Parathyroid Glands Flashcards
How does PTH is regulated?
- decrease of blood Ca
- release of PTH
- target organs response :
- intestine Ca absorption
- bone resorption
- kidney Ca reabsorption - increase blood Ca
- negative feedback on PTH release
How does calcitonin is regulated?
- rise in blood Ca
- release of calcitonin
- target organ response
- bone Ca deposition
- secretion of Ca by kidneys - decrease in blood Ca
What is calcitonin?
the only hormone that decreases endogenous blood Ca
first discovered in fish
however human gene sequence not identical to fish so role in humans not clear
I am the cells that secrete PTH. Who am I?
chief cells or oxyphil cells
I am the cells that secrete calcitonin. Who am I?
parafollicular cells (c-cells)
what are the roles of calcium?
- main structural component of the skeleton
- enzyme activity
- second messenger
- muscle contraction
- membrane excitability
- blood clotting
where is the majority of the total body calcium?
in bones (99%)
How tetany occurs?
- hyperventilation = low pCO2 = low H+
- proteins release their protons to compensate
- Ca binds to proteins
- lower blood Ca
- release of Ca from sarcoplasmic reticulum
- muscle contraction = spasm of skeletal muscle
How is PTH secretion regulated when high blood Ca?
high blood Ca = binds to G coupled receptor => decrese cAMP and increase IP3 => Gi activated to reduce cAMP => PLC to convert IP2 to IP3 => inhibition of PTH exocytosis
How is PTH regulated when low blood Ca?
increase in cAMP and a decrease in IP3
=> expression and exocytosis of PTH
what are the two major proteins in bones?
- osteocalcin (from osteoblasts) binds to hydroxyapaptite (calcium salts)
- osteonectin (fibroblasts) binds collagen and hydroxyapaptite and may serve for calcification
what can serve as an indicator for bone growth?
osteocalcin serum levels
what factors can trigger bone remodeling?
- physical factors (fractures)
- hormonal factors (PTH)
- paracrine factors (IGF-II from osteoblasts)
I am a protein that helps osteoblasts to attach to the bone surface. Who am I?
integrins
How do osteoclasts dissolve hydroxyapaptite?
proton pump (H+ ATPase) move H+ out into the extracellular matrix => acid pH degrading bone
What compound found in urine can indicate bone resorption?
pyridinoline => collagen breakdown product
what are the steps of bone remodeling?
- PTH with vit D stimulate osteoblasts to secrete OAF (osteoclasts activating factor)
- osteoclasts are activated = bone resorption
- macrophages phagocytose debris
- osteoblasts fill the cavity
- osteoid is mineralized
What is the role of PTH related to phosphate?
inhibits reabsorption of phosphate by kidneys
What is PTHrP?
PTH related protein => effects similar to PTH => binds to PTH receptors
What protein is produced by the placenta and fetus and what is its role?
PTHrP
- placental transport of Ca
- dev of chondrocytes
What are the receptors to PTH?
PTHR-1 = binds to PTH + PTHrP (bone + kidneys) PTHR-2 = binds only PTH
What are 3 diseases of the bone and their main characteristics?
- osteoporosis = XS osteoclast function (decreases bone Ca) = frequent fractures
- osteopetrosis = + calcification, decreased osteoclasts activity = brittle bone + prone to fractures
- involutional osteoporosis = decrease BMD with age
How does menopause affect bone remodeling?
At menopause, there is no more follicles that produce estrogen. Estrogen regulates osteoclasts activity by inhibiting cytokines that promote osteoclasts dev and stimulating cytokine TGFB that causes apoptosis of osteoclasts. So with lower estrogen levels, osteoclasts are stimulated and it leads to osteoporosis.
What are the signs and symptoms of hyperthyroidism?
psychic moans
groans
stones
bones
