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203: The endocrine system > Calcium homeostasis > Flashcards

Calcium homeostasis Flashcards

1
Q

Function of calcium

A

Exocytosis in cells.

Build and maintenance of bone.

Blood clotting.

Many biochemical processes.

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2
Q

Serum calcium

- How it is transported [3]

A

Mostly found as free ions [50%]
- These are biologically active

Bound to proteins [40%]:

  • Albumin (90%)
  • Globulin (10%)

Bound to cations [10%]

  • Phosphate
  • Citrate
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3
Q

Physiological range of serum calcium

A

2.15-2.55 mmol/L

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4
Q

Hypocalcaemia

  • Definition
  • Physiology
  • Physical signs
A

Serum calcium <2.15 mmol/L

Physiology
- Low calcium, makes neurones a lot more permeable to Na+ (Ca2+ competes with Na+)

Signs

  • Trousseau’s sign
  • Chvostek’s sign
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5
Q

Consequences of hypocalcaemia

  • Acute [3]
  • Chronic [6]
A

Acute

  • Thirst
  • Polyuria
  • Abdominal pain

Chronic

  • MSK pain/ weakness
  • Constipation
  • Neurobehavioral changes
  • Kidney stones
  • Osteoporosis
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6
Q

Parathyroid hormone

  • Structure
  • Synthesis
  • Secretion
A

Peptide hormone

Made by chief cells of the parathyroid gland.

Secreted in response to low Ca2+ levels.
- Chief cell contains receptors that are Ca2+ sensing

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7
Q

PTH release

A

Ca2+ sensing receptors on chief cells recognise low Ca2+ levels

  • Changes shape of the receptor
  • Chief cells processes modified to release PTH in the presence of Mg2+
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8
Q

PTH action on receptors

A

PTH acts on PTH-1 receptors on bone and kidneys
- Changes the shape of the receptor.

Bone
- Calcium release

Kidneys

  • More absorption of Ca2+ in loop of Henle, DT, CD.
  • Less Phosphate reabsorption in PT [prevents calcium phosphate precipitation]
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9
Q

PTH action on bone

A

PTH activates osteoblasts
- Causes release of rank ligand

Rank ligand activates osteoclasts

  • Break down of bone using H+ and enzymes (CATK, TRAP).
  • Ca2+ release into the blood.
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10
Q

Corrected calcium

A

Calculation of serum Ca2+ based on the amount bound the albumin.

Not accurate if album is <20g/L.

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11
Q

Mg2+ and PTH

- Causes of hypomagnesaemia

A

Mg2+ is a co-factor required for the release of PTH.
- Low Mg2+ = no PTH release= hypocalcaemia.

Causes of hypomagnesaemia

  • GI problems
  • PPIs
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12
Q

Sources of Vit.D

A
  • UV from the sun causes the skin to make cholecalciferol [Vit D3]

Diet

  • Cod liver oil
  • Wild oily fish
  • Fortified foods
  • Irradiated mushrooms
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13
Q

Vit D metabolism

A

In liver
- Vit.D3 Converted to 25-OH, Vit.D

In kidneys
- PTH acts to convert 25-OH, Vit D into 1,25-OH-Vit.D

In bowel

  • 1,25-OH, Vit.D stimulates the insertion of Ca2+ transporters and calbindin
  • Allows more absorption of Ca2+
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14
Q

Feedback of PTH and vitamin D

A

1,25-OH, Vit.D negatively feedbacks to PTH release.

1,25-OH, Vit.D also feedbacks to osteocytes—> Increases FGF-23
- FGF-23 inhibits 1,25-OH production

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15
Q

Hypercalcaemia

  • Definitions
  • Causes
A

Serum calcium >2.55mmol/L

Causes

  • Primary hyperparathyroidism
  • Malignancy (of PT)
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16
Q

Primary hyperparathyroidism

  • Definition
  • Presentation
  • Complications
A

Overactivity of the PT= high PTH levels

Presents as:

  • High Ca2+ levels
  • Low Phosphate levels
  • High PTH levels

Complications

  • Bone cysts
  • Osteoporosis
  • Kidney stones
17
Q

Causes of primary hyperparathyroidism

A

Parathyroid adenoma

Primary hyperplasia of parathyroid.

PT carcinoma

18
Q

Imagining of PT adenoma

A

Sestamibi PT scan

  • Measure gamma rays from radioactive decay of technetium sestamibi
  • Adenoma absorbs radioactive substance very fast so can be spotted in scan.

Neck ultrasound

19
Q

Hypoparathyroidism

  • Definition
  • Causes
A

Under-active parathyroid

Defined by

  • Low calcium
  • Low/ normal PTH
  • High phosphate levels

Causes:

  • Iatrogenic [70%]
  • Autoimmune
  • Hypomagnesemia–> Mg required for PTH secretion
  • Genetic
20
Q

Secondary hyperparathyroidism

  • Definition
  • Causes
A

High PT levels not directly caused by the PT gland.

  • Problem elsewhere leads to PT hyperplasia.
  • Low Ca2+, high PTH.

Causes:

  • Chronic kidney failure [inability metabolise vit.D anf excrete phosphate]
  • Malabsorption of vit.D
  • Lack of sun exposure
  • Extensive bowel surgery
21
Q

Iatrogenic causes of hypoparathyroidism

A

Thyroidectomy
- Removal of thyroid could include removing PT gland.

Radial neck surgery

22
Q

Complications of Vit.D deficiency

A

Osteoporosis/ osteomalacia in adults

Rickets in children

203: The endocrine system (23 decks)

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