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OUM Endocrinology > Parathyroid Physiology > Flashcards

Parathyroid Physiology Flashcards

Cells, Hormone synthesis and actions, Ca2+ homeostasis

1
Q

What are the two types of cells in the parathyroid gland?

A

chief cells and oxyphils

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2
Q

What stimulates the release of PTH?

A

Low serum calcium

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3
Q

What indicates to the chief cells to synthesise and secrete PTH?

A

CaSR’s

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4
Q

If CaSR senses high serum Ca2= what kind of signal does it send the chief cells?

A

inhibitory

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5
Q

PTH is what class of hormone? And is it hydrophilic or hydrophobic?

A

Peptide, hydrophilic

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6
Q

What cells secrete calcitonin?

A

Parafollicular cells of the thyroid gland

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7
Q

What is the stimulus for calcitonin secretion?

A

High serum Ca2+

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8
Q

Describe the synthesis of PTH.

A
  • CaSR on Cheif cells in PTG
  • triggers transcription to mRNA
  • mRNA translated into preprepetide form of PTH
  • cleaved in the ER into propeptide form of PTH
  • transported to golgi for enzyme modification and becomes peptide form of PTH and is pacjkaged into secretory vesicles.
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9
Q

Differentiate the roles of osteoclasts and osteoblasts.

A

Osteoclasts reabsorb bone and osteoblasts deposit bone

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10
Q

Through what mechanism does PTH stimulate osteoclast reabsorption of bone?

A

RANKL /RANK pathway

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11
Q

What chemicals are secreted by osteoclasts to break down and reabsorb bone components?

A

?? Cathepsins, ALP, acids

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12
Q

What is the primary regulator of Ca2+ levels?

A

PTH

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13
Q

What are the direct effects of PTH on the kidneys?

A

PTH acts on the DCT to promote reabsorption of Ca2+ from the filtrate and to excrete phosphate.

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14
Q

Describe the synthesis of vitamin D.

A

Sunlight on the skin converts 7-Dehydrocholesterol into cholecalciferol.
Cholecalciferal travels to the liver where the enzyme 25-hydroxylase converts it to 25 hydroxycholecalciferal. Because PTH causes the kindeys to express 1-alpha hydroxylase, 25-hydroxycholecalciferol is converted to the active form of vitamin D (calcitriol, 1,25- dihydroxycholecalciferol)

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15
Q

What is the role of vitamin D?

A

Vitamin D induces the synthesis of Ca2+ channels in the duodenum that allows absorption of Ca2+ from the GIT into the blood, therefor increasing serum calcium levels.

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16
Q

What is the target cell for calcitonin? and what is it’s effect? By what mechanism?

A

Osteoblasts.
Causes inhibition of Osteoclast activity.
Mechanism: - It tells the osteoblasts to make more RANK and to make less RANKL
So less preosteoclasts mature leading to less osteoclast activity.

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17
Q

Bone is the body’s primary storehouse of what compounds?

A

Ca2+
Phosphate
Carbonate
Magnesium

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18
Q

What is the most prevalent cation in the body?

A

Ca2+

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19
Q

99% of Ca2+ is stored as?

A

Hydroxyapatite

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20
Q

What is the the biologically active form of Ca2+?

A

Ionised Ca2+

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21
Q

What is the normal serum Ca2+ range?

A

8.5-10.5 mg/dL

22
Q

41% of plasma Ca2+ is what
?

A

Bound to albumin

23
Q

Name the 3 molecules involved in Ca2+ homeostasis.

A

PTH
Calcitonin
Vitamin D

24
Q

Over-mineralisation of the bones results in which disorder?

A

Ostegenesis imperfecta

25
Q

Briefly describe the mineralisation of bone.( making of hydroxyapitite)

A

alkaline phosphatase converts inorganic pyrophosphate into inorganic phosphate by joining to calcium to make hydroxyapatite

26
Q

List the intracellular roles of Ca2+

A

o Muscle contraction.
o Hormone secretion.
o Glycogen metabolism.
o Cell division.
o Activation of enzymes.
o Transfer of the ions across the cell membrane.

27
Q

List the extracellular roles of Ca2+

A

o Bone Mineralization.
o Blood coagulation factors.
o Plasma membrane potential.
o Maintenance of intracellular calcium.
o Calcium decreases neuromuscular excitability.

28
Q

The organic matrix of the bone is made up of

A
  • type 1 collagen
  • ECF
  • proteoglycans
  • cell attachment factor
    -osteonectin
    osteopontin
29
Q

What is the role of calcium in neurotransmission?

