A&P Chapter 6: Flashcards
contains no blood vessels or nerves, composed primarily of water, surrounded by the perichondrium that resists outward expansion and contains the blood vessels
skeletal cartilage
layer of dense connective tissue surrounding cartilage like a girdle
perichondrium
made up of chondrocytes, cells encased in small cavities (lacunae) within jelly-like extracellular matrix
cartilage
three types of cartilage
hyaline cartilage, elastic cartilage, and fibrocartilage
provides support, flexibility, and resilience, most abundant skeletal cartilage
hyaline cartilage
covers the ends of long bones
articular (hyaline)
connects the ribs to the sternum
costal (hyaline)
makes up larynx, reinforces air passages
respiratory (hyaline)
supports the nose
nasal (hyaline)
similar to hyaline cartilage, found in the external ear and the epiglottis
elastic cartilage
highly compressible yet with great tensile strength, contains thick collagen fibers (many fibers nearly in parallel to form fibrils), found in menisci of the knee, pubic symphysis, and intervertebral discs
fibrocartilage
cartilage grows in two ways
1.) appositional growth
2.) interstitial growth
cartilage-forming cells in perichondrium secrete matrix against external face of existing cartilage; new matrix laid down on surface of cartilage
appostitional growth
chondrocytes within lacunae divide and secrete new matrix, expandingcartilage from within; new matrix made with cartilage
interstitial growth
occurs during normal bone growth in youth, but can also occur in old age; hardened cartilage os not the same as bone
calcification of cartilage
there are seven important functions of bones
1.) support
2.) protection
3.) movement
4.) mineral and growth factor storage
5.) blood cell formation
6.) triglyceride (fat) storage
7.) hormone prodection
for body and soft organs
support
protect brain, spinal cord, and vital organs
protection
levers for muscle action
movement
calcium and phosphorus, and growth factors reservoir
mineral and growth factor storage
hematopoiesis occurs in red marrow cavities of certain bones
blood cell formation
used for an energy source, is stored in bone cavities
triglyceride (fat) storage
osteocalcin secreted by bones helps to regulate insulin secretion, glucose levels, and metabolism
hormone production
classification of bones
206 named bones in the human skeleton
two groups that divide based on the location
1.) axial skeleton
2.) appendicular skeleton
bones of the skull, vertebral column, and rib cage
axial skeleton
bones of the upper and lower limbs, shoulder, and hip
appendicular skeleton
four shapes of bones
1.) long bone
2.) short bone
3.) flat bone
4.) irregular bone
longer than they are wide (humerus)
long bones
cube-shaped bones of the wrist and ankle
short bones
thin, flattened, and a bit curved (sternum, ribs, scapulae, and most skull bones)
flat bones
more complex shapes (vertebrae, facial and pelvic bones)
irregular bone
small round bones formed in tendons (Patella) also considered short bones
sesamoid bones
three levels of structure
1.) gross
2.) microscopic
3.) chemical
dense outer layer on every bone that appears smooth and solid
compact bone (gross anatomy)
honeycomb of trabeculae; fills the epiphyses and is filled with red bone marrow
spongy bone (gross anatomy)
covers outside of compact bone
periosteum (gross anatomy)
covers inside portion of compact bone; for one growth, repair and remodeling, contains osteoblasts and osteoclast
endosteum (gross anatomy)
a shaft (diaphysis), bone ends (epiphyses), and membranes
structure of a long bone
ubular shaft between proximal and distal ends of long bones
diaphysis
wider section at each end of the bone
epiphysis
Between diaphysis and epiphysis is where bone growth occurs
epiphyseal plate
two types (periosteum and endosteum)
membranes
covers the outer surface of the bone; white, double-layered membrane that covers external surfaces except joints
periosteum
outer layer consisting of dense irregular connective tissue consisting of Sharpey’s fibers that secure to bone matrix
fibrous layer
inner layer abutting bone and contains primitive osteogenic stem cells that gives rise to most all bone cells
osteogenic laye
membrane lining the medullary cavity and spongy bone; for one growth, repair and remodeling, contains osteoblasts and osteoclast
endosteum
found within trabecular cavities of spongy bone and diploë of flat bones, such as sternum
red marrow
sites of attachment for muscles, ligaments, and tendons, Joint surfaces, Foramen (hole) conduits for blood vessels and nerves
bone markings
three types of bone markings
projection, depression, and opening
