26 The Urinary System

1. 26 The Urinary System

2. An Introduction to the Urinary System • Learning Outcomes • 26-1 Identify the components of the urinary system, and describe the functions it performs. • 26-2 Describe the location and structural features of the kidneys, identify major blood vessels associated with each kidney, trace the path of blood flow through a kidney, describe the structure of a nephron, and identify the functions of each region of the nephron and collecting system. • 26-3 Describe the basic processes responsible for urine formation.

3. An Introduction to the Urinary System • Learning Outcomes • 26-4 Describe the factors that influence glomerular filtration pressure and the rate of filtrate formation. • 26-5 Identify the types and functions of transport mechanisms found along each segment of the nephron, explain the role of countercurrent multiplication, describe hormonal influence on the volume and concentration of urine, and describe the characteristics of a normal urine sample.

4. An Introduction to the Urinary System • Learning Outcomes • 26-6 Describe the structures and functions of the ureters, urinary bladder, and urethra, discuss the voluntary and involuntary regulation of urination, and describe the micturition reflex. • 26-7 Describe the effects of aging on the urinary system. • 26-8 Give examples of interactions between the urinary system and other organ systems studied so far.

5. Figure 26-1 An Introduction to the Urinary System Kidney Produces urine Ureter Transports urinetoward theurinary bladder Urinary bladder Temporarily storesurine priorto elimination Urethra Conducts urine toexterior; in males,transports semenas well Anterior view

6. 26-1 Urinary System Functions • Three Functions of the Urinary System • Excretion • Removal of organic wastes from body fluids • Elimination • Discharge of waste products • Homeostatic regulation • Of blood plasma volume and solute concentration

7. 26-1 Urinary System Functions • Functions of the Urinary System • Kidneys — organs that produce urine • Urinary tract — organs that eliminate urine • Ureters (paired tubes) • Urinary bladder (muscular sac) • Urethra (exit tube) • Urination or micturition — process of eliminating urine • Contraction of muscular urinary bladder forces urine through urethra, and out of body

8. 26-1 Urinary System Functions • Homeostatic Functions of the Urinary System • Regulates blood volume and blood pressure • By adjusting volume of water lost in urine • Releasing erythropoietin and renin • Regulates plasma ion concentrations • Sodium, potassium, and chloride ions (by controlling quantities lost in urine) • Calcium ion levels (through synthesis of calcitriol)

9. 26-1 Urinary System Functions • Homeostatic Functions of Urinary System • Helps stabilize blood pH • By controlling loss of hydrogen ions and bicarbonate ions in urine • Conserves valuable nutrients • By preventing excretion while excreting organic waste products • Assists liver • In detoxifying poisons

10. 26-2 The Kidneys • The Kidneys • Are located on either side of vertebral column • Left kidney lies superior to right kidney • Superior surface capped by adrenal gland • Position is maintained by: • Overlying peritoneum • Contact with adjacent visceral organs • Supporting connective tissues

11. 26-2 The Kidneys • Each Kidney Is Protected and Stabilized • By three concentric layers of connective tissue • Fibrous capsule • A layer of collagen fibers • Covers outer surface of entire organ • Perinephric fat capsule • A thick layer of adipose tissue • Surrounds renal capsule • Renal fascia • A dense, fibrous outer layer • Anchors kidney to surrounding structures

12. Figure 26-2a The Position of the Kidneys Renalvein Renalartery Parietalperitoneum Aorta Stomach Externaloblique Pancreas Ureter Spleen Leftkidney Vertebra Connectivetissue layers Fibrous capsule Perinephric fat Renal fascia Quadratuslumborum Psoasmajor Inferiorvena cava A superior view of a transverse section at the level indicated in part (a)

13. Figure 26-2b The Position of the Kidneys Left kidney Renal arteryand vein Diaphragm Adrenalgland 11th and12th ribs Right kidney Lumbar(L1) vertebra Ureter Inferiorvena cava Iliac crest Abdominalaorta Urinarybladder Urethra A posterior view of the trunk

