Skeletal System1

Honors Anatomycopy version

• a combination of CT, epithelial & nervous tissues

• 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

Bone

FUNCTIONS1. 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

FUNCTIONS3. 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

Parts of a long bone1. Diaphysis:

shaft or body; the long cylindrical portion of the bone

2. Epiphysis:distal & proximal ends of bone

Parts of a long bone3. Metaphysis:• region between

diaphysis & epiphysis

• in growing bone includes metaphyseal plate (hyaline cart. that allows bone to lengthen

4. Articular Cartilage:

• layer of hyaline cartilage covering part of epiphysis where bone forms a joint with articulating bone

metaphysis

Structure of Long Bones

7. ENDOSTEUM• thin membrane

that lines marrow cavity

• contains 1 layer of bone-forming cells and CT

Histology of bone• bone consists of widely

separated cells surrounded by large amts extracellular matrix

• *bone is hard due to crystallized inorganic mineral salts

• *bone is flexible due to collagen

1. OSTEOGENIC CELLS• Stem cells from mesenchyme (origin

of all CT)• only bone cells to divide

Types of Bone Cells

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

Types of Bone Cells

3. OSTEOCYTES• mature bone cells• main cells in bone• maintain exchange of nutrients &

wastes with blood

Types of Bone Cells

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

Types of Bone Cells

Types of bone (2)1. Compact bone– few open spaces – outer bone layer of all bones

2. Spongy bone– inside bones

• strongest form of bone• beneath periosteum of all bone• functions: – protection & support – resists stresses produced by

weight & movement

COMPACT BONE

• OSTEON:– aka Haversian Systems– repeating units thru out compact

bone– each one has central canal with

concentrically arranged lamellae (rings), lacunae (filled with 1 osteocyte)

– aligned in same direction along lines of stress

– space between osteon filled with interstial lamellae

Parts of Compact Bone

Compact bone

• absence of osteons• made of lamellae arranged in

irregular columns called trabeculae• 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

Spongy Bone

Spongy bone

Bone growth1. longer:• @ epiphyseal plate1. wider:• called appositional growth• periosteal osteoblasts on outer

surface of bone• osteoclast remove compact

bone inner border

Bone growth: longer

Bone growth: wider

• 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 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 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

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

Fracture & Repair of Bone

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 contraction–Nerve impulses– Blood clotting–Many 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 bone2. 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

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