outward bulge of bone; may be due to increased stress from muscle pull or is a modification for joints
projection
bowl- or groove-like cut-out that can serve as passageways for vessels and nerves, or plays a role in joints
depression
hole or canal in bone that serves as passageways for blood vessels and nerves
openings
five major cells types
1.) osteogenic cells
2.) osteoblast
3.) osteocytes
4.) bone-lining cells
5.) osteoclasts
mitotically active stem cells in periosteum and endosteum; also called osteoprogenitor cells
osteogenic cells
bone-forming cells that secrete unmineralized bone matrix called osteoid; are actively mitotic
osteoblast
mature bone cells in lacunae that no longer divide; maintain bone matrix and act as stress or strain sensors
osteocytes
flat cells on bone surfaces believed to also help maintain matrix (along with osteocytes)
bone-lining cells
on external bone surface, lining cells
periosteal cells (bone-lining cells)
on internal surfaces
endosteal cells (bone-lining cells)
derived from same hematopoietic stem cells that become macrophages; giant, multinucleate cells function in bone resorption (breakdown of bone)
osteoclasts
also called lamellar bone
compact bone
compact bone consists of
- Osteon (Haversian system)
▪ Canals and canaliculi
▪ Interstitial and circumferential lamellae
the structural unit of compact bone
osteon (haversian system)
an osteon cylinder consists of several rings of bone matrix
lamellae
central channel containing blood vessels and nerves
Haversian canal (central canal)
channels lying at right angles to the central canal, bringing blood and nerve supply from the periosteum in to said central canal
Perforating (Volkmann’s) canals
small cavities that contain osteocytes
lacunae
hairlike canals that connect lacunae to each other and to central canal
canaliculi
some fill gaps between forming osteons; others are remnants of osteons cut by bone remodeling; not part of osteon
Interstitial lamellae
just deep to periosteum, but superficial to endosteum, these layers of lamellae extend around entire surface of diaphysis; help long bone to resist twisting
Circumferential lamellae
appears poorly organized but is actually organized along lines of stress to help bone resist any stress
spongy bone
Organic components
osteogenic cells, osteoblasts, osteocytes, bone-lining cells,
osteoclasts, and osteoid
makes up one-third of organic bone matrix, is secreted by
osteoblasts
osteoid
Inorganic components
Hydroxyapatites (mineral salts)
makeup 65% of bone by mass, consist mainly of tiny calcium phosphate crystals in and around collagen fibers, responsible for hardness and resistance to compression
Hydroxyapatites (mineral salts)
the process of bone tissue formation; bone remodeling and repair are lifelong
Ossification (osteogenesis)
up to about week 8, fibrous membranes and hyaline cartilage of fetal skeleton are
replaced with bone tissue
formation of the body skeleton
bone forms by replacing hyaline cartilage, bones are called cartilage (endochondral) bones, form most of skeleton
endochondral ossification
bone develops from fibrous membrane, bones are called membrane bones
intramembranous ossification
5 Stages of Endochondral Ossification
- Formation of bone collar
- Cavitation of the hyaline cartilage
- Invasion of internal cavities by the periosteal bud, and spongy bone formation
- Formation of the medullary cavity; appearance of secondary ossification centers in the epiphyses
- Ossification of the epiphyses, with hyaline cartilage remaining only in the epiphyseal plates
Four major steps are involved
- Ossification centers are formed when mesenchymal cells cluster and become osteoblasts
- Osteoid is secreted, then calcified
- Woven bone is formed when osteoid is laid down around blood vessels, resulting in trabeculae
- Lamellar bone replaces woven bone, and red marrow appears
increase in length, cartilage continually grows and is replaced by bone
Interstitial Growth
increased thickness and remodeling of all bones by osteoblasts and osteoclasts on bone surfaces, specifically the periosteum and endosteum
Appositional Growth
Epiphyseal plate consists of five zones
- Resting (quiescent) zone
- Proliferation (growth) zone
- Hypertrophic zone
- Calcification zone
- Ossification (osteogenic) zone
area of cartilage on epiphyseal side of epiphyseal plate that is relatively inactive
resting (quiescent) zone
area of cartilage on diaphysis side of epiphyseal plate that is rapidly dividing; new cells formed move upward, pushing epiphysis away from diaphysis, causing lengthening
proliferation (growth) zone
