7.4 – Physiology of osseous tissue Flashcards
mineral resorption is the process of…
dissolving bone
resorption is carried out by ___
osteoclasts
hypocalcemia is…
calcium deficiency
hypercalcemia is…
calcium excess
calcium homeostasis depends on balance b/n…
1) dietary intake
2) urinary and fecal losses
3) exchanges w/ the osseous tissue
calcium homeostasis is regulated by ___ hormones
the hormones are…
3
calciferol, calcitonin, and parathyroid hormone
calciferol is a form of ___ produced by the sequential action of the ___, ___, and ___
vitamin D
skin, liver, and kidneys
calcitriol behaves as a ___, a blood-borne chemical messenger from one organ to another.
It is called a ___ only because it is added to the ___ as a safeguard for people who don’t get enough sunlight to initiate adequate synthesis in the skin.
hormone
vitamin
diet
the principal function of calcitriol is to ___ the blood calcium concentration.
it does this in ___ ways
raise
3
3 ways that calcitriol raises blood calcium concentration:
(1)
increases calcium absorption by the small intestine
3 ways that calcitriol raises blood calcium concentration:
(2)
increases calcium resorption from the skeleton
calcitriol binds to osteoblasts, which then stimulate stem cells to differentiate into osteoclasts
the new osteoclasts liberate calcium and phosphate ions from bone
3 ways that calcitriol raises blood calcium concentration:
(3)
it weakly promotes the reabsorption of calcium ions by the kidneys, so less calcium is lost in the urine
calcitonin is produced in the ___ ___
thryoid gland
calcitonin is secreted when the blood calcium concentration…
rises too high
calcitonin ___ the blood calcium concentration by ___ principal mechanisms
lowers
2
calcitonin lowers the blood calcium concentration by 2 principal mechanisms:
(1)
osteoclast inhibition:
calcitonin firstly reduces osteoclast activity –> osteoclasts liberate less calcium from the skeleton
calcitonin lowers the blood calcium concentration by 2 principal mechanisms:
(2)
osteoblast stimulation:
calcitonin secondly increases the number and activity of osteoblasts, which deposit calcium into the skeleton
mineral deposition (mineralization) is a…
crystallization process in which calcium, phosphate, and other ions are taken from the blood plasma and deposited in bone tissue
parathyroid hormone (PTH) is secreted by the ___ ___
parathyroid glands
parathyroid glands release PTH when blood calcium is ___
low
PTH ___ the calcium level by ___ mechanisms
raises
4
PTH raises the calcium level by 4 mechanisms:
(1)
it binds to receptors on the osteoblasts, which in turn stimulate the osteoclast population and promote bone resorption
PTH raises the calcium level by 4 mechanisms:
(2)
it promotes calcium reabsorption by the kidneys, so less calcium is lost in the urine
PTH raises the calcium level by 4 mechanisms:
(3)
it promotes the final step of calcitriol synthesis in the kidneys, thus enhancing the calcium-raising effect of calcitriol
PTH raises the calcium level by 4 mechanisms:
(4)
it inhibits collagen synthesis by osteoblasts, thus inhibiting bone deposition
phosphate homeostasis is ___ regulated as calcium levels
not as tightly regulated
phosphate is required for…
bone strength
component of DNA, RNA, ATP, phospholipids, and other compounds
how does calcitriol affect phosphate levels?
raises phosphate blood level while raising calcium blood level
how does parathyroid hormone affect blood phosphate levels?
lowers the blood phosphate level by promoting its urinary excretion
other factors affecting bone:
why do adolescent girls grow faster but for a shorter time than boys?
adolescent girls grow faster and attain their full height earlier
adolescent girls begin puberty earlier
estrogen has a stronger effect than testosterone
other factors affecting bone:
why do adolescent boys grow slower than girls?
adolescent boys grow slower but for a longer time –> attain full height later
adolescent boys begin puberty later
testosterone has a weaker effect than estrogen
___ ___ eventually deplete the cartilage of the ___ ___, bring about closure of the ___, and put an end to one’s growth in height
sex steroids
epiphysial plates
epiphyses
mineral deposition into bones begin where?
in fetal ossification
what is the process of dissolving bone and releasing minerals into the blood called?
resportion
in the human body, where is 99% of the calcium found?
the bones
if a patient has abnormally high blood calcium levels, they are said to have a condition called ___
hypercalcemia
calcitriol acts on which organs to raise blood calcium levels?
bones
small intestines
kidneys
where does the calcium and phosphate used to mineralize bone come from?
the blood
(osteoblasts build new bone using calcium and phosphate from the blood)
what does the hormone calcitonin do?
calcitonin repsonds to hypercalcemia
there is too much calcium in the blood –>
calcitonin lowers blood calcium levels
calcitonin inhibits osteoclasts and stimulates osteoblasts
–> prevents calcium from coming out of bone, takes calcium out of blood and puts it into bone –> lowers blood calcium levels
in order for minerals such as calcium and phosphate to be liberated from bone, which process must occur?
resorption
PTH is a hormone released by parathyroid glands in response to what?
low blood calcium levels
in the human body, what percentage of calcium in the body is found in the bones?
99%
which mineral is more closely regulated by the body –calcium and phosphate?
calcium
which condition is characterized by excessive excitability of the nervous and muscular systems due to low blood calcium levels?
hypocalcemia
do adolescent girls or boys tend to attain their full height earlier in life?
adolescent girls
vitamin D, also known as ___, raises the blood calcium level
calcitriol
which hormone inhibits osteoclasts and stimulates osteoblasts to lower blood calcium levels?
calcitonin
a low blood calcium level stimulates the release of which hormone?
parathyroid hormone
how does calcitriol affect blood phosphate levels?
it raises them
which hormone has a greater effect on bone growth?
estrogen
calcitriol acts on which organs to raise blood calcium levels?
kidneys
small intestines
bones
what does the hormone calcitonin do?
responds to hypercalcemia –> calcitonin lowers blood calcium levels
inhibit osteoclasts and stimulate osteoblasts
which hormone inhibits osteoclasts and stimulates osteoblasts to lower blood calcium levels?
calcitonin
what does the hormone calcitonin do?
responds to hypercalcemia –> lowers blood calcium levels
inhibits osteoclasts and stimulates osteoblasts
