UPDATED Fluid and electrolyte balance EXAM QUESTIONS AND CORRECT DETAILED ANSWERS WITH RATIONALES|A+ GUARANTEED

How can Kidneys regulate blood pressure? - ANSWER- By regulating water balance How do kidneys prevent shifting of water? - ANSWER- By producing urine of different osmolarity by varying the amount of water reabsorbed by the kidneys Where does the majority of water get reabsorbed? - ANSWER- PCT ~70% What ion is primarily responsible for creating the osmotic gradient causing the movement of water? - ANSWER- Na+ Which cells in the tubular component have the most aquaporins? - ANSWER- PCT What % of urea from the PCT get reabsorbed - ANSWER- ~50% What does the remaining 50% of urea in the PCT act as? - ANSWER- A solute to help increase osmolarity of ISF All fluids in the kidney cortex are __________ - ANSWER- Isosmotic What type of osmotic gradient is present in the interstital fluid of the medulla? - ANSWER- Vertical osmotic gradient with increasing osmolarity as you move down the kidney Juxtamedullary nephrons make up ________% of nephrons - ANSWER- 15% How do juxtamedullary nephrons differ from cortical nephrons? - ANSWER- They have a different peritubular capillary (Vasa Recta) and have a long loop of Henle which creats the osmotic gradient in the medulla What does the loop of Henle do? - ANSWER- The loop of Henle establishes and maintains an osmotic gradient in the medulla of the kidney acting as a countercurrent multiplier What does the countercurrent mechanism accomplish in the nephron loop? - ANSWER- It allows the kidneys to concentrate or dilute urine Is the ascending of descending limb on the loop of Henle permeable to water - ANSWER- Descending limb is permeable to water ascending limb is not due to lack of aquaporins Describe what happens to filtrate as it goes through the loop of Henle - ANSWER- As filtrate goes down the descending limb water leaves into the medulla making the filtrate more concentrated. As it travels up the ascending limb filtrate becomes less concentrated as solutes get pumped out into the medulla increasing the concentration in ISF. Urea contributes to _____% of the osmolarity in the medulla - ANSWER- 40% ensures max water reabsorption What is the osmolarity in the distal tubule? - ANSWER- ~100mOsm What does the vasa recta do? - ANSWER- Helps to maintain the osmotic gradient established by the loop of Henle by countercurrent exchange Describe what happens as blood flows through the Vasa recta - ANSWER- As blood goes down into the medulla water moves into the medulla and solutes are absorbed and as it moves back up to the cortex water is reabsorbed and solutes are moved out into the medulla Blood leaving the Vasa Recta will: - ANSWER- Be slightly more concentrated and have a slightly larger volume Where does the last 30% of water reabsorption take place? - ANSWER- 20% in the DCT & 10% in the collecting duct Is water reabsorption in the DCT and collecting ducts regulated? - ANSWER- Yes by hormones Which hormone controls the synthesis & insertion of aquaporin-2 on DCT and collecting duct principle cells? - ANSWER- Antidiuretic hormone What stimulates the release of ADH? - ANSWER- An increase in plasma osmolarity (Dehydration) What is Diabetes insipidus? - ANSWER- a disorder caused by inadequate amounts of ADH which causes excessive water loss, polyuria & polydipsia are symptoms. What is the metabolic pathway that causes aquaporin-2 insertion? - ANSWER- ADH in the peritubular capillary diffuses and binds to an ADH receptor which activates a G protein activating adenylate cyclase converting ATP to cAMP which activates a protein kinase causing the synthesis and insertion of aquaporin-2 on the apical membrane of the late DCT and collecting duct. What does hypernatremia and hyponatremia lead to? - ANSWER- Hypernatremia is increased Na+ in the blood which increases BP Hyponatremia is decreased Na+ in the blood which decreases BP What ion has the strongest osmotic force - ANSWER- Na+ Where does the bulk of Na+ reabsorption take place? - ANSWER- PCT 70% unregulated Ascending limb 25% unregulated DCT & collecting duct 5% regulated Na+ reabsorption from the PCT into the cell occurs via ______________ - ANSWER- Secondary active transport/cotransport Na+ reabsorption from the cell into the ISF occurs via _________________ - ANSWER- Active transport Na+/K+ pump What ion is coupled with Na+ reabsorption? - ANSWER- Cl- Na+ reabsorption is coupled with ______________ secretion - ANSWER- K+ secretion to prevent changes in electrical potential What hormone influences K+ secretion - ANSWER- Aldosterone What stimulates the release of aldosterone? - ANSWER- Hyperkalemia (Increased K+ lvls in blood) or Angiotensin II What does aldosterone cause? - ANSWER- Causes principle cells to insert more Na+/K+ pumps on the basal membrane & more ion channels on the apical surface. Increases Na+ & K+ gradient Increases reabsorption of Na+ & secretion of K+ Increased Na+ reabsorption causes more water to be reabsorbed increasing blood volume which increases BP What type of hormone is aldosterone? - ANSWER- Steroid hormone released by adrenal cortex What are Macula Densa cells function? - ANSWER- They are specialized chemoreceptors sensitive to Na+ in the DCT and send paracrine signals to granular cells stimulating them to secrete Renin into the bloodstream What are granular cells? - ANSWER- Juxtaglomerular cells that are specialized smooth muscle cells that secrete Renin into the bloodstream