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203: Theme 1: The Endocrine System > Endocrine control of calcium homeostasis > Flashcards

Endocrine control of calcium homeostasis Flashcards

1
Q

Where is calcium important?

A

Exocytosis

  • neurotransmitter secretion
  • hormone secretion

Physical properties of bone

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2
Q

Hypocalcaemia causes neurone excitation

A

Decreased extracellular Ca2+ increases the neuron membrane’s permeability to Na+

Na+ easily depolarises the membrane so causes an action potential

If someone has a first fit, check the serum calcium

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3
Q

Physical signs of hypocalcaemia

A

Carpopedal spasm

Chvostek’s sign

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4
Q

Acute consequences of hypercalcaemia

A

Thirst and polyuria

Abdominal pain

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5
Q

Chronic consequences of hypercalcaemia

A

Constipation

Musculoskeletal aches/ weakness

Neurobehavioral symptoms

Renal calculo

Osteoporosis

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6
Q

Measuring serum calcium

A

Protein bound 40%

  • albumin bound 90%
  • globulin bound 10%

Bound to cations 10%
- phosphate and citrate

Ionised (free) 50%

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7
Q

Normal range of calcium level in the blood

A

2.15-2.55 mmoles/l

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8
Q

Chief cells in the parathyroid gland function

A

Produce parathyroid hormone

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9
Q

Calcium sensing receptors

A

Sensitive to increase in serum calcium

Stimulates uptake of calcium by parathyroid glad

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10
Q

Activation of calcium sensory effects

A

Activation of phospholipase C which leads to DAG and IP3

Inhibition of adenylate cyclase, suppresses intracellular cAMP

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11
Q

Sequence of events after less calcium molecules in blood

A

Altered calcium sensing receptor formation

Modified chief cell process

(Mg2+)

PTH secretion

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12
Q

Type 1 parathyroid hormone receptor

A

Bind both parathyroid hormone and amino terminal peptides of PTHrP

Binding activates adenylyl cyclase and phospholipase C systems

Generates protein kinase A and protein kinase C

Most abundant in bone and kidney

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13
Q

Type 2 parathyroid hormone receptor

A

Binds parathyroid hormone, has very low affinity for PTHrP

Expressed in only a few tissues

Coupled to adenylyl cyclase so ligand binding increases intracellular cyclic AMP

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14
Q

Mutations in type 1 parathyroid hormone receptor

A

Associated with rare human diseases

Jansen’s metaphyseal chondroplasia (short limbed dwarfism) has constitutively active receptor

Blombstrand’s chondroplasia has inactive mutation in receptor gene (leads to early death with defective bine meturation)

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15
Q

Where are the PTH1 receptors?

A

Bone

Kidney

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16
Q

PTH promotes absorption of Ca2+ from bone

A

Rapid phase

  • rise in serum calcium
  • PTH binds to receptor on osteoblast/cyte
  • osteocytic membrane pumps out Ca2+ from bone fluid to extracellular fluid

Slow phase

  • oesteoclasts activated to digest formed bone
  • proliferation of osteoclasts occurs
17
Q

Bone resorption

A

Removing bone tissue by removing bone’s mineralised matrix

Done by osteoclasts

18
Q

Osteoclasts characterised by

A

High expression of tartrate resistant acid phosphate and cathepsin K

19
Q

Actions of PTH on kidneys

A

Rapid calcium reabsorption

  • increased Ca2+ reabsortion in LOH, DT, CD
  • decreased PO4 reabsorption in PT

Renal synthesis of active vitamin D

20
Q

Renal actions of PTH

A

Converts 25OH Vit D to 1,25 OH vit D

That leads to calcium transports and binding proteins in gut cells

So increased calcium absorption

21
Q

Primary hyperparathyroidism diagnosis

A

Serum calcium increased

Serum phosphate reduced

PTH increased

22
Q

Complications of hyperparathyroidism

A

Osteoporosis

Bone cysts

23
Q

Complications of hypercalcaemia

A

Renal stones

24
Q

Locating the parathyroid adenoma

A

Sesta mibi parathyroid scan

Neck ultrasound

25
Q

Features of hypoparathyroidism

A

Serum calcium low

PTH low/ normal

26
Q

Clinical features associated with hypocalcaemia

A

Chvotek’s sign

Tousseau’s sign

Parethesias

Tetany

Seizure’s

Fatigue, anxiety, cramps

27
Q

Causes of hypoparathyroidism

A

Iatrogenic

  • thyroidectomy
  • radical neck surgery

Autoimmune

Hypomagnesaemia

Genetic mutations

28
Q

Common causes of secondary hyperparathyroidism

A

Low/ low normal serum calcium and high PTH

  • low serum 25 OH vit D (lack of sun exposure, GI problems)
  • renal failure
29
Q

Rickets

A

Reduced vitamin D concentration

Softening of the bones in children

Leads to fractures, deformity

30
Q

Osteomalacia

A

Similar to rickets in adults

Looser zone

203: Theme 1: The Endocrine System (22 decks)

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