Wk 7

Question 1

Where is the majority of the body calcium?

Answer 1

Bone

Question 2

What form does calcium come in?

Answer 2

Ionised, Bound and Complex form
Ionised calcium - active form

Question 3

What are the functions of calcium?

Answer 3

• structural integrity and metabolism of bone
• synaptic transmission
• coenzyme function
• excitability of nerve and muscle cells
• excitation (contraction coupling)
• regulation of transmembrane ion transport
• second messenger

Question 4

What are the cells involved in calcium regulation?

Answer 4

Osteoblasts, osteocytes, osteoclasts

Question 5

What are the hormones involved in calcium regulation?

Answer 5

PTH, Calcitonin, Vit D

Question 6

What are the target sites of calcium?

Answer 6

Bone, Kidney, Intestine

Question 7

Where is the parathyroid gland located?

Answer 7

Behind the thyroid gland

Question 8

What is the parathyroid hormone (PTH)?

Answer 8

• from chief cells in parathyroid
• polypeptide hormone
• target cell = plasma membrane receptor

Question 9

Which parts of the body does PTH effect?

Answer 9

• Bones
• Kidney
• Intestine

Question 10

How does PTH effect the bones?

Answer 10

• moves calcium from bone to extracellular fluid (ECF)
• rapid and slow effect
• acts on osteoblasts and increases osteoclasts differentiation
• more osteoclastic action

Question 11

How does PTH effect the kidney?

Answer 11

• increased calcium reabsorption
• increased phosphate excretion
• increased 1 alpha hydroxylase action

Question 12

How does PTH effect the intestine?

Answer 12

• increased calcium absorption
• indirect action (through vit D)
• increases phosphate absorption

Question 13

How is PTH regulated?

Answer 13

Decreased serum calcium - increased PTH

Increased serum calcium - decreased PTH

Increased 1,25DHCC (calcitriol)- decreased PTH secretion

Question 14

Where is calcitonin from?

Answer 14

• from parafollicular cells (thyroid gland)

Question 15

What is the stimulus for secretion for calcitonin?

Answer 15

Increased serum calcium

Question 16

How does calcitonin effect the bone?

Answer 16

• decreased reabsorption
• decreased osteoclastic action

Question 17

How does calcitonin effect the kidney?

Answer 17

• decreased calcium reabsorption
• decreased phosphate reabsorption

Question 18

How does calcitonin effect the intestine?

Answer 18

• decreased calcium absorption

Question 19

What is Vitamin D?

Answer 19

• sterol hormone
• formed from 7 dehydrocholesterol
• 1,25 DHCC formed in the kidney
• requires 1 alpha hydroxylase
• PTH increases 1,25 DHCC formation

Question 20

What is 1,25 DHCC?

Answer 20

Calcitriol
- Most active form of Vit D (very short half life)

Question 21

How does vitamin D effect the intestine?

Answer 21

• increases calcium absorption
• forms calcium binding proteins in the intestine

Question 22

How does vitamin D effect the bone?

Answer 22

• direct action (demineralisation but net effect is bone formation; by increasing serum calcium)
• increases calcium transporters in bone

Question 23

How does vitamin D effect the kidney?

Answer 23

• increased calcium reabsorption

Question 24

What is hypoparathyroidism?

Answer 24

When the parathyroid gland is not active enough and is not making enough PTH.

Question 25

What is hypocalcemia?

Answer 25

Abnormally low calcium levels in the blood.

Question 26

What are the causes of hypocalcemia?

Answer 26

- hypoparathyroidism - resistance to PTH - decreased Vit D synthesis - renal insufficiency

Question 27

What are the effects of hypocalcemia?

Answer 27

- increased nervous system excitability - easy initiation of action potentials - tetanic muscle contractions - spasm of laryngeal muscles - seizures

Question 28

What is the Trousseau's sign?

Answer 28

- carpopedal spasm (tetany in the hand) - very sensitive and specific - present in 94% patients with hypocalcemia

Question 29

What is tetany?

Answer 29

Spastic contraction of skeletal muscle without relaxation (muscle doesn't release properly).

Question 30

What is Chvostek's sign?

Answer 30

Twitching of facial muscles in response to tapping on facial nerve.

Question 31

What is hyperparathyroidism?

Answer 31

Overactive parathyroid gland, that is producing too much PTH.

Question 32

What is primary hyperparathyroidism caused by?

Answer 32

- tumour of parathyroid gland - parathyroid adenomas - hyperplasia (increase in # of cells)

Question 33

What are the effects of primary hyperparathyroidism?

Answer 33

- increased serum calcium - increased bone reabsorption (break down of bones) - osteitis fibrosa cystica (bone disorder)

Question 34

What is secondary hyperparathyroidism caused by?

Answer 34

Hypocalcemia (chronic renal failure)

Question 35

What are the effects of secondary hyperparathyroidism?

Answer 35

Increased PTH

Question 36

What are the hormones that regulate bone remodelling?

Answer 36

- cortisol (bone reabsorption; break down of bones) - testosterone, estrogen, GH, IGF-1 (bone formation)

Question 37

What are the endocrine disorders that cause bone reabsorption?

Answer 37

- hyperparathyroidism - thyrotoxicosis - Cushing's syndrome - acromegaly

Question 38

What are the steps for bone remodelling to decrease bone mass?

Answer 38

1. Osteoblasts 2. RANK ligand 3. RANK ligand + RANK receptor 4. Increased osteoclastic action 5. Decreased bone mass

Question 39

What are the steps for bone remodelling to increase bone mass?

Answer 39

1. Osteoblasts 2. Osteoprotegerin 3. RANKL + OPG 4. No RANK action 5. Decreased osteoclast action 6. Increased bone mass