Calcium, Phosphate And Magnesium Flashcards
What the plasma concentrations of calcium, phosphate and magnesium?
Ca= 1.3
Ph= 1.3
Mg= 1.1
What is the difference in the distribution of these ions in the EC and IC compartments?
Ca mainly in the extracellular compartment
Ph and mg are similar distributed between the EC and IC compartment
What regulatory roles are calcium, phosphate and magnesium involved in?
Calcium: Cell signalling and 2nd messenger Neurotransmitter and hormone release Exocytosis of proteins Muscle contraction Blood clotting Biomineralisation
Phosphate:
Integral component of DNA and RNA
ATP
Phosphate groups can be added or deleted from proteins
Magnesium DNA and protein synthesis Oxidative phosphorylation Enzyme function Ion channel regulation Neuromuscular excitability
What hormones are involved the metabolism of these minerals?
PTH
Vitamin D
FGF-23
PTHrP
CT (calcitonin)
Which organ acts as the main regulator of these minerals homeostasis? How can it adapt its function to maintain homeostasis?
Kidney
NOTE: Ca/Mg sensory receptor in particular
Can decrease or increase the filtered load depending on whether there is a hypo or hyper state
What implications would impaired renal function have on levels of calcium, magnesium and phosphate in the body?
Would lead to impaired reabsorption and increased excretion
I.e. loss of homeostasis
How is vitamin D related to GIT calcium absorption?
Calcitrol (1,25-OH VD3) acts on ileum cell nuclei to cause transcription of Calbindin which acts to form Calbindin-Ca2+ complex to aid with transportation of Ca2+ from microvilli and into vesicles
Which parts of the nephron is associated with the absorption of the different minerals? Why is this clinically significant?
PCT= Ca + Phos primarily
DCT= Mg
Need to be aware that electrolyte imbalance might occur with the use of certain diuretics depending on which part of the nephron they target
What form of calcium regulates feedback mechanisms? What factors can influence this levels of this form of calcium?
Free ionised calcium
Decreased ph= increased Ca2+
Increased ph= decreased Ca2+
Why is it important to know the albumin concentration of a patient if you want to measure their calcium levels?
The concentration of free calcium depends on the concentration of albumin
Calcium concentrations need to be corrected to account for the fact that for 0.02mmol/L calcium binds to each gram of albumin
What are the causes of hypocalcaemia?
CDK and AKI
Vit D deificiency
Hypoparathyroidism
Acute pancreatitis
Magnesium deficiency i.e. Mg is a cofactor for PTH
Artefact i.e. wrong test tube (EDTA is a chelating agent which may lead to apparent hypocalcaemia)
Why is hypocalcaemia commonly associated with acute pancreatitis?
High levels of pancreatic lipase breakdown lipids to free fatty acid which accumulate in abdominal cavity and act to CHELATE calcium
What is the homeostatic response to low Ca2+ levels?
What feedback mechanism prevents excess PTH release?
Parathyroid gland detects low levels and secretes PTH
PTH:
-stimulates osteoclasts to increase bone resorption= Ca2+ and PO4 released
-stimulates 1-alpha hydroxylase production in the kidney which acts to convert 25(OH)D3 to 1,25(OH)D3
-1,25(OH)D3 acts on bone to stimulate release of FGF23 to decrease PO4 reabsoprtion and feeds back to parathyroid gland to prevent excess PTH release and acts on gut to increase Ca2+ and PO4 absorption
What is the homeostatic response to high calcium levels?
Calcitonin released from thyroid gland to decrease calcium reabsorption in kidney and decrease PO4 reabsorption
What are the 2 conditions associated with vitamin D deficiency? How are they different?
Rickets= affects growing bone osteomalacia= affects adult skeleton
Due to lack of mineralisation of osteoid
What are the causes of vitamin D deficiency? How can it be treated?
Impaired availability of vit D
Impaired liver hydroxylation or renal hydroxylation
End organ insensitivity to vit D metabolites
Vit D replacement through diet or sunlight
How can glucocorticoids cause vitamin D deficiency?
Inhibit intestinal vit D dependent calcium absorption
Why might surgery or radiotherapy targeting the thyroid gland lead to hypocalcaemia?
Can lead to iatrogenic damage to parathyroid glands which results in decreased PTH production
How might someone with hypocalcaemia present?
Asymptomatic
Neuromuscular symptoms are fairly common
I.e. pins and needles or spasm due to nerve irritations
What tests are done to differentiate between the different causes of hypocalcaemia?
Biochemical test to look at PTH and PO4
What conditions are indicate by the following test results?
- Increased PTH + decreased PO4
- Increased PTH + PO4
- Decreased PTH + increased PO4
1.
Vitamin D deficiency due to malabsorption or liver disease
Acute pancreatitis
Drugs I.e. Bisphosphonates
2. CKD Tumour lysis Early rhabomyolysis Pseudohypoparathyroidism
3. Reduced parathyroid function Hypomagnesemia Drugs Neonatal hypocalcaemia due to maternal hypercalcaemia AI Surgery
How can you treat hypocalcaemia?
IV calcium= acutely ill w/ neuromuscular symptoms
Oral calcium= mildly symptomatic/asymptomatic
Treat underlying cause:
VD replacement
1,25 D3 products for hypoparathyroidism
What causes hypercalcaemia?
Primary hyperparathyroidism
Malignancy
What are the different causes of primary and secondary hyperparathyroidism?
How can you differentiate between the 2?
Primary:
Increased PTH secretion due to adenoma or parathyroid hyperplasia
Secondary:
Renal failure
Vitamin D deficiency
High calcium in primary
Low calcium in secondary
