BIO chp 6 RS

Skeletal system:

Consists of Bones, cartilage, and ligaments

tightly joined to form strong, flexible framework for the body

Cartilage

the embryonic forerunner of most bones, covers many joint surfaces in the mature skeleton

(covers bones/joints ends)

Ligaments

hold bones together at the joints

(bone to bone)

Tendons

structurally similar to ligaments but attach muscles to bones

Functions of the skeleton

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• Support:

• Movement: muscles pull on bones to move

• Protection: protect organs

• Blood formation: red bone marrow produces blood cells

• Electrolyte balance: reservoir of calcium and phosphate

• Acid-base balance: pH change, absorb/release alkaline salts

• Hormone Secretion: bones secrete osteocalcin and lipocalcin 2, stim. insulin secretion, inc. insulin sensitivity, respond to stress

• Detoxification: bones absorb metals/elements, releases them more slowly for excretion

Features of a long bone

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• Compact (cortical bone)

• Spongy (cancellous) bone

• Diaphysis

• Epiphysis

• Epiphyseal plate

• Periosteum

• Nutrient foramina

• Endosteum

• Articular cartilage

Compact (corticle) bone

• dense outer shell of bone

• surrounds the medullary (marrow) cavity

  • Medullary (marrow) cavity: hollow space containing bone marrow

Songy (Cancellous) bone

loosely organized bone tissue within the ends (epiphyses) of the bone

Diaphysis

Shaft of the bone, In long bone provides leverage

Epiphysis

• expanded portion at each end

• provides strength to the joint

• increased surface area for attachment of tendons and ligaments

Epiphyseal plate

• Hyaline cartilage separating marrow cavities of epiphysis and diaphysis

• present in only children and adolescents aka growth plate

• bones grow in length here

Perosteum

• outer sheath of dense irregular connective tissue

• some of its collagen fibers penetrate into bone matrix as perforating fibers

• has tough outer fibrous layer of collagen. And a inner osteogenic layer of bone forming cells (imp. for growth & healing)

• provides strong attachment and continuity from muscle to tendon to bone

Nutrient formania

holes where blood vessels of periosteum penetrate into the bone

Endosteum

• internal surface covering

• composed of reticular connective tissue with cells that deposit osseous tissue and others that dissolve it

Articular cartilage

• hyaline cartilage at the ends of most adjoining bones.

• enables it to move more easily, with aid of synovial fluid

Osteoclasts

• type of bone cell

• bone dissolving macrophages

• In endosteum and osteogenic layer of periosteum

Osteoclasts job

• osteolysis: bone breakdown actions of osteoclasts (pathological/disease causing)

• Resorption: breakdown of bone by osteoclasts (normal process)

Osteoclasts Looks

• Large cells

• formed by fusion of many stem cells

• multinucleated

• ruffle boarder

What do osteoclasts secrete onto the bone surface

hydrochloric acid (HCI)

What does hydrochloric acid (HCI) do

dissolves minerals of bone matrix

Lysosomal enzymes in Osteoclasts………

digest proteins; digest organic components of bone matrix

Matrix of osseous tissue

• stony material surrounding osteocytes and lacunae

• gives bone flexibility and strength

• 1/3 organic

• 2/3 inorganic

Organic components

• Primary collagen (strong)

• Also, glycosaminoglycans, proteoglycans, and glyocoproteins

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Inorganic components

• primarily hydroxyapatite (calcium phosphate salt)

• Also, calcium carbonate and small amounts of other minerals

In each lamella, the collagen fibers “______“ down the matrix in a……..

• “corkscrew”

• helical petter like the threads of a screw

How is the bone stronger and able to resist tenson in multiple directions

The helices coil in one direction in one lamella and in the opposite direction in the next lamella

Bone resist tension (bending) helix is…

loosely coiled like threads on a wood screw

In weight bearing areas helix is…..

more tightly coiled like they the closely spaced threads on a bolt, and the fibers are more nearly transverse

Primary features of spongy bone

• Lattice of silvers of bone called spicules (rods/spines) and trabeculae (thin plates and beams)

• Porous appearance; spaces filled with bone marrow

• Matrix contains lamellae, but not in concentric layers and no osteons

  • Trabeculae arranged along bones lines of stress

Does spongy bone or compact bone have more surface area exposed to osteoclast action

Spongy bone

Most osteolysis therefore involves the spongy bone, and from a pathological standpoint, so does osteoporosis

true

INTRAMEMBRANOUS OSSIFICATION

Produces flat bones of skull, part of mandible and most of clavicle

Stages of Intramembranous ossifcation

• Mesenchyme condenses into sheet of tissue permeated by blood vessels; mesenchymal cells become osteoblasts that secrete osteoid tissue (prebone)

• Minerals (primarily calcium phosphate) crystalize on collagen of osteoid; osteoblasts promote this mineralization and become trapped in the matrix to become osteocytes

• Spongy bone becomes a honeycomb of trabeculae; mesenchyme adjacent to developing bone condenses to form fibrous periosteum on each surface

