chapter 6 skeletal system Flashcards
Skeletal system components
bones, cartilage, ligaments, other CT that stabilize bones
Functions of skeletal system components
- support: framework and structure of body
- storage of minerals and lipids
Minerals: calcium and phosphate ( for osmotic regulation, enzyme function, nerve impulses) - blood cell production (all formed elements) red marrow: stem cells= hematopoiesis
- protection: surround soft tissues
- leverage for movement ( levers upon which skeletal muscles act)
Bone classification
206 major bones
1. Axial skeleton: protection and support skull, vertebrae, ribs
2. Appendicular skeleton: locomotion and manipulation, limbs and limb girdles
All bones can be classified by shape
- Long bones
- Short bones
- Flat bones
- Irregular bones
- Sesamoid bones
- Sutural bones
Long bones
longer than wide, consist of shaft and 2 ends e.g bones of appendages
Short bones
approximately equal in all dimensions e.g carpals, tarsals
Flat bones
thin, 2 parallel surfaces e.g skull, sternum, ribs, scapula
Irregular bones
complex shapes e.g vertebrae, os coxa
Sesamoid bones
seed shaped form in tendon, e.g patella, total number can vary
Sutural bones
extra bones in sutures of skull
Bones Structure
- a bone is an organ consisting of many tissue types: osseous, nervous, cartilage, fibrous CT, blood, etc
- bones are not flat have projections, depressions and holes for muscle attachment blood and nerve supply
All bones consist of 2 types of bone tissue
- Compact bone
- Spongy bone
compact bone
solid dense bone makes up surfaces and shafts
spongy bone
meshy makes up interior of bones, houses red marrow in spaces
Long bone structure
- diaphysis
- medullary
- epiphysis
- epiphyseal line
- periosteum
- endosteum
- articular cartilage
diaphysis
hollow shoft of compact bone
medullary cavity
center of diaphysis, contains yellow marrow (triglycerides for energy reserve)
epiphysis
expanded end of bone, surface
of compact bone, center filled with spongy bone with red marrow in spaces (produces
blood cells)
epiphyseal line
cartilage that marks
connection of diaphysis with
epiphysis line- adults, narrow,
a.k.a. metaphysis plate - thick, allows growth during childhood
periosteum
2 layer covering around
outside of bone: outer fibrous layer inner cellular layer
endosteum
cellular layer, covers all inside surfaces
articular cartilage
hyaline cartilage on
end where bone contacts another, no periosteum or perichondrium
joint/articulation
connection between two
bones, surrounded by CT
capsule, lined with synovial
membrane joint cavity filled with synovial fluid to reduce friction on articular cartilage
Flat bone structure
-thin layer of spongy bone with red marrow between two layers of compact bone
- covered by periosteum and endosteum
- site of most hematopoiesis
Bone histology
bone= osseous tissue, supporting CT
-consists of specialized cells in a matrix of fibers and ground substance
characteristics of bone
- dense matrix packed with calcium salts
- osteocytes in lacunae
- canaliculi for exchange of nutrients and waste
- two-layer periosteum, covers bone except at articular surfaces
Matrix - 98% of bone tissue
1/3 = osteoid; organic part: collagen fibers + ground substance, tough & flexible
2/3 = densely packed crystals of
hydroxyapatite (calcium salts, mostly calcium phosphate), hard but brittle Cells - only 2% of bone (handout)
osteocytes
Def: mature bone cells
- no cells division
- located in lacunae between layers of matrix called lamellae
- canaliculi link lacunae to each other and blood supply
- osteocytes linked to each
other via gap junctions on
cell projections in canaliculi:
allow exchange of nutrients
and wastes
- osteocytes function to maintain protein and mineral content of matrix
- can also participate in bone repair: become active when broken free of lacuna
Osteoblasts
-perform ostegenesis= produce osteoid (organic componenets of matrix)
-promote deposit of calcium salts which spontaneously form hydroxyapatite
-once enclosed in lacuna by matrix, osteoblast differentiates into osteocyte and no longer produces new matrix
