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Endocrine > The Parathyroid Gland > Flashcards

The Parathyroid Gland Flashcards

1
Q

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

A

Chief cells

Oxyphil cells

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2
Q

What do chief cells do?

A

Produce PTH

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3
Q

What do oxyphil cells do?

A

In cancer of the parathyroid gland, they produce excess PTH.

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4
Q

What does parathyroid hormone do?

A

Increases the level of Ca2+ and Mg2+ in the blood

Decreases the level of phosphate in the blood.

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5
Q

How does parathyroid hormone increase the level of calcium in the blood?

A

PTH increases the number and activity of osteoclasts.

This promotes resorption of the bone extracellular matrix, releasing calcium and phosphate ions into the blood.

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6
Q

How does PTH affect the kidney?

A

PTH slows the rate Ca2+ and Mg2+ are lost from the blood into the urine and increases the rate at which phosphate is lost from the blood into the urine.

Also acts on the kidneys promoting the formation of calcitriol.

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7
Q

What are the overall net effects on ions in the blood in response to PTH secretion and why?

A

More phosphate is lost in the urine than that which is gained in the resorption of bone.
Thus PTH increases Ca2+ and Mg2+ levels in the blood yet decreases phosphate levels.

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8
Q

What is calcitriol?

A

The active form of vitamin D

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9
Q

What does calcitriol do?

A

Calcitriol increases the rate at which Ca2+, Mg2+ and phosphate are absrobed from the gastrointestinal tract into the blood.

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10
Q

Explain the feedback loop in the control of the secretion calcitonin and PTH, starting with high Ca2+ levels in the blood.

A
  1. High Ca2+ levels in the blood stimulate parafollicular cells of the thyroid to secrete calcitonin.
  2. Calcitonin decreases levels of Ca2+ in the blood.
  3. Low levels of Ca2+ in the blood cause the parathyroid gland to secrete parathyroid hormone.
  4. PTH causes bone resorption to increase Ca2+ levels in the blood.
  5. PTH also slows the loss of Ca2+ in the urine.
  6. PTH acts on the kidneys stimulating synthesis of calcitriol.
  7. Calcitriol stimulates reabsorption of Ca2+ from the gi tract into the blood.
  8. Ca2+ levels in the blood increase, and the loop repeats.
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11
Q

Where is Ca2+ in the body stored, and in what proportions?

A

99% of Ca2+ is stored insolubly as hydroxyappatite in bone.

1% is stored in ECF and ICF.

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12
Q

What is calcium concentration in the blood maintained as?

A

2.20-2.60mmol

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13
Q

When measuring calcium concentration in the blood how does the measurement change when using a gas analyser?

A

You only measure the ionised calcium in the blood and hence the range for that is 1.10-1.30mmol

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14
Q

What are the main physiological roles of Ca2+?

A
  1. Ca2+ is important in the coagulation cascade, and plays a key role in blood clotting.
  2. Ca2+ has an important role at the neuromuscular junction.
  3. Plays an important role in nerve transmission.
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15
Q

Where is phosphate located in the body?

A

85% stored in bone

Phosphate is also present as a major intracellular anion.

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16
Q

What are the main intracellular roles of phosphate?

A
  1. Energy production —> glycolysis and ATP
  2. Nucleic acid production (DNA backone)
  3. Cell membrane phospholipids.
17
Q

What are the roles of extracellular phosphate?

A

Bone mineral production

In the kidneys for pH regulation

18
Q

Why are phosphate concentrations in the blood not tightly regulated?

A

It’s extracellular roles are much less important than it’s intracellular roles.

19
Q

What are the symptoms of severe hypophosphataemia?

A
  1. Muscle weakness due to high ATP demmand

2. Rhabdomyolysis

20
Q

What is rhabdomyolysis?

A

Rhabdomyolysis is the death of muscle, which can enter the blood and cause kidney failure as the kidneys may be unable to remove the waste.

21
Q

What can cause chronic hyperphosphataemia?

A

Caused by chronic kidney disease as the kidneys are unable to remove phosphates from the blood.

22
Q

What are the effects of chronic hyperphosphataemia?

A

Phosphates can bind to calcium in the blood and deposit in soft tissue.
This can lead to sudden death due to calcification of blood vessels, also causes hypertension.

23
Q

How is hypocalcaemia treated?

A

Treated with calcium and vitamin D supplements.

24
Q

What are the symptoms of hypocalcaemia?

A
  1. Paraesthesia localised around the mouth and in the tips of the toes and fingers.
  2. Muscle spasm in the hands and feet.
  3. Seizures
  4. Bronchospasm (wheezing)
25
Q

What is paraesthesia?

A

Pins and needles.

26
Q

What are the symptoms of hypercalcaemia?

A
  1. Anorexia
  2. Lethargy
  3. Kidney stones and renal failure
  4. Heart block (lethal).
27
Q

What is heart block?

A

Loss of electrical signalling to the heart.

28
Q

What are the biochemical signs of hypoparathyroidism?

A

Low Ca2+
High phosphate
Low PTH

29
Q

What are the potential causes of hypoparathyroidism?

A
  1. Neck surgery which can damage the parathyroid gland.
  2. Autoimmune destruction of the parathyroid gland (APS1 - signs are hypoparathyroidism and addisons disease).
  3. Hypomagnesia
30
Q

What are the clinical consequences of hypoparathyroidism?

A
  1. Low blood Ca2+ levels.
  2. High phosphate levels.
  3. High bone mass
31
Q

What are the biochemical signs of hyperparathyroidism?

A

High Ca2+
Low phosphate
High PTH

32
Q

What are the main causes of hyperparathyroidism?

A
  1. Tumour of the parathyroid gland

2. Kidney failure or vitamin D deficiency causing low blood calcium levels and thus high PTH production.

33
Q

What are the clinical consequences of hyperparathyroidism?

A

Hypercalcaemia
Hypophosphataemia
Osteoporosis

Endocrine (11 decks)

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