Ross University School of Veterinary Medicine Cellular Biology & Homeostasis Endocrine-Parathyroid PDF 2024

Cellular Biology & Homeostasis ENDOCRINE-PARATHYROID VP 2024 Clara Camargo, DVM 1. Locate the parathyroid glands and briefly describe their macro and microanatomy 2. Understand the physiological relevance of calcium and phosphate to maintain body homeostasis 3. Understand the synthesis, regulation a...

Cellular Biology & Homeostasis ENDOCRINE-PARATHYROID VP 2024 Clara Camargo, DVM 1. Locate the parathyroid glands and briefly describe their macro and microanatomy 2. Understand the physiological relevance of calcium and phosphate to maintain body homeostasis 3. Understand the synthesis, regulation and transport of PTH 4. Describe the effects of the parathyroid hormones on target tissues/organs 5. Understand the role of PTH on calcitriol activation and the importance of it on calcium metabolism 6. Understand the relationship between PTH and calcitonin and their effects on calcium and phosphate homeostasis 7. Understand the symptoms of the main pathologies related to the parathyroid hormones (hyperparathyroidism/secondary nutritional hyperparathyroidism, and hypoparathyroidism) TEMINOLOGY AND ABREVIATIONS AMP (Adenosine Monophosphate) Osteoblast ATP (Adenosine Triphosphate) Osteoclast Bone canaliculi Osteocyte Calcitonin Osteogenic cell (stem cell) Calcitriol Osteolysis ECF (extra cellular fluid) Parathyroid chief cells GI (gastrointestinal) Parathyroid oxyphil cells G-protein coupled receptor Preprohormone Hypercalcemia Prohormone Hypocalcemia PTH (parathyroid hormone) Hormone iCa (Ionized calcium) PARATHYROID GLANDS - ANATOMY PARATHYROID GLAND - ANATOMY Most species have 2 pairs  Pigs and rats have only one pair Location varies between species  Usually at the poles of the 2 lobes of the thyroid glands CHEMICAL STRUCTURE OF HORMONES (Recall) PROTEIN and PEPTIDE HORMONES INSULIN SYNTHESIS Comprises the majority of hormones  Insulin, ACTH, PTH, CCK  LH, FSH and TSH (glycoproteins) Usually synthesized as:  inactive molecule in the ER (pre-prohormone)  cleaved in the Golgi apparatus (prohormone → hormone)  packaged into secretory granules awaiting for secretion PRE-PROHORMONE → PROHORMONE → HORMONE PARATHYROID GLAND There are 2 types of parathyroid cells in the glandular tissue: 1. CHIEF CELLS  Produce PTH (Parathormone or Parathyroid hormone) 2. OXYPHIL CELLS  Unknown function, larger than chief cells, present oxydative and hydrolitic enzyme activity PTH SYNTHESIS Parathyroid cells are very sensitive to a decline in blood ionized calcium [iCa]  Calcium-sensing receptors on gland membrane surface  G-Protein coupled receptors (cAMP-PKAgene transcription)  Decrease in blood [iCa] (hypocalcemia) stimulates PTH release  Normal or increased [iCa] in blood (hypercalcemia) – inhibition of PTH release PTH synthesis is similar to other protein hormones  Prepro-PTH is synthesized in rER and then cleaved to pro-PTH  The “pro” portion is removed (in the Golgi apparatus) and the resulting PTH is secreted by exocytosis  Metabolized by liver and the kidneys  Half-life of 5-10 min PARATHYROID GLAND – Calcium and Phosphate Main gland involved in the Calcium (Ca2+) & Phosphate (PO4) metabolism These ions play a major role in physiological homeostasis PHOSPHATE PO4 CALCIUM Buffer system Muscle contraction Composition of cell membrane and Nerve cell activity Release of hormones by exocytosis Activation of several enzymes Blood coagulation Maintenance of membrane stability Structural integrity of bones and teeth 99% in bones;