Spadarpo-Parthyroid/Bone Flashcards
Parathyroid hormone (PTH):
A. is released into plasma in response to increases in plasma calcium.
B. acts at the kidneys to increase calcium reabsorption and decreased phosphate reabsorption.
C. acts at the kidneys to decrease calcium reabsorption at the distal tubule.
D. acts at the bone to increase bone mineralization.
E. acts at the bone to decrease osteoclastic osteolysis
acts at the kidneys to increase calcium reabsorption and decreased phosphate reabsorption.
PTH is released into plasma in response to reduced plasma calcium levels. At the kidneys it increases distal calcium reabsorption and reduces phosphate reabsorption. It also stimulates the renal conversion of 25-hydroxycholecalciferol to active vitamin D (1,25-dihydroxycholecalciferol), which increases intestinal absorption of calcium.
Decreased plasma calcium levels result in:
A. reduced production of 1,25-dihydroxycholecalciferol.
B. reduced production of 25-hydroxycholecalciferol.
C. increased bone mineralization.
D. increased bone resorption.
E. increased plasma calcitonin.
increased bone resorption.
Decreased plasma calcium concentrations will stimulate the release of parathyroid hormone (PTH), which acts at bone to increase resorption, releasing calcium into the blood. PTH also acts at the kidney to increase calcium reabsorption.
Which of the following increases the rate of excretion of calcium ions by the kidney?
A. Decrease in calcitonin concentration in the plasma
B. Increase in phosphate ion concentration in the plasma
C. Decrease in the plasma level of parathyroid hormone
D. Metabolic alkalosis
Decrease in the plasma level of parathyroid hormone
The concentration of parathyroid hormone strongly regulates the absorption of calcium ion from the renal tubular fluid. A reduction in hormone concentration reduces calcium reabsorption and increases the rate of calcium excretion in the urine. The other choices have little effect on or decrease calcium excretion.
Which of the following stimulates the secretion of parathyroid hormone (PTH)?
A .Decrease in extracellular calcium ion activity below the normal value
B. Calcitonin
C. Respiratory acidosis
D. PTH-releasing hormone from the hypothalamus
Decrease in extracellular calcium ion activity below the normal value
Secretion of parathyroid hormone is regulated by changes in extracellular calcium concentration. Increases in the secretion rate are stimulated by decreases in extracellular calcium ion concentration.
If parathyroid hormone is infused intravenously into an animal, which of the following will be true 2 hours later?
A. Plasma phosphate ion concentrations will be elevated
B. Plasma calcium ion concentrations will be decreased
C. The rate of calcium excretion will be elevated
D. The rate of phosphate excretion in the urine will be increased
The rate of phosphate excretion in the urine will be increased
Administration of parathyroid hormone causes rapid loss of phosphates in the urine, owing to the hormone’s ability to diminish proximal tubular reabsorption of phosphate ions.
A medication, given to help reduce bone loss and reduce fracture risk might be expected to do the following:
A. reduce osteoClast maturation and activity.
B. induce osteoClast to secrete RANK-L (Rank Ligand).
C. increase erosion of trabecular bone.
D. reduce bone mineralization.
E. none of the above.
reduce osteoClast maturation and activity.
Reducing osteoClast maturation and activity conserves bone mass and strength. osteoClasts don’t secrete RANK-L. Erosion of trabecular bone is part of what the medication is aimed at reducing, not increasing. To reduce bone loss, we would need to increase mineralization.
Which of the following increases the rate of deposition and decreases the rate of absorption of bone?
A. Elevation of parathyroid hormone concentration
B. Elevation of estrogen concentration
C. Elevation of extracellular hydrogen ion concentration
D. Reduction in mechanical stress on the bone
Elevation of estrogen concentration
Elevation of estrogen concentration stimulates osteoblastic activity and reduces the rate of degradation of bone by osteoclasts. Elevation in hydrogen ions (acidity) displaces Ca2+ from protein binding, increases extracellular Ca2+, reduces PTH and conserves bone.
The function of which of the following is increased by an elevated parathyroid hormone concentration?
A. Osteoclasts
B. Hepatic formation of 25-hydroxycholecalciferol
C. Phosphate reabsorptive pathways in the renal tubules
D. All of the above
Osteoclasts
An increase in the concentration of parathyroid hormone results in the stimulation of existing osteoclasts and, over longer periods, increases the number of osteoclasts present in the bone.
Which of the following factors favor bone resorption: A. PTH B. RANK-L C. Vit. D D. Glucocorticoids E. All of the above
E. All of the above
Which of the following factors favor bone formation: A. PTH B. RANK-L C. Osteoprotegerin OPG D. Vit D
C. Osteoprotegerin OPG
What are useful bone resorption markers?
CTX-1
TRACP5b
What are useful bone formation markers?
P1NP
BSP
What are the 2 types of bone formation and when do they occur?
- Endochondral bone formation that occurs via a cartilage precursor….all bones form this way (except cranial)
- Intramembranous ossification, most remodeling occurs this way after childhood
What effect does gluccocorticoids have on bone remodeling?
up regulate RANK-L and block OPG and enhance bone resorption (decrease formation)
65yo female complains of back pain in L1 region and x ray shows vertebral compression fraction. She takes prednisone for asthma and DXA bone density scan shows low BMD, vit D is also low. What does she have?
Post-menopausal osteoporosis.
Steroids cause poor Ca2+ absorption in intestines and also down regulate osteblastic bone formation
