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Skeletal System 6.1-6.6 (6.2 Bone Shape and Structure (Structure…
Skeletal System 6.1-6.6
6.1 Skeletal Primary Functions
support
the bones in legs and pelvis support the trunk
the atlas (1st vertebra) supports the skull, etc
energy storage
yellow marrow in the shaft of long bones
serves as an important chemical energy reserve
Hematopoiesis (blood cell formation)
RBC's and WBC's (red marrow)
all blood cells are formed in the red marrow of certain bones
protection
ribs and pelvic bones
the skull protects the brain
the rib cage protects the heart and lungs, etc
Inorganic Salt Storage
bone stores many minerals
calcium
phosphorus
others
also a mean of calcium homeostasis
6.2 Bone Shape and Structure
long bones
consist of a shaft with two ends
thigh bone=femur
upper arm bone=humerus
short bones
cube like
wrist bones=carpals
ankle bones=tarsals
flat bones
thin and usually curved
most skull bones=cranium bones not face bones
breast bone=sternum
shoulder blades=scapula
ribs
irregular bones
not long, short, or flat
vertebrae
auditory ossicles
sesamoid bones
develop within a tendon
the patella is a human sesamoid bone
Structure
Diaphysis
shaft
consists of a central medullary cavity (filled with yellow marrow)
surrounded by a thick collar of compact bone
Epiphysis
(pl) expanded ends
consist mainly of spongy bone
surrounded by a thin layer of compact bone
Epiphyseal line
remnant of epiphyseal disk/plate
cartilage at the junction of the diaphysis and epiphyses (growth plate)
Periosteum
outer, fibrous, protective covering of diaphysis
richly supplied with blood and lymph vessels, nerves (nutrition)
nutrient foramen: perforating canal allowing blood vessels to enter and leave bone
osteogenic layer contains osteoblasts (bone-forming cells) and osteoclasts (bone destroying cells)
serves as insertion for tendons and ligaments
Endosteum
inner lining of medullary cavity
contains layer of osteoblasts and osteoclasts
Articular cartilage
pad of hyaline cartilage of the epiphyses where long bones articulate or join
"shock absorber"
parts of the flat bone
covered by periosteum-covered compact bone
surrounding endosteum-covered spongy bone
in a flat bone, the arrangement looks like a sandwich
spongy bone (meat), sandwiched between two layers on compact bone (bread)
hematopoietic tissue (red marrow) is located in the spongy bone within the epiphyses of long bones and flat bones
Chemical Composition
organic components (35%)
cells
osteoprogenitor cells
derived from mesenchyme
can undergo mitosis and become osteoblasts
osteoblasts
form bone matrix by secreting collagen
cannot undergo mitosis
osteocytes
mature bone cells derived from osteoblasts
principle bone cell
cannot undergo mitosis
maintain daily cellular activites (exchange of nutrients and wastes with blood)
osteoclasts
functions in bone resorption (destruction of bone matrix)
important in development, growth, maintenance and repair of bone
osteoid
primarily collagen which gives bone its high tensile strength
also contains glycolipids and glycoproteins
inorganic component (65%)
hydroxyapatite (minerals salts) which is primarily calcium phosphate which gives bone its hardness or ridgidity
Microscopic structure of compact bone
compact bone is solid, dense, smooth
structural unit=Haversian system or osteon
elongated cylinders cemented together to form the long axis pf a bone
components of Haversian system
osteocytes (spider shpaed bone cells that lie in "lacunae") that have laid down matrix of collagen and calcium salts in concentric lamelle (layers) around a central Haversian canal containing blood vessels and nerves
communicating canals within compact bone
canaliculi connect the lacunae of osteocytes
Volkmann's canals connect the blood and nerve supply of adjacent Haversian systems together
run at right angles to and connects adjacent Haversian canals
microscopic structure of spongy (cancellous) bone
consists of poorly organized trabeculae (small needle like pieces of bone)
with a lot of open space between them
nourished by diffusion from nearby Haversian canals
6.3 Bone Development and Growth
introduction
the "skeleton" of an embryo is composed of fibrous CT membranes (formed from mesenchyme and hyaline cartilage) that are loosely shaped like bones
this "skeleton" provides supporting structures for ossification to begin
at about 6-7 weeks gestation, ossification begins and continues throughout adulthood
ossification patterns
intramembranous ossification
when a bone forms on or withing a fibrous CT membrane
flat bones are formed in this manner ( skull bones, clavicles)
endochondral ossification
occurs when a bone is formed from a hyaline cartilage model
