Functions of the skeletal system
Support, Protection, Movement, electrolyte balance, acid-base balance, blood formation
Support
holds up the body, supports muscles, mandible and maxilla support teeth
protection
brain, spinal cord, heart, lungs
Movement
limb movements, breathing, action of muschle on bone
electrolyte balance
calcium and phosohate ions
Acid-Base balance
buffers against excessive pH changes
Blood Formation
Red bone marrow is the chief producer of blood cells
Flat Bones
protect soft organs, curved but wide and thin
Long bones
longer than wide, rigid levers acted upon by muscles
Short bones
equal in length and width, glide across one another in multpile directions
irregular bones
elaborate shapes that do not fit into other categories
Compact (dense) bone
outer shell of long bone
Diaphysis (shaft)
cylinder of compact bone to provide leverage
medullary cavity
space in the diaphysis of a long bone that contains bone marrow
epiphysis
enlarged ends of a long bone
enlarged to strengthen join and attach ligaments and tendons
spongy (cancellous) bone
covered by more durable compact bone. skeleton three-fourths compact and one-fourth spongy bone by weight
articular cartilage
layer of hyaline cartilage that cover the joint surface where one bone meets another; allows joint to move more freeely and realtively friction free
Nutrient formina
minute holes in the bone surface that allows blood vessels to penetrate
Periosteum
external sheath that covers bone except where there is articular cartilage
Outer layer of Periosteum
fibrous layer of collagen. some outer fibers continuous with the tendons that attach muscles to bone, perforating fibers, strong attachment and continuity from muscle to tendon to bone
Inner layer of Periosteum
inner osteogenic layer of bone forming cells, important to growth of bone and healing of fractures
Osteogenic (osteoprogenitor) cells
stem cells found in endosteum, periosteum, and in central canals.
-arise from embyonic
Osteoblast
bone-forming cells
-line up as asingle layer of cells under endosteum and periosteum
-nonmitotic
-synthesize soft organic matter of matrix which then hardens by mineral deposition
-stress and fractures stimulate osteogenic cells to multiply more rapidly a
Osteocalcin
structural protien of the bone
stimulates insulin secretion of pancrease
increases insulin sensitivity in adipocytes which limit the growth of adipose tissue
Osteocytes
former osteoblast that have become trapped in the matrix they have deposited
-some osteocytes reabsorb bone matrix while other deposit it
-contribute to homeostatic mechanism of bone density and calcium and phosphate ions
Lacunae
tiny cavities where osteocytes reside
canaliculi
little channels that connect lacunae
osteoclast
bone-dissolving cells found on the bone surface
-develop from same bone marrow stem cells that give rise to bloood cells
-different origin from rest of bone cells
-unusually large cells fromed from the fusion of severla stem cells
- Typically have 3 to 4
Ruffled border
side facing bone surface
-several deep infoldings of the plasma membrane which increases surface area and resorption efficiency
Resorption bays
pits on surface of bone where osteoclasts reside
remodeling
results from combined action of the bone-dissolving osteoclasts and the bone-deposting osteoblasts
Matrix
by dry weight 1/3 organic and two thirds inorganic matter
Organic matter of Matrix of Osseous tissue
collagen, carbohydrate-protien complexes, such as glycosaminoglycans, proteoglycans, and glycoprotiens
Inorganinc matter of Matrix of osseous tissue
85% dydroxyapatite, 10% cacium carbonate, other minerals (flouride, sodium, potassium, magnesium)
Bone is a composite
combination of two basic structural materials, a combination of two basic structural materials, a cermaic and a polymer.
-combines optimal mechanical properties of each component
-bone combines the polymer, collagen, with cermic, hydroxyapatite and other
Rickets
soft bones due to deficiency of calcium salts
Osteogenesis imperfecta/ brittle bone disease
excessively brittle bones due to lack of protien, collagen
Spongy bone
-spongy like appearance
Spongy bone
slivers of bone called spicules, thin plates of bone called trabeculae, spaces filled with red bone marrow
Spongy bone
few osteons and no central canals, all osteocytes close to bone marrow
Spongy bone
gives strength with minimal weight
-trabeculae develop along bones lines of stress
Bone marrow
general term for soft tissue that occupies the marrow cavity of a long bone and small spaces amid the trabeculae of spongy bone
Red marrow (myeloid tissue)
in nearly every bone in a child, hemopoietic tissue, in adults, found in skull, vertebrae, ribs, sternum, part of pelvic griddle, and proximal heads of humerus and femur
Yellow Marrow
-most red marrow turns into fatty yellow marrow
-no longer produces blood
-found in older adults and infants
Ossification or osteogenesis
the formation of bone
fetus and infant bone
intramembraneous ossification, endochondral ossification
Intramembranous ossification steps
1. condensation of mesenchyme into soft sheet permeated with blood capillaries
2. depostion of osteiod tissue by osteoblasts on mesenchymal surface; entrapement of first osteocytes; formation of periosteum
