PART 1: BONES Chapter 6

a connective tissue 18% of weight of human body Skeletal System includes bones & cartilage Part 1: Bone Part 2: Axial Skeleton Part 3: Appendicular Skeleton Part 4: Joints

1. SUPPORT skeleton serves as structural framework by supporting soft tissues & providing attachments for tendons of muscle 2. PROTECTION Protects most important soft tissue organs from injury

3. MOVEMENT Skeletal 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

5. BLOOD CELL PRODUCTION red bone marrow produces RBCs, WBCs, & platelets 6. TRIGLYCERIDE STORAGE yellow bone marrow stores triglycerides (chemical energy reserve)

Axial Skeleton skull vertebral column rib cage hyoid Bones that make up the limbs and their girdles (bones that hold limbs to trunk) Appendicular Skeleton

Long Bones longer than they are wide shaft with expanded ends bone(s ) of upper arm, lower arm, digits, thigh, lower leg roughly cubital bones on ankle and wrist Short Bones

Flat Bones thin, flat bones with bit of a curve sternum scapula ribs most skull bones do not fit into other categories vertebrae hip bones Irregular Bones

Compact Bone outside layer of all bones Spongy Bone inside certain bones

has few spaces strongest form of bone beneath periosteum of all bone provides protection & support and resists stresses produced by weight & movement

OSTEON: aka Haversian Systems repeating units thru out compact bone each 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

absence of osteons made of lamellae arranged in irregular columns called trabeculae appears spongy but hard makes up most of inside of short, flat, or irregular bones & epiphysis of long bones lighter than compact bone Function: support & protect red bone marrow

1. DIAPHYSIS: bone’s shaft or body: the long cylindrical, main portion of the bone 2. EPIPHYSIS: distal & proximal ends of the bone

3. 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 freely movable joints

5. PERIOSTEUM tough, 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

7. ENDOSTEUM thin membrane that lines marrow cavity contains 1 layer of bone-forming cells and CT

red bone marrow found : newborns: in all areas of spongy bone adults: most long bones medullary cavity with yellow marrow (fat) extends through diaphysis blood cell production only in head of femur & humerus yellow marrow  to hematopoietic marrow if person becomes very anemic and needs more blood cells than can make in head of femur & humerus

Table 6.1

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

1. OSTEOGENIC CELLS Stem cells from mesenchyme (origin of all CT) only bone cells to divide

2. OSTEOBLASTS bone-building cells synthesize & secrete collagen fibers initiate calcification

3. OSTEOCYTES mature bone cells main cells in bone maintain exchange of nutrients & wastes with blood

4. OSTEOCLASTS huge cells that form by merging of many (50)monocytes in endosteum ruffled border faces bone surface: releases lysosomal enzymes & acids that digest underlying bone (bone resorption): part of normal maintenance, growth, development, & repair of bone

Most bones are formed b/4 birth but each one continually renews itself for rest of life ~5% of bone being any given time Bone Remodeling is the ongoing replacement of old bone tissue by new bone tissue 1. Bone Resorption 2. Bone Deposition

Removal of minerals & collagen fibers from bone by osteoclasts Results in destruction of bone extracellular matrix

Addition of minerals & collagen fibers to bone by osteoblasts

1. Minerals Ca, P, F, Mg, Fe, Mn 2. Vitamins C needed to make collagen fibers & for differentiation osteoblast  osteocyte E & B 12 needed for protein synthesis 3. Hormones IGF’s in childhood (insulin-like growth factors) estrogens & androgens important in puberty

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Fracture: any break in a bone Fractures named by: severity shape or position of fracture line person who 1 st described it

Bone is body’s main reservoir for calcium (stores 99% of total body Ca) Normal blood level Ca mg/100mL Calcium important for: Muscle contraction Nerve impulses Blood clotting Many enzymes require Ca++ as cofactor

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)

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

traditionally tx’d with: weight-bearing exercise calcium & Vit D estrogen replacement

Biphosphonates : decrease osteoclast activity & partially reverse osteoporosis in the spine SERMS: “ 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

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