90. Calciotropic Hormones

Front 1

Where is calcium most important functionally?

Back 1

Intracellularly

Front 2

What is essential about calcium?

Back 2

It must be maintained at a BALANCED intake and excretion

Front 3

What is the normal daily intake of calcium?

Back 3

1000 mg

Front 4

How much calcium do we normally absorb from the intestines? What influences this absorption? What is the NET absorption?

Back 4

350 mg/day; under the influence of Calcitriol; the net absorption is about 100 mg/day

Front 5

What is the other name for calcitriol?

Back 5

1,25-dihydroxy Vit D

Front 6

How much calcium is normally secreted from the ECF via bile and pancreatic juices? Where does it end up?

Back 6

~250 mg/day
Ends up in feces

Front 7

So how much calcium do we lose in feces daily?

Back 7

900 mg/day

Front 8

Where does the 100 net mg of Ca that we absorb from the intestines go?

Back 8

To the ECF

Front 9

How much total calcium is in the ECF normally?

Back 9

1300 mg

Front 10

How much calcium in the ECF is free? How much is protein bound?

Back 10

50% is free, 50% is protein bound

Front 11

What is the calcium in the ECF in exchange with?

Back 11

-Cells
-Bone (deposition/resorption)
-the Gut (absorption/secretion)
-the Kidneys (reabsorption/excretion)

Front 12

How much calcium is filtered by the kidneys daily? What happens to it?

Back 12

9980 mg of Ca is filtered by the kidneys daily; most is reabsorbed so you don't lose it all.

Front 13

What is a major cause of hypocalcemia?

Back 13

Renal failure

Front 14

So how much calcium daily is:
-Filtered
-Reabsorbed
-Excreted?

Back 14

Filtered = 9980 mg
Reabsorbed = 9880 mg
Excreted = 100 mg
(daily)

Front 15

How much calcium is deposited and resorbed from bone daily?

Back 15

500 mg

Front 16

What controls bone calcium resorption?

Back 16

PTH

Front 17

How much calcium is in the bones normally?

Back 17

a TON - 1,000,000 mg

Front 18

What controls calcium reabsorption in the kidneys?

Back 18

PTH

Front 19

Does PTH only control calcium reabsorption in the kidneys?

Back 19

No

Front 20

3 things controlled by PTH in the kidneys:

Back 20

-Calcium reabsorption
-Phosphate reabsorption
-Vit D activation

Front 21

What happens when you deposit and resorb calcium from bone?

Back 21

You deposit and resorb PHOSPHATE too

Front 22

Can you ever resorb calcium from the bone without phosphate

Back 22

NO

Front 23

So how does the body separate the control of body Calcium and Phosphate?

Back 23

By the kidney

Front 24

What protein does calcium circulate bound to?

Back 24

Albumin

Front 25

So how do you measure the active amount of calcium (ionized) in the blood?

Back 25

By measuring Albumin - since 50% of calcium is bound to albumin, the same amount is free.

Front 26

Where is PTH made and released?

Back 26

In the parathyroid glands

Front 27

What does PTH do?

Back 27

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

Front 28

What stimulates the release of PTH from the PT glands?

Back 28

Low blood calcium

Front 29

What inhibits the release of PTH from the PT glands?

Back 29

High blood calcium

Front 30

What else does high blood calcium do?

Back 30

Stimulates Calcitonin release from the Thyroid gland parafollicular cells

Front 31

What is by far the most important hormone that controls calcium?

Back 31

PTH

Front 32

Is calcitonin all that important?

Back 32

No

Front 33

If a skilled surgeon does a thyroidectomy will it affect calcium regulation?

Back 33

Nope

Front 34

If a skilled surgeon does a parathyroidectomy will it affect calcium regulation?

Back 34

Yeah - the patient will die

Front 35

What are the 2 main types of cells in the Parathyroid glands?

Back 35

-Chief cells
-Oxyphil cells

Front 36

Which cells secrete PTH?

Back 36

Chief cells

Front 37

What is the receptor on the PT glands that senses increased serum calcium levels?

Back 37

A normal, 7-transmembrane, g-protein coupled receptor.

Front 38

What is the LIGAND for this receptor?

Back 38

CALCIUM!!

Front 39

What happens when calcium binds its receptor on the PT gland?

Back 39

It inhibits the release of PTH by activating a G-protein coupled cascade

Front 40

What is the hot new hormone?

Back 40

Vitamin D

Front 41

If Vit D is a hormone why do we call it a vitamin?

Back 41

Because deficiency used to cause rickets

Front 42

What are the 2 dietary forms of Vit D?

Back 42

Vit D3 - from animals
Vit D2 - from plants

Front 43

What is Vit D3 called?
What is Vit D2 called?

Back 43

D3 = Cholecalciferol
D2 = Ergocalciferol

Front 44

Which form of Vit D is better? Why?

Back 44

Vit D3 - it has a longer half life

Front 45

What is the first step in metabolism of Vit D?

Back 45

The liver converts it to 25-hydroxycholecalciferol

Front 46

Is the liver enzyme that hydroxylates vit D regulated?

Back 46

No - it happens all the time at a constant rate.

Front 47

What is the best assessment of a person's Vit D levels?

