Flashcards in Bone Phys Deck (56):
An osteon is asst. with what type of bone?
Trabeculae are asst. with what type of bone?
What is the composition of bone?
1. Mineral matrix of calcium and phosphate salts
2. Collagen fibers and water
3. Organic matter
4. Inorganic matter
5. Bony matrix
What is the organic matter of the bone?
Bone cells, collagen fibers, blood vessels and nerves
What is the inorganic matter of the bone?
Ca++ and PO4 salts --> Hydroxyapatite crystals
What is the bony matrix of the bone?
Dense cortical tissue w/ inner elastic trabecular tissue w/in marrow spaces
What is an osteoprogenitor cell?
Osteoprogenitor cells (type of stem cell)
periosteum, endosteum and epiphyseal plates osteoblasts
What is an osteocyte?
mature bone cells maintaining bony matrix
What is an osteoblast?
What is an osteoclast
bone-destroying cells (phagocytic lineage)
What are the functions of the bones?
1. Provide rigidity, hardness, strength & support for body
2. Protects vital internal organs
3. Stores lead and other heavy metals*
A. Released later for excretion
4. Stores minerals calcium & phosphorus
Role in calcium balance
Define tensile strength
Tensile strength (collagen fibers)
strength to endure stretching forces
Define Compressional strength
Compressional strength (calcium salts)
strength to endure squeezing forces
Define Bone remodeling
1. Lifelong process
A. Bone resorption and new bone formation (ossification)
B. Micro-damage to bones during nl activity
2. Following fractures
What are bone turnover markers?
1. serum and urine
A. Nl process of bone resorption results in release of bone mineral and osteoid (unmineralized bone, which is composed of collagen
Why is bone remodeling a dynamic process?
Bone resorption (osteoclasts) and bone formation (osteoblasts)
What is hyaline cartilage?
1. Most abundant, 80% is H2O w/in gel structure
2. Articular cartilage
What is fibrocartilage?
Intervertebral disks, areas of tendons connected to bone, menisci
Where is a primary ossification center?
Where is a secondary ossification center?
Central area of the bone
Ends of the bone
What system regulates bone physiology?
Endocrine system maintains plasma and bone calcium and phosphate balance:
What hormones are involved in maintaining bones?
Parathyroid hormone (PTH)*
Calcitriol (1,25- (OH)2 vitamin D3)**: most active metabolite of VD
How is estrogen related to bone density?
Estrogen supports normal bone metabolism by stimulating osteoblastic activity and limiting osteoclastic activity
What is PTH secretion regulated by?
PTH secretion follows negative feedback regulation
Ca++ stimulates PTH release
Where is 99% of the body's calcium located?
How does the parathyroid gland maintain bone density?
1. When serum Ca++ , PTH is secreted by chief cells of gland
A. inc Bone Resorption
stimulates osteoclast activity to release stored Ca++ ions and PO4
B. Inc Intestinal absorption of Ca++ by enhancing the action of calcitriol
C. inc Ca++ reabsorption and dec PO4 reabsorption @ kidneys
How does the thyroid gland maintain bone density?
1. When serum Ca++ inc, calcitonin is released from parafollicular (or C) cells of gland
2. dec Bone Resorption (inhibits osteoclast activity)
3. No effect on intestines
4. inc excretion of Ca++
True/faslse: vitamin D is not a vitamin
True: steroid hormone
How much of calcium is active/free?
½ of circulating calcium is bound to albumin
Free, ionized calcium is physiologically active
What are the sources of vitamin D?
1. Skin production (d3) from UVB/A rays (90%)
2. jejunal absorption (D2 and D3) 10%
What is the role of calcitonin?
1. Calcitonin inhibits D3 production by the kidney
2. Inhibit bone resorption
How is inactive D3 metabolized to active D3?
Inactive form D3 --> liver 25 (OH)D3 --> Kidneys -->1,25(OH)2D3
What is the active form of Vitamin D3?
1,25(OH)2D3 = calcitriol
What are the sxs of hypocalcemia?
A. Perioral, hands, feet
2. muscle cramps or spasms
What is Chvostek's sign?
Tap over the facial nerve
What is Trousseau's sign?
Carpal pedal spasm when BP cuff is on and inflated above systolic bp
What are the sxs of hypercalcemia?
1. Kidney stones
2. Bone pain, osteoporosis
3. GI upset
4. “thrones”- polyuria and constipation
5. CNS effects
A. Lethargy, fatigue, depression, psychosis, delirium, coma
What is the Mnemonic: for hypercalcemia?
“Stones, bones, abdominal groans, thrones and psychiatric moans”
What is the cause of hypercalcemia?
Cause of hypercalcemia is primary hyperparathyroidism caused by parathyroid adenoma
1. Low bone mass/ Very low bone mass
2. Osteoclast activity > osteoblast activity
A. Weak bones
B> inc risk of fractures
When is peak bone mass?
Peak bone mass 25-29 yo, plateaus, then decreases perimenopausally (in men, age 60?)
What can osteopenia/osteoporosis be caused by?
1. “Softening of bones”
2. Weak and flexible bones d/t defective mineralization of bones
What are the 2 main causes of osteomalacia?
1. Insufficient Ca++ absorption from intestines d/t lack of dietary Ca++ or a deficiency of or resistance to vitamin D
2. PO4 deficiency caused by inc renal losses or dec intestinal absorption
3. Can result from kidney failure or hyperparathyroidism also
What is metabolic rickets?
Metabolic bone disorder d/t defective mineralization of growing bones in children --> permanent bone deformities
What is nutritional rickets?
inadequate exposure to sunlight and/or inadequate intake of vitamin D, calcium or phosphate
What can nutritional rickets be caused by?
1. Underdeveloped countries
2. Prolonged breast-feeding w/o vit D supplementation
3. Soy or rice beverages not fortified w/ vit D
What are the physical signs of rickets?
Femurs bend laterally and affected person has bowlegged appearance (genu varum)
What are the daily requirements of vitamin D?
Vitamin D3 800-1,000 IU Daily
What are the calcium carbonate/citrate daily requirements?
A. >50 yo 1,200 mg
B. 19-50 yo 1,000 mg
C. 9-13 yo 1,300 mg
D. 4-8 yo 800 mg
E. 1-3 yo 500 mg
Where can calcium carbonate be found? Tums
Why does kidney failure lead to osteomalacia?
Inactive VD3 cannot be converted into active VD3, increased risk of fracture