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Endocrinology
Parathyroid Glands, Calcium, & Vitamin D
62
Veterinary Medicine
Professional
11/14/2010

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Term
What are some processes that are reliant on a steady Ca concentration?
Definition
action potentials
contraction
motility
cytoskeletal rearrangements
cell division
secretion
modulation of enzyme activites
Term
How is total body calcium determined?
Definition
Intracellular + extracellular + Ca in bone and teeth
Term
What is the total plasma concentration range?
Definition
8.6 -10.6mg/dl
Term
What type of calcium is the biologically active form?
Definition
Ionized Calcium
Term
When Ca binds to protien, which one is is normally bound to?
Definition
Albumin
Term
What is complex calcium?
Definition
Ca that is complexed to other anions:
phosphate, citrate, bicarb, lactate
Term
How does high blood pH affect protien binding of calcium?
Definition
the equalibrium shift to :
protien bound > ionized Ca
Term
How does acidosis affect Ca binding?
Definition
Shifts the equalibrium to:
protien bound < ionized calcium
Term
What are three instances where ionized calcium decreases?
Definition
1. total body Ca deficit
2. shift causing Ca to be taken up in the bone
3. plasma protien binding Ca increasing (alkalosis)
Term
What three body processes are responsible for the turnover of Ca?
Definition
1.Intestinal Absorption
2.Renal Filtraiton
3.Bone Remodeling
Term
What enhances intestinal absorption of Ca?
Definition
Vitamin D
Term
How is excess dietary Ca eliminated?
Definition
Fecal excretion
Term
Where is the majority of Ca reabsorbed in the kidneys?
Definition
98% in the renal tubules with the remainder secreted in the kidneys
Term
What does bone formation and bone reabsorption do to Ca levels?
Definition
Respectively: decrease and increase levels
Term
What are the two controls on Ca levels in extracellular fluid?
Definition
1. indirect endocrine control
2. direct negative feeback by Ca itself
Term
What receptors mediate Ca and where are they located?
Definition
calcium sensing plasma membrane receptors
*found*
1. PTH and Calcitonin secretiong cells of the parathyroid
2. Vit. D producing cells
3. bone forming and resorbing cells
4. renal tubular calcium resorbing cells
5. intestinal ca resorbing cells
Term
How are the Ca receptors coupled to adenyl cyclase, phospholipase and kinase?
Definition
G-protiens
Term
What are some effects of hypoglycemia?
Definition
1. neuromuscular irritability
2. numbness
3. seizures
Term
What are some effects of hypercalcemia?
Definition
reduced neurotransmission
muscle weakness
coma
nephrotoxicity
Term
What are the important moleucles Phophate is part of?
Definition
ATP, NAD, NADP
2*messengers : cAMP and DNA and RNA
Term
What two anions are balanced by P?
Definition
K and Mg
Term
What is the normal phosphate concentration range?
Definition
2.5 - 4.5mg/dl
Term
True or False
Phosphate Turnover uses the same body mechanisims as calcium.
Definition
TRUE
Term
What are some effects of hypophosphatemia?
Definition
cardiac and respiratory weakness
loss of RBC membrane integrity
abnormal bone formation
Term
What causes soft tissue calcification?
Definition
binding of Ca and P. Ususally occurs with renal failure.
Term
What is the cause of Renal Secondary Hyperparathyroidism?
Definition
excessive dietary phosphorus
insufficent dietary Ca
Term
What is the cause of Nutritional Secondary Hyperparathyroidism?
Definition
Occurs in horses that are fed exclusively high phosphate grains (wheat or rice bran)
Term
What is the function of Magnesium?
Definition
Neuromuscular transmission
co-factor
glucose homeostatsis
Term
What is the acceptable range for plasma Mg?
Definition
1.8 - 2.4mg/dl
Term
Where is Mg predominately in the body?
Definition
Bone > skeletal muscle > heart, liver, other
Term
How is Mg secretion and excretion regulated?
Definition
absorption by the gut
excreted in the urine
self regulate by interacting with Ca receptors
Term
What are the three molecules whose absorption in the gut is enhanced by vitamin D?
