Regulation Of Calcium and Phosphate Flashcards
Extracellular Calcium is either diffusible or not diffusible.
Compare the 2
Diffusible: Free ionised Ca2+, Complexed Calcium (Bound to negatively charged molecules) are both very small so can diffuse through glomerular membrane
Not Diffusible: Ca2+ bound to negatively charged proteins, cant diffuse through glomerular membrane
How much Ca is reabsorbed in the PCT?
By what 2 methods?
How much is reabsorbed in Thick Ascending Limb?
By what 2 methods?
PCT- 65%;
- Solvent drag (dragged back with water) (80%)
- Transcellular pathway (25%)
TAL- 25%
- Paracellular (50%)
- Transcellular pathway stimulated by PTH (50%)
How much Ca is reabsorbed in the DCT?
By what method?
How much is reabsorbed in Collecting Duct?
How much is excreted?
DCT- 8%
- Transcellular
CD- 1.5%
Excreted- 0.5%
How much Phosphate is in bone and Interstitial Fluid?
How much filtered Phosphate is reabsorbed in PCT and excreted?
80% bone, 20% IS Fluid
PCT Reabsorption- 80%
Excreted- 20%
Reabsorption of Phosphate at the Apical membrane of Tubular cells occurs with what ions?
What is a common cause of itching in CKD?
Na+ (2 Na+ per Po4 3-)
High Phosphate concentration
How does adding Ca/ Po4 affect the ion concentration of the other ion in solution
Decreases (used to make Calcium Phosphate)
What are 4 ways PTH acts to raise plasma calcium
- Decreases Phosphate reabsorption (more Ca2Po4 broken down)
- Increases Vit D formation (Increases Gut Ca absorption)
- Increased Ca reabsorption
- Increased bone resorption
Hypocalcaemia leads to Neuomuscular excitability (Convulsions, cramps, cardiac arrhythmias etc)
What are 5 causes
- CKD due to Hyperphosphateaemia and low Vit D
- Hypoparathyroidism
- Rickets and Osteomalacia
- Tissue injury (Cells release intracellular phosphate)
- Alkalosis reduces H+ available to bind to proteins, so Ca2+ binds to proteins instead
How do we treat Hypocalcaemia
- Oral or IV Ca
- Patients with CKD benefit from Alfacalcidol, a Vit D analogue
Hypercalcaemia makes cells less excitable (slow reflexes, muscle weakness, constipation)
What are 6 signs and symptoms
- Polyuria
- Polydipsia
- ‘Moans’ (Depression/ confusion)
- ‘Stones’ (Renal calculi)
- ‘Bones’ (Bone pain and fractures)
- ‘Groans’ (Ab pain, Vomiting and Constipation)
How do we treat Hypercalcaemia?
- Treat underlying cause
- Fluids for rehydration and bisphosphonates
List 7 causes of Hypercalcaemia
- Primary Hyperparathyroidism
- Sudden Acidosis (release of bound Ca2+)
- Increased intestinal absorption (High Vit D/ Ca ingestion)
- Bone Destruction
- Drugs
- Hypermagnesemia
- Teratiary Hyperparathyroidism in CKD
Hypophosphatemia is caused by excess Po4 3- loss
List 6 causes
- Hyperparathyroidism
- Reduced GI absorption
- Decreased intake (alcohol and medications such as antacids)
- Refeeding Syndrome
- Diabetic Ketoacidosis
- Respiratory Alkalosis (pH of cell increases as CO2 diffuses out of cell)
list 5 signs of Hypophosphatemia
- ‘Stones’ (Kidney and gallbladder)
- ‘Thrones’ (Polyuria)
- ‘Bones’ (Pain)
- ‘Groans’ (Constipation and muscle weakness)
- ‘Psychiatric overtones’ (depressed mood and confusion)
How do we treat Hypophosphatemia?
- Oral or IV phosphate
Gradually increase calorie intake in severe Malnutrition
