Lect 8 Flashcards
where is most potassium (98%) located
inside cells
potassium is under control of what three hormones?
- epinephrine
- insulin
- aldosterone
potassium is under control of three hormones. Describe the effect of epinephrine on a1 and b2 receptors
-
alpha 1 receptor activation
- causes a shift of K+ out of cells -> hyperkalemia
-
beta 2 receptor activation
- stimulates K+ uptake into cells -> hypokalemia
potassium is under control of three hormones. Describe the effect of insulin
- increases K+ uptake into cells (after a meal)
- stimulates Na+-K+ ATPase
potassium is under control of three hormones. Describe the effect of aldosterone
- increases K+ uptake into tubule cells and increases K+ excretion
- stimulates Na+-K+ ATPase
hyperosmolarity and exercise favor movement of potassium from where to where?
- from ICF to ECF
acidosis stimulates movement of potassium from where to where
- in acidosis, H+ ions move into cell and K+ moves out of the cell
alkalosis stimulates movement of potassium from where to where
- stimulates movement of K+ into cells
physiological regulation of K+ occurs where in the nephron
distal tubule and collecting duct
- K+ reabsorption in proximal tubule (67%) and loop of henle (20%) does not change in the face of increased or decreased total body K+
effect of a low K+ diet
-
decrease in K+ excretion
- PT and LOH still reabsorb only 87%
- remaining K+ reabsorbed in the distal nephron
in what cells does the K+ reabsorption occur. What mechanism?
- occurs in the alpha intercalated cells of the distal nephron
- K+ reabsorption in exchange for H+ secretion (via ATP)
what is the effect of a high K+ diet
- aldosterone is stimulated
-
promotes K+ secretion via
- stimulation of basolateral membrane Na+,K+ ATPase
- increasing luminal membrane permeability to K+
potassium secretion occurs in what cells
- principle cells
aldosterone has what effect on K+? What mechanisms?
- two mechanisms
- stimulates Na+-K+ ATPase
- stimulates diffusion across luminal membrae down its concentration gradient
describe the distribution of calcium in the body
- 99% in bone
- 1% in the ICF
- 0.1% in ECF
what is the concentration of plasma calcium? what three forms can it exist in
- plasma Ca2+ = 2.5 mM
- 50% ionized Ca2+ = biologically active
- 10% complexed to anions (CaPO4)
- 40% bound to plasma proteins
what form of calcium is biologically active
ionized Ca2+
how does the filtered load calculation change for Ca2+
- only 60% of plasma Ca2+ is filtered (40% is bound)
- FL = (GFR)(PCa)(0.6)
What percentage of filtered calcium appears in the urine?
- only 1% of filtered calcium appears in the urine
where does the reabsorption of calcium happen in the nephron? give percentages
- proximal tubule 67%
- thick ascending limb 25%
- distal tubule 5-10%
- collecting duct <5%
- does not occur in descending limb of LOH
via what mechanism does calcium get transported across apical membrane?
Ca2+ channels
via what mechanisms does calcium get transported across basolateral membrane
- active transport via Ca2+-ATPase
- Na-Ca2+ exchange
- *basolateral membrane is on interstitium side
parathyroid hormone stimulates Ca2+ uptake in what part of nephron
distal tubule
- mediated by cAMP
what effect does thiazide diuretics have on calcium reabsorption
- stimulates Ca2+ reabsorption
- thiazide decreases [Na+] which increases inward movement of Na+ via Na+/Ca2+ exchanger
why is phosphate important in the body
- component of organic molecules (DNA, RNA, ATP)
- major component of bone
- urinary PO4 is an important buffer
what percentage of plasma PO4 is protein bound
10%
- meaning that 90% is filterable at the glomerulus
where does reabsorption of phosphate occur in the nephron
- 85% reabsorbed in the proximal tubule
- 15% is excreted - most important buffer anion
reabsorption of phosphate in the proximal tuble is inhibited by what
parathyroid hormone
