Calcium Metabolism

Question 1

What are some of the functions of Ca

Answer 1

Hormone secretion

Muscle contraction

Nerve conduction

Exocytosis

Activation and inactivation of enzymes

Intracellular second messenger

Regulates heart rhythm

Builds and maintains bones and teeth

Question 2

What are the hormones involved in Ca and phophate homeostasis

Answer 2

Parathyroid hormone

1,25-dihydroxyvitamin D (Calcitrol)

Calcitonin

Question 3

In what form are calcium and phosphate stored in the bone

Answer 3

Hydroxyapatite crystals

Question 4

Where do the hormones involved in Ca and phosphate metabolism act

Answer 4

Bone

Kidneys

GI tract

Question 5

How does calcium exist within the plasma

Answer 5

Free ionized species

Bound to anionic sites on serum proteins

Complexed with low-molecular-weight organic anions

Question 6

What does hypocalcaemia result in

Answer 6

• Hyperexcitability in nervous system - neuromuscular junction leading to:
  
  • Paraesthesia
  • Tetany
  • Paralysis
  • Convulsions

Question 7

What does chronic hypercalcaemia result in

Answer 7

Kidney stones

Constipation

Dehydration

Kidney damage

Tiredness

Depression

Stones, Moans, Groans and Bones

Question 8

How is synthesis of PTH regulated

Answer 8

High serum Ca down-regulates transcription

Low serum Ca up-regulates transcription

Low serum Ca prolongs mRNA survival

Question 9

Where is Vit D obtained

Answer 9

Sun exposure

Food

Supplements

Question 10

What is PTHrP, where is it produced and what does it do

Answer 10

Parathyroid hormone related peptide

It is produced by tumours and may lead to hypercalcaemia - humeral hypercalcaemia of malignancy (HHM)

Question 11

What actions does PTHrP have and not have

Answer 11

Increases calcium release from bone

Reduces renal calcium excretion

Reduces renal phosphate reabsorption

Does not increase renal C-1 hydroxylase activity so does not increase calcitriol concentration

Question 12

What cancers commonly produce PTHrP

Answer 12

Breast

Prostate

Question 13

Where is calcitonin produced

Answer 13

C-cells in the thyroid gland

Question 14

Where are the parathyroid galnds located

Answer 14

Back of the thyroid gland, usually 4

Question 15

What cells are present in the parathyroid gland and what do they produce

Answer 15

Cheif cells - produce PTH

Oxyphil cells

Question 16

What effect does calcitriol have

Answer 16

Increases absorption of Ca by digestive tract - via transcellular uptake and endocytosis and exocytosis of Ca-CaBP complex

Increases resorption of Ca by osteoclasts

Increases reabsorption of Ca by kidneys

Question 17

What effect does PTH have

Answer 17

Increases resorption of Ca by osteoclasts

Increases reabsorption of Ca by kidneys

Stimulates activation of Vit A to increase uptake of Ca in gut by transcellular uptake

Question 18

Describe how vitamin D is activated

Answer 18

Vit D is hydroxylated in the liver to 25-hydroxyvitamin D

25-hydroxyvitamin D is then transported to the kidneys where it is filtered by the glomerulus and enteres PCT where it is converted to the active form by 1a-hydroxylase

Question 19

How is hydroxylation of 25-hydroxyvitmin D regualted

Answer 19

Negative feedback by serum Ca

Stimulated by elevated PTH

Question 20

What causes hypercalcaemia

Answer 20

Malignant osteolytic bone metastases

Multiple myeloma

Question 21

Which cancers causes malignant osteolytic bone metastases and where do they metastasise to

Answer 21

Breast, lung, renal and thyroid cancers

Metastasise to: vertebrae, pelvis, proximal femur, ribs, proximal humerus, skull

Question 22

What are the two forms of hyperparathyroidism

Answer 22

Primary

Secondary

Question 23

What causes primary hyperparathyroidism

Answer 23

One parathyroid gland develops a PTH secreting adenoma

Causes an increased serum Ca and decreased serum phosphate

Question 24

What are the symptoms of primary hyperparathyroidism

Answer 24

Moans - tired, exhausted, depressed

Groans - constipation, peptic ulcers, pancreatitis

Stones - kidney stones, polyuria

Bones - bone and muscle aches

Question 25

What causes secondary hyperparathyroidism

Answer 25

Parathyroid glands become hyperplastic - seen in Vit D deficiency due to dietary/environmental or chronic renal failure as Vit D not activated

Vit D deficiency means Ca absorption low so low serum Ca causing PTH to rise, this activates osteoclasts to release Ca from bone causing bone pain due to osteomalacia

Question 26

What are the symptoms of severe hypercalcaemia

Answer 26

Dehydration

Lethargy

Weakness

Confusion

Coma

Renal failure

Question 27

What is the main treatment of hypercalcaemia

Answer 27

Rehydration

Question 28

Where is hypocalcaemia mostly seen

Answer 28

In post total-thyroidectomy patients

Question 29

What are the symptoms of hypocalcaemia

Answer 29

Tingling around the mouth and in the fingers

Muscle tetany

Carpopedal spasm

Chvostek’s sign - twitching of mouth when facial nerve tapped

Question 30

How does an increase or decrease in serum calcium affect on neuronal activity

Answer 30

Hypercalcaemia suppresses activity by raising threshold

Hypocalcaemia causes excitability by lowering threshold

Question 31

What is osteoporosis

Answer 31

Decreased bone density with normal ratio of mineral to matrix

There is degeneration of constructed bones causing brittle bones

Question 32

What is osteomalacia

Answer 32

Where the mineral to matrix ratio is decreased causing soft bones, prone to bending

Due to Vit D deficiency

Question 33

What are the risk factors for osteoporosis

Answer 33

Postmenopausal women

Low BMI

Long-term oral steroid use

Heavy drinker

Smoker

Prolonged inactivity