chapter 6- skeletal system Flashcards
what is hematopoiesis?
blood cell production
axial skeleton consists of the skull, vertebrae, and the what?
ribs
the compact bone shaft of a long bone is called the what?
diaphysis
the medullary cavity of the bone contains what?
yellow marrow/triglycerides
at the metaphysis, what do you know about the age of a person with a plate instead of a line?
child, still growing
in bone tissue what are found in lacunae linked to each other by canaliculi?
osteocytes
hydroxyapatite is composed of predominantly what mineral?
calcium
one-third of the bone matrix is what consisting of collagen fibers and
ground substance?
osteoid
the cells that perform osteogenesis to repair or remodel bones are the what?
osteoblasts
osteoprogenitor cells are located in the what and inner cellular layer of the periosteum?
endosteum
the concentric lamella around a central canal in compact bone creates a circular structure called a what?
osteon
in spongy bone, the lamella is in branch configurations called what with what in the spaces?
trabeculae, red marrow
the two-layer covering on the outer surface of a bone is called the what?
periosteum
endochondral ossification begins with a bone-shaped piece of what?
hyaline cartilage
osteoclasts solubilize the hydroxyapatite with what?
HCl (hydrochloric acid)
what is secreted by osteoblasts to induce
mineralization of the osteoid?
alkaline phosphate
if blood calcium levels fall below 9mg/cL, what will be
released from the parathyroid gland?
parathyroid hormone
what organ produces calcitonin?
thyroid
even if you drink a lot of milk, a lack of what is made by the kidney will result in you having a calcium deficiency?
calcitriol
a lack of growth hormone in childhood will result in what?
pituitary dwarfism
immediately following a fracture, an external callus of what is formed by the periosteum?
fibrocartilage
the normal aging process results in reduced bone mass called what?
osteopenia
skeletal system components
bones, cartilage, ligaments, other C.T. that stabilize the bones
functions of the skeletal system
- support: framework & structure of body
- storage of minerals & lipids
- blood cell production (all formed elements)
- protection: surround soft tissues
- leverage for movement (levers upon which skeletal muscles act)
minerals
calcium & phosphate (for osmotic regulation, enzyme function, nerve impulses)
yellow marrow
triglycerides (for energy reserves)
red marrow
stem cells -> hematopoiesis
axial skeleton
protection & support skull, vertebrae & ribs
appendicular skeleton
locomotion & manipulation, limbs & limb girdles
bone classification
-206 bones
-all bones can be classified by shape
long bones
-longer than wide consisting of shaft & 2 ends
-ex: bones of appendages
short bones
-approximately equal in all dimensions
-ex: carpals & tarsals
flat bones
-thin, 2 parallel surfaces
-ex: skull, sternum, ribs & scapula
irregular bones
-complex shapes
-vertebrae & os coxa
sesamoid bones
-seed shaped, form in tendon
-ex: patella
-total # can vary
sutural bones
extra bones in sutures of the skull
bone structure
-a bone is an organ consisting of many tissue types: osseous, nervous, cartilage, fibrous C.T., blood, etc.
-consist of 2 types of bone tissue
compact bone
solid, dense bone, makes up surfaces & shafts
spongy bone/cancellous bone
meshy, makes up the interior of bones & houses red marrow in spaces
diaphysis (long bone structure)
hollow shaft of compact bone
medullary (marrow) cavity (long bone structure)
center of the diaphysis, contains yellow marrow
epiphysis (long bone structure)
expanded end of bone, the surface of compact bone with red marrow in spaces
epiphyseal line or plate (long bone structure)
cartilage that marks the connection of diaphysis with epiphysis
epiphyseal line in adults
narrow a.k.a metaphysis
epiphyseal plate in children
thick, allows growth during chilldhood
periosteum
2 layers cover around outside of the bone
what are the 2 layers of the periosteum?
outer fibrous layer & inner cellular layer
endosteum
cellular layer covers all inside surfaces
articular cartilage
hyaline cartilage on the end where bone contacts, another, no periosteum or perichondrium
joint/articulation
-the connection between two bones, surrounded by C.T. 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 & endosteum
-site of most hematopoiesis
bone
-osseous tissue, supporting C.T.
