Bone Histology

Question 1

What consists of compact bone?

Answer 1

outer solid cortex surrounding spongy bone, lamellar bone

Question 2

What consists of spongy/trabecular/cancellous bone?

Answer 2

Inner layer, spaces for BM, lamellar or woven

Question 3

What is the main contribution of bone?

Answer 3

type I collagen fibers, osteoid, bone matrix, ground substance, Inorganic creates hardness (calcium phosphate)

Question 4

What are osteoprogenitor cells and where are the found?

Answer 4

From mesenchyme, stem cell active, give rise to osetoblasts, found in periosteum and endosteum (reactivated during bone repair)

Question 5

What are osteoblasts and where are they found?

Answer 5

Epithelial like cells with cuboidal/columnar shapes, deposit osteoid and control it, strong reaction for alkphos, make osteocytes

Question 6

What are osteocytes?

Answer 6

osteoblasts trapped inside lacunae in the osteoid matrix, have branches called canaliculi which communicate/ give nutrients

Question 7

What are osteoclasts?

Answer 7

derived from monocyte/macrophage, generate secluded acidic environment for bone reabsorption, important in bone remodeling

Question 8

What is periosteum and where can it be found?

Answer 8

can be found on the outer layer of bone, nutrition for osseous tissue, continuous cupply of new cells for growth, does not cover articular surfaces

Question 9

What is different between the inner and out layer of periosteum?

Answer 9

Inner layer consists of osteoprogenitor cells and osteogenic layer

Outer layer is rich in blood vessels and nerves, fibroblasts and collagen, and sharpey’s fibers

Question 10

What is endosteum and and where can it be found?

Answer 10

Inner layer of the bone, covers spongy walls, extends into all cavities of bone, where osteoprogenitor cells can become osteoblasts

Question 11

What is an osteon IN COMPACT BONE?

Answer 11

concentrically arrange lamellae around a longitudinal vascular channel (haversian canal)

Question 12

What is interstitial lamellae?

Answer 12

between osteons, separated from osteon by the cement line (borders entire osteum)

Question 13

What is the outer circumferential lamallae?

Answer 13

external surface of compact bone, lies under the periosteum

Question 14

What is the inner circumferential lamallae?

Answer 14

internal surface of bone, subjacent to endosteum (NEAR SPONGY BONE)

Question 15

What is a haversian canal?

Answer 15

vascular channels in the center of the osteon

Question 16

What are volkmann’s canal?

Answer 16

transverse vascular channels connecting haversian channels

Question 17

What are the steps for intramembranous ossification, of which flat bones use?

Answer 17

1. mesenchyme is condensed into a soft sheet permeated with blood capillaries
2. Osteoblasts deposit osteoid tissue on mesenchymal surface, entrap osteocytes, forming periosteum
3. Honeycomb formed by mineralization, spongy bone created
4. Surface of bone filled in by bone deposition, spongy to compact bone. Spongy in middle

Question 18

What are the first two steps of endochondral ossification for long bones?

Answer 18

1. mesenchyme forms Hyaline cartilage covered with perichondrium which grows in thickness
2. Perichondrium stops producing condrocytes, starts producing osteoblasts, forming first ossification center, chondrocytes start to die

Question 19

What happens during endochondral ossification after the chondrocytes start to die?

Answer 19

3. blood vessels penetrate primary ossification center (medullary cavity), osteoclasts follow dead cartilage to lengthen bone
4. Chondrocyte enlargement and death form secondary ossification center in epiphysis, becomes hollow by osteoclasts eating chondrocytes.

Question 20

What is the final step in endochondral ossification after the chondrocytes are eaten by the osteoclasts?

Answer 20

5. the epiphysis fills spongy bone, cartilage is limited to the epiphyseal plate

Question 21

What is the difference between spongy and compact bone?

Answer 21

Spongy is unorganized osteoblasts, and compact bone is organized osteoblasts

Question 22

What are the steps of a bone fracture and what will be hurt?

Answer 22

1. Formation of fracture hematoma (nervers are in the periosteum so will be painful and have nerve damage)
2. Fibrocartilaginous callus will form (woven bone)
3. Osteoblasts will form bony callus to fill in gaps
4. Bone is remodeled by osteoclasts so bone is smooth

Question 23

What is achondroplasia (AD) and how does it present?

Answer 23

mutation in the FGFR3 gene, inhibits endochondral growth, with mutation stops bone growth very early= dwarfism… normal abdomen, short limbs

Question 24

what are calcium rickets and how do they form?

Answer 24

Ca/Vitamin D deficiency during growth=defect in mineralization of cartilage in growth plate… bowed lower legs

Question 25

What is osteomalacia and what happens?

Answer 25

Adult form of rickets, softening and bending of bone due to vitamin D deficiency or GI disease

Question 26

What is osteoporosis and what occurs?

Answer 26

Loss of normal bone density, caused when there is an increase of osteoclasts eating bone faster than osteoblasts can replace them. (easy fractures)