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LCRS Endocrinology > calcium metabolism > Flashcards

calcium metabolism Flashcards

endocrine control of calcium: recall the principle hormones which regulate serum calcium concentration, their physiological effects, their mechanism of action and their regulation

1
Q

how is [Ca2+] increased

A

parathyroid hormone (PTH) or calcitriol (active form of vitamin D3)

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2
Q

how is [Ca2+] decreased

A

calcitonin

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3
Q

location of parathyroid glands

A

4 present; 2 on each lobe of thyroid

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4
Q

what is the hormone secreted by the parathyroid gland

A

parathyroid hormone (PTH)

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5
Q

what is the hormone secreted by parafollicular cells in the thyroid

A

calcitonin

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6
Q

what is the Ca2+ sensing receptor and how does it function

A

G-protein coupled receptor; changes conformation and activates intracellular signalling pathways

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7
Q

Ca2+ and parathyroid hormone (PTH) release

A

if high [Ca2+], bind to Ca2+ receptor, activating G-protein coupled receptor and activating intracellular signalling pathways to suppress parathyroid hormone release

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8
Q

what is parathyroid hormone (PTH) synthesised as

A

pre-proPTH polypeptide

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9
Q

what does parathyroid hormone (PTH) bind to and activate

A

binds to transmembrane G-protein linked receptors and activates adenyl cyclase

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10
Q

parathyroid hormone (PTH) actions in kidney

A

increases PO4 3- excretion and Ca2+ reabsorption

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11
Q

parathyroid hormone (PTH) action to form vitamin D3

A

stimulates activity of receptor 1a hydroxylase which forms active vitamin D3

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12
Q

parathyroid hormone (PTH) actions in small intestine

A

increase PO4 3- and Ca2+ reabsorption

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13
Q

parathyroid hormone (PTH) actions on bone

A

osteoclasts stimulated and osteoblasts inhibited so increases bone reabsorption

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14
Q

parathyroid hormone (PTH) effect on blood [Ca2+] and how

A

increase Ca2+ absorption in small intestine and kidneys, and increases bone Ca2+ mobilisation, so increase in blood [Ca2+]

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15
Q

how does parathyroid hormone (PTH) act in bone

A

PTH receptors on osteoblasts → PTH binds → release osteoclast activating factors such as RANKL → bind to osteoclast receptors → cause bone reabsorption

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16
Q

parathyroid hormone (PTH) regulation following increase in [Ca2+]

A

negative feedback to parathyroid gland so less release of PTH; vitamin D3 also suppresses PTH;

17
Q

parathyroid hormone (PTH) regulation following decrease in [Ca2+]

A

less suppression of PTH release as fewer Ca2+ ions; catecholamines stimulate PTH production

18
Q

calcitriol (dihydroxy-cholecalciferol; active form of vitamin D3) synthesis

A

7-dehyrdocholesterol in skin (UV light) and diet → cholecalciferol (vitamin D3) → 25 hydroxy-cholecalciferol synthesised in liver and stored in this form → 1,25 dihydroxy-cholecalciferol (calcitriol) synthesised in kidneys

19
Q

calcitriol (active vitamin D3) actions on bone

A

chronic effect of increased osteoblast activity (promote laying down of bone so preserves PO4 3-)

20
Q

calcitriol (active vitamin D3) actions in kidneys and small intestine

A

increases Ca2+ and Po4 3- reabsorption in kidneys and small intestine

21
Q

what does calcitriol reabsorb more as opposed to parathyroid hormone (PTH) and why

A

reabsorb PO4 3- as concerned with maintaining bone mass

22
Q

what do high calcitriol (active vitamin D3) levels stimulate

A

fibroblast growth factor 23

23
Q

what does fibroblast growth factor 23 regulate

A

important role in regulating PO4 3- metabolism by lowering [PO4 3-]

24
Q

how does fibroblast growth factor 23 lower [PO4 3-]

A

inhibits 1a-hydroxylase so inhibits calcitriol production (negative feedback)

25
Q

what is calcitonin synthesised from

A

pre-procalcitonin (polypeptide)

26
Q

what does calcitonin bind to and activate

A

binds to transmembrane G-protein linked receptor and activates adenyl cyclase or PLC as second messenger systems

27
Q

how does calcitonin decrease plasma [Ca2+]

A

inhibits osteoclast activity and increases urinary excretion of Ca2+, causing a decrease in plasma [Ca2+]

28
Q

consequences of excess parathyroid hormone (PTH) in the kidney

A

polyuria, renal stones, nephrocalcinosis

29
Q

consequences of excess parathyroid hormone (PTH) in the GIT

A

gastric acid, duodenal ulcers

30
Q

consequences of excess parathyroid hormone (PTH) in bone

A

bone lesions, bone rarefaction, fractures

LCRS Endocrinology (34 decks)

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