Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
89 Cards in this Set
- Front
- Back
Where is calcium most important functionally?
|
Intracellularly
|
|
What is essential about calcium?
|
It must be maintained at a BALANCED intake and excretion
|
|
What is the normal daily intake of calcium?
|
1000 mg
|
|
How much calcium do we normally absorb from the intestines? What influences this absorption? What is the NET absorption?
|
350 mg/day; under the influence of Calcitriol; the net absorption is about 100 mg/day
|
|
What is the other name for calcitriol?
|
1,25-dihydroxy Vit D
|
|
How much calcium is normally secreted from the ECF via bile and pancreatic juices? Where does it end up?
|
~250 mg/day
Ends up in feces |
|
So how much calcium do we lose in feces daily?
|
900 mg/day
|
|
Where does the 100 net mg of Ca that we absorb from the intestines go?
|
To the ECF
|
|
How much total calcium is in the ECF normally?
|
1300 mg
|
|
How much calcium in the ECF is free? How much is protein bound?
|
50% is free, 50% is protein bound
|
|
What is the calcium in the ECF in exchange with?
|
-Cells
-Bone (deposition/resorption) -the Gut (absorption/secretion) -the Kidneys (reabsorption/excretion) |
|
How much calcium is filtered by the kidneys daily? What happens to it?
|
9980 mg of Ca is filtered by the kidneys daily; most is reabsorbed so you don't lose it all.
|
|
What is a major cause of hypocalcemia?
|
Renal failure
|
|
So how much calcium daily is:
-Filtered -Reabsorbed -Excreted? |
Filtered = 9980 mg
Reabsorbed = 9880 mg Excreted = 100 mg (daily) |
|
How much calcium is deposited and resorbed from bone daily?
|
500 mg
|
|
What controls bone calcium resorption?
|
PTH
|
|
How much calcium is in the bones normally?
|
a TON - 1,000,000 mg
|
|
What controls calcium reabsorption in the kidneys?
|
PTH
|
|
Does PTH only control calcium reabsorption in the kidneys?
|
No
|
|
3 things controlled by PTH in the kidneys:
|
-Calcium reabsorption
-Phosphate reabsorption -Vit D activation |
|
What happens when you deposit and resorb calcium from bone?
|
You deposit and resorb PHOSPHATE too
|
|
Can you ever resorb calcium from the bone without phosphate
|
NO
|
|
So how does the body separate the control of body Calcium and Phosphate?
|
By the kidney
|
|
What protein does calcium circulate bound to?
|
Albumin
|
|
So how do you measure the active amount of calcium (ionized) in the blood?
|
By measuring Albumin - since 50% of calcium is bound to albumin, the same amount is free.
|
|
Where is PTH made and released?
|
In the parathyroid glands
|
|
What does PTH do?
|
Directly: stimulates bone resorption of Ca/Phosphate
Directly: stimulates Ca reabsorption in kidney Indirectly: stimulates calcium reabsorption from the gut by activating Vit D in kidney |
|
What stimulates the release of PTH from the PT glands?
|
Low blood calcium
|
|
What inhibits the release of PTH from the PT glands?
|
High blood calcium
|
|
What else does high blood calcium do?
|
Stimulates Calcitonin release from the Thyroid gland parafollicular cells
|
|
What is by far the most important hormone that controls calcium?
|
PTH
|
|
Is calcitonin all that important?
|
No
|
|
If a skilled surgeon does a thyroidectomy will it affect calcium regulation?
|
Nope
|
|
If a skilled surgeon does a parathyroidectomy will it affect calcium regulation?
|
Yeah - the patient will die
|
|
What are the 2 main types of cells in the Parathyroid glands?
|
-Chief cells
-Oxyphil cells |
|
Which cells secrete PTH?
|
Chief cells
|
|
What is the receptor on the PT glands that senses increased serum calcium levels?
|
A normal, 7-transmembrane, g-protein coupled receptor.
|
|
What is the LIGAND for this receptor?
|
CALCIUM!!
|
|
What happens when calcium binds its receptor on the PT gland?
|
It inhibits the release of PTH by activating a G-protein coupled cascade
|
|
What is the hot new hormone?
|
Vitamin D
|
|
If Vit D is a hormone why do we call it a vitamin?
|
Because deficiency used to cause rickets
|
|
What are the 2 dietary forms of Vit D?
|
Vit D3 - from animals
Vit D2 - from plants |
|
What is Vit D3 called?
