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Phys3 Ca & Phosph

Phys3 Renal Ca+ & Phosphorus

QuestionAnswer
Ca+ exists in 3 forms 1.40% is non-filterable b/c it is protein bound. 2.15% of Ca+ is complexed with small anions (ex: carbonate, citrate, phosphate, & sulfate). 3.45% is ionized Ca+ (this is what is tightly regulated by the body).
How is moment to moment extracellular Ca+ regulation achieved? By shifting Ca+ in and out of BONE
How many hydroxylations does Vit D undergo? TWO: 1.Liver. 2.Kidney (stimulated by PTH).
Vit D in gut facilitates the absorption of what? 1.Ca+ (entry, buffering, absorption into plasma). 2.Phosphate.
Vit D is critical in the synthesis of what in the GI Enterocytes? Intracellular Ca-Binding proteins. **these aid Ca+ entry into the cell through apical membrane & minimize the free Ca+ within the cell.
2 ways Ca+ exits the GI enterocyte's basolateral membrane? 1.Ca ATPase. 2.Na/Ca exchanger when Ca ATPase is saturated.
What stimulates the Ca-ATPase on the basolateral membrane of the enterocytes? Vitamin D
Dec Plasma [Ca] Inc PTH: 1.Kidney: Inc hydrolysis of Vit D, Inc Ca+ reabsorption. 2.GI: Inc Ca+ absorption. 3.Bone: Inc osteoclast activity
Where is the Renal tubule does PTH cause an Inc in Ca+ reabsorption in response to Dec plasma [Ca+]? 1.Thick Ascending limb (25%). 2.Distal convoluted tubule (. 3.Connecting tubule/Collecting Ducts (1.5%).
What are the 3 sites of Ca+ regulation? 1.GI enterocytes. 2.Bone. 3.Kindey
Where is 65% of filtered Ca+ reabsorped? is it subject to hormonal control (ex: PTH)? Proximal Tubule via paracellular reabsorption. NO. **tied to Na+ & water reabsorption, Inc when they Inc b/c water leaving creates an Inc concentration gradient.
How much of the filtered load of Ca+ to you actually excrete? 0.5 to 1% of FL.
How is Ca+ reabsorbed in the Thick Ascending Limb? 1. 50% passive & paracellular (from + voltage w/in tubule, this is caused by ADH). 2. 50% active & transcellular (PTH influences).
What is major regulatory site of Ca+ in the kidney Distal Convoluted Tubule (DCT). 1.PTH stimulates Ca channel on apical mem causing Ca+ to move from the tubule into the cell. 2. Vit D buffers Ca+ in the cell and Activates Ca-ATPase on basolateral mem.
Can plasma Ca+ have a direct effect on Ca+ reabsorption in the kidneys? YES. Ca+ sensing receptor on basolateral mem which will block the tri-transporter on apical membrane which with cause the lumen + voltage to disappear and Dec Ca+ reabsorption.
How do Loop diuretics affect Ca+ reabsorption? DECREASE b/c they will interfere with the lumen + voltage driving paracellular reabsorption.
Are loop diuretics used to treat hypercalcemia? NO
How do thiazide diuretics affect Ca+ reabsorption? INCREASE it. **They block the Na/Cl symporter in DCT, Dec Na w/in the cell, Inc activity of Na/Ca exchanger on the basolateral membrane.
How does volume contraction affect Ca+ reabsorption in PT? Inc Ca+ reabsorption by Inc Na+ & water in PT due to SNS and AngII response.
What is the important role of Phosphate in Acid/Base balance? Buffering H+ secreted in tubule lumen and excreted as titratable acid (H2PO4).
Where does most Phosphate reabsorption occur? 80% occurs in the Proximal Tubule via Na/phosphate symporter.
Does Phosphate have limited reabsorption? YES, any Filtered Load above Tm will be excreted
Does PTH Inc or Dec phosphate reabsorption? DECREASES it by promoting renal phosphate excretion. **PTH inhibits apical sodium/phosphate uptake
What 2 things stimulate PTH secretion? 1.Dec plasma [Ca]. 2.Inc plasma [Phosphate].
Acidosis Causes Inc Ca+ and Phosphate release from bone, which is good b/c filtered phosphate can absorb and buffer H+ ions to raise pH.
Primary Hyperparathyroidism Inc PTH!! causes: 1.Inc bone resorption. 2.Inc plasma Ca+. 3.Dec plasma phosphate. 4.Inc Urinary phosphate excretion. 5.Inc Urinary Ca+ excretion (Ca+ is so high it exceeds ability to absorb).
Created by: WeeG
 

 



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