2. Internal Bone Anatomy + Wolff's Law

Comprehensive practice flashcards reviewing internal bone anatomy, histology (osteons, lamellae, canaliculi, bone cells), Wolff's law, and hormonal regulation of bone remodeling via PTH and calcitonin.

Which bone cells are responsible for breaking down bone?

Osteoclasts (osteoCLAST)

Which bone cells are responsible for building bone up?

Osteoblasts (osteoBLAST)

What are the structural regions and components numbered 1 through 6 on the diagram of the long bone?

1: Spongy bone, 2: Medullary cavity, 3: Compact bone, 4: Epiphysis, 5: Metaphysis, 6: Diaphysis (shaft)

What is an osteogenic cell?

Stem cells that eventually divide into/turn into osteoblasts.

What is an osteocyte, and how does it form?

A mature bone cell that results from an osteoblast after it has surrounded itself with bone (osteoid).

The small space or gap (derived from the Latin for "a gap"; plural: lacunae) that is around an osteocyte once an osteoblast surrounds itself with osteoid is called…?

The lacuna

Concentric circles of bone layers in compact bone formed by lacunae, resembling the rings of a tree are called…?

Lamellae

What is a Haversian (central) canal, and what structures does it contain?

An empty space located at the center of concentric lamellae containing the artery, vein, and nerve (as well as lymph vessels and fluid) that supply that area of bone.

What is an osteon?

A functional unit of compact bone made up of concentric lamellae, lacunae, a central Haversian canal, and ancillary structures. Many osteons together form a bone.

What are the two primary mechanisms by which bones remodel?

1. Mechanical Stress, and 2. Hormones.

What does Wolff's law state regarding bone remodeling?

Bones grow or remodel according to the stresses put on them; mechanical stress increases osteoblast activity, and heavy stress results in thicker, stronger bone.

What blood level triggers the secretion of parathyroid hormone (PTH), and what is its effect on bone?

PTH is secreted in response to low blood serum calcium ($Ca^{2+}$) levels; it increases osteoclast activity, which breaks down bone to elevate calcium levels in the blood.

Which hormone lowers blood calcium levels and what is its effect on bone?

Calcitonin lowers blood calcium levels

It slows down osteoclast activity (decreasing breaking down of bone), stimulating osteoblast activity (increasing bone formation)