Exam 3 - Calcium/phosphate

how is 40% of calcium in found in the blood

bound to plasma

how is 60% of calcium in the blood found

ultra-filterable (connected to anions or free)

the amount of biologically available calcium (ionized calcium) is ___%

50

if plasma protein concentration increases, what happens to the total calcium concentration

increases (increase in protein-bound calcium not ionized calcium)

if plasma phosphate (anion) increases, the fraction of calcium complexed with phosphate will ____ which causes a ____ in the amount of ionized calcium concentration

increase, decrease

how does albumin affect the ionized calcium concentration

contains site for both H+ and Ca2+ ions to bind

in acidemia, there is an excess of ___+ in the blood which means more of this will bind to albumin thus leaving fewer sites for calcium to bind. This means the free ionized calcium concentration will ____

H, increase

in alkalemia, there is a deficit of H+ in the blood meaning less will be bound to ____ which leaves more sites for ___ to bind. This means the free ionized calcium concentration will ____

albumin, calcium, decrease

a decrease in plasma calcium (hypocalcemia) will lead to what kind of symptoms

hyperreflexia, cramps, tingling

what two signs may be used to determine if one has hypocalcemia

chvostek sign - twitching face

trousseau sign - blood pressure cuff spasm

why does hypocalcemia lead to hyperreflexia even though calcium levels are low

the calcium used for muscle contraction is intracellular calcium, hypocalcemia looks at extracellular calcium

a decrease in extracellular calcium causes an excitability of excitable cells and it lowers the threshold potential meaning less inward current is required for ___

depolarization

what affect does calcium have on sodium channels

inhibits them to prevent depol...less calcium = more depol

what is a sign of hypercalcemia

hyporeflexia

is phosphate a key intra or extracellular component

intracellular

parathyroid hormone works on what parts of the body to increase calcium concentrations back to normal

bone, kidney, gut

at what calcium plasma concentration will PTH be released at maximal rates

<10 mg/dL

what form of calcium regulates the parathyroid glands

ionized

what is the mechanism of action of PTH

adenylyl cyclase

PTH has a direct effect on bone when Calcium levels drop, what does it cause to happen

increase bone formation through osteoblasts

increase bone resorption through osteoclasts = more calcium in plasma

what two direct actions does PTH have on the kidney

inhibit phosphate reabsorption

stimulate calcium reabsorption

what part of the kidney does PTH work on to inhibit phosphate reabsorption

proximal convoluted tubule -> phosphaturia = peeing phosphate

why is it important that PTH acts on the proximal convoluted tubule to cause phosphate excretion

if the phosphate remained in the body, it would have complexed with the ionized calcium and caused lower levels of serum calcium

what part of the kidney is stimulated by PTH to stimulate calcium reabsorption

distal convoluted tubule

does PTH have a direct effect on the gut?

no

PTH in the gut indirectly stimulates intestinal Calcium absorption via activation of what

vitamin d

what role does vitamin d have on bone

brings in both calcium and phosphate

Vitamin D3 is produced in the ___ via conversion of 7-dehydrocholesterol by ____ light

skin, UVB

vitamin D2 is produced by ___

plants

what is the principal circulating form of Vitamin D

calcifediol (25-hydroxycholecalciferol)

the most active form of vitamin D is formed in what part of the kidney

proximal convoluted tubule

vitamin d stimulates what in the kidney

calcium and phosphate reabsorption

in the kidney, PTH is different from Vitamin D because it does what to calcium and phosphate

reabsorb calcium

inhibit phosphate reabsorption

the overall action of vitamin d in the bone is for bone _____ but it also works with PTH to stimulate ___ activity to resorb old bone which can be used to provide more calcium for new bone mineralization

mineralization, osteoblast

what will a vitamin d deficiency in children lead to

rickets - not enough calcium and phosphate for mineralization

vitamin d deficiency in adults leads to what

osteomalacia - new bone fails to mineralize

vitamin D resistance occurs when the kidney cannot produce the active form of vitamin d, this means that supplementation would not be useful because it does not get ____. This can be caused by congenital absence of 1alpha-hydroxylase or chronic ___ failure (MC)

activated, renal

primary hyperparathyroidism involves and overproduction of ____ from a parathyroid adenoma which may lead to increased circulating levels of ____ which causes too much __ in the blood, increased bone resorption leading to ____, or decreased renal phosphate reabsorption leading to _____

PTH, PTH, calcium, hypercalcemia, hypophosphatemia

secondary parathyroidism results when the parathyroid glands are normal but are stimulated to secrete excess amounts of ___secondary to ____. With this condition, levels of PTH are ___ and blood levels of calcium are ___ or ___ but never ____

PTH, hypocalcemia, high, low, normal, high

what are some consequences of hypoparathyroidism

hypocalcemia from decreased bone resorption, renal and intestinal Ca+ reabsorption

hyperphosphatemia - increase phosphate reabsorption

what stimulates calcitonin secretion from parafollicular (C cells)

increase calcium levels

what is the major action of calcitonin

inhibit osteoclastic bone resorption