14. Figure 26-3 The Gross Anatomy of the Urinary System Esophagus (cut) Diaphragm Left adrenal gland Inferior venacava Celiac trunk Left kidney Right adrenalgland Left renal artery Right kidney Left renal vein Hilum Superior mesentericartery Left ureter Quadratuslumborummuscle Abdominal aorta Iliacus muscle Left common iliacartery Psoas majormuscle Gonadal arteryand vein Peritoneum (cut) Rectum (cut) Urinary bladder Anterior view

15. 26-2 The Kidneys • Typical Adult Kidney • Is about 10 cm long, 50.5 cm wide, and 3 cm thick (4 in.  2.2 in.  1.2 in.) • Weighs about 150 g (5.25 oz) • Hilum • Point of entry for renal artery and renal nerves • Point of exit for renal veinandureter

16. 26-2 The Kidneys • Sectional Anatomy of the Kidneys • Renal sinus • Internal cavity within kidney • Lined by fibrous renal capsule • Bound to outer surfaces of structures in renal sinus • Stabilizes positions of ureter, renal blood vessels, and nerves

17. 26-2 The Kidneys • Renal Cortex • Superficial portion of kidney in contact with renal capsule • Reddish brown and granular • Renal Pyramids • 6 to 18 distinct conical or triangular structures in renal medulla • Base abuts cortex • Tip (renal papilla) projects into renal sinus

18. 26-2 The Kidneys • Renal Columns • Bands of cortical tissue separate adjacent renal pyramids • Extend into medulla • Have distinct granular texture

19. 26-2 The Kidneys • Renal Lobe • Consists of: • Renal pyramid • Overlying area of renal cortex • Adjacent tissues of renal columns • Produces urine

20. 26-2 The Kidneys • Renal Papilla • Ducts discharge urine into minor calyx, a cup-shaped drain • Major Calyx • Formed by four or five minor calyces

21. 26-2 The Kidneys • Renal Pelvis • Large, funnel-shaped chamber • Consists of two or three major calyces • Fills most of renal sinus • Connected to ureter, which drains kidney

22. Figure 26-4a The Structure of the Kidney Renal cortex Renal medulla Renal pyramid Inner layer offibrous capsule Renal sinus Connection tominor calyx Adipose tissuein renal sinus Minor calyx Major calyx Renal pelvis Hilum Renal lobe Renal papilla Renal columns Ureter Fibrous capsule A diagrammatic view of a frontalsection through the left kidney

23. Figure 26-4b The Structure of the Kidney Renal cortex Renal medulla Renal pyramids Renal sinus Renal pelvis Hilum Major calyx Minor calyx Ureter Renal papilla Renal columns Renal lobe Fibrouscapsule A frontal section of the leftkidney

24. 26-2 The Kidneys • Nephrons • Microscopic, tubular structures in cortex of each renal lobe • Where urine production begins

25. 26-2 The Kidneys • Blood Supply to the Kidneys • Kidneys receive 20%–25% of total cardiac output • 1200 mL of blood flows through kidneys each minute • Kidney receives blood through renal artery

26. 26-2 The Kidneys • Segmental Arteries • Receive blood from renal artery • Divide into interlobar arteries • Which radiate outward through renal columns between renal pyramids • Supply blood to arcuate arteries • Which arch along boundary between cortex and medulla of kidney

27. 26-2 The Kidneys • Afferent Arterioles • Branch from each cortical radiate artery (also called interlobular artery) • Deliver blood to capillaries supplying individual nephrons

28. 26-2 The Kidneys • Cortical Radiate Veins • Also called interlobular veins • Deliver blood to arcuate veins • Empty into interlobar veins • Which drain directly into renal vein

29. 26-2 The Kidneys • Renal Nerves • Innervate kidneys and ureters • Enter each kidney at hilum • Follow tributaries of renal arteries to individual nephrons

30. 26-2 The Kidneys • Sympathetic Innervation • Adjusts rate of urine formation • By changing blood flow and blood pressure at nephron • Stimulates release of renin • Which restricts losses of water and salt in urine • By stimulating reabsorption at nephron

