Parathyroid Hormones, Calcitonin and Vitamin D Flashcards
What is PTH?
Peptide Hormone
Function of Parathyroid Hormone (PTH)
Regulates Calcium and Phosphate Homeostasis
Where is PTH secreted from?
Chief Cells of Parathyroid Glands
Location of parathyroid glands
Two superior and two inferior located between true and false capsule on posterior surface of thyroid gland
Describe the generation of PTH
Secreted as preprohormone
Cleaves into prohormone
Forms mature hormone
Names of parathyroid receptors
PTH1R
PTH2R
What type of receptor are the PTH receptors?
G protein-coupled receptors
How do PTH receptors signal within the cell?
cAMP
Phospholipase C
Protein Kinase C
Intracellular Calcium Stores
Alter gene expression
Where are PTH receptors found?
High density bones and cartilage
Renal tubules
What are the effects which PTH has on the bones?
Stimulates bone-forming osteoblasts
Activates osteoclasts
How does PTH activate osteoclasts?
Cytokine secretion
Receptors activator of nuclear factor K-B (RANK)
How does PTH stimulate cartilage growth?
Stimulates proliferation of chondrocytes
What effects does PTH have on the kidney?
Increases renal calcium reabsorption
Increases renal phosphate excretion
Which parts of the kidney does PTH act on?
Increasing Calcium Reabsorption and Phosphate Excretion: Ascending Loop and Cortical Collecting Duct
Decreasing Phosphate Reabsorption: Proximal Tubules
What effect does PTH have on the gut?
Stimulates formation of calcitriol which increases calcium absorption
What may cause hyperparathyroidism?
Parathyroid Adenomas
What are the effects of hyperpararthyroidism?
Hypercalcemia
Hypophospatemia
What factors increase PTH levels?
Low serum calcium
High serum phosphate
No feedback regulation
What factors decrease PTH levels?
Calcitriol
What are the functions of calcitriol?
Increases intestinal absorption of calcium and phosphate
Increases renal reabsorption of calcium and phosphate
Increases osteoclast activity to release calcium and phosphate
Inhibits PTH secretion
What happens to people with severe Vitamin D deficiency?
Causes hypocalcemia and osteomalacia develops
Overall function of calcitonin
Decreases calcium levels in blood
Where is calcitonin produced?
Parafollicular cells of thyroid gland
How does calcitonin decrease calcium levels?
Opposes effect of PTH on bone osteoclasts
Contributes to bone formation
Reduces calcium loss from bones
Inhibits renal calcium reabsorption
Summary
