Ca2+ , P, Parathyroid Flashcards
Concentration of Ca2+ and P- in extracellular fluid must be very well regulated, what is the allowable variation in percent?
<2%
Free ionized Ca2+ is about ____% of Ca in blood
50%
Why is there less Ca2+ bound to protein in the interstitial fluid?
because there are lower amounts of binding proteins
What is the primary form of Ca2+ within cells
bound to proteins
What are three things that can influence Ca2+ plasma concentration
-changes in plasma protein concentration will cause a change in total plasma but not ionized
-changes in anion concentration which will change the fraction of Ca2+ complexed with anions
-acid base abnormalities which will change the fraction of Ca2+ bound to albumin
if you have an animal in acidocis how will that effect ionized Ca levels
it will increase it due to the H binding to ALB
True/False: plasma phosphate is unbound and freely filtered in the kidney
true
What is the major regulatory hormone of P reabsorption in the kidney
PTH, it inhibits the Na+/P cotransporter in the proximal tubule
Of the phosphate not stored in bone, where does 99% get stored?
intracellularly primarily as organic phosphates
Ca balance is maintained by the interplay of what three organs
bone, kidney, GI
What is the primary hormone responsible for Ca homeostasis
PTH
When is PTH released from the parathyroid
in response to decreased plasma Ca2+ levels
How does PTH restore Ca2+ homeostasis?
increasing bone resporption
reabsorption of Ca2+ in the kidneys
absorption of Ca2+ from the GI tract by activating Vit D
An increase in Ca homeostasis will result in _____ blood P levels
decreased, they are inversely regulated
What mechanism(s) is Ca2+ absorbed from the intestine
both paracellularly and transcellularly
How does Vit D promote Ca2+ absorption from the GI lumen
by increasing calcium binding proteins and increasing number of Ca channels and pumps in the basolateral membrane
Where can Ca2+ regulation by PTH occur in the kidney?why
distal tubule because that is where transport is transcellular
What enzyme does PTH target to activate Vit D in the kidney
1alpha hydroxylase
What is the most important effect of calcitriol?
increases absorption of Ca2+ from the intestine
What cells release PTH
chief cells in the parathyroid
True/False: PTH is synthesized on demand
false, it is a peptide hormone so it is synthesized and then stored in secretory vesicles until it is released via exocytosis
What is the net effect of PTH on P
it decreases plasma phosphate levels
Where is calcitonin released from
parafollicular cells (C cells) in the thyroid
What is the role of calcitonin on Ca2+ homeostasis
it decreases plasma Ca2+ concentrations by inhibiting osteoclasts and bone resorption
What conditions yield eclampsia in animals
a lactating female animal that is losing too much Ca2+ to her milk
