Chapter 6
Steps in fracture repair
1. Fracture hematoma formation -Large clot closes injured vessels -Develops within several hours 2.Callus formation -Internal callus -Network of spongy bone -Unites inner edges of fracture -External callus -Composed of cartilage and bone -Stabilizes outer edges of fracture 3.Spongy bone formation -Cartilage of external callus replaced by spongy bone -Bone fragments and dead bone are removed and replaced -Ends of fracture held firmly in place 4.Compact bone formation -Spongy bone replaced by compact bone -Remodeling over time eliminates evidence of fracture
Steps of intramembranous ossification
1. Mesenchymal cells cluster -Differentiate into osteoblasts -Secrete osteoid matrix -Osteoid matrix becomes mineralized -Forms bone matrix Location in tissue where ossification begins is ossification center 2.Bone grows out in small struts (spicules) -Osteoblasts become trapped in pockets and mature into osteocytes -Mesenchymal cells produce more osteoblasts 3.Blood vessels enter area -Bone spicules meet and fuse -Blood vessels trapped in developing bone 4. Continued deposition of bone by osteoblasts close to blood vessel -Results in spongy bone with interwoven blood vessels 5. Remodeling around blood vessels produces osteons of compact bone -Connective tissue around bone organizes into fibrous layer of the periosteum -Osteoblasts near bone surface remain as cellular layer of periosteum
Steps in endochondral ossification
1.Cartilage model enlarges -Chondrocytes near center of shaft enlarge -Enlarged chondrocytes die and disintegrate -Disintegration leaves cavities within cartilage 2.Blood vessels grow around the edge of the cartilage model -Cells of perichondrium convert to osteoblasts -Osteoblasts form superficial layer of bone along the shaft 3.Blood vessels penetrate cartilage and enter central region -Entering fibroblasts differentiate into osteoblasts -Begin spongy bone production at primary ossification center -Bone formation spreads along the shaft toward both ends 4.Growth continues along with remodeling -Medullary cavity created -Osseous tissue of the shaft thickens -Cartilage near the epiphyses is replaced by shafts of bone -Bone grows in length and diameter 5. Capillaries and osteoblasts migrate into the epiphyses -Create secondary ossification centers 6.Epiphyses fill with spongy bone -Articular cartilage remains exposed to joint cavity -Epiphyseal cartilage (epiphyseal plate) separates epiphysis from diaphysis 7.Bone grows in length at the epiphyseal cartilage -Chondrocytes actively produce more cartilage on epiphyseal side -Osteoblasts actively replace cartilage with bone on diaphyseal side -Epiphyses are pushed away by continued production of new cartilage
Six categories of bone based on shape
1.Flat bones 2.Sutural bones 3.Long bones 4.Irregular bones 5.Sesamoid bones 6.Short bones
Bones that break easily
A tumor of the parathyroid glands that secretes too much PTH will result in which of the following?
it is an incomplete cellular layer that lines the medullary cavity
All the following are characteristics of periosteum EXCEPT __________.
PTH stimulation of osteoclasts
All the following result in decreased calcium levels in the bloodstream EXCEPT __________.
Bone markings
Also known as surface features Related to particular functions Elevations/projections -Muscle, tendon, and ligament attachment -At joints where adjacent bones articulate Depressions/grooves/tunnels -Sites for blood vessels or nerves to lie alongside or penetrate bone
Pott's fractures
Ankle fractures that affect both bones of the leg are called __________.
Calcium and the skeleton
As a calcium reserve, skeleton has primary role in calcium homeostasis Has direct effect on shape and strength of bones -Release of calcium into blood weakens bones -Deposition of calcium salts strengthens bones
osteoblasts begin producing bone faster than chondrocytes are producing new epiphyseal cartilage
At puberty, __________.
Bone growth
At puberty, hormones stimulate increased bone growth, and epiphyseal cartilage is replaced -Osteoblasts produce bone faster than chondrocytes produce cartilage -Epiphyseal cartilage narrows until it disappears -Process called epiphyseal closure -Leaves epiphyseal line in adults
16 weeks
At which point during embryonic development can most of the bones of the adult skeleton be identified?
Intramembranous ossification in development
Begins during the eighth week of embryonic development Can see ossification centers and progressing bone formation at 10 weeks At 16 weeks, most of the bones of the adult skeleton can be identified
Intramembranous ossification
Begins when mesenchymal (stem) cells differentiate into osteoblasts within embryonic or fibrous connective tissue Normally occurs in deeper layers of dermis Bones called dermal bones or membrane bones Examples: roofing bones of skull, lower jaw, collarbone, sesamoid bones (patella)
Axial skeleton (80 bones)
Bones of skull, thorax, and vertebral column Form longitudinal axis of body
Appendicular skeleton (126 bones)
Bones of the limbs and girdles that attach them to the axial skeleton Associated cartilages Ligaments and other connective tissues
calcitonin
C cells of the thyroid gland secrete which of the following?
