Calcium & Phosphorus Flashcards
Name the fundamental roles of calcium
- major cation in bone & teeth
- neurotransmission (synapse)
- skeletal/cardiac/smooth m contraction
- enzymatic reactions
- hormone secretion/mediator
- blood clotting
Most calcium is found in ____
bone
Name 3 forms of calcium
- ionized (50%)
- bound to proteins (41%)
- combined with anions (9%)
What form of calcium is biologically active (what we use)?
Ionized
What is the normal range of calcium levels in the plasma?
8.6-10.6 mg/dl
What term would describe a patient that has a calcium serum level of 11.3 mg/dl?
Hypercalcemia
What term would describe a patient that has a calcium serum level of 8.0 mg/dl?
Hypocalcemia
Calcium is a nervous system ____
depressant
What is the major cation in bone?
calcium
What is the major anion in bone?
phosphate
The majority of calcium and phosphate is tied up together in ____
hydroxyapatite
What is the normal range of phosphate levels in the plasma?
3-4.5 mg/dl
The gut wall has ____ absorption of calcium
poor
(absorb 350mg/day, excrete 250mg/day)
In terms of urinary excretion, most calcium is ____ here
resorbed
(90% prox, 10% distal)
Calcium resorption is ____ dependent
hormone
(serum calcium levels)
Dietary phosphorus is ____ absorbed across the gut wall due to ____
- readily
- calcium binding
When phosphorus levels are below 1mmol/L, what do the kidneys do with phosphate?
resorb ALL phosphate
When phosphorus levels are above 1mmol/L, what do the kidneys do with phosphate?
excretes via overflow mechanism (excretion = excess)
What hormone is consider the major regulator of plasma calcium and phosphorus levels?
Parathyroid hormone (PTH)
Secretion of PTH is ____ related to plasma Ca2+ levels
inversely
the release of PTH is monitored by Ca2+ sensing receptor (CaSR) on cell membrane of ____ gland cells
parathyroid
PTH & Ca2+ form a ____ feedback pair. as Ca2+ levels increase, PTH secretion ____
negative
decreases
____ Ca2+ regulates PTH secretion within minutes
ionized
What is the half life of PTH?
less than 20 mins
if sustained over time:
_______calcemia = shut down PTH synthesis & degrades stores (grandular atrophy)
________calcemia = cause gland hypertrophy
HYPERcalcemia
HYPOcalcemia
What short term effects does PTH have on bones? (normal daily swing)
- down regulate osteoblasts
- release of calcium & phosphate by osteoblasts & osteocytes
What are the long term effects of PTH on bone? (persistent hypocalcemia)
- stimulate production of osteoclasts & activates resorption of bone
- remove calcium phosphate salts from bone lying near these cells waiting to be mineralized
What function does PTH have on the kidneys?
- ^Ca2+ resorption from distal tubule
- MOST dramatic: inhibit resorption of phosphate (less phosphate to bind Ca2+, increasing serum calcium)
- stimulates synthesis of vit D metabolite -> ^PTH -> ^calcitriol
What effect does calcitriol have on the kidney?
- binds with cytosolic receptor and enters nucleus
- stimulates synthesis of calbindin
What effect does calcitriol have on the gut?
facilitates Ca2+ absorption
(phosphate absorption also stimulated by vit D)
What effect does calcitriol have on bone?
- stimulates bone resorption working synergistically with PTH
- receptor on osteoblasts promotes formation of osteoclasts
- receptor for calcitriol found in osteoclasts to increase activity
PTH has an indirect action on the gut via _____ & _____ production & release (kidney). Calbindin facilitates active transport of ____ across the gut wall
- calcitriol & calbindin
- Ca2+
Are there receptors for PTH in cells of gut wall?
no
PTH causes prompt increase of _____ & decreases of _____ in the plasma
Ca2+
phosphate
as plasma levels of Ca2+ rise, PTH levels ____, kidney excretes ____ Ca2+ & urinary Ca2+ levels achieve equilibrium to maintain homeostasis
decrease
more
All actions of PTH on the parathyroid, kidney & gut ____ Ca2+ influx into blood
increase
As PTH levels increase, plasma phosphate levels ____, but it is overwhelmed by the action of PTH on the ____ causing…
- increase
- kidney
- elimination of phosphate in the urine
What is the indirect role of phosphate on PTH?
lowers Ca2+ levels through physiological mechanisms:
- increases renal excretion of Ca2+
- Ca2+ binds with PO4-
–> Ca2+ drops, PTH increases
What is the purpose of increased Ca2+ excretion with increased phosphate levels?
PREVENT metastatic calcification
(seen in hyperparathyroidism)
How does PTH modulate hyperphosphatemia?
increases renal excretion of phosphate
What function does calbindin have on the body?
Increases calcium absorption in the gut (binds Ca2+ in gut)
What term would describe a patient that has a serum phosphate level of 5.2 mg/dl?
Hyperphosphatemia
What term would describe a patient that has a serum phosphate level of 1.9 mg/dl?
Hypophosphatemia
What would happen to Ca2+ and PTH levels if there is an increased phosphate level in the blood?
Calcium drops and an increase in PTH
What effect does vitamin D have on Calcium in the gut?
potent effect of increasing Ca2+ absorption
What must we have to build bone, which also has an important effect on bone resorption via its role in Ca2+ metabolism?
vitamin D
What is the major storage site for vitamin D?
muscle
profound muscle ____ is seen with vitamin D deficiency
weakness
Where is vitamin D converted to more metabolically active metabolites?
Liver & kidney
If PTH is increased, what is vitamin D converted to in the kidney?
calcitriol
(1-25(OH)2D3)
If PTH is decreased, what is vitamin D converted to in the kidney?
24-25(OH)2D3
Where is calcitonin produced?
parafollicular cells of thyroid gland
Calcitonin acts to ____ plasma Ca2+
lower
Calcitonin is a PTH ____
antagonist (does the opposite)
What is the mechanism of action of calcitonin on calcium?
- binds to membrane receptors -> ^cAMP
- cAMP initiates calcitonin action
- sequesters Ca2+ into mitochondria, reducing serum levels (pulls Ca into cells)
What effect does calcitonin have on osteoclasts?
inhibition of osteoclasts (bone resorption)
What effect does calcitonin have on phosphate?
enhances phosphate uptake into bone
(same result as PTH on phosphate, different mechanism)
____ “tries” to conserve Ca2+ (^Ca serum levels)
calcitriol
____ binds Ca2+ in the gut (^Ca absorption
calbindin
____ “tones down” levels of Ca2+ (decrease Ca serum)
calcitonin
