Ca metabolism Flashcards
(55 cards)
which is produced more, T3 or T4?
T4
true or false: all of T3 and T4 come from the thyroid gland
true for T4, false for T3 (some come from the thyroid gland, some T3 is made from the conversion of T4 elsewhere in the body)
which has greater binding affinity? T3 or T4?
T4
which has a greater half-life? T3 or T4?
T4
which has as a more predominant presence of its free form molecules? T3 or T4?
T3
what organs does PTH stimulate?
- osteoclasts
- kidneys
- small intestine
what does PTH do to the osteoclasts?
encourages resorption of bone tissue (bone calcium is released into the circulation)
what does PTH do to the kidneys?
encourages the retention of Ca and activation vitamin D to calcitrol
what does PTH do to the small intestine?
encourages absorption of calcium
what type of cells produce calcitonin?
C cells (in parafollicular cells)
what does calcitonin do?
decreases blood Ca2+ concentration
what are some remedies for rickets?
original treatments: - fish liver oil - sun exposure - UV-irradiation of certain foods recently: - PTH/calcitonin (20th century)
what are some roles of calcium? (6)
- structure in skeleton (bones contain almost all of the calcium in the body)
- blood clotting (mesh formation)
- regulation of enzymes (cofactor)
- second messenger (GPCR/IP3)
- regulate membrane excitability
- muscle contraction
where is most of the calcium? where’s the rest?
- bones - 99%
- the other 1% is present in the extra-bone space (intracellular)
- 0.1% is present in the extracellular fluid (focus of this lecture)
how do you get tetany?
1) hyperventilation –> increased expulsion of CO2 (decreased CO2 in lungs)
2) CO2 turns into carbonic acid at lesser amounts
3) carbonic acid turns into proton and bicarbonate (less protons in circulation)
4) plasma proteins release protons into circulation, leaving proteins negatively charged
5) proteins look for positive ions and bind Ca++, decreasing free calcium concentration
6) compensated by moving Ca++ from intracellular space into circulation from the sarcoplasm
7) tetany
alternatively: chelating agents bind Ca2+
which cells produce PTH?
chief cells and oxyphil cells
what stimulates release of PTH?
low calcium concentration
function of Calcitonin?
not super clear, and maybe not that important to humans; doesn’t elicit much of a response when injected or when in decreased levels
is PTH stored?
yes, in granules
what gets PTH to release from granules?
calcium sensing receptors (CaR) on chief cells detecting low levels of Ca
what kind of receptor are CaRs?
GPCR
what does high concentration of Ca do to CaRs?
- decreased cAMP, increased IP3
- decreases in PTH synthesis and secretion
what does low concentration of Ca do to CaRs?
- increased cAMP, decreased IP3
- increases in PTH synthesis and secretion
what are the 2 important proteins in bones and what do they do?
- osteocalcin: released by osteoblasts, binds with hydroxyapatite (calcium salt)
- osteonectin: released by osteoblasts, binds with collagen and hydroxyapatite
