Histology 2-12-07

Front 1

two general methods of bone formation

Back 1

1. Intramembranous Ossification:
- mesenchyme cells to osteoblasts
- flat bones and peripheral long/short bones

2. Endochondral Ossification:
- hyaline cartilage model replaced with bone

Front 2

Intramembranous Ossification

Back 2

1. mesenchymal cells aggregate without a cartilage intermediate.
2. mesenchymal cells differentiate (after receiving signal) into osteoprogenitor cells and then osteoblasts. Angiogenesis occurs.
3. Bone matrix is deposited by osteoblasts (calcification occurs); primary bone tissue is formed. Osteoclasts remodel the bone.

*mesenchyme--> osteoprogenitor cells--> osteoblasts (produce a collagen matrix)-->osteocytes

Front 3

Fontanelle

Back 3

- soft spots (allow brain growth and helps with delivery of baby)

Front 4

Endochondral Ossification

Back 4

-mesenchyme cells--> chondroblasts (make cartilage)--> chondrocytes--> perichondrium becomes a periosteum and starts to produce osteoblasts (layer of bone is beginning to form- called a bony collar)--> cartilage calcifies--> blood vessels penetrate into spaces and bring in osteoblasts--> osteoblasts attach to spicules and make bone

Front 5

Epiphyseal Plate

Back 5

- responsible for maintaining the growth process (thickness of plate remains constant during growth)
- shrinks as we get older (after we've stopped growing) and eventually closes to a line
- this is how scientists age people

Front 6

Zones:
1. zone of reserve cartilage
2. zone of proliferation
3. zone of hypertrophy
4. zone of calcified cartilage
5. zone of resorption

Back 6

1. exhibits no cellular proliferation or active matrix production

2. cartilage cells undergo division and organize into distinct columns (produce collagen)

3. contains enlarged cartilage cells

4. the hypertrophied cells begin to degenerate and the cartilage matrix becomes calcified.

5. calcified cartilage is in direct contact with CT (small blood vessels present- source of bone-producing cells)

Front 7

Bone Growth

Back 7

-remodeling and resorption- done by the osteoclasts
- during growth remodeling and resorption occurs

Front 8

Bone Fracture Repair

Back 8

after bone breaks:
- macrophages get rid of dead cells and CT while also cleaning up the area
- fibroblasts lay down hyaline cartilage and blood vessels come in
- new primary bone (spongy-like) forms and is associated with hyaline cartilage and seals the two ends together
- osteoclasts remodel and replace with compact bone

Front 9

Bone Diseases

Back 9

1. Rickets and Osteomalacia- poor diet (low calcium or vitamin D) causes bad bone formation

2. Osteopetrosis- there are more osteoblasts than osteoclasts so the bone becomes harder and more brittle

3. Osteoporosis- bone density decreases; osteoclasts aren't being as inhibited (osteoclast bone loss > bone formation)

4. Scurvy- lack of vitamin C (essential for collagen that sets up bone framework)- start to lose teeth

Front 10

Adipose Tissue

Back 10

- specialized type of CT developed from the same mesenchyme cells
- adipocytes (these cells can also produce hormones)
- associated with loose CT
- Two Types:
1. White/Yellow (unilocular)
2. Brown (multiocular)

Front 11

White (unilocular) Tissue

Back 11

- underneath CT
- storage, insulation, cushion of organs
- cells are closely associated but separate
- peripherally positioned nucleus
- blood vessels are associated
- hypodermis
- Localization: both external and internal

Front 12

Brown (multiocular) Tissue

Back 12

- smaller cells with multiple lipid deposits (not just one large one like white tissue)
- nucleus is in the middle
- losts of mitochondria present (what causes the brown staining)
- function of brown tissue: heat generation
- infants have more brown tissue

Front 13

Brown Adipose Thermoregulation

Back 13

- UCP-1 protein separates the flow of electrons from generating ATP; instead they generate heat
-also found in hibernating animals
-called Non-Shivering Thermogenesis

Front 14

Adipose Tissue Distribution

Back 14

- pear-shaped or apple-shaped
- external/internal
- upper/lower (its worse to gain fat in the upper part of the body)

Front 15

Obesity

Back 15

-body mass index (wt/h^2) > 30 kg/m^2 (~30% above ideal weight)
- two main forms: hypertrophic and hyperplastic
- nonuniform mobilization