parathyroid and calcium regulation Flashcards
what is calcium homeostasis essential for
bones and teeth
all cells
nerve and muscle function
blood clotting
what are the three hormones responsible for calcium homeostasis
patathyroid hormone PTH
calcitonin
vitamin D
what percentage of bone and teeth is calcium
99
what percentage of soft tissue cells is calcium
0.9
what percentage of ECF is calcium
0.1
what is the ECF broken into and the calcium percentage
0.05 protein bound or inorganic complexes
0.05 free ionized
what kind of calcium is bioactive
only free ionized Ca2+
what parts of calcium cocentration are regulated
both ECF plasma conc of ionized calcium and total body calcium
what is 0.05 free ca in ECF regulated by
exchange bw bone and ECF
renal excretion
what kind of regulation is ECF free ionized ca regulation
min to min regulation
how is total body calcium regulated
by GI absorption of ca
renal excretion
what kind of regulation is total body ca regulation
long term regulation
what are the two types of cells of the parathyroid gland
cheif cells
oxyphil cells
what do chief cells have
calcium ion sensing receptor
what kind of hormone is PTH
peptide hormone
what kind of feedback loop is PTH regulated by
negative feedback
negative feedback of PTH
PTH synth and secretion stiumulated by low plasma ionized Ca
PTH raises free ionized Ca in ECF
what does PTH act on
bone, kidney, and
GI tract- via vit D
what does PTH act on
bone, kidney, and
GI tract- via vit D
how long does it take for complete skeletal turnover
every 10 yrs
what do osteoblasts do
create new bone by secreting organic matrix- osteoid and then mineralizing it with calcium crystals
what do osteocytes do
involved in calcium regulation but do not create new bone
where do osteocytes arise from
entombed osteoblasts
what do osteoclasts do
dissolve bone- bone resoption by solubilizing the crystals
what does PTH stimulate
movement of ionized Ca from bone fluid to ECF- fast response time
bone dissolving activity of osteoclasts- slower response time- coincident release of ca and phosphate
PTH tips bone remodeling in favour of resorption
PTH fast exchange effect to inc ca method
ca is moved from the labile pool in the bone fluid to the plasma by PTH activated Ca pumps located in the osteocytic-osteoclastic bone membrane
PTH slow exchange effect to inc ca method
ca is moved from the stable pool in the mineralized bone to the plasma through PTH induced dissolution of bone by osteoclasts
what is the osteocytic-osteoblastic bone membrane formed by
filmy s=cytoplasmic extension of interconnected osteocytes and osteoblasts
where is the bone fluid labile pool of ca
in canailculi
where is the ca in the plasma
in central canal
what controls osteoclast activity
osteoblast derived factors
PTH effect on kidneys
PTH inc renal reabsorption of ca and inc excretion of phosphate
PTH induces activation of vit D
what effects does calcitonin have on bone remodelling compared to PTH
opposite
what kind of hormone is calcitonin
peptide hormone
what does calcitonin do
decreases movement of ionized calcium from bone fluid to ECF
inhibits activity of osteoclasts and therefore derceases bone reserption
inrceases renal calcium excretion
what does the inverse regulation of PTH and calcitonin release act through
the same calcium sensing receptor mechanism
what is the bioactive form of vitamin D
1,25 (OH)2 vitamin D3–calcitriol
what is calcitriol derived from
inactive vitamin D produced in skin by action of sunlight or present in some food
what is the biologically inactive precurson of vitamin D3 called
7- dehydrocholesteorl
what kind of hormone is vitamin D
steroid hormone
how is vitamin D activated
by addition of 2 hydroxyl groups
how is vitamin D activated
by addition of 2 hydroxyl groups
1st added in liver- 25 OH vitamin D
2nd added in kidneys 1,25 OH2 vitamin D3
what is the kidney hydroxylation enzyme stimulated by
PTH
low plasma ionized calcium
low plasma ionized phosphate
prolactin during lactation
what happens when plasma ionized calcium is high
renal hydroxylation produces an inactive form
24,25 OH2 Vit D3 by a different enzyme
what are the effects of activated vitamin D3
inc total body ca by inc GI ABSORPTION OF cA
-this is a dose dependant response
-slow long lasting response
-adjts ca intake from the diet to match needs via changes of ration activation./ inactive vit D
increases ECF ionized calcium by enhancing response of bone to PTH- resoption
problems of calcium homeostasis
-hyperparathyriodism
-hypoparathyroidism
-vid D deficiency
-osteoporosis
hypoparathydoism
rare condition usually caused by automimmune disease of physical damage to the glands
low PTH secretion results in low plasma ionied calcium level
causes increased neuromuscular excitability by increasing nrve membrane permeability to Na
-paresthesia- pins and needles
-tetany- muscle spasms
-potentially lethal due to failure of respiration
what is the primary form of hyperthyroidism due to
usually due to hypersecreting patathyroid tumor
- hypercalcemia results from high PTH
what is hyperparathyroidism due to
chronic renal disease or vitamin D deficiency causing hypocalcemia which causes high PTH production
hyperparathyroidism- high PTH level with elevated Ca causes
depressed muscel and nerve excitability
-high ECF ca conc
inc risk of fractures
-demineralization of bone
risk of kidney stones
-high conc of calcium in renal filtrate
hyperparathyroidism with vid D deficiency what does it do
impairs Fi absorption of Ca
resulting high PTH causes bone demineralization
-in children- rickets
-in adults- osteomalacia
how is rickets treated
vitamin D therapy
what affects vitamin D production
skin pigmentation
african- dark skin tone is 100% deficient
what are the heath risks of vit d deficiency
elevated risk of cancer, cardiovascular disease, autoimmune disease, multiple sclerosis, osteoporosis
what lowers risk of premature death
vitamin d supplements
where are vitamin D3 receptors expressed
everywhere in the body
osteoporosis
condition in which bone resorption is greater then bone formation
-reduced osteoblast activity incrased osteoclast activity
-plasma calcium, phosphate PTH, and vitamin D levlels are usually normal
-reuslts in reduction of bone mass
what decreases with aging
bone density and bone mass
what inhibits bone resorption and how does it do it
estrogen by deceasing osteoclasts activity and increasing osteoblast activity
when is there increased incidence of osteoporosis
post menopausal women when estrogen levels are reduced
what does prevention of osteoporosis include
adequate calcium and vid D throughout life
doing weight bearing exercise
not smoking
