Chapter 6

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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


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