Pathology of the Endocrine system 2 Flashcards
What is the function of the parathyroid glands?
Production of parathyroid hormone
What are the functions of parathyroid hormone?
- Mobilisation of calcium from bone
- Enhances absorption of calcium from the small intestine
- Suppressed calcium lost in urine
How is calcium mobilised from bone?
PTH indirectly stimulates osteoclasts to reabsorb bone mineral, liberating Ca into blood
How does PTH enhance calcium absorption from the SI?
Indirectly; by stimulating production of the active form of vitamin D in the kidney; vitamin D induces synthesis of a Ca-binding protein in intestinal epithelial cells that facilitates efficient absorption of Ca into blood
How does PTH supress loos of Ca in urine?
PTH stimulates tubular reabsorption of Ca and stimulates loss of phosphate ions in urine
Reduced PTH release leads to?
Hypoparathyroidism
What are the consequences of hyperparathyroidism?
Hypocalcaemia → increased neuromuscular excitability → spasms, tetany, tremors
Name some causes of hypoparathyroidism
- Agenesis of parathyroid glands
- Inflammation (autoimmune parathyroiditis; dogs)
- Surgical excision (eg. with thyroidectomy)
- Tumour infiltration
- Trauma
- Vit D intoxication
- Postnatal hypocalcaemia in cattle
Describe Postnatal hypocalcaemia in cattle
- Parturient paresis in dairy cattle
- Complex metabolic disease (characterised by severe hypocalcaemia and hypophosphataemia near time of parturition and initiation of lactation)
- Ca levels <50% normal (in spite of PTH↑), hardly any bone resorption
- Influenced by composition of diet
What are the consequences of hyperparathyroidism?
Ca mobilisation from bone → hypercalcaemia
Primary hyperparathyroidism is due to?
Hyperplasia, adenoma or carcinoma of parathyroid gland
Secondary hyperparathyroidism is due to?
- Consequence of chronic renal insufficiency
- Consequence of dietary Ca/P imbalance
Tertiary hyperparathyroidism is due ti?
Final stage kidney disease with non-responsive, autonomous hyperparathyroidism
Describe Pseudohyperparathyroidism
- Humoral malignant hypercalcaemia
- Mainly in dogs with adenocarcinoma of the anal sac (para-anal) gland or lymphomas (release of PTH-like protein!)
How does hyperparathyroidism appear grossly?
Gross lesion is of bilaterally enlarged (hyperplastic) parathyroid glands
Describe the mechanisms of renal secondary hyperparathyroidism
- Reduced renal Ca resorption and phosphate secretion
- Reduced Vit D activation
- Hyperphosphataemia
- Hypocalcaemia
What are the two main consequences of renal secondary hyperparathyroidism?
- Fibrous osteodystrophy
- Metastatic calcification: calcium deposited within tissues
What is fibrous osteodystrophy?
Calcium is liberated from the bone to return blood calcium back to normal. Mineralised matrix of the bone is replaced by a soft collagenous connective tissue
What are the clinical signs of fibrous osteodystrophy?
Bone pain (lameness), loss of teeth, deformity of maxilla and mandible
What are the gross findings of fibrous osteodystrophy?
“soft”, demineralised bones [Test skull, ribs!]
Which cells are enhanced in fibrous osteodystrophy?
Osteoclasts
What is normal bone substituted by in fibrous osteodystrophy?
- insufficiently mineralized osteoid
- collagenous connective tissue
Atrophy of the parathyroid glands is due to?
Goitre or thyroid cysts (compression)
Secondary hyperplasia of the parathyroid glands is due to?
Hypocalcaemia