1. a. Water homeostasis is crucial to life. Define blood osmolarity. The osmotic pressure of blood/Measurement of the amount of solute concentrate.
b. What is the nephron’s role regarding osmolarity? Filtration, reabsorption & secretions c. What two factors regulate body fluid osmolarity? - Formation of a medullary osmotic gradient - The amount of ADH (antidiuretic hormone) present at the collecting ducts. d. Describe the collecting duct role relative to urine concentration. Depending on the body fluid osmolarity, the collecting duct reabsorbs water & forms concentrated urine or if water is allowed to pass, dilute urine is formed.
Medullary Osmotic Gradient 2. Identify the three factors in the nephron determine the osmotic gradient. 1- Differences in water and solute permeability and reabsorption in different sections of the limbs of the loop of Henle
2- Urea cycling in the medulla
3- Countercurrent exchange of fluid in the vasa recta
3. Countercurrent Multiplier
a. Active transport of solutes is the primary cause of medullary osmotic gradient. Describe, for example, ion activities along the ascending loop of Henle in the kidney medulla. This is the active transport of Na+ ions drives passive reabsorption of Cl- ions. Addition of these ions to the interstitial fluids of the medulla increases its osmolarity.
b. Explain how/why filtrate osmolarity increases along the descending loop of Henle. Squamous epithelial cells of the descending limb of the loop are permeable to water but not to most solvents. Water leaves the filtrate but the solutes cannot enter, thus increasing the filtrate osmolarity.
c. Explain how/why filtrate osmolarity decreases along the ascending loop of Henle.