most bones of the skeleton are formed in this manner
primary ossification center hardens as fetus and infant
secondary ossification centers develop in child and harden during adolescence and early adulthood
6.4 Bone Remodeling and Repair
rate of remodeling values
distal femur is replaced every four months
diaphysis may not be fully replaced during one's lifetime
osteoclasts
large multinucleated cells responsible for bone resorption
secretes lysosomal enzymes that digest the organic matrix
secrete acids that decompose calcium salts into Ca++ and PO4- ions, which can then enter blood
control of bone remodeling/ calcium homeostatis
parathyroid hormone (PTH)
secreted by the parathyroid glands when blood calcium levels are low
stimulates osteoclast activity (resorption of bone occurs), which releases Ca++ into the blood
causes kidney tubules to reabsorb Ca++ back into the blood
causes intestinal mucosa to increase dietary absorption of Ca++
causes an increase in blood calcium levels (back to normal)
calcitonin
secreted by the thyroid gland when blood calcium levels are high
inhibits bone resorption, increases osteoblast activity (causes a deposition of bone matrix)
causes the kidney tubules to secrete excess Ca++ into the urine
results in a decrease in blood calcium levels (back to normal)
negative feedback loop
1.) hormone: calcitonin
2.) osteoblasts use excess Ca++ to lay down bone matrix, kidney tubules secrete excess Ca++ into urine
3.) blood Ca++ falling
4.) normal blood Ca++ homeostatis
5.) stress: blood Ca++ falling
6.) parathyroid glands
7.) parathyroid hormone
8.) osteoclasts reabsorb bone matrix, kidney tubules reabsorb Ca++ back into bloodstream, intestinal mucosa absorbs Ca++
factors affecting bone development
minerals needed for bone remodeling
calcium (component of hydroxyapatite matrix)
phosphorus (component of hydroxyapatite)
magnesium (needed for normal osteoblast activity)
boron (inhibits calcium loss)
manganese (needed for new matrix)
vitamins needed for bone growth, remodeling, and repair
vitamin D
greatly increases intestinal absorption of dietary calcium and retards its urine loss
deficiency causes rickets in children and osteomalacia in adults
vitamin C
helps maintain bone matrix (collagen synthesis)
deficiency causes scurvy
vitamin A
required for bone resorption, controls the activity, distribution and coordination of osteoblasts and osteoclasts during development
vitamin B12
may play a role in osteoblast activity
hormones needed for bone growth and remodeling
human growth hormone (hGH)
secreted by pituitary
responsible for the general growth of all tissues
stimulates reproduction of cartilage cells at epiphyseal plate
sex hormones
estrogens and androgens (testosterone)
aid osteoblast activity (promote new bone growth)
degenerate cartilage cells in epiphyseal plate (close epiphyseal plate)
estrogen effect is greater than androgen effect
thyroid hormones (T3 and T4)
T3- triiodothyronine
T4- thyroxine
stimulates replacement of cartilage by bone in epiphyseal plate
PTH and calcitonin
exercise imcreases bone growth
6.5 Aging Process
age related skeletal changes are apparent at the cellular and whole body level
height begins to decrease incrementally at around age 33
bone loss gradually exceeds bone replacement
after menopause, females lose bone more rapidly than males
by age 70, bone loss between sexes is similar
fractures increase as bone age
ostepenia
osteoporosis
severe bone loss
affects normal function
29% of women
after menopause risk go up cause less estrogen being produced
18% of men
cause of androgens are still produced
fractures
cracks or breaks in bones
caused by physical stress
open and closed
greenstick
incomplete convex surface of the bend
fissured
incomplete longitudinal break
comminuted
complete and fragments the bone
transverse
complete at right angle to the bone
oblique
complete at an angle other than right
spiral
complete caused by excessive twisting
6.6 Axial and appendicular skeleton
skeletal organization-axial
includes the bones of the skull, hyoid bone, vertebral column, and thoracic cage
skull
cranium
brain case or helmet
composed of eight bones including frontal, occipital, sphenoid, ethmoid, parietal, and temporal
frontal bone
forehead
articulates with parietal bones along coronal suture
forms superior portion of orbit
contains 2 frontal (paranasal) sinuses
parietal bone
behind frontal bone
articulations
anteriorly with frontal bones at coronal suture
posteriorly with occipital bone at lambiodal suture
laterally with temporal bones at squamous suture
between bones at sagittal suture
occipital bone
base of skull
articulates with paired parietal bones along the lambdoidal suture
