1. Bones and Skeletal Tissues

2. Skeletal Cartilage
Skeletal cartilage is made of cartilage and surrounded by perichondrium, a dense irregular connective tissue.
Three main types
Hyaline = most abundant
Elastic = more flexible than hyaline
Fibrocartilage = withstands large amount of pressure

3. Where are they found?
Hyaline = articular, costal, respiratory, and nasal cartilage
Elastic = external ear and epiglottis of larynx
Fibrocartilage = knee and intervertebral discs
See figure 6.1 in book

4. Growth of Cartilage
Appositional = results in outward expansion due to production of cartilage matrix on the outside of the tissue.
Interstitial = expansion from within in the matrix due to division of chondrocytes and secretion of matrix

5. Classification of Bones
Two main divisions
Axial = skull, vertebral, and rib cage
Appendicular = bones of upper and lower limbs, and the girdles that attach them to the axial

6. Shapes
Long Bones = longer than they are wide. Have a definite shaft and two ends. All limb bones except the patellas, carpals, and tarsals
Short Bones = cube shaped/short. Examples carpals and tarsals
Flat Bones = thin, flattened, often curved bones that includes most of the skull bones, sternum, and ribs
Irregular = complicated shapes and do not fit neatly into the other categories. Vertebrae for example

7. General Functions of Bones
1. Support the body.
2. Protect vital organs
3. Allow for movement
4. Store minerals (calcium/phosphorus)
5. House hematopoietic tissue in marrow cavities, which produce blood cells

8. Bone Structure Bones are organs!!!
They contain nervous tissue, connective tissue, epithelial tissues in their blood vessels and MOST IMPORTANTLY
Osseous tissue or bone tissue which is the main tissue found in bones.

9. Bone Markings
Projections = grow outward from the bone surface. Often sites of muscle attachment and joints.
Depressions and Openings = allow for the passage of nerves and blood
See Table 6.1

10. Bone Texture Spongy and Compact
Compact = external layer, the dense outer layer that appears smooth and solid.
Spongy = internal part of the bone, a honeycomb of small needle-like or flat pieces called trabeculae. In living bones, the space between trabeculae is filled with red or yellow bone marrow

11. Yellow Marrow
Found in a central tubular cavity in the long shaft of the bone. This cavity is called the Medullary Cavity.
Filled with fat in adults hence called yellow marrow.

12. Red Marrow
Found in the trabecular cavities of spongy bone. It contains hematopoietic tissue and thus is involved with blood production.
In infants, the medullary cavity and all areas of spongy bone contain red marrow.
In adults, the medullary cavity extends into the ends of bones, and thus there is less red marrow tissue. Found in ends of large long bones, flat bones such as the sternum, and some irregular bones such as the hip.

13. Long Bone Structure
Diaphysis = the long axis of the bone. Made of a relatively thick collar of compact bone, that surrounds the medullary cavity.

15. Epiphyses = the ends of the bone
Epiphyses = the ends of the bone. Compact bone surrounds the exterior and spongy bone is in the interior.
The joint surface is covered with a thin layer of articular (hyaline) cartilage.
Epiphyseal Line = line between the diaphysis and the epiphysis. There is a remnanent of the epiphyseal plate which is a disc of hyaline cartilage that grows during childhood to lengthen the bone

16. Membranes in Long Bone
Periosteum = a white double membrane surrounding the entire bone except the joint surface.
It has an outer layer of dense irregular connective tissue.
It has an inner “osteogenic” layer made of osteoblasts (bone forming) and osteoclasts (bone destroying) cells.

17. Periosteum cont.
Richly supplied with nerve fibers, lymphatic vessels, and blood vessels. These enter the diaphysis through a nutrient foramen.

18. Endosteum
Membrane covering internal bone surfaces such as the trabeculae of spongy bone. It also contains osteoblasts and osteoclasts.

19. Stucture of Short Irregular and Flat Bones
Thin plates of compact bone on the outside covered with periosteum.
Endosteum covered spongy bone on the inside middle layer.
In flat bones the middle layer is called the diploe.