- bone fracture frees osteocytes which revert to osteoblasts to produce matrix again
Osteoprogenitor (mesenchymal cells)
-bone stem cell that produces
daughters that become
osteoblasts for repair and
growth
-located in endosteum and inner
periosteum
Osteoclasts
-large, multinuclear
-derived from monocytes
(macrophages)
-perform osteolysis =
-digest and dissolve bone matrix, release minerals for use in blood, or recycling during bone remodeling
Structure of Compact Bone
-consists of osteons: parallel to surface
-each osteon around
central canal: contains blood vessels and nerves
-perforating canals perpendicular to osteons connecting osteons
-osteon built of layers of matrix secreted by osteoblasts
-each layer = concentric lamella
-osteocytes located in lacunae between lamellae
-osteocytes connected to neighboring cells and central canal via canaliculi
-interstitial lamellae fill spaces between osteons
-circumferential lamellae run
perimeter inside and out in
contact with endosteum
and periosteum
-compact bone designed to
receive stress from one
direction
-very strong parallel to
osteons
-weak perpendicular to
osteons
Structure of Spongy bone
-lamellae=meshwork called trabeculae (no osteons)
-red marrow fills spaces around trabeculae
-osteocytes in lacunae linked by canaliculi
-no direct blood supply (no central canals)
nutrients diffuse into canaliculi in trabeculae from red marrow
-spongy bone makes up low stress bones, or areas of bone where stress comes from multiple directions
-provides light weight strength
Periosteum
- fibrous outer layer: dense irregular CT
- cellular inner layer: osteoprogenitor cells
Functions of Periosteum
- Isolate bone from surrounding tissues
- Site for attachment (tendons, ligaments, joint capsules)
- Route for nerves and blood vessels to enter bone
- Participates in bone growth and repair
Endosteum
-thin cellular layer
-lines medullary cavity, central canals, and covers trabeculae
-consists of osteoprogenitor cells
-cells become active during bone growth and repair
Bone Growth
-begins 6-8 weeks post fertilization
-continues through puberty (18-25y)
Osteogenesis=ossification=formation of bone
NOT calcification=hardening of matrix or cytoplasm with calcium, can happen to many tissues
Two types of ossification
- Intramembranous
- Endochondral
Intramembranous
forms flat bones
Endochondral
forms long bones
Intramembranous ossification
bone develops from mesechyme or fibrous CT in deep layers of dermis, e.g. skull bones,
mandible, clavical
Endochondral ossification
bone develops from hyaline cartilage models. The cartilage grows by interstitial and appositional growth and is slowly
replaced by bone from the inside out
Bone remodeling
bones not static: constantly recycled/renewed
- 5-7% of skeleton recycled / week
-osteoclasts secrete:
1. Lysosomal enzymes: digest osteoid
2. Hydrochloric acid: solubilize calcium salts
Osteoblasts secrete:
- Osteoid (organic matrix)
- Alkaline phosphate induces mineralization of osteoid (complete mineralization takes ~1 week)
Bones adapt:
- stressed bones growth thicker
- bumps and ridges for muscle attachment enlarge when muscles used heavily
- bones weaken with inactivity: up to 1/3 of mass lost with few weeks inactivity
-heavy metals can get incorporated
*condition of bones depends on interplay between osteoclast and osteoblast activity
Skeleton as calcium reserve
- calcium important to normal function of neurons and muscle
- blood calcium: 9-11mg/100ml
- if blood levels to high: nerve and muscle cells nonresponsive
- if blood levels too low: nerve and muscle
cells hyper-excitable to convulsions, death
Calcium homeostasis depends on:
- Storage in the bones
- absorption in the GU
- Excretion at the kidneys
If blood calcium is low
Parathyroid hormone triggers
1.Increase osteoclast activity
2. enhanced calcitriol action
3. decreased calcium excretion at kidney
If blood calcium is high
Calcitonin (from thyroid gland) triggers:
1. Inhibition of osteoclast activity ( ^storage)
2. Increased calcium excretion at kidney
calcium and phosphate salts
from food, for mineralization of matrix
Calcitriol
from kidney
