Endo-Ca and Pi homeostasis Flashcards
PTH receptors (G-protein coupled Rs) are expressed in
bone and kidney
major hormones that regulate Ca homeostasis
Calcitriol
PTH
Calcitonin
PTH-R of bone expressed on
osteoblasts
Factors that inhibits Calcitriol synthesis via negative feedback
impacts on calcitriol synth:
High Vit D level
H. ECF Ca
H. ECF pi
Vit D impact on PTH
PTH secretion is inhibited by that
Calcitriol effect
inc. plasma conc of BOTH Ca and Pi
Ca salt content distribution in bone, ICF and ECF
99% in bone (hydrozyapetite crystals major form)
1% in ICF +ECF–> .1% ECF and 0.9 ICF
leads to decreased PTH secretion
an increase in plasma Ca
Which form of the Ca is affected by hypo and hypercalcemia
ionized form
Controls Ca2+ homeostasis
plasma Ca
DBP
transport protein
VitD-Binding protein
Cells with Ca-sensing plasma membrane R (Ca-R)
PTH-secreting cells
Calcitonin secreting cells
kidney and intestinal epithelium
Bone ? unclear
Calcitriol synth. stimulated by
impacts on Calcitriol synthesis:
PTH
L. ECF Ca
L. ECF Pi
T/F
ionized [Ca] pools in the ECF and ICF are at equilibrium
T
Rapid PTH responses of kidney cells expressing PTH-R
dec. Ca excretion with urine (within min)
Inc phosphate excretion with urine (within minutes)
PTH effect
inc Ca- dec Pi
The calcium salt contents of:
Bone
Body fluids: ECF and ICF
Bone- 99%
Body fluid: 1% ( 0.1% ECF and 0.9% ICF)
Percent distribution of calcitriol
99.6% and metabolites bound to Vit-D binding proteins (DBP)
and 0.4% as free form
indirect PTH inhibition bu Vit D
- feedback (through plasma conc of Ca)
PTH secretion is regulated bu
ionized plasma Ca
The active form of Vit D and its classification
Calcitriol
classified as steroid hormone
Rapid Ca mobilization response to PTH
From Soluble form
besides calcitriol, calcityonin and PTH what other hormones affect Ca homeostasis
glucocorticoids
thyroid H
GH
EST and And
given Ca conc. is 10 mg/ dl
and pi is 4 mg/dl what are the %distributions of various forms
Ca: 50% ionized- 45% protein bound and 5% complexed with ions
Pi: 84% ionized (Free), 10% protein bound and 6% complexed with ions
Vit D
1,25 (OH)2D3- PTH inhibitor
PTH inhibition directly and indirectly
Vit D actions
are actions of it:
Essential for acquiring adequate amounts of Ca2+ and Pi from the diet
• Increasesplasma[Ca2+]andplasma[Pi]
•Regulates processes of bone resorption and deposition
(osteoblasts)
• Inhibits PTH secretion
alkalemia
dec. ionized Ca
A common condition that results:
inc. protein binding of Ca
W/o affecting the total plasma conc. of Ca
Alkalosis
Hormones controlling the Ca/Pi homeostasis
PTH, Vit D, Calcitonin
VDR
a TF in target tissues:
Small intestine, kidney, bone, PT gland
Direct PTH inhibition by Vit D D
by acting on paratyroid gland
Slow response of PTH-R expressing cells of the kidney
Which takes hours to days
stimulation of 1,25(OH)2D3 synthesis
Acidemia
inc inoized Ca
Slow Ca mobilization response of osteoblasts to PTH
via bone remodeling
Calcitonin
dec plasma level of both Ca and Pi
an increase in plasma concentration decreases PTH secretion via
Ca-sensing receptor mediated mechanisms
normal ranges of total plasma level pf Ca and Pi
Ca: 8.8- 10.3 mg/dl ~ 10
Pi: 2.5-4.5 mg/dl ~ 4
Nuclear vitamin D receptor
VDR
Alkalosis impact on plasma protein-bound Ca and ionized form
protein-bound Inc.
ionized form decreases.
