Parathyroid Gland Pathology Flashcards
What is the main function of the chief cells?
they secrete PTH
What is the similarity and difference between calcitriol and PTH?
- They both increase total body calcium
- PTH is involved in the minute/ fine tuning of blood calcium
- Calcitriol is more long term
What is the function of calcitonin?
Decreases total body calcium
What are the two clinical consequences of hypocalcaemia?
due to hypoparathyroidism
- excessive neuromuscular tetany/ paresis in ruminants (milk fever)
- Elevated phosphorus
Name 4 clinical signs of hyperparathyroidism
- Vomiting and anorexia due to hypercalcaemia
- polyuria/ polydipsia
- Generalised muscle weakness
- Fibrous osteodystrophy (osteolysis with fibrous tissue replacement)
In what animal species is fibrous osteodystrophy a common problem?
Common husbandry problem in reptiles
* Nutritional, Causes metabolic bone disease
* Animals have swollen jaws and limbs
* rubber jaw
* prone to fractures
What does primary hyperparathyroidism look like?
- Multinodular hyperplasia
- Adenomas (these typically only affect one gland)
What is secondary hyperparathyroidism?
When the glands themselves are fine but a problem in another organ causes them to secrete more PTH
Name three things nutritional secondary hyperparathyroidism is caused by
- deficient dietary calcium
- deficient vitamin D
- Excess Phosphorus
What is Pseudohyperparathyroidism?
target organ resistance or unresponsiveness to PTH
What is Humoral hypercalcemia of malignancy?
- Certain tumours secrete PTH-like peptide
- Has similiar effects to PTH
- any tumour can produce PTHrp but some do it more frequently- e.g Lymphoma or apocrine gland anal sac adenoma
What is the gross pathology of nutritional secondary hyperparathyroidism?
Diffuse hypertrophy and hyperplasia of the parathyroid gland
What is an example of a problematic diet that may cause nutritional hyperparathyroidism?
All meat diets in dogs and cats
* inadequate Vit D3 in new world primates
* grain diets in horses and goats
* all fruit or all meat diet in reptiles
What three effects does calcitriol have?
- Increases calcium absorption
- Increases Calcum retention
- Increases osteoclasts resorption (FGF23 expression)
What two effects does FGF23 have?
- Decreased PTH expression in the parathyroid
- Inhibited phosphate resorption
What four things cause hypoparathyroidism?
- Idipathic hypoparathyroidism
- Surgical removal/Trauma
- Destruction related to local inflammation
- Trophic atrophy
What species are affected by hyperparathyroidism?
- Dogs
- Cats
- New world primates
- Goats
- Birds
- Reptiles
What effect does FGF23 have?
- Occurs when there is increased phosphate retention
- therefore decreases calcitriol
- increases PTH levels
What causes increased phosphate retention?
- Decreased Glomerular filtration rate
- Hyperphosphataemia then stimulates FGF23 secretion
What is ‘milk fever’?
Hypocalcaemia and Hypophosphataemia near parturition due to increased Ca2+ and Phosphorus
* * causes paresis in cows and tetany in dogs (eclampsia and muscle spasms)
What increases the risk of milk fever in cows?
High calcium diets
What is the effect of PTH on the kidney?
- Decreased phosphate resorption -> phosphaturia
- Increased activity of 1-a-hydroxylase -> increase in active vitamin D
- overall decreased phosphate and increased calcium
What is the effect of PTH on the bones?
increased osteoclast and osteocyre activity
* causes long term osteoclast hyperplasia
* net increases phosphate as well
What is the effect of calcitriol on the gut, kidney and bones respectively?
- Increases calcium resorption in the gut
- Increases calcium retention in the kidney
- Increases osteoclast resorption in the bones (stimulates FGF23)
What is the main role of FGF23?
- Inhibitis phosphate resorption
- inhibits 1-a-hydroxylase so there is less of teh active form of vit D (calcitriol)
- also inhibits PTH
What is the function of thyroid C-Cells?
- Produce calcitonin in response to hypercalcaemia
- respond to plasma concentrations of Ca2+
What is the function of calcitonin?
- Reduces blood calcium by inhibiting osteoclasts, increase in renal phosphate and Calcium secretion
- opposes the effects of PTH