20. Bone Fractures and Repair
Classification of Fractures
A. Non-displaced fractures = maintain their original position
B. Displaced fractures = Bone ends out of alignment
C. Complete fracture = bone broken completely through
D. Incomplete = not completely through the bone

21. E. Linear fracture = along the long axis of the bone.
F. Transverse = perpendicular to the long axis of the break
G. Open/Compound fracture = penetrates the skin
H. Closed/Simple fracture = does not penetrate the skin

22. Treatment and Recovery
A fracture is treated first with a reduction.
Closed/External reduction is done when the physician aligns the broken ends of the bone together with hands.
Open/Internal reduction is done when the broken ends are aligned and set in place with pins or wires.

23. After the bone is reduced, it is immobilized by a cast or traction so healing can occur.

24. Healing for a Simple Fracture
1. Hematoma formation = a mass of clotted blood forms at the site.
2.Fibrocartilaginous callus formation = capillaries grow into the hematoma area and begin cleaning up the debris. Fibroblast cells and osteoblast cells from nearby periosteum and endosteum begin reconstructing bone.

25. 2. (cont.) The fibroblasts produce collagen fibers across the break and some become chondroblasts producing cartilage. The osteoblasts begin forming spongy bone tissue. The whole mass together forms the fibrocartilaginous callus.

26. 3. Bony Callus formation = Within a week bony trabeculae begin to appear in the fibrocartilaginous callus and begin to convert it to bony/hard callus of spongy bone. Up to two months for this process.
4. Bone remodeling = Beginning during bony callus formation, the extra material on the diaphysis exterior and the medullary cavity is removed and compact bone tissue is produced to make the shaft walls.

27. Time and Other Factors
About 6-8 weeks for small to medium sized bones in youth and young adults.
Longer for larger and weight bearing bones.
Longer for elderly due to poor circulation.

28. BONE IS CONNECTIVE TISSUE!
Cells:
I. Osteogenic cells-occur in endosteum, the inner layer of periosteum, and within haversian canals.
Multiply continually can differentiate into osteoblasts 

29. II. Osteoblasts
Bone FORMING cells of the bone matrix.
They are non-mitotic
However there number can build up in response to stress or fractures.

30. III. Osteocytes
Former osteoblasts that have become trapped within their own matrix.
They reside in tiny cavities called lacunae, which are connected to each other by slender channels called canaliculi.
Communication, is the number one job of these cells…..

31. IV. Osteoclasts
Bone-dissolving cells found on the surface of bone.
LARGE CELLS
3-4 nuclei (sometimes up to 50)
(Fused monocytes)

32. The Matrix: NOT JUST A MOVIE!
1/3 organic material
2/3 inorganic material
Organic
Inorganic

33. Bone Composition Organic:
A. osteogenic, osteoblasts, osteocytes, osteoblast -- all cell types
B. Osteoid -- ~1/3 of matrix including ground substance and collagen fibers
Resilent and great tensile strength “sacrificial bonds” dissipate energy thus preventing fractures

34. Inorganic: ~65% by mass of inorganic salts
Inorganic: ~65% by mass of inorganic salts. Mainly calcium phosphate crystals. This accounts for the hardness of bones which resists compression. Drink your milk!!

35. This mix of collagen, proteins, and minerals makes bone durable and strong.
½ as strong as steel at resisting compression and just as strong as resisting tension.
And obviously bones remain long after death, leaving remains that allow us to study humans from the past

36. Microscopic Anatomy of the Bone
The Structural Unit of Compact Bone =
Osteon or Haversian System

37. Has concentric tubes of bone matrix called lamellae surrounding a central canal that serves as a passageway for blood vessels and nerves.

38. Volkmann’s (perforating) canals lie at right angles to long axis and connect the blood and nerve supply of the periosteum to the central canals and medullary cavity.

39. Osteocyctes occupy lacunae at the junction of lamellae.

40. Circumferential lamellae = just beneath the periosteum around the entire circumference of bone.
Interstitial Lamellae = lie between intact osteons filling the space in between

41. Spongy bones lacks osteons, but has trabeculae that align along lines of stress.