1. NOTES: Skeletal System (Ch 7, part 3)

2. BONE FUNCTION:  Support and Protection
• bones shape and form body structures
• bones support and protect softer, underlying tissues

3. BONE FUNCTION:  Body Movement
• bones and muscles function together as LEVERS
• a lever consists of: a rod, a pivot (fulcrum), a resistance, and a force that supplies the energy

4. BONE FUNCTION:  Blood Cell Formation (Hematopoeisis)
• depending on stage of life, blood cell formation occurs in the :
-yolk sac (embryo)
-liver and spleen
-bone marrow

5. -RED: makes RBCs, WBCs, and platelets
• Marrow can be:
-RED: makes RBCs, WBCs, and platelets
-YELLOW: stores fat
Ratio changes over lifetime
Child: all red marrow
Increase in yellow over lifetime

7. BONE FUNCTION:  Storage of Inorganic Salts
• matrix of bone tissue contains large quantities of calcium phosphate ( makes bones hard)
• bone also stores small amounts of magnesium, sodium, potassium, and carbonate

8. Individual bones are the organs of the skeletal system
Individual bones are the organs of the skeletal system. A bone contains very active tissues.

9. Some of the cells that make up these tissues:
Osteoprogenitor cells: unspecialized; can undergo mitosis & develop into osteoblasts
Osteoblasts: cells that form bone matrix (no longer dividing); secrete collagen

10. OSTEOPROGENITOR  OSTEOBLAST 

11. Osteocytes: mature bone cells; exchange nutrients/waste with blood
Osteoclasts: break down bone matrix
OSTEOPROGENITOR  OSTEOBLAST  OSTEOCYTE

12. Throughout life, osteoclasts continually break down bone matrix and osteoblasts replace it; these opposing processes of resorption and deposition of calcium help to maintain calcium levels in the body.

13. Blood calcium levels vary; when blood calcium is:
LOW: parathyroid hormone is released which causes osteoclasts to break down bone, releasing calcium salts
HIGH: calcitonin is released which causes osteoblasts to form bone tissue and store calcium
salts

15. CALCITONIN
PARATHYROID HORMONE

16. Bones are classified by SHAPE:
Long bones
Flat
Irregular (ex: zygomatic, hyoid)
Short (ex: carpals/tarsals)

17. BONE STRUCTURE:
*Bone structure reflects its function.

18. Parts of a long bone: • EPIPHYSES:
-enlarged portions at ends of a long bone;
-covered with articular cartilage;
-articulate (form JOINTS) with other bones.

19. Parts of a long bone: • DIAPHYSIS:
-shaft of bone (located between the epiphyses)
• PERIOSTEUM:
-tough, vascular covering that
encloses the entire bone
except where the articular
cartilage is
Articular cartilage

21. **the center of the diaphysis is a hollow chamber (MEDULLARY CAVITY), lined with a thin layer of cells ENDOSTEUM)
and filled with soft connective tissue (YELLOW MARROW)

23. Types of Bone Tissue:
 COMPACT BONE: has a continuous matrix with no gaps; found in the wall of the diaphysis

24. Types of Bone Tissue:
 SPONGY BONE (a.k.a. cancellous bone): has irregular interconnecting spaces between bony plates that reduce the weight of bone.

25. **both compact and spongy bone are strong and resist bending

26. NOTES- Skeletal System Part 4: Microscopic Structure of Bone, Bone Development & Growth, & Bone Remodeling

27. Microscopic Structure of Bone:
• Intercellular material = mostly COLLAGEN (gives bone its strength and elasticity) and inorganic salts (make bone hard and resistant to crushing).
• The structural unit of compact bone
is called the Osteon or Haversian
System
• Compact bone contains OSTEONS
running in cylindrical rings cemented
together which give long bones
strength
Transverse cut

28. In an osteon you would find…
Inorganic matrix deposited in concentric layers called LAMELLAE
Lamellae form concentric rings around a central or Haversian Canal
Contain nerves and blood vessels that supply osteocytes
Volkmann’s Canals run at a right angle to
central canals and
connect the vascular
and nerve supplies to
the periosteum

30. In each lamella there are cavities called Lacunae which hold Osteocytes (mature bone cells)
Lacunae also have tiny canals radiating out from them called CANALICULI
Nutrients diffuse through these to reach osteocyte

36. AMGEN BONE VIDEO- CLICK!

37. Bone Development and Growth:
Process by which bone forms is called ossification
Bone starts out as hyaline cartilage in the right shape & then becomes calcified & gains a blood supply
2 types:
1) Intramembranous Ossification
(will become flat bones)
2) Endochondral Ossification

38.  Intramembranous Ossification
• osteoblasts completely surrounded by matrix are mature OSTEOCYTES
EXAMPLE: the broad, flat bones of the skull form in this way and fuse together at sutures.

39. Intramembranous: “within” “membrane”

42. Bone Development and Growth
Endochondral Ossification: (“chondro” = cartilage)
• Most bones in the body develop in this way
• Bones develop in early embryos as hyaline cartilage “models”; later replaced by bone tissue

43. endochondral: “within” “cartilage”

45. Endochondral Ossification
• In the middle of the diaphysis, OSTEOCLASTS break down bone tissue and the resulting space becomes the medullary cavity, which later fills with marrow
• The bone in the central regions of the epiphyses and diaphysis remain spongy bone
• The hyaline cartilage that remains on the ends of the epiphyses persists throughout life as articular cartilage

47. Endochondral Bones
• An epiphyseal plate remains between the primary and secondary ossification centers
• Long bones continue to lengthen until the epiphyseal plate are ossified (hardened) in adolescence
• A developing long bone thickens as compact bone is deposited beneath the periosteum (appositional growth)

49. Growth occurs at the epiphyseal plate

51. Factors Necessary for Bone Growth:
Growth hormone GH: stimulate cartilage cells at epiphyseal plate
Thyroid hormone TH: replace cartilage at plate; needed for GH
Sex hormones estrogens & androgens promote bone formation
Vitamins A & C Vit. A: osteoclast/osteoblast activity Vit. C: collagen synthesis
**Genetics & nutrition play a role

52. Bone Remodeling: Bone continually renews itself
Takes place at different rates in various body regions
Distal portion of femur replaced every 4 months
Osteoclasts destroy matrix (resorption)
Osteoblasts deposit new bone
Approximately 20% of bone tissue is replaced annually by this process on a cyclical basis throughout the skeleton. The entire remodeling process occurs over approximately 4 to 8 months, with a range of 3 months to 2 years.

53. Osteoclasts are transported to the bone
Osteoclasts are transported to the bone. The osteoclast cells release acids and enzymes that resorb the existing bone structure. After the osteoclasts resorb the bone, osteoblasts appear and coat the resorbed area with adhesive substances. Moreover, osteoblast cells produce bone proteins, such as collagen, to help calcium attach to the bone proteins. Only by attaching calcium to bone proteins, the new-bone can be formed.