Flashcards in Lecture 61 Deck (25)
What are important functions of calcium?
1) Important structural component of the skeleton
2) Muscle contraction
3) Nerve pulse transmission
4) Blood clotting
5) Secretion of hormones --> Endocrine + Exocrine glands
What are functions of calmodulin?
1) Ca2+ binding protein
2) Found in every cell
3) Activates enzymes (ex: Ca2+ ATPase)
What is the normal concentration of serum calcium and what are its components?
1) 10mg/100mL serum calcium
2) 51% Ca2+ ion, 46% Calcium complexed to proteins (such as albumin), & 3% Calcium complexed to other ions
What are hormones that maintain calcium levels?
1) PTH Increases Ca2+
2) Calcitonin decreases Ca2+
3) Vitamin D increases Ca2+
What are target tissues for calcium related hormones?
Describe 5 characteristics of PTH
1) 84 amino acids in length
2) 9,500 MW
3) Synthesized in parathyroid gland
4) Low Ca2+ causes increased transcription --> translation --> synthesis --> PreproPTH --> ProPTH (90aa) --> PTH (84aa) --> Released into blood from PTG
5) High Ca2+ causes: decreased transcription --> translation --> synthesis --> PTH
(auto negative feedback)
What effect does PTH have on bone?
PTH increases the number of osteoclasts in bone
Where are bone receptors for PTH located and what do they do when activated?
1) Receptors for PTH are on osteoblasts
2) Release RANK ligand (osteoclast differentiating factor), which converts proosteoclasts to osteoclasts (resorbs bone)
What function does PTH have on the kidney?
1) Increased calcium reabsorption in the distal tubule
2) Decreased PO4 (inhibits phosphate reabsorption from proximal & distal tubules)
What function does PTH have on the intestine?
1) No receptors for PTH in intestine (indirect effect)
2) When PTH acts on the kidney, it synthesizes the active form of Vitamin D, which increases calcium reabsorption in the intestine (indirect effect)
Where can hypercalcemia malignancy occur and what are its effects?
1) Lung + Kidney tumors
2) Synthesize extra calcium
3) Have similar hormone to PTH called PTH Gene related peptide (PTHRP), which acts on PTH receptors
Where is calcitonin synthesized?
What is the approximate weight and length of calcitonin?
What is the function of calcitonin?
1) Decreases serum calcium
2) Secreted in response to Ca2+
Where does calcitonin act and what does it do?
1) Acts on bone by shrinking osteoclasts
2) In kidney, it is possible for calcitonin to increase Ca2+ excretion, but only when there are supraphysiological levels of Ca2+
3) No effect of calcitonin on intestine
4) Calcitonin inhibits gastrin in the stomach
How can one obtain vitamin D?
1) Fatty fish
2) Fortified dairy products
3) 7-dehydrocholesterol is converted to vitamin D by UV irradiation
What is the function of Vitamin D binding proteins?
Transport Vitamin D to the liver
What happens to vitamin D in the liver?
1) Vitamin D is converted to 25-hydroxy vitamin D3
2) 25-hydroxy vitamin D3 is the major circulating form of vitamin D, although it is not the active form
What happens to 25-hydroxy vitamin D3 once it is formed?
1) 25-hydroxy vitamin D3 is transported to the kidney to form 1,25-dihydroxy vitamin D3 (most active form of Vitamin D, also known as calcitrol)
2) PTH helps to add hydroxyl group to position 1 (negative feeback inhibits PTH)
What is renal osteodystrophy?
It is a renal disease that causes a lack of synthesis of 1,25-dihydroxy vitamin D3
What is an alternate form of 25-hydroxy vitamin D3 that can be produced in the kidney?
24,25-dihydroxy vitamin D3 can be synthesized as an inactive metabolite
Does PTHRP affect Vitamin D hydroxylase?
No, unlike PTH, which helps add the hydroxyl group to position 1 of 25-hydroxy Vitamin D3
What effect does Vitamin D have on the intestine?
1) Vitamin D receptor is activated by 1,25-dihydroxy Vitamin D3
2) The receptor goes to the nucleus to promote transcription of calcium binding protein (Calbindin) and calcium channel protein (TRPG)
What effect does Vitamin D have on the kidney?
Vitamin D enhances PTH action at the distal tubule for reabsorption of calcium