Factors that decrease blood calcium levels
Calcitonin Secreted from C cells in the thyroid gland Responses -In bones: -Osteoclast activity inhibited; calcium deposited in bone matrix -In intestines: -Calcium absorption decreased with decreasing PTH and calcitriol -In kidneys: -Inhibits calcitriol release and calcium reabsorption
General categories of fractures
Closed or simple -Completely internal (no break in skin) -Only seen on x-rays Open or compound -Project through the skin -More dangerous due to: -Infection -Uncontrolled bleeding
Bone matrix
Collagen fibers account for ~1/3 bone weight -Provide flexibility Calcium phosphate (Ca3(PO4)2) accounts for ~2/3 bone weight -Interacts with calcium hydroxide (Ca(OH)2) to form crystals of hydroxyapatite (Ca10(PO4)6(OH)2) salts -Incorporates other salts (calcium carbonate, CaCO3) and ions (Na+, Mg2+, F-) -Provides strength
Irregular bones
Complex shapes with short, flat, notched, or ridged surfaces Examples: vertebrae, bones of pelvis, facial bones
Diaphysis
Contains medullary cavity (marrow cavity) -Filled with two types of marrow -Red bone marrow (involved in red blood cell production) -Yellow bone marrow (adipose tissue; important as energy reserve)
Maintaining calcium levels
Controlled by activities of: -Intestines -Absorb calcium and phosphate under hormonal control Bones -Osteoclasts erode matrix and release calcium -Osteoblasts use calcium to deposit new matrix Kidneys -Varying levels of calcium and phosphate loss in urine under hormonal control
Articular cartilage
Covers portions of epiphysis that form articulations
Fracture
Crack or break due to extreme mechanical stress Most heal as long as blood supply and cellular parts of periosteum and endosteum survive Repair involves four steps
Appositional growth in bones
Deeper lamellae recycled and replaced by osteons Osteoclasts remove matrix at inner surface to enlarge medullary cavity
Gigantism
Disorder causing lengthened bones Overproduction of growth hormone before puberty Can reach heights of over 2.7 m (8 ft. 11 in.) Puberty often delayed Most common cause is a pituitary tumor Treated by surgery, radiation, or medications suppressing growth hormone release
fibrodysplasia ossificans progressiva (FOP)
Ectopic bones may occur in which of the following conditions?
Diaphysis (shaft)
Elongated body of a long bone
Achondroplasia
Epiphyseal cartilage of long bones grows slowly -Replaced by bone early in life Short, stocky limbs result Trunk is normal size No effects on sexual or mental development
Head
Expanded proximal end of a bone that forms part of a joint
Compact bone
Functional unit is osteon (Haversian system) -Organized concentric lamellae around a central canal -Osteocytes (in lacunae) lie between lamellae -Central canal contains small blood vessels
Compact bone
Functional unit is osteon (Haversian system) (continued) -Canaliculi connect lacunae with each other and central canal -Strong along its length
Fibrodysplasia ossificans progressiva (FOP)
Gene mutation that causes bone deposition around skeletal muscles Bones develop in unusual places -Called heterotopic (hetero, place) or ectopic (ektos, outside) bones No effective treatment
Periosteum has a fibrous outer layer.
How does periosteum differ from endosteum?
Bone surface within joint cavities
In which of the following areas would a periosteum be absent?
