THE SKELETAL SYSTEM

1. THE SKELETAL SYSTEM PART 1: BONES

2. Bone • made up of CT, epithelial tissue, & nerve 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

3. FUNCTIONS • 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

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

6. Structure of Bone: Long Bones • DIAPHYSIS: • bone’s shaft or body: the long cylindrical, main portion of the bone 2. EPIPHYSIS: • distal & proximal ends of the bone

7. Structure of Long Bones 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 shock @ freely movable joints

8. Metaphysis

9. Structure of Long Bones 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

10. Periosteum & Marrow Cavity

11. Structure of Long Bones 7. ENDOSTEUM • thin membrane that lines marrow cavity • contains 1 layer of bone-forming cells and CT

12. HISTOLOGY of BONE • 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

13. Types of Bone Cells • OSTEOGENIC CELLS • stem cells from mesenchyme (origin of all CT) • only bone cells to divide

14. Types of Bone Cells 2. OSTEOBLASTS • bone-building cells • synthesize & secrete collagen fibers • initiate calcification

15. Types of Bone Cells 3. OSTEOCYTES • mature bone cells • main cells in bone • maintain exchange of nutrients & wastes with blood

16. 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

17. Osteoclasts

18. TYPES of BONE: COMPACT BONE • has few spaces • strongest form of bone • beneath periosteum of all bone • provides protection & support and resists stresses produced by weight & movement

20. Parts of Compact Bone • 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

22. Spongy Bone Tissue • 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

23. Spongy Bone

24. Bone Remodeling • 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 tissue • Bone Resorption • Bone Deposition

25. Bone Resorption • removal of minerals & collagen fibers from bone by osteoclasts • results in destruction of bone extracellular matrix

26. Bone Deposition • addition of minerals & collagen fibers to bone by osteoblasts

27. Factors Affecting Bone Growth & Remodeling • Minerals • Ca, P, F, Mg, Fe, Mn • Vitamins • C needed to make collagen fibers & for differentiation osteoblast osteocyte • E & B12 needed for protein synthesis • Hormones • IGF’s in childhood (insulin-like growth factors) • estrogens & androgens important in puberty

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

29. Types of Fractures of Bone

30. Types of Bone Fractures

31. Types of Bone Fractures

32. Types of Bone Fractures

33. Fracture Repair

34. Calcium Homeostasis • 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)

35. Control of Calcium • 2 hormones control Ca in/out bone: • Calcitonin • decreases blood Ca levels by putting more Ca into bone • Parathyroid Hormone (PTH) • increases blood Ca levels by taking Ca out of bone (increasing osteoclastresorption)

37. Homeostatic Imbalances in Bone • 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