MEH - Calcium Metabolism Flashcards Preview

CJ: UoL Medicine Semester Two (ESA2) > MEH - Calcium Metabolism > Flashcards

Flashcards in MEH - Calcium Metabolism Deck (29):
1

Where is most calcium stored in the body?

In the skeleton

2

How much calcium is stored in the average adult human?

Around 1000g - 99% of this is in the bones in hydroxyapatite crystals

3

How does the skeleton help with calcium metabolism?

It helps to buffer serum calcium levels and releases calcium phosphate into the interstitium

4

How does parathyroid hormone affect calcium levels? (It is active when serum calcium is low)

- stimulates bone resorption and release of calcium into circulation
- stimulates calcium resorption in kidney

5

How does dietary vitamin D affect calcium levels?

It increases intestinal absorption of dietary calcium and renal reabsorption of calcium, and increases bone resorption

6

What is the role of calcitonin?

It counteracts the effects of PTH

7

What do chief cells in the parathyroid gland do?

Produce parathyroid hormone

8

How long is the half life of parathyroid hormone?

4 minutes

9

What is the structure of PTH?

It is a straight chain polypeptide hormone

10

Why must PTH be continually synthesised?

Chief cells degrade the hormone as well as synthesising it, so it is not stored

11

What are the actions of PTH on bone?

- induces osteoblastic cells to synthesise and secrete cytokines on the cell surface
- cytokines stimulate differentiation and activity in osteoclasts and protect from apoptosis
- PTH decreases osteoblast activity
- resorption of mineralised bone and release of calcium and phosphate into extracellular fluid

12

What is the typical dietary calcium intake per day?

1000mg/day

13

What is vitamin D?

Lipid soluble vitamin which comes in two forms - D3 (made in skin and from dairy), and D2 (from yeast and fungi)

14

Where does vitamin D come from?

Can be derived from plants or the action of sunlight on cholesterol in the skin

15

What does vitamin D3 bind to in the circulation?

Transcalciferin

16

What is the half life of vitamin D3?

0.25 days

17

What is the main action of calcitriol?

Decreases the urinary loss of calcium by stimulating reabsorption in the kidney

18

Where is calcitonin secreted?

Parafollicular cells of the thyroid gland

19

How is calcitonin used clinically?

To lower serum calcium in cases of hypercalcaemia

20

True or false - calcium is not involved in blood clotting?

False - it is factor IV in the clotting cascade

21

Give some causes of hypercalcaemia in a hospital setting

Malignant osteocytic bone metastases, multiple myeloma

22

Give some common cancers which can metastasise to bone causing hypercalcaemia

Breast, lung, renal, thyroid

23

What causes primary hyperparathyroidism?

One of the four parathyroid glands develops an adenoma and secretes excessive parathyroid hormone, causing serum calcium to rise

24

What are the symptoms of primary hyperparathyroidism?

Bones, (kidney) stones, abdominal groans and 'psychic moans'

25

What are the effects of hypercalcemia on neurones?

Lethargy, confusion, coma due to suppression of neuronal activity

26

What are the effects of hypocalcemia on nerves?

Leads to 'excitable' nerves because it lowers the threshold for depolarisation

27

Why is it important to keep patients who have severe hypercalcemia hydrated?

The polyuria can lead to dehydration which exacerbates the hypercalcemia

28

What is osteomalacia?

The ratio of mineral to matrix is decreased, so there is not enough mineral content. It leads to soft bones which are prone to bending.

29

What is osteomalacia referred to in children?

Rickets

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