Exam 2: Bones and Skeletal Tissue

Chapter 6a

Characteristics of skeletal cartilages?

-no blood vessels (avascular, 80% water)

-no nerves

-perichondrium: dense (irregular) connective tissue girdle= contains blood vessels for nutrient delivery to cartilage

What are hyaline cartilages?

-most abundant type

-provide support, flexibility, and resilence

-found in costal cartilage, nose, and knee joints

What are elastic cartilages?

-similar to hyaline cartilages, but contain elastic fibers

-found in epiglottis and pinna (outer ear)

What are fibrocartilages?

collagen fibers providing great tensile strength

-absorbs compressive shock

-in vertebral discs and pubic symphysis

Types of cartilage growth?

-appositional (to apply)

-interstitial (in between)

-calcification of cartilage

What is appositional growth?

cells secrete matrix against the external face of existing cartilage

What is interstitial growth?

chondrocytes divide and secrete new matrix, expanding cartilage from within

When does calcification of cartilage occur?

-during normal bone growth

-during old age

-But it’s NOT BONE!!!

Two main groups for bones of the skeleton?

-axial skeleton (skull, vertebral column, rib cage): protects and supports

-appendicular skeleton (appendages, limbs, hips, and shoulder bones)

What are the classifications of bones by shape?

-long bones

-short bones

-flat bones

-irregular bones

What are long bones?

-longer than they are wide

-all limb bones (except the few short bones)

What are short bones?

-cube shaped bones in wrist and ankle

-sesamoid bones (within tendons, like patella): these bones reduce friction

What are flat bones?

-thin, flat, slightly curved

-found in sternum, scapulae, ribs, most skull bones

What are irregular bones?

-complicated shapes fit no other category

-found in vertebrae, hip bones, etc.

Functions of bones?

-support: for body and soft organs

-protection: for brain, spinal cord, and vital organs

-movement (anchorage of muscles): levers for muscle action

-storage: minerals (calcium and phosphorus) and growth factors (metabolism)

-blood cell formation (hematopoiesis): in marrow cavities

-triglyceride (energy) storage: in bone cavities

-Hormone production: osteocalcin (regulates insulin, secretion, glucose, homeostasis, and energy expenditure)

What are bone markings?

-bulges, depressions, and holes

-sites of attachment for muscles, ligaments, and tendons

-joint surfaces

-conduits for blood vessels and nerves

Bone marking projections that are sites of muscle and ligament attachment?

-tuberosity: rounded projection (ischial of hip bones)

-crest: narrow, prominent ridge (illiac crest)

-trochanter: large, blunt, irregular surface

-line: narrow ridge of bone (intertrochanteric line)

-tubercle: small rounded projection (adductor tubercle on femur)

-epicondyle: raised area above a condyle (medial epicondyle dorsal to adductor tubercle)

-spine: sharp, slender projection (ischial spine, scapula)

-process: any bony prominence (spinus process on vertebrae)

Bone marking projections that help to form joints

-head: bony expansion carried on a narrow neck

-facet: smooth, nearly flat articular surface

-condyle: rounded articular projection

-ramus: armlike bar

Bone marking depressions and openings: for blood vessels and nerves?

-groove: furrow

-fissure: narrow, slitlike opening

-foramen: round or oval opening through a bone

-notch: indentation at edge of structure

What are other bone marking depressions and openings?

-meatus: canal-like passageway

-sinus: cavity within a bone: filled with air, lined with mucosae

-fossa: shallow, basinlike depression

What are the different textures of bone?

-compact bone: dense outer layer

-spongy (trabecular) bone: honeycomb of trabeculae, open spaces filled with bone marrow

What are the structures of long bone?

-diaphysis (shaft)

-epiphyses

What is diaphysis (shaft)?

-compact bone collar surrounds medullary (marrow) cavity

-medullary cavity in adults contains fat (yellow marrow)

What is epiphyses?

-expanded ends (bone ends)

-spongy bone interior (compact bone exterior)

-epiphyseal line (remnant of growth plate)

-articular (hyaline) cartilage on joint surfaces (cushion/shock absorber)

What are the different membranes of bone?

