6.7 Bones role in Calcium Homeostasis

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what is a cofactor

an additional substance needed for an enzymatic reaction to occur

99% of the body's calcium

is stored in bone

When blood Ca2+ rises above normal,

parafollicular cells in the thyroid gland secrete calcitonin (CT)

If some stimulus cause the blood Ca2+ to decrease,

parathyroid gland cells (receptors) detect this change and increase in their product of molecule known as cycle adenosine monophosphate (cyclic AMP)

Parathyroid hormone (PTH) is secreted by

thyroid gland

parathyroid hormone (PTH)

Ca2+ exchange is regulated by hormones and is one of the most important

The net result is that calcitonin (CT) promotes

bone formation decreases blood Ca2+ level

Hypercalcemia-

Neurons and muscle cells become relatively unresponsive

Hypocalcemia

Neurons become so excitable that convulsions can occur

Calcitonin inhibits

activity of osteoclasts , speeds up blood Ca2+ uptake by bone, and accelerates Ca2+ deposition into bones

parathyroid hormones (PTH) increases

blood Ca2+ levels

If the calcium concentration goes to low

breathing may cease (respiratory arrest)

the role of bone in calcium homeostasis is to help

buffer the blood Ca2+ level , releasing Ca2+ into blood plasma using osteoblasts when the level rises

Another hormone works to decrease blood Ca2+ level

calcitonin (CT)

The PTH stiumtes formation of

calcitoriol (active form of vit D)

blood clotting also requires

calcium ions

many enzymes require

calcium ions a a cofactor

Bone is the body main

calcium reservoir, storing 99 percent total of body's calcium

Deviations from normal ECF calcium concentration

can be fatal

one way to maintain the level of calcium in the blood is to

control the rates of calcium resorption from bone into blood and of calcium deposition from blood into bone

Calcitonin (CT) works to

decrease blood calcium levels

PTH also acts on the kidneys (effectors) to

decrease loss of Ca2+ in the urine, so more is retained in the blood

If the calcium concentration goes to high

heart may stop (cardiac arrest)

PTH acting of kidneys to decrease loss of Ca2+ in the urine and stimulation of formation of calcitriol both

help elevate blood Ca2+ level

calcitoriol is a

hormone that promotes absorption of calcium from foods in the gastrointestinal tract into the blood

Overall functions of parathyroid hormones (PTH)

i. Increases the number and activity of osteoclasts ii. Causes the kidneys to decrease loss of calcium in the urine iii. Stimulates formation of calcitriol

overall functions of calcitonin (CT)

i. Inhibits activity of osteoclasts ii. Causes kidneys to increase calcium excretion in the urine

Parathyroid hormone (PTH) works to

increase blood calcium levels

the presence of higher PTH increases the number and activity of

osteoclasts (effectors), which step up the pace of bone resorption

Even small changes of calcium ions concentration outer this range may

prove fatal response- heart may stop if the concentration goes to high or breathing may cease if the level falls to low

Many physiological processes require

stable calcium levels in the ECF

both nerve and muscle cells depend on a

stable level of calcium ions in extraceullualr fluid to function properly

The resulting reales of Ca2+ from bone into blood, returns

the blood Ca2+ level to normal

For the reason that enzymes require Ca2+,

the blood plasma level of calcium ions is very closely regulated bertwee n9 and 11mg/100 mL

The gene for PTH within the nucleus of a parathyroid gland cell (control center) detects

the intracellular increase in cyclic AMP (the input)

As a result, PTH synthesis speeds up, and more PTH (output) is

then released into the blood

Despite the effects of CT, the role of CT in mortal calcium homeostasis is

uncertain because it can be completely absent without causing symptoms

Parathyroid hormone secretion operates

via a negative feed back system


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