Regulation of Calcium & Phosphate Metabolism Flashcards
What is involved in the regulatory system to maintain extracellular fluid levels of Ca2+ and P?
vitamin D
parathyroid hormone
calcitonin
What processes are involved for Ca2+?
neurotransmission
learning and memory
muscle contraction etc
Calcium is found in higher concentration in [extracellular/intracellular] fluid
extracellular
Why is calcium higher in extracellular fluid?
because membrane is fairly impermeable to calcium
What pumps do calcium use to be transported?
Ca2+/ATPase
Ca2+/Na+
Which form of calcium is biologically available?
ionized Ca2+
Give an example of calcium in bound form (40%)
albumin with calcium
Give an example of calcium as a complex (10%)
phosphate, HCO3-
Intracellular Ca2+ is in [higher/lower] concentrations
lower
More Ca2+ intracellularly is bound in ______
proteins
What things can you also to change cytosolic Ca2+ in the cell?
change membrane permeability
mobilizing intracellular store (ER, SR)
If Ca2+ intake goes down, the body adjusts by increasing the amount of Ca2+ [absorbed/secreted]
increasing
absorbed
What is hypocalcemia and its effects?
decrease in plasma Ca2+
causes twitching/cramping of skeletal muscle
[Hypercalcemia/hypocalcemia] causes paresthesia (numbness/tingling) and seizures
hypocalcemia
What is hypercalcemia and its effects?
increase in plasma Ca2+
constipation, polyuria, polydipsia, lethargy, coma, death
parathyroid disorders, vitamin D toxicity, renal failure
How do you alter forms of Ca2+ in plasma?
changes in plasma protein concentration
changes in complexing anion concentration
acid-base disturbances
What are the effects of acid-base disturbances on ionized Ca2+ concentration?
acidemia
alkelemia
In acid-base disturbances, there is a change in the fraction of Ca2+ bound to _______
plasma albumin
Define acidemia
more H ions in blood
more H ions bind to albumin
free ionized Ca2+ increases
Define alkelemia
less H ions in blood
more Ca2+ binds to albumin
ionized Ca2+ blood decreases
[Acidemia/Alkelemia] is a sign of hypocalcemia
Alkelemia
Calcium homeostasis involves what processes?
interaction of bone, kidney, and intestine
+ parathyroid hormone, calcitonin and vitamin D
What is bone resorption?
breaking down bone
What stimulates bone resorption (release of Ca2+ into blood from bone)
PTH
vitamin D
What inhibits bone resorption? aka stimulates bone deposition
calcitonin
What part of the body absorbs Ca2+?
intestine
Absorption of Ca2+ [increases/decreases] with age
decreases
Excess Ca2+ is ____ by the kidneys
excreted
What hormone helps reabsorb Ca2+? How much?
PTH in kidneys
98%
What is special about phosphate and diet?
percentage absorbed from the diet is fairly constant
What does phosphate do?
balances many cations
regulation of phosphate balance = urinary excretion
storage of phosphate in muscle
There are _____ parathyroid glands
4
Parathyroid glands contain ______ and _______
chief cells
oxyphil cells
What do chief cells in parathyroid glands do?
source of PTH
What are oxyphil cells?
appear at puberty
increase in age (not sure of function)
PTH stimulates an increase in [Ca2+/phosphate] and decreases [Ca2+/phosphate]
Ca2+
phosphate
What is activated when plasma Ca2+ falls?
Ca2+ receptor
The Ca2+ receptor is [stimulated/inhibited] with high plasma concentration
inhibited
What is hyperparathyroidism? (primary form)
caused by benign tumor or hyperplasia of one or both parathyroid glands
high circulating PTH
hypercalcemia
In hyperparathyroidism in primary form, circulating PTH is [high/low]. There is [hypercalcemia/hypocalcemia] and [hyperphosphatemia/hypophosphatemia]
high PTH
hypercalcemia
hypophosphatemia
What is hyperparathyroidism? (secondary form)
caused by increased phosphate in blood, which precipitates Ca2+ results in hypocalcemia
causes secondary increase in PTH
may result from renal failure of increased dietary phosphate
What causes hypoparathyroidism?
accidental surgical removal
autoimmune destruction
idiopathic
What does hyperparathyroidism result in?
decreased PTH
hypocalcemia
hyperphosphatemia
In hypoparathyroidism, circulating PTH is [high/low]. There is [hypercalcemia/hypocalcemia] and [hyperphosphatemia/hypophosphatemia]
low
hypocalcemia
hyperphosphatemia
How is calcitonin synthesized?
as a preprohormone by parafollicular cells of the thyroid gland
What are the effects of calcitonin?
decreased blood Ca2+ and phosphate by:
inhibiting bone resorption
increasing urinary phosphate excretion
inhibiting renal reabsorption of Ca2+
What are stimulators of calcitonin?
increased blood Ca2+
vitamin D (via feedback)
ingested food (no need to release from bone or reabsorb in kidney)
What is vitamin D required for?
bone FORMATION
increases Ca2+ absorption from GIT
Vitamin D [increases/decreases] Ca2+ absorption from GIT
increases
If vitamin D is synthesized in the skin, the precursor is ________
7-dehydrocholesterol
After synthesis or absorption in the gut, it goes to the ______ and converted to ________
liver
25-hydroxyvitamin D
After the liver, 25-hydroxyvitamin D goes to the ______ and then converted to _______
kidney
1,25-dihydroxyvitamin D
Intermediates and active vitamin D circulate bound to _________
protein carriers
Where can vitamin D be stored?
adipose and liver (fat-soluble)
How is vitamin D excreted?
in bile
Most vitamin D actions occur in ______
intestines
What happens in the intestine in vitamin D?
stimulates Ca2+ absorption via calbindin
stimulates absorption of phosphate and Mg2+
Calcium absorption can be _____ or ______
active
passive
When Ca2+ intake is [high/low], the process is active and [transcellular/paracellular]
low
transcellular
When Ca2+ intake is [high/low], the process is passive and [transcellular/paracellular]
Where does the transcellular process of Ca2+ occur?
duodenum
Where does the paracellular process of Ca2+ occur?
jejunum
ileum
Active, transcellular process requires _______
vitamin D
Vitamin D acts through cytosolic receptor and [increases/decreases] production of calbindin
increases calbindin
What does calbindin do when calcium absorption is active?
binds Ca2+ inside cells and facilitates transport to basolateral membrane
Vitamin D stimulates bone resorption in presence of ______
PTH
Vitamin D [increases/decreases] Ca2+ transport and uptake by SR in skeletal muscle cells
increases
Vitamin D [increases/decreases] PTH synthesis via a _______
decreases
negative feedback loop
Increased blood phosphate [increases/decreases] PTH secretion via a P receptor
increases
______ also stimulates vitamin D synthesis
PTH
What stimulates PTH release?
decreased blood Ca2+
increased blood phosphate
decreased Mg
Inhibition of PTH release is from [increased/decreased] blood Ca2+
increased
