Osteoporosis Pathophysiology Flashcards
What can cause a low bone mineral density BMD?
- Increase in bone degradation
- Decrease in bone deposition
What is a diagnosis of osteoporosis
T score equal or below -2.5
What machine is used to measure BMD? Where in the body is BMD measured?
DEXA (dual energy x-ray absorptiometry)
Common places
- Femoral neck (in hip)
- Spine L1-L4
Differentiate between the comparisons for T score and Z score?
Diagnosis?
T-score
- compares your BMD to the peak bone mass of young adults
- Osteoporosis: more than 2.5 standard deviations below
- Osteopenia: 1-2.5 SD below
Z-score
- Compares your BMD to people of your age, sex, weight, + ethnic origins
- Concern if more than 2 SD below (means there is something else other than age affecting it)
What are uses of calcium?
- Contract muscles
- Send signals
- Activate neurons
What are sources of VIT D
D2 Ergocalciferol: found in food, yeast
- supplement D2 for vegans
D3: Cholecalciferol: made in skin through sunlight
- more active
What is the purpose of Vit D? What is the MOA (3)
Purpose: Vit D raise serum calcium in response to hypocalcemia
By:
- inc absorption of calcium in intestines
- inc reabsorption of calcium in kidney
Increase bone resorption
- stimulates osteoblasts to secrete RANKL –> activate osteoclasts –> draws Ca (resorb) from bone to increase serum calcium
What is the absorption/purpose of phosphate?
Define hypercalcemia
Absorbed in small intestine
Purpose:
- stores and releases energy
- used in production of bone, lipids, protein
Hypercalcemia
- too much Ca stuck in phosphate
- leeching of calcium from bones
What is the purpose of parathyroid hormone?
What triggers release?
What slows release?
Raise serum calcium
- low serum calcium or high serum phosphate triggers release of PTH
High serum Vit D slows release of PTH
What is the mechanism of PTH? (3)
- increase reabsorption of calcium and excretion of phosphate in kidneys
- increase Vit D activation in kidneys
Increase bone resorption/formation
What is source/purpose of calcitonin?
Source: from the parafollicular cells of the thyroid
Purpose: lowers serum calcium
What is the mechanism of calcitonin? (3)
- Decrease absorption of calcium in intestines
- Decrease reabsorption of calcium in kidneys
- Inhibit osteoclasts
Explain trabecular bone
Location?
Function?
Inner bone structure with a high metabolic turnover
- Mostly in spine
Function: provides calcium during periods of deficiency
Explain cortical bones
Location?
Outer shell of bones
- Mostly in long bones
Toughness associated with collagen
Stiff (mineral content/bone density)
Function of osteoblast
Build bone
- Secrete collagen to give bones shear and tensile (pulling) strength
- Secrete proteoglycans to help bone salt deposition
