9 Questions
What is the role of osteoblasts in bone remodeling?
Covering the inner surface of the canal with osteoid
What is the name of the small central canal that remains after bone remodeling is complete?
Haversian canal
What happens when serum calcium levels decrease?
Parathyroid chief cells secrete PTH
Calcitriol promotes the mineralization of bone using calcium and phosphate.
True
Where is approximately 85% of the body's phosphate stored?
Bones
What is the main inorganic form of phosphate in the plasma?
HPO4 and H2PO4−
Hypercalcemia leads to increased excitability of the nervous system.
False
Bone is a type of __________ tissue with a calcified extracellular matrix (ECM).
connective
Match the following hormones with their effects on bone:
PTH = Increased bone formation and increased apoptosis of osteoclasts Estrogen = Inhibits apoptosis of osteoblasts and stimulates apoptosis of osteoclasts Vitamin D = Stimulates osteoblasts and osteoclast differentiation
Study Notes
Calcium Regulation
- Only 0.1% of total body calcium is in the extracellular fluid, while the rest is stored in bones
- Calcium in plasma: 41% bound to plasma proteins, 9% bound to anionic substances, and 50% ionized and diffusible through capillary membrane
Phosphate Regulation
- Approximately 85% of body's phosphate is stored in bones, 14-15% in cells, and less than 1% in extracellular fluid
- Inorganic phosphate in plasma exists in two forms: HPO4 (1.05 mmol/L) and H2PO4 (- 0.26 mmol/L)
- pH of extracellular fluid affects the concentration of HPO4 and H2PO4 -
Effects of Calcium Imbalance
- Hypocalcemia (serum calcium < 8.5 mg/dL or ionized calcium < 4.65 mg/dL) can cause tetany, seizures, and increased neuronal membrane permeability to sodium ions
- Hypercalcemia (serum calcium > 10.5 mg/dL or ionized calcium > 5.25 mg/dL) can cause depressed nervous system, lack of appetite, and constipation
Bone Structure and Function
- Bone is a type of connective tissue with a calcified extracellular matrix (ECM)
- Bone matrix consists of organic and inorganic components: collagen, ground substances, glycoproteins, hydroxyapatite, and various ions
- Hydroxyapatite crystals fail to precipitate in normal tissues due to inhibitors like pyrophosphate
Mechanism of Bone Calcification
- Osteoblasts secrete collagen molecules that polymerize to form collagen fibers, which then form osteoid
- Osteoblasts become entrapped in osteoid and become quiescent, becoming osteocytes
- Calcium salts precipitate on collagen fibers, and over time, hydroxyapatite crystals form
Regulation of Bone Mineralization
- Pyrophosphate inhibits hydroxyapatite crystallization and calcification of bone
- Tissue-nonspecific alkaline phosphatase (TNAP), nucleotide pyrophosphatase phosphodiesterase 1 (NPP1), and ankylosis protein (ANK) regulate pyrophosphate levels
Bone Remodeling
- Osteoblasts, osteoclasts, and osteocytes work together to build and remodel bones
- RANK, RANKL, and osteoprotegerin (OPG) regulate osteoclast activity and bone resorption
- Mechanical load, hormones (PTH, estrogen, vitamin D), and medication (bisphosphonates, glucocorticoids) also regulate bone remodeling
This quiz covers the regulation of calcium and phosphate levels in the body, including distribution, plasma proteins, and diffusibility. Learn about the role of calcium in bodily functions and its importance in maintaining healthy bones and cells.
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