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22 Cards in this Set

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  • Back
Where is Ca found in the body?
Bones, soft-tissue, plasma
How much of body's Ca is in plasma, and what form is it found in?
Three fractions:
Free (50%)
Bound to albumin (45%)
Complexed w/citrate/phosphate (5%)
Which form is regulated?
Only the free Ca is regulated
In what form is Ca found in bone?
In the mineral phase. Similar to structure of hydroxyapatite.

HUGE surface area: 100-200m2/g!
What roles does Calcium play in our bodies?
Extracellular: Passive
Intracellular: regulator via Ca2+ binding proteins
What are some examples of passive roles of Ca?
- Needed for enzymatic function (trypsin, lipase, amylase)
- Ca in the blood clotting pathway (required by some blood clotting proteins)
What is Calcium's role intracellularly?

What is the important protein?
Regulator via Ca2+ binding proteins:
- Enzyme activity: Calmodulin
- Muscle contration
- Glycogen breakdown
How does calmodulin act a mediator of Ca signaling?
Calmodulin is a ubiquitous intracellular protein. It binds to 4 Ca++'s:
1. Ca released from intracellular compartment
2. Binds to calmod.; causes conformational change
3. Change in conformation activates enzymes
Name enzymes that are activated by Calmodulin
Adenylate Cyclase
Phosphorylase kinase
Ca2+ dependent protein kinase
What are special about the enzymes:
Adenylate Cyclase
Activate cAMP synthesis and breakdown.
Transitory signal created.
How is muscular contraction initiated?
By Ca release from sarcoplasmic reticulum.
How does Ca get released from the sarcoplasmic reticulum?
1. Nerve impulse open voltage-gated Ca channels of nerve ending
2. Ca enters, acetylcholine released from nerve ending
3. Acetylcholine triggers opening of cation channels of muscle cell; Na enter cell
4. Increased Na leads to opening of Ca channel on sarco. Ret., and Ca floods into cell
After Ca released into muscle cell, what happens next?
Calcium binds to troponin of troponin-tropomyocin complex causing a conformation change which allows myosin-actin crossbridging (and muscle contraction) to occur
Describe Troponin
It's a three-protein complex made of subunits T, I, C. C is calmodulin-like and binds with 4 Ca ions.
How does the muscle later relax?
When nerve impulses stop, Ca levels drop, and Ca taken back up into sarcoplasmic reticulum.

MgATP binds to myosin, breaking the bridge between it and actin.
Describe Ca's role in glycogen breakdown
One of the enzymes along the pathway (phosphorylase kinase) has four subunits, one of which (delta) is similar to calmodulin. Ca binds to it, and the conformational change results in much higher activity. (gamma is the active subunit)
What is phosphorylase kinase's role?
phosphorylase kinase phosphorylates phosphorylase which then hydrolyzes glycogen to glucose-1-Pi
What is the flight or fight response?
A flood of Ca results in muscle contraction and in glycogen breakdown.
How does the average intake of calcium compare with the RDA?
For women, low in all age groups; for men, younger and older group intakes are inadequate.
Does adequate intake of Ca alone produce the strongest bones?
It must be coupled with weight-bearing exercise - even in youngsters!
What happens to Ca status at menopause?
Bone resorption rate greatly increases: osteoclast apoptosis inhibited due to reduced estrogen.
Does Ca/Vit D supplementation increase bone mass?
Maybe, but it has been shown to reduce fracture rate: it is thought that the rate of bone remodeling is reduced, leading to stronger bones.