area with older chondrocytes closer to diaphysis; cartilage lacunae enlarge and erode, forming interconnecting spaces
hypertrophic zone
surrounding cartilage matrix calcifies; chondrocytes die and deteriorate
calcification zone
chondrocyte deterioration leaves long spicules of calcified cartilage at
epiphysis-diaphysis junction; Ultimately replaced with spongy bone
ossification zone
closure occurs when epiphysis and diaphysis fuse
epiphyseal plate
growing bones widen as they lengthen through
appositional growth
beneath periosteum secrete bone matrix on external bone
osteoblasts
remove bone on endosteal surface
osteoclasts
most important hormone in stimulating epiphyseal plate activity
in infancy and childhood
growth hormone
modulates activity of growth hormone, ensuring proper
proportions
thyroid hormone
consists of both bone deposit and bone resorption
bone remodeling
packets of adjacent osteoblasts and osteoclasts coordinate
remodeling process
remodeling units
function of osteoclasts
resorption
accomplished by osteoclasts
bone resorption
accomplished by osteoclast
bone deposition
Negative feedback loop that controls blood 𝐶𝑎2+ levels
hormonal controls (control of remodeling)
produced by parathyroid glands in response to low blood calcium levels
parathyroid hormone (PTH)
produced by parafollicular cells of thyroid gland in response to high
levels of blood calcium levels
calcitonin
low levels of calcium cause hyperexcitablility
hypocalcemia
high levels of calcium cause nonresponsiveness
hypercalcemia
a bone grows or remodels in response to forces or demands placed upon it
Wolff’s law (Response to mechanical stress)
Observations supporting Wolff’s law
- Handedness (right or left handed) results in bone of one upper limb being thicker and stronged
- Curved bones are thickest where they are most likely to buckle
- Trabeculae form along lines of stress
- Large, bony projections occur where heavy, active muscles attac
causes remodeling by producing electrical signals when bone
is deformed
mechanical stress
are breaks
fractures
Position of bone ends after fracture
- Nondisplaced: ends retain normal position
▪ Displaced: ends are out of normal alignment
Completeness of break
- Complete: broken all the way through
▪ Incomplete: not broken all the way through
Whether skin is penetrated
- Open (compound): skin is penetrated
▪ Closed (simple): skin is not penetrated
cast or traction is needed for healing
Immobilization
Repair involves four major stages
- Hematoma formation
- Fibrocartilaginous callus formation
- Bony callus formation
- Bone remodeling
torn blood vessels hemorrhage, forming mass of clotted blood; site is swollen, painful, and inflamed
hematoma formation
capillaries grow into hematoma, phagocytic cells clear debris
fibrocartilaginous callus formation
within one week, new trabeculae appear in fibrocartilaginous callus
bony callus formation
begins during bony callus formation and continues for several months; excess material on diaphysis exterior and within medullary cavity is removed
bone remodeling
Three major bone diseases
- Osteomalacia and rickets
– Osteoporosis
– Paget’s disease
bones are poorly mineralized, results in soft, weak bones, pain upon bearing weight
osteomalacia
results in bowed legs and other bone deformities because bones ends are enlarged and abnormally long
rickets
a group of diseases in which bone resorption exceeds deposit
osteoporosis
Risk factors for osteoporosis
- most often aged, postmenopausal women (affects 30% of women aged 60–70 years and 70% by age 80)
- men are less prone due to protection by the effects of testosterone
Treating osteoporosis
- Calcium
▪ Vitamin D supplements
▪ Weight-bearing exercise
▪ Hormone replacement therapy
decrease osteoclast activity and number, partially reverse osteoporosis in spine
bisphosphonates
monoclonal antibody shown to reduce fractures in men with prostate cancer; improves bone density in elderly
denosumab
Preventing osteoporosis
- Plenty of calcium in diet in early adulthood
– Reduce consumption of carbonated beverages and alcohol
– Plenty of weight-bearing exercise
excessive and haphazard bone deposit and resorption cause bone to grow fast and develop poorly
Paget’s Disease
- Embryonic skeleton ossifies predictably, so fetal age is easily determined from X rays or sonograms
- Most long bones begin ossifying by 8 weeks, with primary ossification centers developed by week 12
Developmental Aspects of Bone
Birth to Young Adulthood
- At birth, most long bones ossified, except at epiphyses
- Epiphyseal plates persist through childhood and adolescence
- At ~ age 25, all bones are completely ossified, and skeletal growth ceases