vessels: avascular → damage = slow to heal (ex: osteoarthritis)
– remnant of endochondral ossification → major means through which bones develop in a cartilage model
periosteum
peri = around
surrounds bone’s outer surface (except where articular cartilage is located → where tendons/ligaments are going to insert)
– outer fibrous layer → dense irregular CT
– inner osteogenic layer → cellular; appositional growth (outside of bone/width)
– attached to bone → send fibers to interweave with matrix of bone
– gives bone shiny appearance
medullary cavity
medulla = marrow
contains yellow bone marrow and blood vessels
– triglyceride storage
– neurovasculature – travel throughout bone
– reduces weight of bone → if area was filled in with compact bone it would be heavier - affect movement & energy consumption
endosteum
endo = within
membrane/layer of cells and small amount of CT lining medullary cavity or trabeculae
osteogenic cells (osteoprogenitor stem cells)
derived from mesenchyme (embryonic tissue by which all CT forms)
cell division – only bone cells capable of cell division – these cells become osteoblasts → when begin to secrete extracellular matrix
located:
– deep side of periosteum
– endosteum
– neurovascular canals
osteoblasts
bone-building cells (osteo_b_lasts _b_uild)
synthesize & secrete collagen fibers/organic components → initiates calcification – hardening of bone
become osteocytes when done secreting
history of osseous tissue – extracellular matrix
material located between cells – surrounds widely separated cells
~15% water
~30% collagen fibers (organic material)
~55% crystallized mineral salts (inorganic material)
mineral salts
- calcium phosphate → most abundant
- calcium hydroxide
↓
hydroxyapatite
– combine with other mineral salts + ions that will be deposited within organic framework of collagen fibers
– inorganic material will harden eventually → hardness associated with bone
** have to have both organic and inorganic materials for process of calcification to occur
histology of osseous tissue
hardness = crystallized inorganic tissue
flexbility = collagen fiber
– tensile strength → resistance of being stretched/torn apart
** need balance of organic and inorganic materials for properly functioning bone
osteocytes
cytes = cells
mature bone cells
maintain daily metabolism of bone
trapped in extracellular matrix but not dead → passing nutrients, chemical signals via gap junctions + metabolic waste to nearest blood vessel for disposal
– strain sensor: mechanosensor that allows control of adaptive responses to mechanical loading on bone
→ too much/not enough stress on a bone: utilize hormonal/mechanical signals in bone mass regulation
osteoclasts
clast = break
osteo_c_lasts _c_onsume bone → break down extracellular matrix (resorption) – daily maintance
derived from fusion of a type of WBC (monocytes)
– ruffled border → bone facing
– deeply folded plasma membrane - releases powerful lysosomal enzymes & acids → break down extracellular matrix of bone
– increasing blood calcium when needed
cells present in osseous tissue
compact bone
stregnth in bending
forms external layer of all bones & bulk of diaphyses
cortical & dense
spongy bone
strength in compression – resist stress
contains larger spaces
forms majority of short, flat, & irregular bones → epiphyses
trabecular, cancellous
compact bone - osteons (Haversian systems)
dynamic structural units
aligned in same direction along lines of stress (longitudinal axis)
lines of stress are dynamic
→ learning to walk
→ weight training
compact bone - concentric lamellae
circular plates of mineralized/calcified extracellular matrix
surrounds central canal: neurovasculature & lymphatics
→ get to deeper parts of bone & innervate
compact bone - perforating [Volkmann’s] canals
transverse canals
neurovasculature from the periosteum
→ central to function
compact bone - circumferential lamellae
external (outer) & internal (inner) circumference
– external is attached to periosteum via perferoating [sharpey’s] fibers → interweave the fibers associated with ligaments & tendons - musculoskeletal unit
important in appositional growth → growth of outer surface/bone width growth
spongy bone
consists of trabeculae (=little beams) oriented along lines of stress - often coming from multiple directions
– not arranged in osteons but contain many components found in osteons → concentric lamellae; osteocytes
– contain larger spaces → filled with bone marrow - rich vascular supply
bone formation
around 6th week of embryonic development in utero
mesenchymal ‘skeleton’ → embryonic tissue - CT derived from it
2 types of ossification
intramembranous ossification
intra = within; membran = membrane
within mesenchymal ‘skeleton’ → bone directly replaces mesenchymal skeleton
endochondral ossification
endo = within; chondral = cartilage
mesenchymal ‘skeleton’ → cartilage model → bone
what is the difference between ossification & calcification?
