Parathyroid and Calcium Metabolism Flashcards
What hormone is responsible for the number of receptors in the intestine for absorption of calcium?
Vit D
How many parathyroid glands are present in a patient?
4, 2 on each thyroid
What is the principle cell present in the parathyroid gland?
Chief cells
How does PTH act on the bone?
- Binds to osteoblasts
- Increases activity of osteoclasts to breakdown and release Ca and phosphorus
- Decreases bone density
How does PTH act on the kidney?
- Blocks reabsorption of phosphorus
- Increased excretion of phosphorus
- Increases calcium absorption from tubules
- Activates 1-alpha hydroxyase which stimulates production of Vit D
What is the feedback loop that regulates PTH secretion
↓ Ca = ↑ PTH
↑ Ca = ↓ PTH
How does Vitamin D effect calcium levels?
- Facilitates intestinal absorption of calcium in the gut
What are the actions of calcitonin?
- Reduces blood calcium
- Suppresses reabsorption of Ca+ and phosphorus in kidney, increased excretion
- Inhibits bone resorption by inhibiting osteoclasts
How does hypercalcemia affect kidney function?
Interferes with ADH, can’t concentrate urine, isosthenuric and PU/PD
(nephrogenic diabetes insipidus)
What are the clinical side effects of hypercalcemia?
- PU/PD
- Dystrophic calcification in organs
- Cardiac dysfunction
- Inappetence, V/D
- Constipation in cats
DDx for Hypercalcemia?
DRAGONSHIT
- Vit D toxicity
- Renal failure
- Addisons
- Granulomatous dz
- Osteolysis (fracture, multiple myeloma)
- Neoplasia
- Spurious
- HyperPTH
- Idiopathic
- Toxins (ethylene glycol)
What neoplasias can cause hypercalcemia?
- Anal sac adenocarcinoma
- Mammary carcinoma
- Lymphoma
- Multiple myeloma (from osteolysis)
How can ultrasound help diagnose hyperPTH?
If 1 parathyroid is overreactive, other parathyroid glands are usually small and atrophied
- Overactive parathyroid may be large or normal
What are the causes of secondary hyperPTH, and what would you expect PTH and Calcium levels to be in this case?
- Nutritional deficient Ca+ diet
- Renal dz (loosing too much Ca+)
Secondary hyperPTH: will show ↑ PTH and ↓ Ca
What are the causes of primary hyperPTH, and what would you expect PTH and Calcium levels to be in this case?
Idiopathic hyperplasia of the parathyroid gland
Primary hyperPTH: will show ↑ PTH and ↑ Ca
What breeds are associated with primary HyperPTH?
- Keeshond
- GSD
- Norwegian elkhound
- Siamese cats
What is the emergency treatment of hypercalcemia?
- Diuresis (fluids) to flush out Ca+
- Furosemide (once hydrated)
- Glucocorticoids (decreases Ca+ reabsorption, BUT don’t give if neoplasia can’t be ruled out)
- Calcitonin (short term only, eventually body makes AutoAb to salmon calcitonin)
- Bisphosphates (good for chronic conditions and multiple myeloma… binds to bone and inhibits osteoclasts)
How are bisphosphates beneficial in treating hypercalcemia?
Binds to bone and inhibits osteoclasts, has a long half life
Good for chronic conditions and multiple myeloma
What are the disadvantages of using bisphosphates to treat hypercalcemia?
- PO can cause esophagitis
- Injection can cause AKD
- Given on empty stomach
- Spontaneous fractures in cats
Why is calcitonin only recommended for acute treatment of hypercalcemia?
Usually using salmon calcitonin… body will eventually make AutoAb against it… not for chronic use
What are the causes of hypoparathyroidism?
Primary - lymphocytic parathyroiditis
Iatrogenic - complication of thyroidectomy
What breeds are associated with Hypoparathyroidism?
- Toy poodles
- Mini schnauzers
- Labs
- GSD
- Terriers
What are clinical signs of hypoparathyroidism?
CS due to hypocalcemia
- Seizures
- Twitching
- Ataxia
- Facial rubbing, biting at feet (Cats > dogs)
- Arrhythmias
- Pyrexia (fever) from tremors
What are the PTH, Calcium and phosphorus levels in a hypoparathyroid patient?
↓ PTH, ↓ Ca, ↑ phosphorus
What is the emergency treatment of hypocalcemia?
- 10% calcium gluconate slowly IV, monitor ECG
- Continue for a couple days until PO drug takes effect
- Monitor temp
Maintenance: - PO calcium
- PO Vit D3
