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Endocrinology > The parathyroid gland (calcium and phosphate regulation) > Flashcards

The parathyroid gland (calcium and phosphate regulation) Flashcards

1
Q

Adult human contains around ……… of calcium

A

1000g

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2
Q

99% of calcium is sequestered in

A

bones as hydroxyapatite crystals (Ca10(PO4)6(OH)2)

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3
Q

how much calcium is exchanged between bone and ECF each day

A

300-600 mg

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4
Q

skeleton provides

A
  • Structural support
  • Major reserve of calcium
  • Helps to buffer serum levels
  • Releasing calcium phosphate into interstitium
  • Up taking calcium phosphate
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5
Q
A
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6
Q

serum calcium

A

2.2-2.6 mH

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7
Q

calcium is distributed between three itner convertible fractions

A
  • Mostly ionised calcium
  • Protein bound calcium
  • Complexed calcium (pi, citrate etc)
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8
Q

role of calcium

A
  • Builds and maintains bones and teeth
  • Heart rhythm
  • Eases calcium
  • Assists normal blood clotting
  • Normal nerve function
  • Normal kidney function
  • Lowers BP
  • Activity of some enzymes
  • Intracellular signalling
  • Nervous transmission at NMJ
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9
Q

calcium and clotting

A

Calcium is an important clotting factor – Factor IV

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10
Q

what is used in blood tests to stop blood clotting

A

EDTA- calcium chelator –> stops the blood clotting

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11
Q

what is used to chelate calcium in donor blood

A

citrate

  • Citrate levels may become high in patients blood
  • Will need to give recipients of massive blood transfusions intravenous calcium
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12
Q

which hromones regulate calcium and phosphate

A

parathryoid hormone (PTH)

calcitriol

calcitonin

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13
Q

Parathyroid hormone (PTH)

A

produced and released by the parathyroid gland

  • secretes in response to low plasma calcium
  • affects bone, intestines and kidney
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14
Q

calcitriol

A

released by the kidney from vitamin D

  • increases plasma calcium
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15
Q

calcitonin

A

released from the thryoid parafollicular cells

  • decreases plasma calcium and phosphate
  • minor role
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16
Q

the parathryoid

A

4 sit on the thyroid

  • Unique appearance
  • Doesn’t look like a normal gland
  • Capsule around parathyroid gland
  • 2 cell types
    • Chief cells- produce parathyroid
    • Oxyphil- not sure what they do (maybe old chief cell)
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17
Q

the parathryoid can be accidentally

A

Removed during thyroid surgery

  • Important to try and preserve - regularly monitor serum calcium
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18
Q

PTH synthesis

A
  • Synthesis regulated both by transcriptional and post transcriptional levels
  • Low serum calcium unregulated gene transcription
  • Low serum calcium prolongs survival of mRNA
  • High serum calcium down regulates
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19
Q

features of PTH synthesis

A
  • No serum binding protein
  • Straight chain polypeptide hormone - preprohormone (115AA long), cleaved to 84AA
20
Q

PTH continually syntheses but little stored

A
  • Chief cells degrade hormone as well as synthesis it
  • Cleavage of PTH in chief cell accelerated by high serum calcium levels
21
Q

PTH affect on bones

A

Activates osteoclasts- calcium and phosphate released into the blood

22
Q

PTH affect on intestines

A
  • Activates Vitamin D to become calcitriol and hence increases trans cellular uptake from GI tract
  • GI tract can absorb more calcium
23
Q

PTH and the kidney

A
  • increases reabsorption of calcium
  • PTH reduces the reabsorption of phosphate from the proximal tubule of the kidney, which means more phosphate is excreted through the urine.

*However, PTH enhances the uptake of phosphate from the intestine and bones into the blood. In the bone, slightly more calcium than phosphate is released from the breakdown of bone*

24
Q

kidney stones

A

Calcium + Phosphate forms hydroxyapatite crystals which causes stonesà don’t want to have a peak of calcium and phosphate at the same time- therefore body has adapted to increase calcium (reabsorption), and increase phosphate excretion. Whilst PTH causes phosphate to be released from bone and increased absorption in the intestines, there is a net loss of PO4 as the loss in urine will always be greater than that gained from bones.

