Histology (Bones) Part 2

Bone is a type of connective tissue with a calcified extracellular

matrix (ECM), specialized to support the body, protect many

internal organs, and act as the body’s Ca2+ reservoir.

• True

• False

Osteoblasts differentiate from (stem) osteoprogenitor cells and

secrete components of the initial matrix, called osteon, that allow

matrix mineralization to occur.

• True

• False

Answer explanation

Not OSTEON but OSTEOID

Important components of osteoid include type II collagen, the

protein osteocalcin, which binds Ca2+ and matrix vesicles with

enzymes generating PO4

-.

• True

• False

Answer explanation

Type I collagen

High concentrations of Ca2+ and PO4

- ions cause formation of

hydroxyapatite crystals, whose growth gradually calcifies the

entire matrix.

• True

• False

Osteocytes differentiate further from osteoblasts when they

become enclosed within matrix lamellae and act to maintain the

matrix and detect mechanical stresses on bone.

• True

• False

Answer explanation

It should be lacunae not lamellae

Osteoclasts are very small cells, formed by fusion of several blood

monocytes, which locally erode bone matrix during osteogenesis

and bone remodeling.

• True

• False

Answer explanation

Osteocytes are LARGE cells.

Periosteum is a layer of dense connective tissue on the inner surface

of bone, bound to bone matrix by bundles of type I collagen called

perforating (or Sharpey) fibers.

• True

• False

Answer explanation

Periosteum is located at the OUTER surface of the bone.

Regions of periosteum adjacent to bone are rich in osteoprogenitor

cells and osteoblasts that mediate much bone growth and

remodeling.

• True

• False

The endosteum is a thick layer of active and inactive osteoblasts,

which lines all the internal surfaces within bone; osteoblasts here are

also required for bone growth.

• True

• False

Answer explanation

The endosteum is a THIN layer of active and inactive osteoblasts,

In long bones of the limbs, these two types of mature bone tissue

occur in both the knobby, bulbous ends, called epiphyses, and in

the intervening shaft or diaphysis.

• True

• False