ossification: process by which bone forms in 4 situations: 1) initial formation of bone; 2) growth of bone during juvenile/adolescent period; 3) remodeling of bone; 4) repair of bone
calcification: osteoblasts will lay down organic materials of extracellular matrix which will initiate calcification [= tissue hardening]
→ process within ossification
intramembranous ossification
forms:
– flat bones of skull (fontanels)
– most of facial bones
– mandible
– medial part of clavicle
** also important in bone widening and thickening (bone remodeling) throughout life → depositing new tissue on the bony surface even past age bones can no longer grow in length
endochondral ossification
most bones of body form this way initially
– stops after skeletal maturity → bone formation during adulthood (width) - intramembranous
more complex than intramembranous ossification
endochondral ossification - cartilage model
chondroblasts
hyaline cartilage – producing cartilage
interstitial & appositional growth
interstitial vs appositional growth
interstitial growth → cartilage
– growth from within
– typically increase in length
appositional growth → cartilage & bone
– growth of outer surface - deposition of tissue
– typically increase in width (thickness)
– bony appositional growth occurs by intramembranous ossification at bone surface
bone remodeling
natural process → repairs microfractures, reshaping bone in response to use/disuse, releasing minerals into blood as needed
– health if balance
balance between osteoblasts (bone builder) and osteoclasts (bone resorption)
– bone deposition & bone resorption
factors that affect bone: minerals
varying levels of
– calcium } vital in extracellular matrix calcification
– phosphorous } stored within bone
⇢ release: increased bone calcium
– magesium, fluoride, manganese
⇢ smaller roles in strengthening or forming extracellular matrix
factors that affect bone: vitamins
vitamin C: presence important in collagen synthesis (organic material)
vitamin D: production of active form of vit D (calcitriol) is complex
⇢ involves integumentary system, liver, kidneys
– calcitriol increases absorption of calcium ⇢ increase blood calcium levels
factors that affect bone: hormones
calcitonin (CT): inhibits bone resorption
– endocrine thyroid gland
– inhibit osteoclasts from breaking down bone and releasing calcium into bloodstream ⇢ decrease blood calcium
parathyroid hormone (PTH): promotes bone resorption
– parathyroid gland
– inhibit osteoblast collagen synthesis, inhibit bone deopsition⇢ increase blood calcium
sex hormones (ex: estrogen, testosterone): big role in bone length growth
– bone remodeling
– estrogen + testosterone can both stimulate osteoblasts
human growth hormone (hGH): general growth of all body tissues (including bone)
– secreted by pituitary gland
** exercise: weight-bearing activity can stimulate osteoblasts; bone remodeling
fractures - open vs closed
open: compound
– breaks through skin
– generally more emergent
closed: simple
– does not break through skin
fractures - comminuted; impacted; greenstick
comminuted: ‘shattered’
– com = together; minuted = crumbled
impacted: fragmented bone forcefully driven into other fragmented part
greenstick: partial fracture
– juveniles ⇢ bones not fully formed/calcified – contain more organic material
repair of bone fractures
- formation of fracture hematoma
- formation of fibrocartilaginouos callus
- formation of bony callus
- remodeling of bone
treatments for fractures
** depends on location & age
– reduction: ‘setting a fracture’ ⇢ realign
– closed reduction ⇢ fractured ends aligned by manual manipulation – skin intact
– open reduction ⇢ fractured ends aligned by surgical intervention
osseous tissue: aging
** rates change: decrease in sex hormones; osteoclast activity outpaces osteoblasts
2 main effects on osseous tissue with aging:
- loss of bone mass ⇢ demineralization – loss of calcium/mineral levels
- brittleness ⇢ production of collagen slows
osteoporosis
overly porous bone
– por = passageway; osis = condition
bone resorption at higher pace than bone deposition
– affects spongy bone more than compact bone
⇢ spongy – more metabolically active, more surface area exposed to osteoclasts
osteoporosis symptoms
- bone pain
- fractures
- shrinkage of vertebrae ⇢ cascade of microfracture in vertebral body
common in
- vertebral bodies
- distal ends of radius
- proximal end of femur
- wrist/hip
osteoporosis indicence
higher incidence in:
- middle-aged and elderly individuals
- individuals assigned female at birth ⇢ bones = smaller; estrogen – slow at menopause
other risk factors:
- family history
- ancestry
- small body build
- inactive lifestyle
