PART 1: BONESChapter 6

THE SKELETAL SYSTEM

a connective tissue18% of weight of human bodySkeletal System includes bones &

cartilagePart 1: BonePart 2: Axial SkeletonPart 3: Appendicular SkeletonPart 4: Joints

Bone

FUNCTIONS1. SUPPORT skeleton serves

as structural framework by supporting soft tissues & providing attachments for tendons of muscle

2. PROTECTIONProtects most

important soft tissue organs from injury

FUNCTIONS3. MOVEMENTSkeletal muscles

attach to bones, when the muscle contract the bones move

4. MINERAL HOMEOSTASIS

Bone stores calcium, phosphorus which both help make bone strong

If body needs these minerals bone releases them

FUNCTIONS5. BLOOD CELL

PRODUCTIONred bone marrow

produces RBCs, WBCs, & platelets

6. TRIGLYCERIDE STORAGE

yellow bone marrow stores triglycerides (chemical energy reserve)

Axial Skeletonskullvertebral columnrib cagehyoid

Bones that make up the limbs and their girdles (bones that hold limbs to trunk)

Classification of the Skeletal System

Appendicular Skeleton

Classification of the Skeletal System

Long Boneslonger than they are

wideshaft with expanded

endsbone(s ) of upper

arm, lower arm, digits, thigh, lower leg

roughly cubitalbones on ankle and

wrist

Classification of Bones

Short Bones

Flat Bonesthin, flat bones with

bit of a curvesternumscapularibsmost skull bones

do not fit into other categories

vertebraehip bones

Classification of Bones

Irregular Bones

Classification of Bone TissueCompact Bone

outside layer of all bones

Spongy Boneinside certain bones

has few spaces strongest form of bonebeneath periosteum of all boneprovides protection & support and

resists stresses produced by weight & movement

TYPES of BONE: COMPACT BONE

OSTEON:aka Haversian Systemsrepeating units thru out compact boneeach one has central canal with

concentrically arranged lamellae, lacunae (filled with 1 osteocyte)

aligned in same direction along lines of stress

space between osteon filled with interstial lamellae

Parts of Compact Bone

absence of osteonsmade of lamellae arranged in

irregular columns called trabeculaeappears spongy but hardmakes up most of inside of short, flat,

or irregular bones & epiphysis of long bones

lighter than compact boneFunction: support & protect red bone

marrow

Spongy Bone Tissue

Spongy Bone

Structure of Bone: Long Bones1. DIAPHYSIS: bone’s shaft or

body: the long cylindrical, main portion of the bone

2. EPIPHYSIS:distal & proximal

ends of the bone

Structure of Long Bones3. METAPHYSIS:Region in mature

bone where diaphysis meets epiphysis

in growing bone include metaphyseal plate (hyaline cartilage that allows bone to grow in length)

4. ARTICULAR CARTILAGE

hyaline cartilage covering part of epiphysis involved in joint

reduces friction & absorbs shock @ freely movable joints

Metaphysis

Structure of Long Bones5. PERIOSTEUMtough , dense,

irregular CT surrounds bone wherever it is not covered by hyaline cartilage

helps in repair of fractures

attachment pt for ligaments

6. MEDULLARY CAVITY

aka Marrow Cavity

space w/in diaphysis that contains yellow bone marrow in adults

Periosteum & Marrow Cavity

Structure of Long Bones7. ENDOSTEUMthin membrane

that lines marrow cavity

contains 1 layer of bone-forming cells and CT

red bone marrowfound :newborns: in all areas of spongy boneadults: most long bones medullary cavity with

yellow marrow (fat) extends through diaphysisblood cell production only in head of femur &

humerusyellow marrow to hematopoietic marrow if

person becomes very anemic and needs more blood cells than can make in head of femur & humerus

Hematopoietic Tissue in Bone

Table

6.1

Bone Markings

Bones are hard due to calcification: calcium carbonate & other minerals (Mg, F, K, S) form crystals around collagen fibers

bone hardness depends on crystallized inorganic mineral salts

bone flexibility depends on collagen fibers

HISTOLOGY of BONE

1. OSTEOGENIC CELLS Stem cells from mesenchyme (origin

of all CT) only bone cells to divide

Types of Bone Cells

2. OSTEOBLASTSbone-building cellssynthesize & secrete collagen fibersinitiate calcification

Types of Bone Cells

3. OSTEOCYTESmature bone cellsmain cells in bonemaintain exchange of nutrients &

wastes with blood

Types of Bone Cells

4. OSTEOCLASTShuge cells that form by merging of

many (50)monocytesin endosteumruffled border faces bone surface:

releases lysosomal enzymes & acids that digest underlying bone (bone resorption): part of normal maintenance, growth, development, & repair of bone

Types of Bone Cells

Osteoclasts

Most bones are formed b/4 birth but each one continually renews itself for rest of life

~5% of bone being remodeled @ any given time

Bone Remodeling is the ongoing replacement of old bone tissue by new bone tissue1. Bone Resorption2. Bone Deposition

Bone Remodeling

Removal of minerals & collagen fibers from bone by osteoclasts

Results in destruction of bone extracellular matrix

Bone Resorption

Addition of minerals & collagen fibers to bone by osteoblasts

Bone Deposition

1. Minerals Ca, P, F, Mg, Fe, Mn

2. Vitamins C needed to make collagen fibers & for

differentiation osteoblast osteocyte E & B12 needed for protein synthesis

3. Hormones IGF’s in childhood (insulin-like growth

factors) estrogens & androgens important in

puberty

Factors Affecting Bone Growth &

Remodeling

https://www.youtube.com/watch?v=0dV1Bwe2v6c

https://www.youtube.com/watch?v=5gpysdG1HoE

Bone Remodeling

Fracture: any break in a boneFractures named by:

severityshape or position of fracture lineperson who 1st described it

Fracture & Repair of Bone

Types of Fractures of Bone

Types of Bone Fractures

Types of Bone Fractures

Types of Bone Fractures

Fracture Repair

Bone is body’s main reservoir for calcium (stores 99% of total body Ca)

Normal blood level Ca 9 -11 mg/100mL

Calcium important for:Muscle contractionNerve impulsesBlood clottingMany enzymes require Ca++ as

cofactor

Calcium Homeostasis

2 hormones control Ca in/out bone:1. Calcitonin

Decreases blood Ca levels by putting more Ca into bone

2. Parathyroid Hormone (PTH) Increases blood Ca levels by taking

Ca out of bone (increasing osteoclast resorption)

Control of Calcium

1. Osteoporosis Condition of porous bones

(resorption > deposition) Causes: deficient Ca in diet USA: > 1 million fractures (hip,

wrist, vertebrae) & afflicts 30 million Americans

Decreased stature, hunched back, bone pain

Homeostatic Imbalances in Bone

traditionally tx’d with:weight-bearing exercisecalcium & Vit Destrogen replacement

Treatment of Osteoporosis

Biphosphonates : decrease osteoclast activity & partially reverse

osteoporosis in the spineSERMS:

“selective estrogen receptor modulators “ mimic estrogen’s beneficial bone-sparing properties without targeting the uterus or breasts

Statins: (lower serum cholesterol) have been found to

also increase bone mineral density (up to 8% over 4 yrs)

Denosubmab: (monoclonal aby drug)↓ fractures& improves bone density

Treatment of Osteoporosis

http://highered.mheducation.com/sites/0072495855/student_view0/chapter6/animation__osteoporosis.html

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