Lecture 22 - Calcium Balance

Question 1

What is the effect of changes in calcium concentration on neuron excitability?

L22 S4

Answer 1

Increased calcium (hypercalcemia):
-depresses the nervous system

Decreased calcium (hypocalcemia):
-increases excitability of the nervous system

Question 2

Where is the body’s calcium found?

L22 S5

Answer 2

Bone:

• ~99%
• 1,000,000 mg

Cells:

• 1%
• 13,000 mg

Extracellular fluid

• 0.1%
• 1,300 mg

Question 3

Where is the body’s phosphate found?

L22 S6

Answer 3

Bones:
-85%

Cells:
-14%

Extracellular fluid:
-1%

Question 4

What is the normal level of calcium in the blood?
What level of calcium is lethal?

L22 S7

Answer 4

Normal:
-9.5 mg/dL

Lethal:
-4 mg/dL

Question 5

How is calcium absorbed and secreted by the body?

L22 S8

Answer 5

Absorption:
Poorly absorbed in intestine without vitamin D

35% is absorbed with the help of vitamin D but due to sloughed off cells, only about 10% makes it into the body.

Excretion:

• 90% in intestines
• 10% in urine (reabsorption rate of 99%)

Question 6

What prevents hydroxyapatite from forming in normal tissues?

L22 S10

Answer 6

Pyrophosphate

Question 7

How is calcium concentration maintained even during addition or removal of large amounts of calcium?

L22 S12

Answer 7

The bones contain large amount of exchangeable calcium which acts as a buffer and brings calcium levels back to normal within 30-60 minutes.

Question 8

How is calcium absorbed by the body and how does vitamin D play a role in this?

L22 S17-18

Answer 8

Vitamin D stimulates formation and insertion of calbindin, calcium transporter, in apical border of cell

Calcium exits the cell via diffusion

Question 9

What affect does parathyroid hormone have on the calcium level?

L22 S20

Answer 9

PTH causes reabsorption of calcium from the bone

Question 10

What effect does PTH have on bone reabsorption?

L22 S23

Answer 10

Activation of calcium pumps in existing osteoclasts

Formation of new osteoclasts

Question 11

What effect does PTH have on renal function?

L22 S26-27

Answer 11

Increases reabsorption of calcium

Decreases phosphate reabsorption

Question 12

What is the effect of calcitonin?

L20 S30

Answer 12

Decrease blood plasma concentrations (this is typically counter rapidly by PTH release)

Question 13

What occurs in hypoparathyroidism?

L22 S31

Answer 13

• osteoclast activity ceases
• blood calcium level drops to 6-7 mg/dL
• phosphate levels increase
• signs of tetany occur