Calcium & phosphate Flashcards
What are the 5 functions of calcium?
Neuromuscular excitability and muscle contraction Bone strength (calcium hydroxyapatite crystals)
Intracellular 2nd messenger system and co enzymes
Hormone/neurotransmitter stimulus secretion coupling
Blood coagulation (Factor IV)
Where is the majority of calcium stored?
99% stored within skeletons as calcium hydroxyapatite crystals
How is extracellular calcium regulated?
Parathyroid hormone and calcitriol (vitamin D)
What are the three main functions of phosphate?
Inorganic phosphate is essential for cellular metabolism and skeletal mineralisation.
Component of nucleic acids (RNA and DNA), as well las fundamental for phospholipids
Mediator of intracellular signalling (2nd messengers, and regulates protein activity(
Component of high energy ATP molecules
Describe the relationship between extracellular phosphate and extracellular calcium?
Inversely proportional relationship
Which cells synthesis vitamin D3?
Keratinocytes within epidermis
Which source of Vitamin d is synthesised by the body or obtained from dietary sources?
Cholecalciferol (D3)
What is vitamin d2?
Ergocalciferol
Which precursor molecule is converted into previtamin-d3 in the skin?
7-dehydrocholesterol
How is pre-vitamin D3 converted into Vitamin-D3?
UV radiation
Where does the initial hydroxylation of vitamin d3 occur?
Liver
Which enzyme catalyses the hydroxylation of vitamnin-d3?
25-hydroxylase
What is the fate of vitamin-d3 in the liver?
Initiation hydroxylation of vitamin d3 into 25-hydroxy-cholecalciferol.
Where the second hydroxylation for vitamin d occur?
Proximal convoluted tubule (Kidney)
Which enzyme catalyses the second hydroxylation of vitamin d?
1-alpha-hydroxylase
Which molecule is formed from the second hydroxylation of vitamin d?
1,25-dihydroxycholecalciferol
Calcitriol
What is active vitamin D?
Calcitriol
What is the function of calictriol?
Autoregulates synthesis by decreasing transcription of 1-alpha-hydroxylase, negative feedback.
Increased osteoblast activity
Increased calcium absorption
Increases phosphate and calcium reabsorption
Which receptors does vitamin D bind to?
vitamin D receptors (VDR), causes VDREs activation
How does vitamin d increases calcium absorption?
Calcitriol acts on the gastrointestinal tract to increase the production of calcium transport proteins (Calbindin-D proteins), increases uptake of calcium from the gut into the body
increases plasma calcium maintaining, PTH secretion at low levels, and favours osteoblast action
What effect does calitriol have on PTH?
Exerts negative feedback ,inhibits release
How does vitamin D increases calcium and phosphate reabsorption?
Decreases urinary loss of calcium, and phosphate, to filtrate by stimulating reabsorption within the proximal convoluted tubule
Where are parathyroid hormones secreted from?
Parathyroid glands
Which cells secrete and synthesis parathyroid hormone?
Chief cells
What is the precursor of PTH?
pre-pro-PTH
Where does pre-pro-PTH cleavage occur?
Cleaved by proteases into smaller peptides, by endoplasmic reticulum and Golgi body