Definition
Mg and Ca and P
Term
Hypomagnesemia mimics what?
Definition
Hypocalcemia
Term
what are the effects of hypermagnesemia?
Definition
neuromuscular blockade by supressing aceytlcholine
respiratory blockade
*caused by renal failure, endo disorders, drug overdose)
Term
PTH stands for what.
Definition
parathyroid hormone
Term
what is the PTH precursor and what cell secretes it?
Definition
pre-pro-PTH is secreted by Chief Cells
Term
What are the mechanisims that control PTH secretion?
Definition
1. plasma Ca concentration and - feedback
2.Ca receptor in the PT cell memebrane
3.Mg
4. increased phosphorus (decreases Ca --> PTH secretion
5. Vitamin D
Term
what is the biologically active form of Vitamin D?
Definition
1,25 OH2 Vitamin D
Term
What is the overall effect of Vitamin D?
Definition
to increase plasma ionized calcium
Term
how does PTH work with Vit. D?
Definition
it increases synthesis of Vit. D
Term
what is the second messenger for PTH?
Definition
adenylyl cyclase ->cAMP by g-protiens
Term
What is the overal effect of PTH?
Definition
increase plasma Ca
decrease plasma Phosphate
Term
what are the three major organs that PTH acts on?
Definition
1. gut
2. bone
3. kidney
Term
True or False.
PTH receptors are on osteoblasts and osteoclasts.
Definition
TRUE
Term
True or False.
PTH accelerates removal of Ca from bone.
Definition
True
Term
True or false.
PTH in low intermittent doses has an anabolic action to stimulate bone formation.
Definition
TRUE
Term
where are PTH receptors found in the kidney?
Definition
ascending loop of henle
distal tubules of the kidney
Term
what is the most dramatic effect of PTH on the kidney?
Definition
inhibition of reabsorption of P which in creases the P in the urine
Term
True or False
PTH helps reabsorption of Na and Bicarb in the proximal tubule.
Definition
FALSE!!!!
*INHIBITS IT**
Term
Where is Vit. D synthesized?
Definition
kidney
Term
What normally causes hyperparathyroidism?
Definition
TUMOR = primary
hypocalcemia with elevated PTH (vit. D deficiency)= secondary
Term
In cancer patients with hypercalcemia what will the PTH levels look like and why?
Definition
Low PTH because of high PTH related protien that is able to interact with PTH receptors (that increase Ca absorption in the gut by stimulating Vit. D synthesis)
Term
Calcitonin has antagonistic and synergistic relationships with PTH. What are they?
Definition
Antagonistic = Ca plasma levels
Synergistic = P plasma levels
Term
what are the two main sources of vitamin D?
Definition
UV light (Vit. D3)
Dietary ingestion (VitD3 and D2)
Term
what is the process of synthesis of the biologically active form of Vitamin D?
Definition
1. Vit.D3 from skin and diet hydroxylated in the liver
2.forms 25-OH Vitamin D
3.transport to the kidney to be hydroxylated again
4. forms 1,25 OH2 Vit D or
24,25 OH Vitamin D
Term
What is the rold of 24, 25 OH Vit. D?
Definition
It is the inactive form of 1,25 OH2 Vit. D to prevent excess formation
Term
How is Vit D excreted?
Definition
enterohepatic recycling
Term
what is the mediator of vit. D?
Definition
calbindins (calcium binding protiens)
Term
Vit D affects what systems and hormones?
Definition
Bone : increases processes with PTH
Kidney: enhance Ca reabsorption
PTH: repress gene for PTH formation
Immune System: stimulate cytokine production
Term
how does Vit. D interact with Ca and Insulin?
Definition
aids in Ca enhanced Insulin secreation by beta cells
Term
What systems are affected by Vit D deficiency?
Definition
Skeletal
Muscular
Cardiac
**causes a secondary hyperparathyroidsim**
Term
What are the issues connected with excess Vit. D?
Definition
high Ca --> renal calculi
high P --> soft tissue calcification
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