What is Vit D2 called? |
D3 = Cholecalciferol
D2 = Ergocalciferol |
|
Which form of Vit D is better? Why?
|
Vit D3 - it has a longer half life
|
|
What is the first step in metabolism of Vit D?
|
The liver converts it to 25-hydroxycholecalciferol
|
|
Is the liver enzyme that hydroxylates vit D regulated?
|
No - it happens all the time at a constant rate.
|
|
What is the best assessment of a person's Vit D levels?
|
Measurement of 25-hydroxycholecalciferol
|
|
What happens to 25-hydroxyVit D?
|
It goes to the kidney to get hydroxylated at the 1 position
|
|
What enzyme is in the kidney to do this?
|
1-hydroxylase
|
|
Primary effect of 1,25-dihydroxy vit D:
|
Increased intestinal absorption of calcium.
|
|
What does the increased serum calcium achieved by Vit D do?
|
INHIBITS PTH SECRETION
|
|
So what is the best index of body Vitamin D stores?
|
Serum 25-hydroxy Vit D
|
|
Why is 25-Hydroxy Vit D the best index of Vit D stores?
|
Because it won't be affected by changes in 1-hydroxylase enzyme activity
|
|
Why won't 1-hydroxylase activity effect the amount of 25-OH Vit D in the body?
|
Because there is 1000X more 25-hydroxy Vit D than 1,25-dihydroxy vit D; such a tiny amount is ever converted that the overal amt of 25-OH Vit D is constant.
|
|
What WILL changes in 1-hydroxylase enzyme activity affect?
|
Levels of 1,25-dihydroxy vit D
|
|
So what is the best index of renal 1-hydroxylase activity?
|
Measuring serum levels of 1,25-dihydroxy vit D
|
|
What type of a hormone is Vit D?
|
A steroid hormone
|
|
Where is the target receptor of Vit D?
|
In the nuclei of intestinal epithelial cells
|
|
What are the results of Vit D binding its nuclear receptor?
|
-Increased Ca/Na countertransporter
-Phosphate absorption -Ca absorption |
|
So what are the 3 direct effects of PTH?
|
1. Stimulates calcium resorption from bone
2. Stimulates Vit D 3. Stimulates Calcium reabsorption in kidney |
|
And what does Vit D do?
|
Increases calcium and phosphate reabsorption in the gut
|
|
What happens if you don't have PTH?
|
You don't have a normal life
|
|
Too low of calcium:
|
tetany
|
|
Too high of calcium:
|
weakness
|
|
What stimulates phosphate reabsorption in the gut?
|
1,25-dihydroxy vit D
|
|
What stimulates phosphate resorption from bone?
|
PTH
|
|
What stimulates phosphate secretion in urine?
|
PTH
|
|
Where is the only place where phosphate and calcium regulation is independent of each other?
|
In the kidney
|
|
3 effects of hypocalcemia ( in order):
|
1. PTH glands stimulated
2. Decreased blood phosphate due to PTH's phosphaturic effect 3. Increased blood calcium |
|
What causes hypercalcemia?
|
Increased PTH secretion
|
|
What is the usual cause of primary hyperparathyroidism?
|
Benign tumors in the pt glands
|
|
Why do benign tumors secrete so much PTH?
|
Because they are refractory to the negative feedback effect of high serum calcium
|
|
What will hypercalcemia caused by something other than PT tumors result in?
|
Decreased PTH secretion
|
|
What is hypercalcemia that leads to suppressed PTH secretion usually due to?
|
-Too much Vit D, or -Hypercalcemia of malignancy
|
|
What gets released in Hypercalcemia of malignancy?
|
PTHrp - an analog that is released by tumors
|
|
What does PTHrp do?
|
Binds the same receptor as PTH, so the body thinks it needs to increase serum calcium.
|
|
Do patients with hypercalcemia often present with symptoms?
|
No; they're most often asymptomatic and are discovered by blood workups for other reasons.
|
|
What is the cause of hypocalcemia?
|
Deficiency in PTH secretion
|
|
What is the most common cause of hypocalcemia due to low PTH?
|
A thyroidectomy gone bad.. the surgeon accidently yanked out the PT glands along with it.
|
|
What is the result of hypocalcemia?
|
Tetany
|
|
What is the treatment for hypocalcemia due to low PTH?
|
Recombinant PTH or Vit D
|
|
If you give Vit D what does it have to be? Why?
|
Has to be the already active version because if PTH is low, there's nothing to stimulate Vit D activation in the kidney!
|
|
If the PT glands are NORMAL, what does hypocalcemia cause?
|
Increased PTH secretion
|
|
What is it called when hypocalcemia induces increased PTH secretion?
|
2ndary hyperparathyroidism
|
|
In what patients is 2ndary hyperparathyroidism most common? WHY?
|
Renal failure patients - because they can't activate vit D, so they can't absorb calcium from the gut.
|
|
What is another common cause of hypocalcemia and hyperPTH?
|
Sprue - malabsorption
|
|
So 3 causes of hypocalcemia / 2ndary hyperparathyroidism:
|
-Renal failure
-Sprue -Low Vit D |
|
What is Vit D Deficiency in
-Children -Adults |
Children = Rickets
Adults = Osteomalacia |
|
If a patient has primary hyperparathyroidism in only one PT gland, will the 3 other glands be big or small?
|
Small
|