1. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 24 Structure and Function of the Kidney

2. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Functions Kidneys filter the blood Remove water- soluble wastes Help control blood pressure and composition Help maintain red blood cell levels

3. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Three Components of Urine Formation Filtration Reabsorption Secretion

4. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Filtration Happens in the Glomerulus

5. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Glomerular Filtration Glomerular capillary cells sit along a basement membrane Bowman’s capsule epithelium cells sit along the same basement membrane They stand up away from the membrane on pseudopods Fluid filters across the basement membrane and between the pseudopods

6. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Glomerular Filtration Rate Glomerular Filtration Rate = 125 mL/min Discussion: How would it change if you: –Constricted the efferent arterioles? –Constricted the afferent arterioles? –Decreased the blood pressure? Which of the following will increase GFR? –Epinephrine– Prostaglandins –NO– Endothelin

7. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins If 125 mL of Ultrafiltrate Is Formed Each Minute, How Much Is Formed in a Day? Actual urine excretion is 1.5 L a day Proximal convoluted tubule reabsorbs about 60% of nutrients and ions in the urine –Absorbs at an automatic rate –The amount of a solute it can reabsorb is the transport maximum –Nutrients not reabsorbed pass out in the urine Water follows the solutes back into the blood

8. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false: If GFR increases, urine output (UO) will decrease.

9. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer False If GFR increases, it means that fluid is moving more quickly across the basement membrane/through the pseudopods. This means that more fluid will become filtrate and less fluid will be reabsorbed into the blood. If less fluid is reabsorbed, more fluid is left to be excreted (increasing UO).

10. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins When Urine Reaches Distal Tubule Juxtaglomerular cells measure blood flow in the afferent arteriole and urine flow and composition They can release renin, which turns on the Na + /K + ATPase in the distal tubule Na + and water are reabsorbed K + is secreted (Image modified from Bowne, P.S. [2004]. Kidneys tutorial. Used with author’s permission.)

11. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Renin-Angiotensin-Aldosterone Pathway Turns on the Na + /K + ATPase in the distal tubule Na + and water are reabsorbed –Raises blood volume –Does not change blood osmolarity K + is secreted –Lowers blood K +

12. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Discussion: What changes in these variables would turn on the RAA pathway? Blood volume Blood K + Urine volume Urine Na +

13. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Reabsorbing Water Alone to Reduce Blood Osmolality This happens in the inner layer of the kidney, the medulla. The loop of Henle contains ion pumps.

14. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Osmolality (cont.) The NaCl pumped into the medulla makes it salty It is hypertonic to the urine in the collecting duct. Water moves from the collecting duct into the salty medulla and enters the blood

15. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which renal structure reabsorbs water? a.Proximal loop b.Distal loop c.Collecting duct d.Glomerulus

16. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer c.Collecting duct Reabsorption of water occurs in the medulla (the inner layer of the kidney). Na + Cl - leaves the loop of Henle, which makes it hypertonic to the urine in the collecting duct. Water moves from the collecting duct into the blood (reabsorption).

17. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Amount of Water Absorbed Depends on how much can move out of the collecting duct Antidiuretic hormone makes the duct permeable to water

18. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Antidiuretic Hormone (ADH) Makes collecting duct more permeable to water More water can be reabsorbed from the urine into the blood Blood osmolarity decreases

19. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false: Increased ADH decreases urine output (UO).

20. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer True ADH makes the collecting duct more permeable to water, so that more water can leave the duct and be reabsorbed into the blood. More reabsorption means that there is less fluid to be excreted ( ↓ UO).

21. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Scenario A man was given a drug that stopped the ion pumps in the loop of Henl Question: What happened to: –Medulla osmolarity? –Na + levels in the distal convoluted tubule? –Amount of water reabsorbed from the collecting duct? –Renin levels? –Blood K + ?

22. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Removing NaCl and Water from Your Blood Atrial natriuretic peptide and B-type natriuretic peptide –ANP is made by overstretched atria –BNP is made by overworked ventricles ºBoth cause the kidneys to stop reabsorbing NaCl ºThe NaCl and water are lost in the urine, reducing blood volume and decreasing the stretch and workload of the heart

23. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Discussion: What will happen to urine if: –Aldosterone is given? –ADH levels are high? –BNP levels are elevated?

24. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Discussion: A man has severe renal disease Question: Why does he develop –Anemia? –Weak bones?

25. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question What hormone secreted by the kidneys stimulates RBC formation in the bone marrow? a.Renin b.Erythropoietin c.Aldosterone d.Angiotensin

26. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer b.Erythropoietin Erythropoietin literally means “producing erythrocytes/RBCs.” Decreased levels of this hormone lead to anemia; increased levels lead to polycythemia.

27. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Kidney Functions The kidneys clear wastes out of the blood Renal clearance is a measurement of how much blood the kidneys clean in a minute –If the blood contains 1 mg waste/100 mL blood  –If the person produces 1 mL urine per minute  –And if the urine contains 1 mg waste/mL  Question How much blood did the kidney clean in one minute?

28. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Kidney Functions (cont.) What is the percent of kidney function when serum creatinine is: 2 mg/dL? 3 mg/dL? 10 mg/dL? If the kidneys fail, waste builds up in the blood

29. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Kidney Functions (cont.) Kidney function = Normal serum creatinine Current serum creatinine If the kidneys fail, waste builds up in the blood

30. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Discussion What would each of these test results indicate? Severe proteinuria Casts with red blood cells in them Low specific gravity Serum creatinine = 6 mg/dL BUN = 35 mg/dL, serum creatinine = 1.2 mg/dL