Chapter 7: Bones

Question 1

Osteogenic cells

Answer 1

Stem cells found in endosteum, periosteum, and in central canals.
Develop from embryonic mesenchyme, give rise to most other bone cells.
Multiply continuously to produce new osteoblasts.

Question 2

Osteoblasts

Answer 2

Bone-forming cells.
Line up in single layer under endosteum and periosteum.
Non-mitotic.
Synthesize soft organic matter of matrix, which then hardens by mineral deposition.

Question 3

Osteocytes

Answer 3

Former osteoblasts that have become trapped in the matrix they deposited.
Reside in lacunae, which are connected by canaliculi.
Some reabsorb bone matrix and others deposit bone matrix.
Contribute to homeostatic mechanism of bone density.

Question 4

Osteoclasts

Answer 4

Bone-dissolving cells.
Found on bone surface.
Develop from bone marrow stem cells.
Large cells, formed from the fusion of several stem cells.

Question 5

Bone remodeling

Answer 5

Results from combined action of osteoclasts (dissolve bones) and osteoblasts (bone-depositing).

Question 6

Bone resorption

Answer 6

Osteoclasts break down bone tissue and release those minerals into the blood

Question 7

Mineral deposition

Answer 7

Crystallization process in which calcium, phosphate, and other ions are taken from the blood plasma and deposited in bone tissue

Question 8

What three hormones regulate calcium homeostasis?

Answer 8

Calcitriol, calcitonin, and parathyroid hormone.

Question 9

Calcitriol

Answer 9

Form of vitamin D.
Raises blood calcium concentration - by increasing calcium absorption by the small intestine, increasing calcium resorption from the skeleton, promotes kidney reabsorption of calcium ions so less is lost in urine.

Question 10

Calcitonin

Answer 10

Lowers blood calcium concentration in two ways: reduces osteoclast activity so less calcium is lost from bones, and, stimulates osteoblasts, increasing the number and activity, which deposits calcium into the skeleton.
Important in children.

Question 11

Parathyroid hormone

Answer 11

Secreted by parathyroid glands.

PTH raises calcium blood levels.

Question 12

Phosphate homeostasis

Answer 12

Not regulated as tightly as calcium levels (since no immediate functional disorders arise)
Calcitriol promotes is absorption by small intestine and promotes bone deposition.
PTH lowers blood phosphate levels by promoting its urinary excretion.