1. Bones and Skeletal Tissues
Structure and Function of Cartilage and Bone
Bones and Skeletal Tissues

2. Cartilage (review) Characteristics Resists tension AND compression
Lots of collagen (strong) AND elastic fibers (flexible)
High content of proteoglycans 80% water (resiliency/spring properties)
No nerves or blood vessels
Chondroblasts make matrix until end of human adolescence
Mature Chondrocytes found in cavities called lacunae (pit)
Surrounded by the perichondrium (dense irregular connective tissue) that serves to:
Resists outward expansion
Nourish cartilage tissues

3. Light Micrograph of Joint (Articular Surface)

4. Hyaline Cartilage (review)
Looks glassy (hyalin = glass)
Few chondrocytes, all found in lacunae
Mostly matrix – lots of collagen

5. Hyaline Cartilage (add notes)
Provides flexibility w/resilience
Most abundant skeletal cartilage
Locations:
Articular – covers the ends of long bones, moving joings
Costal – connects ribs (sternal)
Respiratory –in larynx (voicebox), reinforces air passages of lungs
Nasal – supports the nose

7. Elastic Cartilage (review)
Looks almost identical to hyaline BUT more elastic fibers  more flexible!
Matrix appears more fibrous
More lacunae, closely spaced.

8. Elastic Cartilage (add)
Elastic fibers allows for repeated “bending”
Found in:
the external ear
Epiglottis (flap closes in larynx when we swallow)

10. Hyaline Cartilage
Elastic Cartilage

11. Fibrocartilage (review)
Intermediate between dense regular CT and hyaline
Consists of rows of chondrocytes and collagen fibers
Compressible AND resists tension

12. Fibrocartilage (add)
Due to compressibility, found in areas that need padding due to stretch/pressure:
menisci (singular: meniscus) of the knee
intervertebral discs

15. Bones and Cartilages of the Human Body
Figure 6.1

16. Growth of Cartilage
Appositional – cells in the perichondrium secrete matrix at the surface of existing cartilage
Grows “outward”
Interstitial – lacunae-bound chondrocytes inside the cartilage divide and secrete new matrix, expanding the cartilage from within
Grows from the inside of tissue
Area of appositional growth (black arrows)
Area of interstitial growth (white arrows)

17. Function of Bones
Support – “framework” that supports the body; cradles soft organs
Protection –protective case for brain, spinal cord, vital organs
Movement – levers for muscles
Mineral storage – reservoir for minerals, especially calcium and phosphorus
Blood cell formation – hematopoiesis occurs within the marrow cavities of bones

18. Bone Composition (organic)
4 cell types:
Osteo
genic
cells
mitotic stem cells in membranes covering bones that create other bone cells
Osteoblasts:
Young, bone cells that makes un-mineralized bone matrix, “osteoid” (ground substance, collagen, glycoproteins,etc.)
Osteocytes:
mature, bone cells that maintains osteoid
Osteoclasts:
Large cells that dissolve and break-down bone and its osteoid

19. Bone Composition (inorganic)
Mineral Salts (Hydroxyapatites)
65% bone by mass
mainly calcium phosphate, deposited around collagen of osteoid
responsible for hardness and compression resistance of bone
Deposited by osteoblasts, source of calcium and phosphate in blood plasma.

20. Skeletal Classification
Axial skeleton – long axis of body
bones of the skull, vertebral column, and rib cage
Appendicular skeleton – bones of the limbs and girdle (shoulder, hip)

21. Classification of Bones: By Shape
Long bones – longer than they are wide (ex. humerus)
Named for relative length and width, not size (ex. fingers are also long bones!)

22. Classification of Bones: By Shape
Short bones
Cube-shaped bones of the wrist and ankle
Bones that form within tendons (ex. patella)

23. Classification of Bones: By Shape
Flat bones – thin, flattened, and a bit curved
(ex. sternum, ribs, shoulder blades, skull)
Figure 6.2c

24. Classification of Bones: By Shape
Irregular bones –complicated shapes
(ex. vertebrae and pelvis)

25. Bone Textures
Compact bone – dense outer layer made up of osteons. Very supportive.
Spongy bone – honeycomb of trabeculae filled with yellow marrow (fat) or red bone marrow (hematopoietic)
Trabeculae:
- needle-like extensions of bone
- disperse pressure without much weight
- resists compression on ends of bones
- marrow fills in between spaces

26. Membranes of Bones
Porous with “nutrient foramens” to supply bone with nerves, lymph, and blood vessels
Inner layer:
osteogenic stem cells that differentiate (specialize) into bone cells like osteoblasts (bone forming) or osteoclasts (bone dissolving) cells.
Outer layer: protective, fibrous dense irregular connective tissue
Attach periosteum to bone
Endosteum: delicate membrane covering internal surfaces of compact bone (next to marrow) or the trabeculae of spongy bones
Periosteum: double-layered membrane on external surface of bones

27. Structure of Long Bone
Consists of a diaphysis (shaft) and an epiphyses (ends)
Diaphysis –
Forms the axis
Compact bone that surrounds hollow medullary cavity that contains yellow marrow (fat)

28. Structure of Long Bone Epiphyses
compact bone exterior; spongy bone interior
joint surface covered w/ articular (hyaline) cartilage
cushions opposing bone ends during movement
Epiphyseal line, for bone lengthening, separates the diaphysis from the epiphyses

29. Structure of Long Bone

30. Structure of Short, Irregular, and Flat Bones
Thin periosteum-covered compact bone on the outside with endosteum-covered spongy bone (diploë) on the inside
Have no diaphysis or epiphyses
Bone marrow fills spaces within trabeculae

31. Location of Hematopoietic Tissue (Red Marrow)
In infants
Found in the medullary cavity of long bones and all areas of spongy bone
In adults
Found in the diploë of flat bones, hip, and the head of the femur (thigh) and humerus (upper arm)

32. Micro-anatomy of Compact Bones
Haversian system or Osteons: the structural unit of compact bone
Volkmann’s canals: connects blood and nerve supply of the periosteum to the Haversian canal
Haversian or Central Canal: central channel containing blood vessels and nerves
Osteon
periosteum
Volkmann’s Canals

33. Micro-anatomy of Compact Bones
Lamella: an osteon’s weight-bearing, concentric matrix tubes (mostly of collagen)
Interstitial lamella: collagen matrix that fills in gaps between osteons
Circumferential lamella – extend under periosteum around the entire circumference of diaphysis

34. Micro-anatomy of Compact Bones
Osteocytes: trapped in cavities called lacunae, in between lamella
Osteoblasts:
Initially make matrix that hardens around them (lamella).
As they mature, osteoblasts become osteocytes.
Canaliculi: hairlike canals that connect lacunae to each other and the central canal