Flashcards in Chemical Pathology 10 - Calcium metabolism Deck (66)
Around what percentage of the body's calcium is in the skeleton?
What % of serum calcium is free/ionised?
Which form of serum calcium is biologically active?
Recall the 3 forms of serum calcium?
Bound to albumin
Complexed with citrate/phosphate
What is "corrected calcium"?
Calcium corrected for albumin level
How can ionised calcium be measured?
What is the key role of circulating calcium?
Nerve and muscle function
Where in the body is calcium level detected for calcium homeostasis?
Which cells are involved in releasing calcium from bone?
Recall the 3 ways in which PTH can act to increase serum calcium
1. Increase bone Ca resorption
2. Increase renal Ca resorption
3. Indirectly: increase 1-alpha hydroxylase action in kidneys - this increased vit D activation, and vit D increases gut absorption of vit D
What type of hormone is PTH?
What type of hormone is vitamin D?
Steroid hormone (derived from cholesterol)
What are the actions of PTH?
1. Increased resorption of calcium from bone and kidney
2. Renal phosphate wasting
3. Increase renal 1 alpha hydroxylase, which activates vit D
Recall the pathway of vit D synthesis
1. Cholecalciferol obtained from diet or converted by sunlight exposure from 7-dehydrocholesterol
2. 100% of absorbed cholecalciferol is converted to storage form (vit D3) in liver conversion by 25 hydroxylase
3. Activated by renal 1-alpha-hydroxylase - an enzyme under control of PTH - to the active form (1,25-(OH)2 D3)
Which hormone stimulates 1-alpha-hydroxylase production by the kidney?
In which disease can 1 alpha hydroxylase be produced outside the kidney, and where?
Sarcoidosis - in sarcoid lung tissue
Does sarcoidosis cause hypo or hypercalcaemia?
Sacroid tissue releases 1 alpha hydroxylase -->
Vit D activated outside the kidney --> calcium increased
Where is 1-alpha-hydroxylase produced in sarcoidosis?
Lung sarcoid tissue
What is calcitriol another name for?
Where is 25 hydroxylase found?
What effect does 1,25(OH)2 vit D (active form) have on calcium and phosphate?
Increases calcium and phosphate absorption from intestines
Why is bone-specific ALP high when there is increased bone turnover?
Alkaline phosphatase pushes calcium and phosphate into bone
When it does this, some Alk phos is leaked into blood
Therefore, when you have increased bone turnover, you can measure the bone-specific AlkPhos in the blood and it will be high
Which electrolyte is necessary for PTH synthesis?
What is the difference between osteoporosis and osteomalacia in terms of bone structure and mass?
Osteoporosis = less bone of normal structure
Ostemalacia = normal amount of bone of wacky structure
What type of bone disease is caused by renal failure?
1. Can't make 1 alpha hydroxylase --> lack of calcium absorption into bone
2. Can't excrete phosphate in kidney failure
Which conditions are caused by vit D deficiency in children and adults?
Recall 4 risk factors for vit D deficiency
Lack of sunlight exposure
Malabsorption (eg coeliac)
Recall 4 clinical features of osteomalacia, including the biochemistry
Bone and muscle pain
Increased fracture risk
Looser's zone fractures
Biochem: low Ca and Pi, raised ALP
Recall 4 clinical features of Rickets
Widened epiphyses at the wrists