3. honeycomb of bony trabeculae formed by continu
Endochondral Ossification steps
1. Early cartilage model
2. Formation of primary ossification center, bony collar, and perioseteum.
3. Vascular invasion, formulation of primary marrow cavity, appearance of secondary ossification center
4. Bone at birth, with enlarged cavity and appearan
Intramembranous Ossification
produces the flat bones of the skull and ,most of the clavicle. Such bones develop within a fibrous sheet similar to the dermis of the skin. aka dermal bones
Endochondral Ossification
a process in which bone is preceded by hyaline cartilage "model" that becomes replaced by osseous tissue. Begins in
Wolff's law of bone
architecture of bone determined by mechanical stresses placed on it and bones adapt to withstand those stresses
-Remodeling is a collaborative and precise action of osteoblasts and osteoclasts
-Bony processes grow larger in response to mechanical stress
Calcium Homeostasis
-Calcium and phosphate are used for much more than bone structure
-Phosphate is a component of DNA, RNA, ATP, phospholipids, and pH buffers
-Calcium needed in neuron communication, muscle contraction, blood clotting, and exocytosis
-Minerals are deposited
Hypocalcemia
Calcium deficiency
Hypocalcemia
causes:
Vitamin D deficiency
Diarrhea
Thyroid tumors
Underactive parathyroids
Pregnancy and lactation
Accidental removal of parathyroid glands during thyroid surgery
Calcium Homeostasis Hormones
Calcitriol, calcitonin, and parathyroid hormone
Calcitrol
a form of vitamin D produced by the sequential action of the skin, liver, and kidneys
Calcitrol
produced by
-Epidermal keratinocytes use UV radiation to convert a steroid, 7-dehydrocholesterol to previtamin D3
-Liver adds a hydroxyl group converting it to calcidiol
-Kidneys add another hydroxyl group, converting that to calcitriol
(most active form
Calcitrol
effects
Calcitriol behaves as a hormone that raises blood calcium concentration
-Increases calcium absorption by small intestine
-Increases calcium resorption from the skeleton
-Promotes kidney reabsorption of calcium ions, so less lost in urine
-Necessar
Rickets
abnormal softness in bones in children without adequate vitamin D
Osteomalcia
abnormal softness in bones in adults without adequate vitamin D
Calcitonin
secreted by C cells (clear cells) of the thyroid gland when calcium concentration rises too high
Calcitonin
Lowers blood calcium concentration in two ways
-Osteoclast inhibition
Reduces osteoclast activity as much as 70%
Less calcium liberated from bones
-Osteoblast stimulation
Increases the number and activity of osteoblasts
Deposits calcium into the skeleton
Parathyroid Hormone (PTH)
secreted by the parathyroid glands which adhere to the posterior surface of thyroid gland
stress fracture
break caused by abnormal trauma to a bone
Pathalogical Fracture
break in a bone weakened by some other disease
ex bone cancer, osteoporosis
Fractures classified by structural characteristics
-direction of fraction line
-break in skin
-multiple pieces
Fracture repair process
1.formation of hematoma and granulation tissue
2.Soft callus formation. Deposition of collagen and fibrocartilage converts granulation tissue to a soft callus.
3.Hard callus formation Osteoblasts deposit a temporary
bony collar around the fracture to unit
Hypocalcemia
-causes excessive excitability of the nervous system and leads to muscle tremors, spasms, or tetany
tetany
the inability of the muscle to relax
Hypercalcemia
causes depression of the nervous system, emotional disturbances, muscle weakness, sluggish reflexes, and sometimes cardiac arrest.
insterstitial growth
growth in height for children and adolescents
Cartilage growth from within, by multipilcation of chondrocytes and deposition of new matrix in the interior.
dwarfism is a result of lack of interstitial growth in childhood and adolescence
appositional growth
bone growth in adulthood.
Growth by forming new layers on the surface of pre-existing layers; process of increasing in thickness rather than length.
In bones, this method of growth is accomplished by the addition of newly formed cartilage on the surface o
parathyroid function
removes phosphate, promotes calcium absorption, inhibits collagen, raising effects of calciferol
nondisplaced fracture
is one in which the bone pieces remain in proper anatomical alignment
displaced fracture
at least one piece is shifted out of alignment with the other
comminuted fracture
bone is broken into thre or more pieces
greenstick fracture
the bone is incompletely broken on one side but the other side is bent