25
Q

bone deposition is mediated by

A

0steoblasts which produce collagen and matrix which is mineralised to hydroxyapatite

26
Q

bone reabsorption is mediated by

A

osteoclasts

  • produced acid micro-environment dissolving hydroxyapaptite releasing calcium and phosphate into the blood (PTH stimulates osteoclasts)
27
Q

PTH has a quick action on the bone

A
  • 1-2 hrs PTH stimulates osteolysis
    • PTH induces osteoblastic cells to synthesis and secrete cytokines on cell surface
    • Cytokines stimulate differentiation and activity in osteoclasts and protect them from apoptosis
    • PTH decreases osteoblasts activity exposing bone surface to osteoclast
    • Reabsorption of mineralised bone and release of Pi and Ca2+ onto extracellular fluid
28
Q

Calcitriol (1,25(OH)2D) physiological role

A

Release of calcium from bone by enhancing actions of PTH

Absorption of calcium in intestine via vitamin D

Increase reabsorption of ca2+ and phosphate

29
Q

calcitriole is the active form of

A

vitamin D normally produced in the kidney

30
Q

the body makes vitamien D when it is exposed to sun (acts like a hormone)

A
31
Q

which foods are fortified with vitamin D

A

Cheese, butter, margarine, fortified milk, fish and fortified cereals are food sources of vitamin D

32
Q

synthesis of calcitriol

A
  1. Sun stimulates the production of Vitamin D3 in the skin
  2. Vitamin D3 is converted to 25(OH)D (pre-hormone substrate) in the liver
  3. 25(OH)D is converted to 1,25(OH)2D (Calcitriol) in the kidney under influence of PTH
33
Q

physiological action of calcitonin: bone

A

decreased reabsorption of bone

34
Q

physiological action of calcitonin: kidney

A

decreased reabsorption of calcium and phosphate

35
Q

physiological action of calcitonin: GI

A

no affect

36
Q

increased plasma calxcium

A

decrease PTH secretion

37
Q

decrease in plasma calcium

A

increase PTH secretion

38
Q

symptoms of chronic hypercalcaemia

A

Stones (hydroxyapatite)

Moans (depression)

Groans (abdominal pains)

Bones (muscle ache)

Tiredness

Dehydration

Constipation

39
Q

severe hypercalcaemia (>3mmol/L) symptoms

A
  • Polyuria can lead to dehydration which then exacerbates the hypercalcaemia
    • Lethargy
    • Weakness
    • Confusion
    • Coma
    • Renal failure
  • Rehydration mainstay treatment
  • In patients with a ligand hypercalcemia and come this is not necessarily terminal event. After rehydration many can turn home
40
Q

cancer and hypercalcaemia

A
  • Malignant osteolytic bone metastasis
  • Multiple myeloma
  • Common cancers that metastasize to bone causing lytic lesions and hypercalcemia
    • Breast
    • Lung
    • Renal
    • Thyroid
41
Q

cancer and hyper/hypocalcaemia

A

Hypercalcaemia is commonly associated with cancer which is usually advanced and portends a poor prognosis. Hypocalcaemia is more often seen as a complication of therapy aimed at reducing skeletal morbidity rather than an effect of the cancer itself

42
Q

hypocalcaemia

A

Hypocalcaemia causes hyper-excitability of the neuromuscular junction.

43
Q

symptoms of hypocalcaemia

A

Symptoms include pins and needles, tetany, paralysis, and convulsions.

44
Q

common sites for bone metastasis

A

Vertebrae

Pelvis

Proximal parts of the femur

Ribs

Proximal part of the jumerus

Skull

More than 90% found in this distribution

45
Q

lytic lesions causes by metastsies can cause

A

hypercalcaemia

Endocrinology (12 decks)

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