Bone I

Question 1

True or false: Bone is an organ system

Answer 1

True. It’s constantly being remodeled and must respond to changes in the
environment.

Question 2

What are characteristics of woven bone? Does it have an ordered structure?

Answer 2

It’s primary bone and is the first bone to appear in embryonic development and in
fracture repair. It’s not ordered and is characterized by random disposition of collagen
fibers. It’s rich in osteocytes. It’s temporary and later replaced by secondary bone
(usually when the toddler starts walking).

Question 3

Give details on lamellar bone

Answer 3

it’s also called secondary bone and is the type of bone usually found in adults. It has
an organized pattern (at approximately right angles) where lamellae are organized either
parallel to each other or concentrically around a vascular canal.

Question 4

What are other names for trabecular bone?

Answer 4

Cancellous bone, spongy bone. Trabecular bone is an inner meshwork

Question 5

What is another name for compact bone?

Answer 5

A: Cortical bone. Compact bone has a rigid outer shell

Question 6

What is wrong in osteoporosis?

Answer 6

there’s a decrease in bone mass. Bone does not remodel very well with age. Also
some endocrine issues

Question 7

What is still okay in osteoporosis?

Answer 7

the ratio of mineral to matrix is normal

Question 8

What deficiency is there is osteogenesis imperfecta?

Answer 8

There’s a collagen type I deficiency

Question 9

Name the four fundamental cells in bone. Give their roles as well.

Answer 9

Osteoprogenitor (stem), osteoblast (synthetic), osteocyte (maintenance, repair), and
osteoclast (dissolve, remodel).

Question 10

What’s the only way bone can grow?

Answer 10

through appositional growth

Question 11

Where are osteoprogenitor cells located?

Answer 11

they line the bone surface

Question 12

What are some characteristics of osteoprogenitor cells?

Answer 12

They’re mesenchymal derived, mitotic (not synthetic), a pre-osteoblast cell type,
spindle shaped (thin) and migratory

Question 13

Are osteoblasts mitotic?

Answer 13

NO!! The suffix –blast is a misnomer. Instead, they are synthetic.

Question 14

Which cells are responsible for synthesizing all the osteoid? Where are they located?
What are the shapes of these cells?

Answer 14

Osteoblasts. They are cuboidal in shape and secrete their materials at the base of the
cell. They are located at the surface of the bone matrix.

Question 15

What is the effect of PTH on osteoblasts? What other effects does PTH have on these
cells?

Answer 15

PTH inhibits osteoblast. It also inhibits alkaline phosphatases and collagen synthesis.

Question 16

How do osteoblasts communicate with each other?

Answer 16

A: Gap junctions

Question 17

What is the primary function of osteocytes?

Answer 17

maintenance. They are reserve cells found within the calcified bone matrix in lacunae

Question 18

Who are osteocytes derived from?

Answer 18

derived from osteoblasts that have been engulfed in the matrix

Question 19

When are osteocytes “activated”?

Answer 19

They’re activated in repair (they can differentiate back into osteoblasts if there’s a
fracture). Also, they are mechanicoreceptors for bone remodeling.

Question 20

What is the primary role of osteoclasts?

Answer 20

they dissolve bone and are thus involved in remodeling

Question 21

What are osteoclasts derived from?

Answer 21

they are derived from mononuclear phagocytic system (similar to macrophage)

Question 22

Which bone cells are large and multinucleated?

Answer 22

osteoclasts

Question 23

Where do osteoclasts reside? How do they attach themselves there?

Answer 23

They reside on bone surfaces, attached via integrins and cadherins to osteopontin.
More specifically, they are found in depressions called “Howships’s Lacunae”.

Question 24

How do osteoclasts exert their influence on bone?

Answer 24

A: secrete acid collagenases and acid phosphatases and other proteolytic enzymes that
decalcify bone and digests osteoid.

Question 25

Q: Osteoclasts are stimulated by PTH indirectly. Explain.

Answer 25

A: Osteoclasts don’t have PTH receptors. PTH stimulates osteoblast to secrete RANKL.
Osteoclasts DO HAVE RANKL receptors. Osteoclast action results in elevated blood
calcium

Question 26

Q: What hormone inhibits osteoclasts?

Answer 26

A: They are inhibited directly by calcitonin (from C-cells of thyroid).

Question 27

Q: What is the bone matrix composed of?

Answer 27

A: Organic (osteoid) – fibers are collage type 1. “Glue” is GAGs, proteoglycans,
glycoproteins (ie osteonectin) and these help anchor the Ca2+ phosphate crystals.
Inorganic is hydroxylapatite crystals—the “hardener”. For mineralization to occur the
combined local concentration of Ca2+ and phosphate must be above a threshold.
Calcium-binding glycoproteins and the phosphatases released in matrix vesicles by
osteoblasts promote calcification of the matrix by creating a high concentration of Ca2+
and phosphate locally. The high ion concentrations cause crystals of CaPO4 to form on
the matrix crystals. Mineralization lags behind the front of osteoid deposition.

Question 28

Q: Describe the pathophysiology of Padget’s disease.

Answer 28

A: Elevated osteoclast activity resulting in elevated resorption of bone and compensatory
deposition of primary woven bone.

Question 29

Q: Describe the effects of bone cancer (ie osteosarcoma).

Answer 29

A: Malignant tumors of osteoblasts, more common in children, cells represent
osteoprogenitor and therefore little/weak matrix is made. The skeleton is often the site of
metastases from tumors originating from malignancies in other organs like breast, lung,
prostate, and thyroid.

Question 30

Q: What is osteomalacia? What’s the disease called in children?

Answer 30

A: Characterized by improper mineralization. It’s called rickets in children. There’s
insufficient Ca2+ and phosphate resulting in softening of the bone and therefore increases
in fracture. Often a result of vitamin D deficiency which is important for the absorption
of Ca2+ and phosphate by the small intestine

Question 31

Q: True or false: both cortical and trabecular bone start out as woven and become
lamellar in the adult.

Answer 31

A: True.