7. Parathyroid gland Flashcards
Hormones / vitamins related to the physiology of calcium and phosphate metabolism
- parathyroid hormone (PTH)
- Calcitonin
- Vitamin D
synthesized and stored in the chief cells of the parathyroid glands.
synthesis is regulated by a feedback mechanism involving the level of blood calcium
PTH
function is to control calcium concentration in the extracellular fluid
by affecting the rate of transfer of calcium into and out of bone, resorption in the kidneys, and absorption from the GI tract.
PTH
PTH
its effect on this organ is the most rapid
- reabsorption of calcium
- excretion of phosphorus
Kidney
second major hormone for Ca metabolism and skeletal remodeling
must be metabolically activated before it can function physiologically
Vitamin D
cholecalciferol (animal origin)
vitamin D3
ergocalciferol (plant origin)
vitamin D2
vitamin D is formed in the skin from this cholesterol metabolite, after exposure to ulraviolet light
7-dehydrocholesterol
1,25-dihydroxyvitamin D
calcitriol
hydroxylation of vitamin D in the liver to form this
calcitriol
a 32-amino acid polypeptide hormone secreted by the parafollicular cells (C-cells)
Calcitonin
interacts with target cells, primarily in bone & kidney
Calcitonin
result of decreased entry of calcium from the skeleton into plasma, resulting from a temporary inhibition of PTH-stimulated bone resorption
hypocalcemic effects of Calcitonin
impaired ability to concentrate urine and a direct stimulation of the thirst center
- polydipsia
- polyuria
hypercalcemia
most common tumor associated with hypercalcemia
lymphoma (lymphosarcoma)
Diagnosis of hypercalcemia
- thoracic & abdominal radiographs
- lymph node aspirates & biopsy
- multiple bone marrow aspirate
hypercalcemia tumor usually occuring in older dogs of either sex (90%)
- malignant
- metastasize to regional lymph nodes
adenocarcinoma of the apocrine gland (anal sac)
reduction of serum calcium
surfical resection
malignancy in dogs and cats (hypercalcemia) is 10-15%
multifactorial pathogensis, involving myeloma cells produciing osteoclast-activating factor
presence of extensive bony lysis contribute to increased serum calcium
multiple myeloma
treatment of multiple myeloma
chemotherapy
excessive secretion of PTH by one or more abnormal (usually neoplastic) parathyroid glands
rare in dogs & cats
primary hyperparathyroidism
most common cause of primary hyperparathyroidism
solitary adenoma
diagnosis of thisi involves finding multiple enlarged parathyroid gland
secondary hyperparathyroidism
diagnostic alternative if no other cause of hypercalcemia can be determined
exploratory surgery