-Periosteum: around the bone

-Endosteum

What is included in the periosteum membrane?

-outer fibrous layer

-inner osteogenic layer: mostly osteogenic cells (stem cells): give rise to all bone cells except bone destroying cells

-nerve fibers, nutrient blood vessels, and lymphatic vessels enter the bone via nutrient foramina (bone marrow→ spongy bone→ compact bone)

-secured to underlying bone by perforating (Sharpey’s) fibers

What is included in the endosteum membrane?

-delicate membrane on internal surfaces of bone

-also contains osteogenic cells

What is the structure of short, irregular, and flat bones?

-periosteum-covered compact bone on the outside

-endosteum-covered spongy bone within

-spongy bone called diploe in flat bones

-bone marrow between the trabeculae

Where is red marrow, ie, hematopoietic tissue found?

-cavities in adults: trabecular cavities of the heads of the femur and humerus, trabecular cavities of the diploe of flat bones (more productive than in long bones)

-cavities in infants: medullary cavities and all spaces in spongy bone

What are the different cells of bone?

-osteogenic (osteoprogenitor) cells

-osteoblasts

-osteocytes

-osteoclasts

-bone lining cells

What are osteogenic (osteoprogenitor) cells?

stem cells in periosteum and enosteum that give rise to osteoblasts and bone lining cells

-flattened squamous, self-renewing

What are osteoblasts?

bone forming cells

secrete bone matrix

responsible for bone growth

-cube shaped when secreting, matrix is composed of collagen

What are osteocytes?

mature bone cells, maintain matrix

-spider-looking cells, “sensing” what goes on with bone and communicates with other cells on what the bone needs

What are osteoclasts?

cells that break down (resorb) bone matrix

-multinucleated

What are bone-lining cells?

found on bone surfaces not being remodeled— look like stem cells, act like osteocytes (might be involved with maintaining the matrix)

-squamous

What is included in microscopic anatomy of compact bone?

-osteon (aka Haversian system): structural unit

-perforating (Volkmann’s) canals

-lacunae

-canaliculi

What is included in Osteon (Haverian system)?

-lamellae: weight bearing (withstand torsional stress), column like matrix tubes (run parallel with bone)

-central (Haversian) canal: contains blood vessels and nerves

What are perforating (Volkmann’s) canals?

-at right angles to the central canal

-connects blood vessels and nerves of the periosteum and central canal

What are lacunae?

small cavities that contain osteocytes

What are canaliculi?

hairlike canals that connect lacunae to each other and the central canal

-contain osteocyte extensions with gap junctions

What is included in the microscopic anatomy of spongy bone?

trabeculae

• align along lines of stress

• no osteons

• contain irregularly arranged lamellae, osteocytes, and canaliculi

• capillaries in endosteum supply nutrients

What is the chemical composition of organic bone?

-osteogenic cells, osteoblasts, osteocytes, and osteoclasts

-osteoid (ground substance and collagen fibers)

What is an osteoid?

organic bone matrix secreted by osteoblasts (1/3 of matrix)

What is included in osteoid?

-ground substance: proteoglycans, glycoproteins)

-collagen fibers: provide tensile strength and flexibility, sacrificial bonds break easily on impact to dissipate energy—prevent force rising to fracture level

What is the chemical composition of inorganic bone?

-resist compressive forces

-hydroxyapatite (mineral salts)

-65% of bone by mass

-mainly calcium phosphate crystals

-responsible for hardness and resistance to compression

What happens during bone development?

