SOLUTIONS TO THE STUDY GUIDE FOR MODULE #15 1. a. Retroperitoneal � Behind the parietal peritoneum b. Erythropoiesis � The production of red blood cells (erythrocytes) c. Renal blood flow rate - The rate at which blood flows through the kidneys (1 liter/min) d. Filtrate - Blood plasma without proteins, found in the nephrons of the kidneys e. Glomerular filtration rate - The rate at which filtrate is produced in glomerular filtration (125 mL/minute) f. Tubular maximum - The maximum rate of reabsorption by active transport through the nephron tubules g. Buffer system - A mixture of an acid and a base which resists changes in pH 2. a. kidneys b. ureters c. urinary bladder d. urethra e. renal artery f. renal vein g. renal pelvis h. renal pyramid i. medulla j. cortex k. renal column l. renal capsule m. minor calyx 3. The urinary bladder contains stratified transitional epithelium, so that it can stretch. 4. The medulla has the higher concentration of solutes in its interstitial fluid. The medulla�s interstitial fluid is as much as four times more concentrated than normal interstitial fluid. 5. The seven functions of the urinary system are: urine formation, pH control, blood pressure regulation, stimulation of red blood cell formation by the red bone marrow, vitamin D activation, transport of urine, and storage and release of urine. 6. When cleaning a desk drawer, you can dump everything out of the desk drawer and then start putting back the things you want to keep. Anything left in the pile at the end is waste. If you make a mistake and put something in the drawer, you can always take it out again and return it to the waste pile. This is like urine formation. The kidney receives all contents of the blood plasma (except proteins), and then it puts back the things that the blood needs. Anything else is waste. If something gets back into the blood, it can be put back into the urine before the process is finished. 7. a. renal corpuscle b. Bowman�s capsule c. glomerulus d. descending limb of the loop of Henle e. loop of Henle f. ascending limb of the loop of Henle g. proximal tubule h. distal tubule i. cortex j. medulla k. collecting duct 8. The proximal tubule and descending limbs of the loop of Henle are always permeable to water. The ascending limb of the loop of Henle is never permeable to water. The distal tubule and collecting duct are permeable to water based on the amount of ADH present. 9. The four steps are filtration, reabsorption, secretion, and water reabsorption. Water reabsorption is often grouped together with reabsorption so that there are only 3 steps to urine formation. 10. In glomerular filtration, filtrate makes it through the filter. Blood cells and proteins do not. 11 A high GFR comes from the high permeability of the glomerular capillaries and the high glomerular capillary pressure. 12. Glomerular capillary pressure is high because the efferent arteriole is thinner than the afferent arteriole. GCP is fought by capsular pressure and colloid osmotic pressure. The difference between GCP and the sum of these two pressures is 7 mmHg. If the GCP loses 7 mmHg of pressure, no more glomerular filtration occurs, which leads to renal shutdown. 13. To be actively reabsorbed, a substance usually needs a carrier and ATP. The exception to this is protein, which needs only ATP, because proteins are absorbed by pinocytosis. 14. Water is the main substance which is passively reabsorbed. Urea is another prime example. 15. If the reabsorption T-max is high, it means that a lot of the substance is actively reabsorbed. As a result, it will go into the blood and not be left in the urine. Thus, you expect to find only a little of it in the urine. 16. If a substance is secreted by the nephron, it is going back into the urine. Thus, the concentration decreases in the blood. 17. a. In the proximal tubule, the filtrate has just entered the nephron. Thus, it has roughly the same concentration of solutes as does blood plasma. b. As the filtrate descends into the medulla, water leaves the nephron, concentrating the filtrate. Thus, the filtrate has a higher concentration of solutes in the lower portion of the descending limb of the loop of Henle. c. As the filtrate descends into the medulla, water leaves the nephron, concentrating the filtrate. Thus, the filtrate has a higher concentration of solutes at the bottom of the loop of Henle. d. As the filtrate rises up the ascending limb of the loop of Henle, solutes are actively transported out of the filtrate, but water is not allowed to follow. Thus, the concentration of solutes in the filtrate is lower than that of plasma. e. At the distal tubule, the active transport of solute out of the nephron has been going on for quite a while. Thus, the concentration of solutes in the filtrate is lower than that of blood plasma. This can vary, depending on the level of ADH present. Notice that we did not ask you about the filtrate in the collecting duct. That�s because the concentration of solutes in the filtrate at the collecting duct depends on the amount of ADH present. 18. The internal urinary sphincter is controlled automatically. This provides for urination in babies. As we develop, we learn to control the external urinary sphincter, which allows us to decide when we urinate. 19. The juxtaglomerular cells detect and respond to changes in blood pressure and sodium level in the blood. 20. Aldosterone is the hormone stimulated by the secretions of the juxtaglomerular cells. The answer is not renin, angiotensinogen, angiotensin I, or angiotensin II, because these molecules are not hormones. However, angiotensin II stimulates the release of aldosterone from the adrenal cortex, so aldosterone is the hormone affected by the juxtaglomerular cells. 21. The atrial natriuretic hormone reduces blood pressure and the sodium level in the blood. It is secreted in the heart atria in response to atrial stretching. 22. When blood pH drops below 7.35, we have acidosis. When blood pH rises above 7.45, we have alkalosis. 23. When a base enters a buffer, the acid in the buffer will react with it. Thus, in the bicarbonate buffer, carbonic acid will react. In the phosphate buffer, dihydrogen phosphate will react. 24. The three processes, in order of effectiveness, are: buffer systems, ventilation depth and speed, and H+ secretion in the kidney. 25. The less effective processes are the faster ones. Thus, in order of increasing speed, we have H+ secretion in the kidney, ventilation depth and speed, and buffer systems.