Pituitary growth failure
Inadequate growth hormone production Reduced epiphyseal cartilage activity; abnormally short bones Rare in United States due to treatment with synthetic growth hormone
Endosteum
Incomplete cellular layer lining medullary cavity Active during bone growth, repair, remodeling Covers spongy bone and lines central canals Where layer is incomplete, exposed matrix is remodeled by osteoclasts and osteoblasts -Osteoclasts in shallow depressions called osteoclastic crypts (Howship's lacunae)
Appositional growth in bones
Increases bone diameter of existing bones Osteogenic cells differentiate into osteoblasts that add bone matrix under periosteum -Adds successive layers of circumferential lamellae -Trapped osteoblasts become osteocytes
Congenital talipes equinovarus (clubfoot)
Inherited developmental abnormality -Affects 2 in 1000 births -Boys roughly twice as often as girls May affect one or both feet Abnormal muscle development distorts growing bones -Feet turn medially and are inverted Treated with casts or supports
Marfan syndrome
Inherited metabolic condition Excessive cartilage formation at epiphyseal cartilages Results in very tall person with long, slender limbs Affects other connective tissues throughout the body -Commonly causes cardiovascular problems
Endochondral ossification
Initial skeleton of embryo formed of hyaline cartilage Cartilage gradually replaced by bone through endochondral (endo-, inside + chondros, cartilage) ossification -Uses cartilage as small model -Bone grows in diameter and length -Diameter growth involves appositional bone deposition
Minerals
Inorganic ions contributing to the osmotic balance of body fluids Vital in many physiological processes
Sutural bones (Wormian bones)
Irregular bones formed between cranial bones Number, size, and shape vary
Spongy bone
Lamellae form struts and plates (trabeculae) creating an open network -No blood vessels in matrix -Nutrients reach osteons through canaliculi open to trabeculae surfaces Red bone marrow is found between trabeculae
Disorders causing lengthened bones
Marfan syndrome
Osteocytes
Mature bone cells that cannot divide Maintain protein and mineral content of surrounding matrix Occupy lacunae (pockets) -Separated by layers of matrix (lamellae) -Interconnected by canaliculi
Osteogenic cells
Mesenchymal (stem) cells that produce cells that differentiate into osteoblasts -Important in fracture repair -Locations -Inner lining of periosteum -Lining endosteum in medullary cavity -Lining passageways containing blood vessels
The importance of calcium
Most abundant mineral in body 1-2 kg (2.2-4.4 lb) ~99 percent deposited in skeleton Variety of physiological functions (muscle contraction, blood coagulation, nerve impulse generation) -Concentration variation greater than 30-35 percent affects neuron and muscle function -Normal daily fluctuations are <10 percent
Neck
Narrow connection between the head and diaphysis of a bone
divide to produce daughter cells that differentiate into osteoclasts
Osteoprogenitor cells are characterized by the following EXCEPT __________.
Acromegaly
Overproduction of growth hormone after epiphyseal plates close Bones get thicker, not longer -Especially those in face, jaw, and hands Alterations in soft-tissue structure changes physical features
Factors that increase blood calcium levels
Parathyroid hormone (PTH) -Secreted from parathyroid glands -Responses -In bones: -Osteoclasts stimulated to erode matrix, releasing stored calcium -In intestines: -Calcitriol effects enhanced and calcium absorption increased -In kidneys: -Increased release of hormone calcitriol, stimulating calcium reabsorption in kidneys
osteoblasts
Parathyroid hormone binds to receptors on _____ causing the release of another hormone called RANKL.
Long bone organization
Periosteum—outermost layer Compact bone—outer bone tissue layer -Circumferential lamellae (circum-, around + ferre, to bear) at outer and inner surfaces -Interstitial lamellae fill spaces between osteons -Osteons -Connected by perforating canals (perpendicular to surface) Spongy bone—innermost layer
Disorders causing shortened bones
Pituitary growth failure Achondroplasia
Osteoblasts
Produce new bony matrix (osteogenesis or ossification) -Produces unmineralized matrix (osteoid) -Then assists in depositing calcium salts to convert osteoid to bone Become osteocytes once surrounded by bony matrix
Long bones
Relatively long and slender Examples: various bones of the limbs
Osteoclasts
Remove and remodel bone matrix Release acids and proteolytic enzymes to dissolve matrix and release stored minerals -Process called osteolysis (lysis, loosening)
Short bones
Small and boxy Examples: bones of the wrist (carpals) and ankles (tarsals)
Sesamoid bones
Small, flat, and somewhat shaped like sesame seed Develop inside tendons of knee, hands, and feet Individual variation in location and number
Blood supply and innervation of the periosteum
Smaller blood vessels supply superficial osteons Lymphatic vessels collect lymph from bone and osteons Sensory nerves innervate diaphysis, medullary cavity, and epiphyses
Flat bones
Thin, roughly parallel surfaces Examples: cranial bones, sternum, ribs, scapulae Protect underlying soft tissues Provide surface area for skeletal muscle attachment
circumferential lamellae
To form perforating fibers, osteoblasts from the cellular layer of the periosteum cement collagen fibers from tendons, ligaments, and joint capsules into which structures?
