6.7 Bones role in Calcium Homeostasis
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