• Osteoblasts beneath periosteum create zones of compact bone on each side of spongy bone

Many bones have _____ shapes with ______ centers of ossification

complex, multiple

Steps of endochondral ossification in a simple bone, a metacarpal bone:

• mesenchyme develops into hyaline cartilage covered with perichondrium; perichondrium produces chondrocytes, and cartilage model grows

• Primary ossification center forms; chondrocytes enlarge, die and walls calcify; osteoblasts deposit bone collar and perichondrium is a periosteum

• Blood vessels invade ossification center; osteoclasts create primary marrow cavity; metaphysis (cartilage to bone) present at each end and secondary ossification center forms

• secondary marrow cavity forms at end of bone

• infancy and childhood: epiphyses fill with spongy bone, cartilage limited to articular cartilage and epiphyseal plate

• Epiphyseal plate persists until adulthood and serves as growth plate

• By late teens to early twenties, cartilage within epiphyseal plate is consumed and bones grow no longer

Metaphysis

• growth zone at the junction between the diaphysis and epiphysis of along bone

• cartilage is replaced by osseous tissue and bone grows in length

Bone resorption primarily stimulated by one hormone

• Parathyroid hormone

Parathyroid hormone

• causes osteoblasts to release osteoclast-stimulating factor that stimulates osteoclasts to resorb bone

• Prim purpose is to maintain appropriate level of blood calcium

Aging skeletal system - changes with age

• Loss of bone mass, strength

• After age 35-40 osteoblasts become less active, creates imbalance between bone deposition and resorption

• Osteopenia and osteoporosis

After age 40 women lose _____ of their bone mass per decade and men lose about ____.

8%,3%

Bone loss from jaws is a contributing factor in …..

tooth loss

With age bones become more _____ as ______ synthesize less protein. Fractures occure more ___ and heal more ____.

brittle, osteoblasts, easily, slowly

Arthiritis

family of joint disorders associated with aging

Osteopenia

net loss of boneO

steoporosis

loss of bone is severe enough to compromise physical activity and health

Stress fracture

break caused by abnormal trauma

Pathological fracture

• break resulting from a stress that normally wouldn’t fracture a bone

• Bone more susceptible because weakened by disease such as osteoporosis

Bone is also classified according to direction of …

fracture line

Closed reduction procedure

• procedure to fix a fracture; broken parts aligned without surgery

• like wearing a cast

Open reduction-internal fixation (ORIF)

surgical repair with plates, screws pins

Classification of Fractures: Closed

skin is not broken (simple fracture)

Classification of Fractures: Open

Skin is broken; (compound fracture)

Classification of Fractures: Complete

Bone is broken into two or more pieces

Classification of Fractures: Incomplete

Partial fracture that extends only partway across bone; pieces remain joined

Classification of Fractures: Nondisplaced

The portions of bone are still in correct anatomical alignment

Classification of fractures: Displaced

portions of bone are out of anatomical alignment

Classification of Fractures: Comminuted

bone is broken into three or more pieces

Classification of fracture: Greenstick

bone is bent toward one side and has incomplete fracture on opposite side

Classification of Fractures: Hairline

Fine crack in which sections of bone remain aligned; common in skull

Classification of fractures: Impacted

one bone fragment is driven into the marrow cavity or spongy bone of the other

Classification of fractures: Depressed

broken portion of bone forms a concavity, as in skull fractures

There s a net loss of bone by age

40

Osteopenia

• measurable decline in bone density

• spongy bone is affected because it has the greatest surface area for osteoclast to work one

Osteopenia Risk factors

• sex, body build, ancestry, age, sedentary lifestyle, poor dietary, smoking, excessive alcohol consumption

Osteoporosis

• bones are eroded enough that they easily fracture

Osteoporosis can result in

spinal deformities, such as hyperkyphosis (exaggerated thoracic curvature), leading to fractures of hips, wrist & spine.

For women osteoporosis rises sharply after ______ due to loss of _____

menopause, estrogen

Assessment of bone density:

bone densitometry, or the DEXA (dual energy X-ray absorptiometry) scan. Gold Standard

Osteoporosis treatment revolves around

drugs to stimulate bone deposition (osteoblasts) or slow its resorption (osteoclasts)

Acromegaly

result of adult growth hormone hypersecretion, resulting in thickening of the bones and soft tissue, especially noticeable in the face, hands, and feet

Osteitis deformans (paget disease)

• excessive osteoclast proliferation and bone resorption, with osteoblasts attempting to compensate by depositing extra bone. this results in rapid, disorderly bone remodeling and weak, deformed bones.

• osteitis deformans usually passes unnoticed, but some cases it causes pain, disfiguration, and fractures. It is most common in males over the age of 50

Osteomyelltis

• inflammation of osseous tissue and bone marrow as a result of bacterial infection.

• often fatal before the discovery of antibiotics and is still very difficult to treat

Osteosarcoma

• Bonce cancer affecting especially the limb bones of adolescents and young adults

• large tumors near the knee, with death, if not quickly treated usually resulting from metastasis to the lungs