Hormones in calcium metabolism Flashcards
how is PTH synthesized? where?
as prepro-PTH in ribosomes
regulation of PTH synthesis and release
- calcium binds to calcium sensing receptor
- PLC-DAG-PKC-PLA2-arachadonic acid-luekotrienes
- leukotrienes inhibit PTH
how is PTH synthesis related to calcium?
a relaxed calcium sensor receptor leads to PTH synthesis and secretion
where are calcium sensor receptors located?
- parathyroid chief cells
- thyroidal C cells
- kidney tubules
via which two pathways is PTH action mediated?
adenylate cyclase pathway
PLC pathway
what are the PTH target organs?
kidney
bone
how does PTH affect the kidney?
stimulates calcium reabsorption by the kidney (stimulates insertion and opening of calcium channels)
how does vitamin D affect the kidney?
stimulates calcium reabsorption by the kidney (activates calcium ATPase and controls calbindin)
what is the role of PTH in bone remodeling?
- PTH stimulates production of RANKL
- osteoclast precursors bind to RANK
- inhibits osteoprotegerin (which normally acts to inhibit the RANK-RANKL interaction)
what is the main cause of hypoparathyroidism?
surgical removal of parathyroid glands
what are the symptoms of hypoparathyroidism?
- hypocalcemia
- increased plasma phosphate
- tetany
ergocaciferol
vitamin D2
cholecalciferol
vitamin D3 (circulating hormone - clinical relevance for measurement)
which vitamin D is produced by the human body in response to sunlight / diet?
vitamin D3 - cholecalciferol
vitamin D synthesis pathway
- cholesterol
- sunlight (UVB) converts 7-dehydrocholesterol to cholecalciferol (D3)
- in the liver D3 is converted to 25-hydroxyvitamin D
- in the kidney 25-hydroxyvitamin D is converted to 1,25-hydroxyvitamin D (calcitriol)
calcitriol
1,25-hydroxyvitamin D
what is the circulating form of vitamin D?
25-hydroxyvitamin D
which part of vitamin D synthesis is calcium involved in?
calcium inhibits hydroxylation of 25-hydroxyvitamin
which part of vitamin D synthesis is PTH involved in?
stimulates activity of 1a-hydroxylase (conversion to 1,25-hydroxyvitamin D in kidney)
what are the target organs of vitamin D?
intestines
kidney
bone
parathyroid glands
what does calcitriol do in the intestines?
- stimulates intestinal calcium absorption
- stimulates renal calcium reabsorption
- stimulates bone remodeling
calcitonin is synthesized by what cell type?
C cells of thyroid
what are the actions of calcitonin?
- bone: inhibits bone resorption
- kidney: increases urinary calcium excretion
how does calcitonin treat osteoporosis?
inhibits osteoclast-mediated bone resorption
definition: calcistat
the multi organ systemic network that regulates calcium homeostasis
