Parathyroid, Calcium, Calcitonin And Phosphate Flashcards
Inc in calcium ion concentration above normal cause this effect on CNS
depression
Dec in calcium concentration cause the nervous system to
Bec
be more excited
inc neuronal permeability to sodium ions allowing easy initiation of AP
Form most important for most functions of calcium in the body
Ionic form
At plasma Ca concentration 50% below normal,
Peripheral nerves become excitable they begin to discharge spontaneously initiating trains of nerve impulses that pass to peripheral skeletal ms
Tetany
Seizures
Hypercalcemia has this effect
Depressed Sluggish reflex Dec QT interval Lack of appetite Constipation (dep contractility of GI muscle)
Promotes Ca absorption in intestine
Vitamin D
Phosphate is absorbed in the
and excreted in the
intestine
kidney
Most important factor controlling reabsorption of Ca in distal portion of nephron and the rate of excretion is
PTH
organic matrix of the bone
90-95% collagen
10% ground substance
extend primarily along lines of tensional forces and give bone its tensile strength
collagen
Ground substance is made up of
Proteoglycan (chondroitin sulfate + hyaluronic acid)
Bone salts
calcium
phosphate
Major: hydroxyapatite
Collagen fibers provide
Calcium provides
Tensile strength
Compressional strength
Collagen fiber lying adjacent to hydroxyapatite and overlap arrangement provide strength to bone
Despite state of supersaturation, hydroxyapatite does not precipitate bec of
pyrophosphate
Bone calcification
Osteoblast producr collagen molecules + ground substance
Collagen monomers polymerize rapidly to form collagen fibers becoming osteoid where calcium salts readily precipitate
Osteoblasts trapped in osteoids becoming osteocytes
Calcium precipitation on collagen surface forming minute nidi growing into hydroxyapatite
Osteoblast secrete inhibitor to pyrophosphate preventing crystalization.
Osteoclast is activated by
PTH binding to receptors of adjacent osteoblast causing them to release osteoprotegrin ligand, a cytokine also known as RANKL
OPGL activates receptors on prosteoclast cells causing them to differentiate into mature multinucleated osteoclasts
Mature osteoclasts develop ruffled border and release enzyme that promote bone resorption
This cytokine produced by osteoblasts inhibit bone resportion acting as decoy receptor binding to OPGL inhibiting diff of preosteoclast into mature osteoclast that resorb bone
Osteoprotegerin
Osteoclastogenesis inhibitory factor OCIF
Stimulate production of OPGL through inhibition of OPG and stimulating OPGL formation
Vitamin D
PTH
Osteoblasts forms bone by
bone is called
Bone being laid down in successive layers of concentric circles (lamellae) on inner surface of cavity until tunnel is filled
Deposition stops when bone encroaches blood vessels supplying area
osteon
Canal through which the blood vessels in the bone run is
Haversian canal
Stimulates deposition and calcification of bone
Stress
Fracture heals by
Formation of callus
Stress on opposite ends of bone accelerate osteoblastic activity
Vit D is converted into to inc calcium absorption in intestine
1 25 dihydroxycholecalficerol
Formed in the skin as a result of irradiation of 7 dehydrocholesterol by UV, most important compoung from sterol
Cholecalciferol Vit D3
Cholecalciferol is activated by
in the
25 hydroxycholecalciferol
liver
Feedback inhibitory effect on 25 hydroxy generation is impt bec
1 regulates the concentration of 25 hydroxy in plasma despite inc intake of D3
2 high degree of feedback prevents excessive action of Vit D When D3 intake is altered and conserves Vit D stores in liver
25 hydroxychole is converted to
in the
requires
1,25 dihydroxycin the proximal tubule
Most active
PTH
Plasma conc of 1,2 is affected inversely by
Calcium in plasma
Calcium inversely affects creation of 1,25 bec
1 it has slight effect in preventing conversion of 25 hydroxy to 1,25
2 rate of secretion of PTH is greatly supressed when plasma calcium ion rises above 9-10 hence lower conversion of 25 to 1,25
a high calcium conc 25 is converted to 24,25 dihydroxycholecalciferol
Vitamin D activation happens
By binding with receptor at DNA
forming complex with another intracellular receptor retinoid X receptor
complex binding to DNA ane activating transcription
1,25 dihydroxy is a hormone that promotes calcium with phosphate absorption in intestine by formation of
calbindin
a calcium binding protein in the brushborder to transport calcium in cell cytoplasm
Rate of calcium absorption is directly proportional to quantity of calcium binding protein remains despite elimination of 1,25
Also forms calcium stimulated ATPase in brush border of epithelial cell and ALP in eithelial cell
1,25 also promotes calcium and phosphate in serum by acting on renal tubule
calcium reabsorption and preventing secretion
Vitamin D causes this effect on bone
absorption
Absence of Vit D Inhibits effect of PTH on in bone absorption
Vitamin D causes bone calcification in amount
smaller amounts
PTH is secreted by
parathyroid gland cell
Chief cell
Oxyphil
PTH on calcium and phosphate concentration on. ECF
inc calcium and phosphate absorption from bone
rapid effect of PTH to dec excretion of calcium by kidneys
Decline in phosphate due to inc renal phosphate excretion
PTH effect on kidney
Inc tubular reabs of calcium, mg and hydrogen ion
Inc secretion of phosphate, sodium, potassium and amino acid
PTH effect on intestine
Inc calcium and phosphate reabsorption
PTH affects target organ by
cAMP
Inc osteocyte osteoclast and target cell
Hormone secreted by thyroid to dec calcium concentration
Secreted by the cells called
which are remnants of
Calcitonin
Parafollicular C cells
ultimobranchial gland
Musce especially sensitive to tetanic spasm in low ca plasma
Laryngeal muscle
Causes death
