1. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Chapter 26 The Urinary System

2. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Functions of the Kidneys  Filter 200 liters of fluid from blood daily  Allow the body to remove in urine:  Toxins  Metabolic wastes  Excess ions  Allow needed substances to return to the blood  Regulate:  Volume & constituents of blood  Maintain proper balance between:  Water and salts  Acids and bases

3. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Other Renal Functions  Gluconeogenesis:  During prolonged fasting  Production of hormones:  Rennin:  Helps regulate blood pressure  Erythropoietin:  Stimulates RBC production  Activation of Vitamin D:  Metabolize vitamin D to its active form

4. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Other Organs of the Urinary System  Urinary bladder:  Provides a temporary storage reservoir for urine  Paired ureters:  Transport urine from the kidneys to the bladder  Urethra:  Transports urine from the bladder out of the body

5. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Organs of The Urinary System

6. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Kidney Location and External Anatomy  Kidneys lie in the superior lumbar region (retroperitoneal)  Right kidney is lower than the left (crowded by liver)  Lateral surface is convex; the medial is concave  Renal hilum (vertical cleft):  Leads to the renal sinus  Exit point for:  Ureters  Renal blood vessls  Lymphatic vessels  Nerves

7. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Layers of Tissue Supporting the Kidney  Renal capsule:  Fibrous capsule that prevents kidney infection  Adipose capsule:  Fatty mass that cushions the kidneys  Helps attach them to the body wall PLAY InterActive Physiology ®: Anatomy Review, page 4

8. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Internal Anatomy (Frontal Section)  Cortex:  The light colored, granular superficial region  Medulla:  Exhibits cone-shaped medullary (renal) pyramids separated by columns  The medullary pyramid and its surrounding capsule constitute a lobe  Renal pelvis:  Flat funnel-shaped tube  Lateral to the hilus within the renal sinus

9. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings PLAY InterActive Physiology ®: Anatomy Review, page 6 Internal Anatomy  Minor & major calyces:  Small & large branches of the renal pelvis  Collect urine draining from papillae ( papillae minor calyces major calyces)  Major calyces empty urine into the pelvis  Urine flows through the pelvis and the ureters to the bladder

10. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Internal Anatomy Figure 25.3b

11. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Blood and Nerve Supply  About one-fourth (1200 ml) of the cardiac output flows through the kidneys each minute  Arterial & venous flow into & out of the kidneys follow similar paths  Nerve supply is via the renal plexus  Vascular Pathway: Note the absence of segmental veins on the venous side

12. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Nephron  Nephrons are:  The structural and functional units that form urine  They consist of:  Glomerulus  A tuft of capillaries associated with a renal tubule  Glomerular (Bowman’s) capsule  Blind, cup-shaped end of a renal tubule  Completely surrounds the glomerulus PLAY

13. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Nephron  Renal corpuscle:  Refers to both the glomerulus & its Bowman’s capsule  Glomerular endothelium:  Fenestrated epithelium  Allows solute-rich, (virtually protein-free), filtrate to pass from the blood into the glomerular capsule PLAY InterActive Physiology ®: Urinary: Anatomy Review, pages 7-9

14. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Nephron Figure 25.4a, b

15. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Anatomy of the Glomerular Capsule  The external parietal layer is a structural layer  The internal visceral layer consists of:  Modified, branching epithelial cells called podocytes  Podocytes terminate in foot processes  Openings between foot processes form filtration slits  Slits allow filtrate to pass into the capsular space PLAY InterActive Physiology ®: Anatomy Review, page 10

16. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Renal Tubule Has three major parts:  Proximal convoluted tubule (PCT):  Composed of cuboidal cells  Cells have:  Numerous microvilli  Functions include:  Reabsorbs water and solutes from filtrate  Secretes substances into filtrate

17. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Renal Tubule  Loop of Henle:  A hairpin-shaped loop of the renal tubule  Has descending and ascending limbs  Descending limb:  Proximal part is similar to and continuous with the PCT  Remaining part is the thin segment (simple squamous cells)  Ascending limb is:  The thick segment (cuboidal cells)  Distal convoluted tubule (DCT):  Cuboidal cells without microvilli  Function more in secretion than reabsorption

18. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Renal Tubule Figure 25.4b

19. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Collecting Ducts  Two important cell types are found here:  Intercalated cells  Cuboidal cells with microvilli  Help maintain the body’s acid-base balance  Principal cells  Cuboidal cells without microvilli  Help maintain the body’s water & Na + balance PLAY InterActive Physiology ®: Anatomy Review, pages 12–15, 17–19

20. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Nephrons  Two types of nephrons:  Cortical nephrons:  85% of nephrons in kidneys  Located in the cortex  Juxtamedullary nephrons:  Located at the cortex-medulla junction  Their loops of Henle deeply invade the medulla  Have extensive thin segments than cortical nephrons  Involved in the production of concentrated urine

21. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Nephron Anatomy Figure 25.5a

22. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Capillary Beds of the Nephron  Every nephron has two capillary beds:  Glomerulus (produces filtrate)  Peritubular (Reclaims most of that filtrate)  Each glomerulus is:  Fed by an afferent arteriole  Drained by an efferent arteriole

23. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Capillary Beds of the Nephron  Blood pressure in the glomerulus is high  Glomerular pressure is high because:  Arterioles are high-resistance vessels  Afferent arterioles have larger diameters than efferent arterioles  Fluids and solutes are forced out of the blood throughout the entire length of the glomerulus

24. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Capillary Beds  Peritubular beds are:  Low-pressure, porous capillaries  Arise from efferent arterioles  Cling to adjacent renal tubules  Readily absorb water and solutes  Empty into nearby venules (venous system)  Vasa recta:  Long, straight efferent arterioles  Found in the juxtamedullary nephrons  Paralleling the longest loop of Henle

25. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Capillary Beds Figure 25.5a

26. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Juxtaglomerular Apparatus (JGA)  Is a nephron region of contact between:  The most distal part of the ascending limb of loop of Henle, &  The afferent (sometimes efferent) arteriole  Both the limb & arteriole are modified at the point of contact  The arteriole walls have cells called:  Juxtaglomerular (JG) or granular cells that:  Are enlarged smooth muscle cells  Have secretory granules containing renin  Act as mechanoreceptors  Sense afferent arteriole blood pressure

27. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Juxtaglomerular Apparatus (JGA)  The ascending limb of loop of Henle have tall, closely packed group of cells called:  Macula densa that:  Lie adjacent to JG cells of the afferent arteriole  Function as chemoreceptors  They respond to changes in filtrate NaCl content  A third group of cells making the JGA are called:  Extraglomerular Mesangial cells that:  Are interconnected by gap junctions  May pass signals between macula densa & granualr cells PLAY

28. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Juxtaglomerular Apparatus (JGA) Figure 25.6

29. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Filtration Membrane  Filter membrane is a filter that lies between:  The blood, and  The interior of the glomerular capsule  It is borous allowing free passage of water & solutes  It is composed of three layers  Fenestrated endothelium of the glomerular capillaries  Visceral membrane of the glomerular capsule (made of podocytes)  Basement membrane composed of fused basal laminae of the two other layers

30. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Filtration Membrane Figure 25.7a

31. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Filtration Membrane PLAY InterActive Physiology ®: Anatomy Review, page 11 Figure 25.7c

32. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Mechanisms of Urine Formation  The kidneys filter the body’s entire plasma volume 60 times each day  The filtrate:  Contains all plasma components except protein  Then loses water, nutrients, and essential ions  Ultimately becomes urine  The urine contains:  Metabolic wastes  Unneeded substances

33. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Mechanisms of Urine Formation  Urine formation & adjust- ment of blood composition involve three major processes: 1. Glomerular filtration 2. Tubular reabsorption 3. Tubular secretion Figure 25.8

34. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Glomerular Filtration  The glomerulus is more efficient than other capillary beds because:  Its filtration membrane is more permeable  Its blood pressure is higher  It has a higher net filtration pressure  Plasma proteins:  Are not filtered (kept in)  Maintain osmotic pressure of the blood

35. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Net Filtration Pressure (NFP)  The pressure responsible for filtrate formation  NFP equals:  The difference between Glomerular Hydrostatic Pressure (HP g ) and the Osmotic Pressure of Glomerular Blood (OP g ) combined with the Capsular hydrostatic pressure (HP c ) NFP = HP g – (OP g + HP c )

36. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Glomerular Filtration Rate (GFR)  Is the amount of filtrate formed by the kidney per minute  It changes with changes in glomerular blood pressure  It is directly proportional to the NFP  Factors governing filtration rate at the capillary bed:  Total surface area available for filtration  Filtration membrane permeability  Net filtration pressure

37. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Glomerular Filtration Rate (GFR) Figure 25.9

38. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Glomerular Filtration  If the GFR is too high:  Needed substances cannot be reabsorbed quickly enough  Loss of needed substances in the urine  If the GFR is too low:  Everything is reabsorbed  Wastes are accumulated in circulation

39. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Glomerular Filtration  Three mechanisms control the GFR  Renal autoregulation (intrinsic system)  Neural controls (extrinsic system)  Hormonal mechanism (renin-angiotensin system)

40. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Intrinsic Controls  Under normal conditions:  Renal autoregulation maintains a nearly constant glomerular filtration rate  Autoregulation involves two types of control  Myogenic:  Responds to changes in pressure in renal blood vessels  Flow-dependent tubuloglomerular feedback:  Senses changes in the juxtaglomerular apparatus

41. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Extrinsic Controls  When the sympathetic nervous system is at rest:  Renal blood vessels are maximally dilated  Autoregulation mechanisms prevail  Under stress:  The sympathetic N.S. releases norepinephrine  The adrenal medulla releases epinephrine  Afferent arterioles constrict inhibiting filtration  The sympathetic nervous system also:  Stimulates the renin-angiotensin mechanism PLAY

42. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Renin-Angiotensin Mechanism  Is triggered when the JG cells release renin  Renin converts (enzymatically) angiotensinogen (plasma globulin) to angiotensin I  Angiotensin converting enzyme (ACE) ( lung capillary endothelium) converts angiotensin I to angiotensin II  Angiotensin II stabilizes:  Systemic blood pressure  Extracellular fluid voulme