•stem cells developed from fibroblasts
•produce osteoblasts & osteocytes.
•In endosteum, periosteum , central canals.
•Mitotically active; stress & fractures stimulate division.
•“Bone formers” synthesize organic matrix.
•Non-mitotic, mitosis and differentiation of osteogenic cells is the only way they are generated
•hormonal function: osteocalcin-stimulates and increases insulin
•former osteoblasts trapped in matrix in lacunae
•connected by canaliculi.
•Communicate with neighboring cells via gap junctions. Maintain homeostasis, sense strain to stimulate remodeling
•Large, bone-dissolving cells found on bone surface
•Formed by fusion of 3 – 50 bone marrow stem cells
•Related to WBCs (different cell lineage than other bone cells).
•Ruffled border facing bone surface increases surface area, for bone resorption.
•In resorption bays that they have eaten into the bone.
what are the two kinds of bone marrow?
red and yellow
what does hemopoietic tissue mean and what type of bone marrow fits this description?
tissue that produces blood cells; red bone marrow
produces the flat bones of the skull and most of the clavicle. such bones develop within a fibrous sheet similar to the dermis of the skin, so they are sometimes called dermal bones
a process in which a bone develops from a preexisting model composed of hyaline cartilage. it begins around the _ week of fetal development and continues into a person's __
endochondral ossification; 6th; 20's
a process similar to intramembranous ossification where bones continually grow throughout life in diameter and thickness
states that the architecture of a bone is determined by the mechanical stresses placed upon it, and the bone thereby adapts to withstand those stresses
wolff's law of bone
describe the stages of intramembranous ossification:
1. condensation of mesenchyme into soft sheet permeated with blood capillaries
2. deposition of osteoid by osteoblasts on mesenchymal surface; entrapment of first osteocytes; formation of periosteum
3. honeycomb of bony trabeculae formed by continued mineral deposition; creation of spongy bone
4. surface bone filled in by deposition, converting spongy bone to compact bone. persistence of spongy bone in the middle layer
what are the five zones of metaphysis?
1. zone of reserve cartilage
2. zone of cell proliferation
3. zone of cell hypertrophy
4. zone of calcification
5. zone of bone deposition
a crystallization process in which calcuim phosphate, and other ions are taken from the blood plasma and deposited in bone tissue, mainly as crystals of hydroxyapatite
abnormal calcification of tissues is called..
the process of dissolving bone
the calcium concentration in the blood plasma is normally __ to __ mg/dL
9.2 to 10.4
a calcium concentration that causes excessive excitability of the nervous system and leads to muscle tremors, spasms, or tetany.
_______ normally bind and neutralize negatively charged groups on the cell surface, contributing to the difference between the positively charged outer surface of the membrane and the negatively charged inner surface
a blood calcium excess in which excessive amounts of calcium bind to the cell surface, increasing the charge difference across the membrane and making sodium channels less responsive. thus, nerve and muscle cells are less excitable than normal.
depression of the nervous system, emotional disturbances, muscle weakness, sluggish reflexes, and sometimes cardiac arrest
hypocalcemia can result from:
vitamin D deficiency, diarrhea, thyroid tumors, underactive parathyroid glands, pregnancy/lactation, **accidental removal of the parathyroid glands during thyroid surgery
calcium homeostasis is regulated by these three hormones:
calcitriol, calcitonin, and parathyroid hormone
a hormone that is a form of vitamin D produced by the sequential action of the skin, liver and kidneys. it behaves as a hormone who's function is to raise the blood calcium concentration.
calcitriol promotes _____, and is also necessary for _____. without it, calcium and phosphate levels in the blood are too low for normal deposition, resulting in a softness of the bones called ____ in children and ____ in adults
bone resorption; bone deposition; rickets; osteomalacia
a hormone secreted by C cells (clear cells) of the thyroid gland when blood calcium concentration rises too high. it lowers the concentration by two principal mechanisms:
osteoclast inhibition; osteoblast inhibition
_____. within 15 min after calcitonin is secreted, it reduces osteoclast activity by as much as 70%, so osteoclasts liberate less calcium from the skeleton
____. within an hour, calcitonin increases the number and activity of osteoblasts, which deposit calcium into the skeleton
a hormone secreted by the parathyroid glands to raise blood calcium levels to stimulate bone deposition, therefore increasing or decreasing bone mass