Parathyroid Hormone and Calcitonine

Parathyroid Hormone and calcitonine together

is your bodies primary regulator of calcium

-both target your bone cells, but do it in opposite ways

what produces parathyroid hormone

parathyroid gland on the surface of the thyroid gland

what produces calcitonin

C-cells in the thyroid gland

calcitonin

-bone sparing

-inhibits osteoclast activity in the level of the bone, promotes bone deposition

bone sparing

movement of calcium into the bones

bone resorbtion

calcium from your bones is released into the bloodstream

what percentage of calcium is stored in the bones and teeth?

99% with a 500mg turnover daily

bone remodeling and turnover continues, but slows after what point?

puberty

%of calcium from dietary sources alone

30-50%

Estrogen on your bones

decreases bone resorption

-stimulates osteoblasts for building bone

After menopause

ovaries stop producing estrogen so your bones break down more than they get built up

growth hormones on bones

stimulate osteoblasts

-mimics estrogen

prolactin

increases calcium reabsorption

-inhibits 1 alpha hydroxylase

calcium uptake during pregnancy

3x the normal amount

most bone density data is based on a small group of

25-30 year olds

parathyroid hormone

allows the bones to release calcium for use in the blood

two types of cells in a parathyroid gland are

chief cells and oxyphil cells

oxyphil cells

sense calcium

chief cells

calcium sensing AND production of parathyroid hormone

-also some importance in production of Vitamin D

PTH is synthesized as a

prohormone then cleaved into 8 amino acids

-calcium is the sensor

chief cells

-important for when blood calcium levels are low

-chief cells use GalphaI receptors

-cells stay open if calcium is not high, allowing calcium to be moved from bones into the blood. Once calcium is high, calcium binds Galphai and stops calcium from leaving bones

name of the disease for low blood calcium

hypocalcemia

name of the disease for too high blood calcium

hypercalcemia

Parafollicular c-cells

-important for when there is very high levels of calcium in the blood

-use of a Galphaq to detect high calcium and open channels to allow calcium back into your bones

osteoblast activity being converted into osteoclast activity

-in the presence of low blood calcium, parathyroid hormone binds Galphas and causes a RANK to bind to the rank receptor and stimulate cothepsinK to release available calcium and release it into the blood

when an osteoblast matures, it becomes an

osteocyte

what resorbs osteocytes?

osteoclasts

following PTH through the kidney

PTH binds Galphas on the basolateral side of an epithelial cell in the DCT, production of calbindin-D

-calcium attaches to calbindin-D and is reabsorbed

-must have sodium for it to work properly

result of PTH binding in the basolateral membrane of epithelial cells in the DCT

-opening of calcium channels in the apical membrane

calbindin-D

-vitamin D specific

-when 7-dehydrocholesterol on your skin is exposed to UV light from the sun, it is converted into CCF (previtamin D) and released to target the liver

-In the liver, an enzyme called 25 hydroxylase binds to create 25 hydroxicolacalciferol which is transfered to the kidney (what doctors measure for in your blood)

-in the kidney, it binds to 1-alpha hydroxylase to become 1,25 dihydroxycholacalciferol, or bioactive vitamin D

Vitamin D targets

skeleton, small intestine, kidney, and the parathyroid gland

vitamin D on skeleton

increased bone resorption and higher blood calcium

vitamin D on small intestine

increased calcium reabsorption from your diet

vitamin D on your kidney

increased calcium reabsorption and targets the JGA to check for calcium

vitamin D on the parathyroid gland

decreased PTH due to feedback loops