foramen magnum (large hole)- opening in occipital bone where nerve fibers pass from brain into spinal cord
occipital condyles- rounded processes on either side of foramen magnum which articulate with the first vertebra (atlas)
temporal bone
lie inferior to parietal bones at squamous suture
zygomatic process- bar like extension that meets the zygomatic bone
external auditory meatus- opening in tympanic region which opens to the inner portions of the ear
styloid process- needle like extension (attachment for some neck muscles)
mastoid process- a rounded process that extends down from mastoid region of temporal bone (attachment for neck muscles)
mandibular fossa- depression where mandibular condyle articulate
sphenoid bone
butterfly shaped bone that spans the length of the cranial floor
lateral portions are wedged between many other skull bones= "keystone"
contains two sphenoid (paranasal) sinuses
sella turcica- portion of sphenoid bone which rises up and form a saddle shaped mass that houses the pituitary gland
ethmoid bone
complex shaped bone composed of two masses on either side of nasal cavity
contains two ethmoid (paranasal) sinuses
cribriform or horizontal plate connects two masses of ethmoid bone horizontally
perpendicular plate projects downward fro cribriform plate to form superior portion of nasal septum
nasal concha- delicate scroll-shaped plates that project into nasal cavity
crista galli- process that extends from horizontal plate that serves as the attachment for meninges ( membranes) that surround the brain
facial skeleton
shapes the face and provides attachment for various muscles that move the jaw and control facial expressions
maxillary bones (maxillae)
upper jaw
contains two maxillary (paranasal) sinuses
palatine bones
complete posterior portion of hard palate
cleft palate
zygomatic bones
cheek bones
temporal process projects posteriorly and articulates with the zygomatic process of temporal bone
lacrimal bones
median walls of orbit
composed of seven bones
contains lacrimal foramen for tear drainage
nasal bones
bridge of nose
vomer
inferior portion of nasal septum
the perpendicular plate of the ethmoid bone forms the superior portion of nasal septum
inferior nasal conchae
mandible
lower jaw
largest, strongest bone in the face
mandibular condyle articulates with the mandibular fossa of the temporal bone and temporomandibular joint (TMJ)
only movable bone in the skull
hyoid bone
location: in neck, between lower jaw and larynx; held in place by muscles and ligaments
function: supports tongue
infantile skull
differs from the adult skull in the following ways
fontanels: soft spots, allow "molding" of skull in birth canal
large forehead and small face
larger orbits
vertebral column
33 infantile or 26 adult irregular bones are divided into 5 regions
cervical region= 7 vertebrae (bones) in neck
atlas
axis
thoracic region= 12 vertebrae in thoracic cavity
lumbar region= 5 large vertebrae in abdominal cavity
sacrum= 5 fused vertebrae that articulate with coxal bones of pelvis
coccyx= 3-5 vertebare which make up tailbone
4 curvatures exists in the sagittal plane
primary curvatures
exist at birth
concave anteriorly
thoracic curvature is in the thoracic region
pelvic curvature is in the sacral and coccygeal regions
secondary curvatures
develop during infancy
convex anteriorly
cervical curvature is in cervical region
develops as baby starts to hold up head
lumbar curvature
develops as baby begins to stand
intervertebral disk
protective pad of fibrocartilage between individual vertebra
a slightly movable joint
a typical vertebra
body
discoid shaped anterior region
vertebral arch
posterior region
pedicle= short bony posterior projection
lamina= flattened plates that articulate posteriorly into spinosus process
vertebral foramen
opening between body and vertebral arch through which the spinal cord passes
spinosus process
midline posterior projection
transverse processes
laterally from pedicle
thoracic cage
includes the ribs, sternum, thoracic vertebrae, and costal cartilages
ribs
12 pairs
articulate anteriorly with sternum through costal (hyaline)
articulate posteriorly with thoracic vertebrae
three types
true ribs
1 more item...
false ribs
1 more item...
floating ribs
1 more item...
typical rib structure
head
superior facet
inferior facet
neck
tubercle
articular
non-articular
costal angle
costal groove
body
sternum
three parts
manubrium
3 more items...
body
2 more items...
xiphoid process
1 more item...
the skeletal system consists of 206 bones and joints
skeletal organization-appendicular
includes the limbs of the upper and lower extremities, and the bones that attach those limbs to the trunk (pectoral and pelvic girdles)