-referred to as osteogenesis (ossification): bone tissue formation

-stage 1= bone formation: begins in the 2nd month of development

-stage 2= postnatal bone growth: until early adulthood (~18 in females, ~21 in males)

-stage 3= bone remodeling and repair: lifelong

What are the two types of ossification?

intramembranous and endochrondral

Intramembranous ossificaiton

-intra= within, inside

-membrane bone develops from fibrous membrane

-forms most flat bones, e.g. cranial bones and clavicle

Endochondral ossification

-endo=within, inner

-cartilage (Endochondral) bone forms by replacing hyaline cartilage

-forms most of the rest of the skeleton

Step 1 of intramembranous ossification?

ossification center appear in fibrous connective tissue membrane

-centrally located mesenchymal cells cluster and differentiate into osteoblasts → ossification center

Step 2 of intramembranous ossification?

bone matrix (Osteoid) secreted within fibrous membrane and calcifies

-osteoblasts begin to secrete osteoid—calcified in a few days

-trapped osteoblasts → osteocytes

Step 3 of intramembranous ossification?

woven bone and periosteum form

-osteoid laid down between blood vessels randomly (but usually form along lines of stress) → network of trabeculae called woven bone

-vascularized mesenchyme condenses on external surface of woven bone→ becomes periosteum

Step 4 of intramembranous ossification?

Lamellar bone replaces woven bone just deep to periosteum and red marrow appears

-trabeculae just deep to periosteum thicken—later replaced with mature lamellar bone→ compact bone plates

-spongy bone (diploe) made of distinct trabeculae persist internally, its vascular tissue becomes red marrow

What is different with endochondral ossification?

-uses hyaline cartilage models

-requires breakdown of hyaline cartilage prior to ossification

step 1: endochondral ossification?

bone collar forms around hyaline cartilage model

-osteoblasts of new periosteum secrete osteoid against hyaline cartilage

step 2: endochondral ossification?

cartilage in the center of the diaphysis calcifies and then develops cavities

-chondrocytes enlarge, signal calcification, then die when calcification cuts off nutrients→ cavities stabilized by bone collar

Step 3: endochondral ossification?

the periosteal bud invades the internal cavities and spongy bone begins to form

-bud= nutrient artery and vein, nerve, red marrow elements, osteogenic cells, osteoclasts

-osteoclasts partially erode calcified cartilage matrix, osteoblasts secrete osteoid to cover rest with bone

Step 4: endochondral ossification?

the diaphysis elongates and a medullary cavity forms as ossification continues; secondary ossification centers appear in the epiphyses in preparation for stage 5

• primary ossification center enlarges

• osteoclasts break down spongy bone → medullary cavity

• cartilaginous epiphyses: hyaline cartilage proliferates → elongation

• ossification chases cartilage formation (along length of shaft)

Step 5: endochondral ossification?

epiphyses ossify, when completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages

• secondary ossification centers appear in epiphyses near birth

• cartilage in center calcifies → cavities → periosteal bud → bone trabeculae (no medullary cavity in epiphyses)

• ossification centers: only primary in short bone, several in irregular bone

What are the two types of postnatal bone growth?

-interstitial growth: length of bones (bone growth length-wise stops during adolescence)

-appositional growth: thickness and remodeling of all bones by osteoblasts and osteoclasts on bone surfaces

How does the length of long bones grow?

The epiphyseal plate cartilage organizes into four important functional zones

-the epiphyseal plate stays relatively same thickness wise during the zones

1. resting zone: relatively inactive

2. proliferation (growth): cartilage cells undergo mitosis

3. Hypertrophic: older cartilage cells enlarge

4. calcification: matrix becomes calcified, cartilage cells die, matrix begins deteriorating

5. Ossification (osteogenic): new bone is forming, medullary cavity is growing

How are hormones regulated during bone growth?

-growth hormones stimulate epiphyseal plate activity (from internal pituitary)

-thyroid hormone modulates activity of growth hormone

-testosterone and estrogens (at puberty)

• promote adolescent growth spurts (low level estrogen)

• end growth by inducing epiphyseal plate closure (high level estrogen)

Bone deposit

5-10% of skeleton is replaced annually, spongy bone replaced faster than compact

-occurs where bone is injured or added strength is needed

-requires a diet rich in protein, vitamins C,D,A, calcium, phosphorus, magnesium, and manganese

How are sites of new matrix bone deposits revealed?

-osteoid seam: unmineralized band of matrix

-calcification front: abrupt transition zone between the osteoid seam and the older mineralized bone