Lecture 10: Bone Histology

Question 1

What is another name for Mature or Secondary bone?

Answer 1

Lamellar Bone

Question 2

What exists between the inner and outer circumferential lamellae, outside of the individual osteons?

Answer 2

Interstitial lamellae

Question 3

What can be found in the inner layer of the periosteum?

What is this layer called?

Answer 3

Osteoprogenitor cells

Osteogenic layer

Question 4

Where do osteoprogenitor cells come from?

Answer 4

Mesenchyme

Question 5

What can be found in the endosteum?

Answer 5

Osteoprogenitor cells

Question 6

What are the four steps of intramembranous ossification?

Answer 6

1: Mesenchyme condenses due to signaling molecules
2: Osteoblasts differentiate and begin forming osteoid around the blood vessels inside the condensed mesenchyme
3: Osteoblasts begin calcifying that osteoid forming a honeycomb around the blood vessels
4: Bone develops outward until the spongy bone is covered

Question 7

What can be found in the outer layer of periosteum?

What is this layer called?

Answer 7

Blood Vessels and Nerves

Fibroblasts and Collagen

Sharpey’s Fibers

Fibrous layer

Question 8

What cells activity is associated with high Alkaline Phosphatase activity?

Answer 8

Osteoblast activity

(specifically as they are becoming osteocytes, they give off “AlkPhos”)

Question 9

Where is red bone marrow primarily found in adults and children?

Answer 9

In the flat bones in adults, and in all bones in young children

Question 10

What do osteoprogenitor cells differentiate into?

Answer 10

Osteoblasts

Question 11

What lamellae are adjacent to the endosteum?

Answer 11

The Inner Circumferential Lamellae

Question 12

Actions of which zone of endochondral ossification cause lengthining of the bone?

Answer 12

Zone of hypertrophy

Question 13

What are the four steps of bone fracture repair?

Answer 13

1: Hematoma Formation
2: Soft (Fibrocartillagenous) callus formation
3: Hard (bony) callus formation
4: Bone remodeling

Question 14

Where are osteoprogenitor cells found?

Answer 14

Inner layer of the periostium

Endosteum

Question 15

What is the normal function of FGFR3?

What changes to cause Achondroplasia?

Answer 15

FGFR3 stops growth during adulthood

It activates prematurely

Question 16

What is the heredity of Achondroplasia?

Answer 16

Autosomal Dominant

Question 17

What are Sharpey’s fibers, and what is their function?

Answer 17

They are collagen fibers that penatrate the outer circumferential lamellae.

They anchor they periosteum to the bone itself

Question 18

Where would you find the endosteum?

Answer 18

Covering the spongey walls.

(Said another way, on the walls of the medullary cavity)

Question 19

What lamellae lie just deep to the periosteum in bone?

Answer 19

The Outer Circumferential Lamellae

Question 20

How do osteoclasts resorb bone? (Two enzymes)

Answer 20

They create a localized secluded acidic environment using H⁺-ATPase, then degrade the organic matrix via Cathepsin K Protease

Question 21

Where do osteoclasts come from?

Answer 21

The Monocyte Lineage

Question 22

In what zone of endochondral ossification is the medullary cavity produced by osteoclasts?

Answer 22

Zone of resorption

(Osteoclasts eat the dead chondrocytes)

Question 23

What might be a more primary disease that could cause Osteomalacia?

Answer 23

GI disease (Calcium / Vitamin malabsorption)

Question 24

What causes Rickets?

Answer 24

Calcium or Vitamin D deficiency during growth, causing deficient mineralization of cartilage in the growth plate

Question 25

What do we call Vitamin D or Calcium deficiency in adults?

Answer 25

Osteomalacia

Question 26

When might osteoprogenitor cells be the most active?

Answer 26

During times of bone repair

Question 27

In endochondral ossification, what surrounds the cartilagenous blueprint?

Answer 27

Perichondrium

Question 28

What separates the interstitial circumferential lamellae from the osteon?

Answer 28

The cement line

Question 29

What lies at the center of the osteon?

Answer 29

The Haversian Canal

Question 30

What are the symptoms of Rickets?

Answer 30

Delayed closure of the fontanelles Bowed lower limbs Bossing of the skull Bowing of distal radius and ulna

Question 31

What gene is involved in achondroplasia?

Answer 31

FGFR3 gene (*Fibroblast Growth Factor Receptor)*

Question 32

What cell deposits and mineralizes the osteoid?

Answer 32

Osteoblasts

Question 33

In endochondral ossification, what is the bone's blueprint made of?

Answer 33

Hyaline Cartilage

Question 34

When might we see woven bone?

Answer 34

During fracture repair During Remodeling During initial bone formation

Question 35

What population is more likely to get osteoporosis?

Answer 35

Elderly and postmenopausal females

Question 36

What connects Haversian Canals?

Answer 36

Volkman's Canals

Question 37

In which zone of endochondral ossification do the chondrocytes begin to die?

Answer 37

Zone of calcified cartilage

Question 38

Osteocytes create a complex network of branches to communicate with each other and with the nutrient supply - what is this network made of?

Answer 38

Canaliculi

Question 39

Why do you feel pain when you've broken a bone?

Answer 39

Because of the nerve endings in the fibrous outer layer of the periosteum

Question 40

On what part of the bone is there no periosteum?

Answer 40

The articular surfaces (joints)

Question 41

When does an Osteoblast become an Osteocyte?

Answer 41

When it entraps itself in its lacuna.

Question 42

What is the mechanism of osteoporosis?

Answer 42

Imbalance in Osteoblast and Osteoclast action leading to demineralization of the bone.

Question 43

What forms the soft callus in bone repair?

Answer 43

Chondroblasts

Question 44

What is another name for immature or primary bone?

Answer 44

Woven bone

Question 45

In endochondral ossification, what forms the primary ossification center?

Answer 45

Hypertrophy and subsequent death and phagocytosis (by osteoclasts) of chondrocytes in the middle of the **diaphysis**. This creates an opening known as the primary ossification center.