-consists of specialized cells in a matric of fibers & ground substance
characteristics of bone
- dense matrix packed with calcium salts
- osteocytes in lacunae
- canaliculi for exchange of nutrients & water
- two-layer periosteum, cover bone except at articular surfaces
-cells = only 2% of bone
matrix of bones
-98% of bone tissue
-1/3 = osteoid
-2/3 = densely packed crystals of hydroxyapatite, hard but brittle
osteoid
organic part, collagen fibers + ground substance, tough & flexible
hydroxyapatite
calcium salts, mostly calcium phosphate (hard but brittle)
osteocytes
-mature bone cells
-no cell division
-located in lamellae
-canaliculi link lacunae to each other & blood supply
-linked to each other via gap junctions on cell projections on canaliculi
lamellae
-lacunae between layers of matrix
-hold osteocytes
what is the function of osteocytes?
-maintain protein & mineral content matrix
-also participate in bone repair: become active when broken free of lacuna
osteoblasts
-perform osteogenesis
-produce osteoid
-promote the deposit of calcium slats which spontaneously form hydroxyapatite
osteoprogenitor cells (mesenchymal cells)
-bone stem cells that produce daughters that become osteoblasts for repair & growth
-located in endosteum & inner periosteum
osteoclasts
-large, multinuclear
-derived from monocytes (macrophages)
-perform osteolysis
osteolysis
digest & dissolve bone matrix, osteoclasts release minerals for use in blood or recycling during bone remolding
structure of compact bone
-consists of osteons parallel to the surface
-each osteon around central canal
-perforating canals perpendicular to osteons connecting osteons
-osteon built of layer of matrix secreted by osteoblasts
-each layer = concentric lamella
-interstitial lamellae fill spaces between osteons
-circumferential lamellae run perimeter inside & out
*designed to receive stress from one direction
-very strong parallel to osteons but week perpendicular
central canal
contains blood vessels & nerves
perforating canals
allow blood vessels to enter the bones from periosteum
structure of spongy bones
-trabeculae (no osteons)
-red marrow fills space around trabeculae
-no direct blood supply (no central canals)
-nutrients diffuse into canaliculi in trabeculae from red marrow
-makes up low-stress bones or areas of bone where stress cones from multiple directions
-provides lightweight strength
trabeculae
meshwork of spongy bone
fibrous outer layer of periosteum
dense irregular C.T.
cellular inner layer of periosteum
osteoprogenitor cells
functions of the periosteum
- isolate bone from surrounding tissues
- site for attachment (tendons, ligaments, joint capsules)
- route for nerves & blood vessels to enter the bone
- participates in bone growth & repair
endosteum
-thin cellular level
-lines medullary cavity, central canals & covers trabeculae
-consists of osteoprogenitor cells
-cells become active during bone growth & repair
bone growth
-begins 6-8 weeks post-fertilization
-continues through puberty (18-25y)
-two types: intramembranous (forms flat bones) & endochondral (form long bone)
osteogenesis (ossification)
formation of bone
calcification
hardening of matrix or cytoplasm with calcium, can happen to many tissues
intramembranous ossification
-bone develops from mesenchyme or fibrous C.T. in deep layer of dermis
-ex: skull bones, mandible, clavicales
intramembranous ossification step 1
ossification center appears in the fibrous connective tissue membrane
intramenmbranous ossification step 2
bone matrix (osteoid) is secreted within the fibrous membrane
intramembranous ossification step 3
woven bone & periosteum form
intramembranous ossification step 4
bone collar of compact bone forms & red marrow appears
endochondral ossification
bone develops from hyaline cartilage models, the cartilage grows by interstitial & appositional growth and is slowly replaced by bone from the inside out
endochondral ossification step 1
primary ossification center begins to form: chondrocytes in the diaphysis enlarge & surrounding matrix calcifies killing the enclosed
endochondral ossification step 2
blood vessels grow into edge of cartilage: cells of inner layer of perichondrium differentiate into osteoblasts which secrete osteoid, osteoid is mineralized & a bone collar forms around the diaphysis