A

Ca2+ triggers synaptic vesicle exocytosis, thereby releasing the neurotransmitters contained in the vesicles and initiating synaptic transmission.

30
Q

What are the 3 mechanisms that increase intracellular Ca2+ concentration?

A
  1. Voltage-gated Ca channels are activated by membrane depolarization, allowing Ca to enter the cytosol.
  2. Hormones or neurotransmitters can open ligand-gated channels on the cell membrane, allowing Ca to enter the cytosol.
  3. Hormones and neurotransmitters (such as norepinephrine and angiotensin II) can, via the phospholipase-C (PLC) pathway, cause an increase in intracellular inositol triphosphate (IP3).
31
Q

What is calcium’s role in muscle contraction?

A

Calcium role is exposing myosin binding sites on actin to facilitate muscle contraction.

32
Q

What are the name of the 2 receptors that form a complex linking the sarcoplasmic reticular membrane and the membrane of the t-tubules, that allows entry of Ca2+ for muscle contraction?

A

Ryanodine receptor and DHP receptor

33
Q

Most Procoagulants and anti-coagulants are produced where?

A

the liver

34
Q

What is required for anticoagulants and procoagulants ot bind to calcium in the clotting cascade?

A

vitamin-k-dependant gamma carboxylation of glutamic acid

35
Q

What is required for calcium to promote conversion of factor X to Xa in the clotting cascade?

A

The exposure of tissue factor to factor VIIa and Ca2+

36
Q

What is the role of Ca2+ in blood clotting?

A
37
Q

IN summary, what is Ca2+’s role in the clotting cascade?

A

acceleration of the pathway.

38
Q

The principle hormones involved in homeostasis are? And what are their 3 target organs?

A

Vitamin D
Calcitonin
PTH
Intestine
Bone
Kidney

39
Q

What are the actions of PTH?

A

o Increases bone resorption by activating osteoclasts activity
o Increases renal Ca reabsorption by the distal renal tubules
o Increases renal phosphate excretion by decreasing tubule phosphate reabsorption
o Increases the formation of 1,25 dihydrocholecalciferol by increasing the activity of alpha-hydroxylase in the kidney

40
Q

What are the actions of Vitamin D?

A

-decreases PTH production
- Increases bone growth and formation and sometimes calcium and phosphate relese from the bone inconjunction with PTH
- increases calcium reabsorption from the kidney
- inccreases calcium and phosphate ansorption fromthe intestines.

41
Q

What are the actions of calcitonin?

A

o Inhibits bone resorption
o Increases renal Ca excretion

42
Q

Calcium concentration in maintained via?

A

Maintained via absorption from the gut and excretion via the kidney with bone acting as a buffer with Ca2+ in reserve.

43
Q

Maintaining a constant plasma [Ca2+] is important for:

A

o nerve transmission
o nerve conduction
o muscle contraction
o cardiac contractility
o blood clotting
o bone formation
o excitation–secretion coupling
o cell-to-cell adhesion
o cell-to-cell communication.

44
Q

Hypocalcemia in general causes:

A

Neuromuscular excitability

45
Q

In hypocalcemia, Neuromuscular excitability manifests as?

A

Pins and needles sensations
tetany
paralysis
convulsions

46
Q

What is the most common cause of hypocalcemia?

A

Accidental damage or removal of parathyroid glands during a thyroid surgery.

47
Q

Aside from removal or damage to the PTG’s, what are other possible causes of hypocalcemia?

A

Hypoparathyroidism
vitamin D deficiency nor disorder

48
Q

What are the two clinical signs of hypocalcemia?

A

Trousseau’s sign (hand spasm)
Chvostek’s sign (face twitch)

49
Q

Acute hypercalcemia causes what clinical manifestations?

A

Fits
vomiting
polyuria

50
Q

Chronic hypercalcemia signs are?

A

Stones: (kidney stones/failure)
Bones: (pain, usually osteitis fibrosa cystica)
Groans: (abdominal Sc: nausea, comiting, constipation, indigestion)
Psychiatric Moans: (Nervous system sx: lethargy, fatigue, memory loss, psychosis, depression)

51
Q

What are 5 causes of hypercalcemia?

A
  1. primary hyperparathyroidism
  2. extensive skeletal metastases
  3. PTHrH secretion from tumours
  4. Vitamin D excess
  5. granulomatous diseases
52
Q

What is more dangerous, hypocalcemia or hypercalemia and why?

A

Hypocalcemia, can quickly lead to convulsions and death

OUM Endocrinology (7 decks)

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