Specific types of fractures
Transverse fractures -Break shaft across long axis Spiral fractures -Produced by twisting stresses -Spread along length of bone Displaced fractures -Produce new and abnormal bone arrangements -Nondisplaced fractures retain normal alignment Compression fractures -Occur in vertebrae subjected to extreme stresses -Often associated with osteoporosis Greenstick fractures -One side of shaft broken, one side bent -Generally occurs in children -Long bones have yet to fully ossify Comminuted fractures -Shatter affected area producing fragments Epiphyseal fractures -Occur where bone matrix is calcifying -A clean transverse fracture of this type heals well -If not monitored, breaks between epiphyseal plate and cartilage can stop growth at site Pott's (bimalleolar) fracture -Occurs at ankle and affects both medial malleolus and lateral malleolus Colles fracture -Break in distal radius
Growth and maintenance require extensive blood supply
Vascular features -Nutrient artery and nutrient vein (commonly one of each per bone) -Nutrient foramen (tunnel providing access to marrow cavity) -Metaphyseal artery and metaphyseal vein -Carry blood to/from metaphysis -Connect to epiphyseal arteries/veins
Sesamoid
What category of bone is most commonly located in tendons near joints of the hands and knees?
genetic mutation that affects the structure of connective tissue throughout the body
What characteristic may cause life-threatening issues in individuals with Marfan syndrome?
Bone is deposited by superficial osteoblasts.
What is responsible for appositional growth?
Phosphate
What major anion binds with calcium in bones?
Feet
What part of the body is involved with the disorder of congenital talipes equinovarus?
synovial fluid
What supplies the articular cartilage of long bones with oxygen and nutrients?
Diaphysis
What term refers to the shaft of a long bone?
Chondrocytes
What type of cells are found within the epiphyseal plate?
Within the dermis
Where does intramembranous ossification usually occur?
Deep to the periosteum
Where will appositional growth occur?
Between flat bones of the skull
Where would you find sutural bones?
femur
Which bone is NOT formed via intramembranous ossification?
Heads
Which bone markings are found on the proximal epiphyses of both the humerus and femur?
Marfan syndrome
Which condition, due to excessive cartilage formation at the epiphyseal cartilages, results in individuals who are very tall, with long, slender limbs?
Osteoblast
Which of the following cell types produces and secretes osteoid?
fractures that are produced by twisting stresses that spread along the length of the bone
Which of the following describes spiral fractures?
Pituitary growth failure
Which of the following disorders can be treated with hormone replacement therapy?
Acromegaly
Which of the following disorders is associated with excessive secretion of growth hormone?
Achondroplasia
Which of the following disorders results in unusually short stature?
Parathyroid hormone
Which of the following hormones increases the effects of calcitriol?
Calcitonin
Which of the following hormones reduces blood calcium concentration?
Derived from osteoprogenitor cells
Which of the following is NOT associated with osteoclasts?
trochanter
Which of the following is not a surface feature of the pelvis?
Fracture hematoma formation
Which of the following occurs first in fracture repair?
Formation of medullary cavity
Which of the following occurs within a primary ossification center but NOT a secondary ossification center?
Meatus
Which of the following terms refers to a canal in a bone?
Lamella
Which of the following terms refers to layers of bone matrix?
Compound fracture
Which of the following types of fractures has the highest risk of infection?
Orient along stress lines
Which of these is associated with trabecular bone?
kidney
Which organ prevents calcium loss in response to PTH stimulation?
The epiphysis consists largely of trabecular bone.
Which statement regarding the internal structure of long bone is correct?
trochlea
Which surface feature is a smooth, grooved articular process shaped like a pulley?
compression fracture
Which type of fracture occurs in vertebrae that are subjected to extreme stresses?
The periosteum
Wraps the superficial layer of compact bone Two layers 1.Fibrous outer layer 2.Cellular inner layer Functions 1.Isolates bone from surrounding tissues 2.Route for blood and nervous supply 3.Actively participates in bone growth and repair Perforating fibers allow for strong attachment
Bones
are classified according to shape and structure and have varied bone markings
sinus
chamber within a bone, normally filled with air
Metaphysis
connects epiphysis to shaft
sulcus
deep, narrow groove
Bone markings
elevations or projections
fissure
elongated cleft or gap
Epiphysis
expanded area at each end of the bone -Consists largely of spongy bone (trabecular bone) -Outer covering of compact bone (cortical bone) -Strong, organized bone
ramus
extension of a bone that makes an angle with he rest of a structure
Intramembranous ossification
forms bone without a prior cartilage model
Canal or meatus
large passageway through a bone
Trochanter
large, rough projection
line
low ridge, more delicate than a crest
bones
play an important role as mineral reservoirs
spine
pointed or narrow process
Process
projection or bump
crest
prominent ridge
fossa
shallow depression or recession bone surface
Facet
small, flat articular surface
Tuberosity
small, rough projection that takes up a broad area
foramen
small, rounded passageway for blood vessels or nerves to pass through bone
Tubercle
small, rounded projection
Trochlea
smooth, grooved articular process shaped like a pulley
Condyle
smooth, rounded articular process
Functions of the skeletal system
support, store minerals and lipids, produce blood cells, protection, leverage