endochondral ossification step 3
capillaries & fibroblasts migrate into the primary ossification center, fibroblast differentiate into osteoblasts & secrete osteoid which is mineralized into trabeculae, spongy bone is formed & continues forming growing toward epiphyses
endochondral ossification step 4
remolding occurs: osteoclasts degrade trabeculae in the center to create the marrow cavity, the bone increases in length by interstitial growth of the epiphyseal plate followed by replacement of plat cartilage by spongy bone, bone increases in diameter by appositional growth from the cellular layer of periosteum
endochondral ossification step 5
secondary ossification centers from in the epiphyses
endochondral ossification step 6
epiphyses become ossified with spongy bone, hyaline cartilage remains on the articular surface, ossification continues at both ossification centers until all epiphyseal cartilage has been replaced with bone -> epiphyseal closure
bone remolding
-bones not static: constantly recycled/renewed
-5-7% of skeleton recycles/week
osteoclasts secrete
- lysosomal enzymes: digest osteoid
- hydrochloric acid: soluble calcium salts
osteoblasts secrete
- osteoid (organic matrix)
- alkaline phosphate: induces mineralization of osteoid
fracture repair 1-2 steps
- fracture hematoma forms, seals off dead osteocytes & broken blood vessels
- cells of periosteum create external callus of fibrocartilage, cells of endosteum create internal callus of spongy bone, ends of fracture stabilized by callus
fracture repair 3-4 steps
- osteoblast replace cartilage with spongy bone fracture gap now filled with all spongy bone
- a bulge from the callus marks the fracture point, spongy bine replaced with compact bone & excess callus material removed
bone adapt
-stressed bones grow thicker
-bumps & ridges for muscle attachment enlarge when muscles used heavily
-bones weaken with inactivity (up to 1/3 of mass lost with few weeks of inactivity)
-heavy metals can be incorporated
*condition of bones depends on interplay between osteoclast & osteoblast activity
skeleton as calcium reserve
-calcium important to normal function of neurons & muscles
-blood calcium: 9-11mg/100ml
calcium homeostasis depends on
- storage in the bones
- absorption in the GI
3.exertion at the kidneys
if blood calcium levels low
-parathyroid hormone triggers
1. increase osteoclast activity (decrease storage)
2. enhanced calcitriol actions (increase storage)
3. decreased calcium excretion at kidney
if blood calcium levels high
-calcitonin (from thyroid gland) trigger
1. inhibition of osteoclast activity (increase in storage)
2. increased calcium excretion in kidney
nutritional & hormone effects on bone
many nutrients & hormones are required for normal bone growth & maintenance
calcium & phosphate salts
from food, for mineralization of matrix
calcitriol
from kidney, for absorption of calcium & phosphate
vitamin C
from food, for collagen synthesis & osteoblast differentiation
vitamin A
from carotene in food, for normal bone growth in children
vitamin K & B12
from food, for synthesis of osteoid proteins
growth hormone
from pituitary gland, for protein synthesis & cell growth
thyroxine
from thyroid, for cell metabolism & osteoblast activity
estrogens & androgens
from gonads, for epiphyseal closure
calcitonin & parathyroid hormone
from parathyroid gland, to regulate calcium & phosphate levels in body fluids, affects bone composition
gigantism
too much growth hormone prior to epiphyseal closure bones grow excessively large
acromegaly
too much growth hormone after closure, bones don’t grow but all cartilage does (ribs, nose, ears, articular cartilage)
pituitary dwarfism
not enough growth hormone, bones fail to elongate
scurvy
lack vit.C, low collagen content, reduced bone mass, bones brittle
osteomalacia (rickets in children that lead to permanent deformitya0
lack vit.D -> lack calcitriol, osteoid produced but not mineralized, bones flexible
osteopenia
-reduction in bone mass
-all adults suffer at some degree
-osteoclasts out-work osteoblasts (sex hormones in youth inhibit osteoclasts)
-women: 8%
-men: 3%
osteoporosis
-reduction in bone mass that compromises function
-more common in women
-greater rate of osteoporosis when bones are thinner to start