Back 47

Measurement of 25-hydroxycholecalciferol

Front 48

What happens to 25-hydroxyVit D?

Back 48

It goes to the kidney to get hydroxylated at the 1 position

Front 49

What enzyme is in the kidney to do this?

Back 49

1-hydroxylase

Front 50

Primary effect of 1,25-dihydroxy vit D:

Back 50

Increased intestinal absorption of calcium.

Front 51

What does the increased serum calcium achieved by Vit D do?

Back 51

INHIBITS PTH SECRETION

Front 52

So what is the best index of body Vitamin D stores?

Back 52

Serum 25-hydroxy Vit D

Front 53

Why is 25-Hydroxy Vit D the best index of Vit D stores?

Back 53

Because it won't be affected by changes in 1-hydroxylase enzyme activity

Front 54

Why won't 1-hydroxylase activity effect the amount of 25-OH Vit D in the body?

Back 54

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.

Front 55

What WILL changes in 1-hydroxylase enzyme activity affect?

Back 55

Levels of 1,25-dihydroxy vit D

Front 56

So what is the best index of renal 1-hydroxylase activity?

Back 56

Measuring serum levels of 1,25-dihydroxy vit D

Front 57

What type of a hormone is Vit D?

Back 57

A steroid hormone

Front 58

Where is the target receptor of Vit D?

Back 58

In the nuclei of intestinal epithelial cells

Front 59

What are the results of Vit D binding its nuclear receptor?

Back 59

-Increased Ca/Na countertransporter
-Phosphate absorption
-Ca absorption

Front 60

So what are the 3 direct effects of PTH?

Back 60

1. Stimulates calcium resorption from bone
2. Stimulates Vit D
3. Stimulates Calcium reabsorption in kidney

Front 61

And what does Vit D do?

Back 61

Increases calcium and phosphate reabsorption in the gut

Front 62

What happens if you don't have PTH?

Back 62

You don't have a normal life

Front 63

Too low of calcium:

Back 63

tetany

Front 64

Too high of calcium:

Back 64

weakness

Front 65

What stimulates phosphate reabsorption in the gut?

Back 65

1,25-dihydroxy vit D

Front 66

What stimulates phosphate resorption from bone?

Back 66

PTH

Front 67

What stimulates phosphate secretion in urine?

Back 67

PTH

Front 68

Where is the only place where phosphate and calcium regulation is independent of each other?

Back 68

In the kidney

Front 69

3 effects of hypocalcemia ( in order):

Back 69

1. PTH glands stimulated
2. Decreased blood phosphate due to PTH's phosphaturic effect
3. Increased blood calcium

Front 70

What causes hypercalcemia?

Back 70

Increased PTH secretion

Front 71

What is the usual cause of primary hyperparathyroidism?

Back 71

Benign tumors in the pt glands

Front 72

Why do benign tumors secrete so much PTH?

Back 72

Because they are refractory to the negative feedback effect of high serum calcium

Front 73

What will hypercalcemia caused by something other than PT tumors result in?

Back 73

Decreased PTH secretion

Front 74

What is hypercalcemia that leads to suppressed PTH secretion usually due to?

Back 74

-Too much Vit D, or -Hypercalcemia of malignancy

Front 75

What gets released in Hypercalcemia of malignancy?

Back 75

PTHrp - an analog that is released by tumors

Front 76

What does PTHrp do?

Back 76

Binds the same receptor as PTH, so the body thinks it needs to increase serum calcium.

Front 77

Do patients with hypercalcemia often present with symptoms?

Back 77

No; they're most often asymptomatic and are discovered by blood workups for other reasons.

Front 78

What is the cause of hypocalcemia?

Back 78

Deficiency in PTH secretion

Front 79

What is the most common cause of hypocalcemia due to low PTH?

Back 79

A thyroidectomy gone bad.. the surgeon accidently yanked out the PT glands along with it.

Front 80

What is the result of hypocalcemia?

Back 80

Tetany

Front 81

What is the treatment for hypocalcemia due to low PTH?

Back 81

Recombinant PTH or Vit D

Front 82

If you give Vit D what does it have to be? Why?

Back 82

Has to be the already active version because if PTH is low, there's nothing to stimulate Vit D activation in the kidney!

Front 83

If the PT glands are NORMAL, what does hypocalcemia cause?

Back 83

Increased PTH secretion

Front 84

What is it called when hypocalcemia induces increased PTH secretion?

Back 84

2ndary hyperparathyroidism

Front 85

In what patients is 2ndary hyperparathyroidism most common? WHY?

Back 85

Renal failure patients - because they can't activate vit D, so they can't absorb calcium from the gut.

Front 86

What is another common cause of hypocalcemia and hyperPTH?

Back 86

Sprue - malabsorption

Front 87

So 3 causes of hypocalcemia / 2ndary hyperparathyroidism:

Back 87

-Renal failure
-Sprue
-Low Vit D

Front 88

What is Vit D Deficiency in
-Children
-Adults

Back 88

Children = Rickets
Adults = Osteomalacia

Front 89

If a patient has primary hyperparathyroidism in only one PT gland, will the 3 other glands be big or small?

Back 89

Small