Renal & Urinary System Physiology-Critical thinking
1. A hemoglobin molecule has a smaller diameter than an albumin molecule, but very little hemoglobin passes from the blood into the filtrate. Explain why. Under what circumstances do large amounts of hemoglobin enter the filtrate?
2. Ethyl alcohol inhibits ADH secretion. Given this information, describe the mechanism by which alcoholic beverages affect urine production.
3. To relax after an anatomy and physiology examination, Mucho Gusto goes to a local bistro and drinks 2 quarts of low-sodium beer. What effect does this beer have on urine concentration and volume? Explain the mechanisms involved.
4. Harry is doing yard work one hot summer day and refuses to drink anything until he is finished. He then drinks glass after glass of plain water. Assuming that he drinks enough water to replace all the water he lost as sweat, how does this much water affect urine concentration and volume? Explain the mechanisms involved.
5. A patient has the following symptoms: slight increase in extracellular fluid volume, large decrease in plasma sodium concentration, very concentrated urine, and cardiac fibrillation. An imbalance of what hormone is responsible for these symptoms? Are the symptoms caused by oversecretion or undersecretion of the hormone?
6. Propose several ways to decrease the GFR.
7. Design a kidney that can produce hyposmotic urine, which is less concentrated than plasma, or hyperosmotic urine, which is more concentrated than plasma, by the active transport of water instead of Na+. Assume that the kidney’s anatomical structure is the same as that in humans, but feel free to change anything else you choose.
8. If only a very small amount of urea, instead of its normal concentration, were present in the interstitial fluid of the kidney, how would the kidney’s ability to concentrate urine be affected?
9. Some patients with hypertension are kept on a low-salt (low-sodium) diet. Propose an explanation for this therapy.
10. Research has shown that mammals with kidneys having relatively thicker medullas can produce more concentrated urine than humans. Explain why this is so.
11. Marvin Motormount was driving too fast on a remote mountain road at 3 a.m. when his car left the road and rolled down a steep hill. Marvin sustained numerous cuts and bruises. When medical help arrived 2 hours later, his systolic blood pressure was 70 mm Hg, and his pulse was weak (thready). Intravenous saline was administered immediately, and plasma and then whole blood were administered in the emergency room. After another hour, Marvin’s blood pressure had returned to normal and he no longer appeared pale. While he was in the hospital, Marvin’s urine volume decreased to less than 30 mL/h (<400 mL/day). A blood sample indicated elevated blood levels of urea, creatinine, and uric acid. He also exhibited hyperkalemia and some cardiac arrhythmia, and his arterial pH was <7.35 (below normal). Over the next few days, his red blood cell count decreased and he bruised easily. His jugular veins were distended, and there was some peripheral and pulmonary edema. From the following list, select the conditions that applied to Marvin at this time.
1. hypoxic injury to the kidney
2. increased reabsorption of wastes
3. decreased H+ secretion
4. decreased K+ secretion
5. increased HCO3- reabsorption
6. decreased erythropoietin secretion
a. 1,2,3,4,5,6
b. 2,3,4,5
c. 1,2,3,4
d. 1,2,3,4,6
e. 1,2,6
12. Which of the
following will help compensate for the low pH of the patient in question 11?
a. increased respiration
b. increased HCO3- reabsorption
c. increased H+ secretion
d. All of these are correct.
e. Both a and b are correct.
13. Even though mutations of aquaporin-3 and aquaporin-4 in the collecting duct have not been described in the literature, if mutations occurred that resulted in a reduced number of these aquaporins in the cells of the collecting ducts, how would urine volume and concentration be affected? Would ADH be an effective treatment?13. Renin-secreting tumors are usually found in the kidneys but rarely in other organs, such as the liver, lungs, pancreas, and ovaries. Predict the effects of renin-secreting tumors on blood K+ levels, and explain the effects on action potential conduction in nerves and muscle tissues.
15. Drugs that increase urine volume are called diuretics. Some diuretics inhibit the active transport of Na+ in the nephron. Explain how these diuretic drugs cause increased urine volume.
16. Use your knowledge of kidney physiology answer the following questions.
a. Why did the two infants have high blood Na+ levels and dilute urine?
b. Predict how the infants’ plasma levels of ADH changed during the water deprivation test, given the diagnosis of NDI.
c. Why does an abnormal aquaporin-2 gene result in excessive urine production? d. Predict plasma levels of ADH following a water deprivation test in an individual with central diabetes insipidus.
e. Why is treatment with a thiazide diuretic helpful to patients with NDI?
17. Amanda, an inexperienced runner, competed in her first marathon last spring in Phoenix, Arizona. During the run, the temperature reached 35°C (95°F) with 30% humidity. Amanda drank very little water during the race. When she finished 4½ hours later, she was dizzy and disoriented and had an increased heart rate. She was also very pale. Friends took her to a hospital, where the doctor diagnosed severe dehydration and prescribed IV fluids. Amanda did not urinate until nearly 12 hours later. Explain the physiological responses that resulted in her reduced urine production.
18. A person is suspected of having chronic renal failure. To assess kidney function, urea clearance is measured and found to be very low. Explain what a very low urea clearance indicates for this patient. Compare that with the effect of chronic renal failure on the tendency for the blood K+ level to be higher than normal and the blood Na+ level to be lower than normal.
19. Cystitis is inflammation of the urinary bladder. It typically results from infection by bacteria from outside the body. Are males or females more prone to cystitis? Explain.
20. David’s grandfather suffers from hypertension. His doctor tells him that part of his problem stems from renal arteriosclerosis. Why would this cause hypertension?
21. Mannitol is a sugar that is filtered, but not reabsorbed, by the kidneys. What effect would drinking a solution of mannitol have on the volume of urine produced?
22. The drug Diamox is sometimes used to treat mountain sickness. Diamox inhibits the action of carbonic anhydrase in the proximal convoluted tubule. Polyuria (the elimination of an unusually large volume of urine) is a side effect associated with the medication. Why does polyuria occur?
23. Sylvia is suffering from severe edema in her arms and legs. Her physician prescribes a diuretic (a substance that increases the volume of urine produced). Why might this help alleviate Sylvia’s problem?
24. Why may a person on a low sodium diet develop hyperkalaemia?
25. Why does haemoglobin get excreted in the urine in significant amount while albumin does not?
26. How does aldosterone affect acid-base balance?
27. What would happen if a significant number of glomerular capillaries were clogged, as can happen in someone with very high blood glucose concentrations for a long period of time (as can occur in untreated diabetes mellitus)?
28. What would be the effect of an increase in plasma albumin (the most abundant plasma protein) on glomerular filtration rate (GFR)?
29. Certain types of lung tumors secrete one or more hormones. What would happen to plasma and urine osmolarity and urine volume in a patient with a lung tumor that secretes vasopressin?
30. What effect would an ACE inhibitor have on renin secretion and angiotensin II production? What effect would an angiotensin II receptor blocker (ARB) have on renin secretion and angiotensin II production?
31. What would be the effect of denervation (removal of sympathetic neural input) of the kidneys on Na1 and water excretion?