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BRS > Endocrinology- Regulation of Ca2+ and Phosphate > Flashcards

Endocrinology- Regulation of Ca2+ and Phosphate Flashcards

1
Q

Where is the majority of calcium in the body? And what compound is it stored as?

A

Skeleton and teeth

stored as hydroxyapatite crystals

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2
Q

What 2 types of plasma calcium are there

A

Ionised (unbound) - Ca2+, BIOLOGICALLY ACTIVE compoment

Bound- plasma protiens OR anions such as bicarbonate

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3
Q

Which 2 hormones increase serum levels of calcium and posphate?

how are they synthesized?

A

parathyroid hormone - secreted by para gland

Vit D- synthesized in skin or diet. actions via kidney and bone, gut

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4
Q

Which hormones decrease Ca2+ and phosphate levels?

A

Calcitonin- not essneital, only reduces acutely

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5
Q

Where is calcitonin synthesized?

A

By thyroid parafollicular cells, no negative effect if removed

(not essential for regulation)

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6
Q

What are the 2 inactive molecules of Vit D and where are each one from?

A

Vitamin D3 (Cholecaliferol)- Skin when exposed sunlight

Vitamine D2 (Ergocalciferol) - from diet

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7
Q

How does Skin make Cholecalciferol?

A

7-dehydrocholesterol (produced by skin cells) UV LIGHT

—->pre- vitamin D3

—–> Vit D3

(then goes off to produce activated Vit D3)

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8
Q

What happens to the Vitamin D2 and D3 after take in (First step)?

A

1st hydroxylation- to liver

convert to 25(OH)cholecalicferol

by 25-hydroxylase enzyme

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9
Q

What happens to the Vitamin D2 and D3 after take in (second step)?

A

2nd- hydroxylation

transported to kidney converted

by 1-alpha-hydroxylase

to 1,25 diol cholecalciferol WHICH IS ACTIVE VIT D

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10
Q

Which molecule should be measured to determine Vitamin D levels?

A

25(OH)cholecalciferol as active Vitamin D is difficult to measure

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11
Q

Does calcitriol -ve feedback itself? And how?

A

Yes,

regulates own synthesis by decrease transcripiton of

1-alpha hydroxylase enzyme of 2nd hydroxylation

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12
Q

What effects does calcitriol have to increase phosphate levels and calcium?

A

Increases Ca2+ and phosphate reabsoportion from kidnet

increased Ca2+ and phosphate absorption from small intestine

Increased Ca2+ absoprtion into bones

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13
Q

Where are parathyroid glands located?

A

4 small pieces on poterior of thryoid gland

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14
Q

What types of cells in parathryoid glands secrete PTH?

A

Chief cells

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15
Q

How is PTH secreted from the chief cells?

A

As a large precursor pre-pro-PTH

cleaved in cell to PTH

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16
Q

How is PTH secretion from chief cells regulated?

A

have G coupled Ca2+ sensing receptor

detect circulating Ca2+ levels + secrete inversely to it

17
Q

Effects of PTH?

A

increases osteoclast activity, increasing bone and Ca2+ resaborption

increase calcium reabsorption and excretion of phosphate from kidney

increase Vit D synthesis so increase absorption of minerals from small intestine

18
Q

How does PTH regulate serum levels of Ca2+?

A

increases Ca2+ plasma concentration

by increasing Ca2+ mobilisation from bones and it’s reabsoprtion from kidney

absorption of Ca2+ from small intestine via increasing vitamin D

19
Q

How does PTH regulate serum levels of phosphate ?

A

It doesn’t

as phosphate levels increase by absorption in small intenstine

but increases excretion in kidney

so overall no increase

20
Q

What affect does PTH have on bones to regulate serum levels of calcium?

A

Binds to osteoblasts to release oeseoclast activating factors like RANKL

stimulate OSTEOCLAST bone eating cells,

breakdown bone into calcium and phosphate, which then go to kidneys. (Ca2+ is reabsorbed phosphate excreted)

21
Q

What effect does calcitrol when low calcium serum levels on bones?

What effect does calictrol when normal calcium serum levels on bones?

A

increease calcium reabsoprtion from bone

clasts > blasts

increase bone formation

blasts > clasts

BOTH PTH and CALICITROL have similar effects on bone

22
Q

How is PTH (negatively) regulated?

A

2 ways

1).increase in plasma Ca2+

detected by parathyroid glands + secrete less PTH

2). Chief cells also have vitamin D receptors, too much Vit D less PTH

23
Q

Which types of cells produce calcitonin?

What is it’s effect?

A

Parafollicular cells of Thyroid cells

Reduce serum calcium levels

24
Q

How does calcitron decrease serum levels of Calcium?

A

Increase Ca2+ secretion by kidney

decrease osteoclast (bone consumtion cells) activity

25
Q

What molecule regulates phosphate?

And where is it produced?

A

FGF-23

specific cells in Bones

26
Q

How does it reduce phosphate levels?

A

2 ways

  1. Prevents re uptake of phosphate in kidney from urine( proximal tubule)

blocks/prevents Na+/phosphate co-transporter

  1. inhibits calcitriol, less phosphate absoprtion from gut
27
Q

How does PTH excrete phosphate in kidney?

A

same way as FGF 23

Prevents re uptake of phosphate in kidney from urine( proximal tubule)

blocks/prevents Na+/phosphate co-transporter

28
Q

Main affect of HYPOcalcaemia and HYPERcalcaemia

A

HYPO- less Ca2+ in blood serum, Ca more Na influx

greater excitation of neurones membranes

HYPER- more Ca2+ in blood serum, Ca blocks Na influx

less excitation of neurones membranes

29
Q

What function does Ca2+ have on Na+ channels?

A

At resting state sodium channels are stablizied by Ca2+,

prevents spontanous depolarisation

If low

30
Q

Symptoms of hypocalcaemia?

A

sensitises, excitable tissues, cramps, tingling

paresthesia (chilling, burning, numbness)- hands, mouth

convulsions - fits

arrhythmias - problem HR

tetany- can’t relax muscle

31
Q

What is Chvostek’s sign?

A

Tap facial nerve below zygomatic arch,

twitching of facial muscles, more sensitized

common with hypocalcaemia

32
Q

What is trousseau’s sign?

A

increase BP induced carpopedal spasm-muscles contract + can’t stop ,

neuromusclar irritability

33
Q

Causes of hypocalcaemia?

A

hypoparathyroidism

surgical- neck surgery, affect parathyroid gland

autoimmune- attacks any organs

magnesium. defincity- need to make PTH

agensis- failure organ grow

vitamin D deficincy- sun & diet

34
Q

Causes of vitamin D deficincy?

A
35
Q

Consequence of Vitamin D deficiency?

A

has importance in mineralism of bone increase bone formation, increase osteoblast activity> osteoclasts when Ca2+ levels are high

soft bones

rickets- bendt bones

osteomalacia- fractures, proximal mypoathy hips weakness

36
Q

Symptoms of hypercalcaemia?

A

stones- kidney lots of calcium excreted causes stones + neuphrocalcinosis

adbominal moans- gut is long muscle, anoxia, dypsia- heart burn, conspitation, pancritis-inflmation

pyshic groans- fatigue, depression, altered mentation

atonal muscles

37
Q

Causes of hypercalcaemia?

A

primary hyperparathyroidism- PTH gland adeonma

no negative feedback so increase PTH and Ca2=

cancer spread to bone, metastases.

local factors activate osteoclastsm increase calcium reabsoprtion from bone

excess vit D

38
Q
A

BRS (19 decks)

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