31. Figure 26-5a The Blood Supply to the Kidneys Corticalradiateveins Corticalradiatearteries Interlobararteries Cortex Segmentalartery Medulla Adrenalartery Renalartery Renalvein Interlobarveins Arcuateveins Arcuatearteries A sectional view, showing major arteries and veins

32. Figure 26-5b The Blood Supply to the Kidneys Glomerulus Cortical radiate vein Afferentarterioles Cortical radiate artery Arcuate artery Corticalnephron Arcuate vein Juxtamedullarynephron Renalpyramid Interlobar vein Interlobar artery Minor calyx Circulation in a single renal lobe

33. Figure 26-5c The Blood Supply to the Kidneys Renal artery Renal vein Segmental arteries Interlobar veins Interlobar arteries Arcuate arteries Arcuate veins Cortical radiate veins Cortical radiate arteries Afferent arterioles Venules NEPHRONS Peritubularcapillaries Glomerulus Efferentarteriole A flowchart of renal circulation

34. 26-2 The Kidneys • The Nephron • Consists of renal tubule and renal corpuscle • Renal tubule • Long tubular passageway • Begins at renal corpuscle

35. 26-2 The Kidneys • The Nephron • Renal corpuscle • Spherical structure consisting of: • Glomerular capsule (Bowman’s capsule) • Cup-shaped chamber • Capillary network (glomerulus)

36. 26-2 The Kidneys • Glomerulus • Consists of 50 intertwining capillaries • Blood delivered via afferent arteriole • Blood leaves in efferent arteriole • Flows into peritubular capillaries • Which drain into small venules • And return blood to venous system

37. 26-2 The Kidneys • Filtration • Occurs in renal corpuscle • Blood pressure • Forces water and dissolved solutes out of glomerular capillaries into capsular space • Produces protein-free solution (filtrate) similar to blood plasma

38. 26-2 The Kidneys • Three Functions of the Renal Tubule • Reabsorb useful organic nutrients that enter filtrate • Reabsorb more than 90% of water in filtrate • Secrete waste products that failed to enter renal corpuscle through filtration at glomerulus

39. 26-2 The Kidneys • Segments of the Renal Tubule • Located in cortex • Proximal convoluted tubule (PCT) • Distal convoluted tubule (DCT) • Separated by nephron loop (loop of Henle) • U-shaped tube • Extends partially into medulla

40. Figure 26-6 The Functional Anatomy of a Representative Nephron and the Collecting System NEPHRON Proximal convoluted tubule Distal convoluted tubule • Secretion of ions, acids,drugs, toxins Reabsorption of water,ions, and allorganic nutrients • Variable reabsorption ofwater, sodium ions, andcalcium ions (underhormonal control) Renal tubule Capsular space Glomerulus Efferent arteriole Afferent arteriole Glomerular capsule Ascendinglimb of loop ends Descendinglimb of loop begins Renal corpuscle Production of filtrate Thickascendinglimb Thindescendinglimb Descendinglimb Ascendinglimb KEY Filtrate Water reabsorption Nephron loop Variable water reabsorption Further reabsorption of water(descending limb) and bothsodium and chlorideions (ascending limb) Solute reabsorptionor secretion Variable solute reabsorptionor secretion

41. Table 26-1 The Organization of the Nephron and Collecting System

42. 26-2 The Kidneys • Organization of the Nephron • Traveling along tubule, filtrate (tubular fluid) gradually changes composition • Changes vary with activities in each segment of nephron ANIMATION Kidney Function: Urinary System Structure

43. 26-2 The Kidneys • Each Nephron • Empties into the collecting system • A series of tubes that carries tubular fluid away from nephron • Collecting ducts • Receive fluid from many nephrons • Each collecting duct: • Begins in cortex • Descends into medulla • Carries fluid to papillary duct that drains into a minor calyx

44. Figure 26-6 The Functional Anatomy of a Representative Nephron and the Collecting System COLLECTING SYSTEM KEY Filtrate Water reabsorption Variable water reabsorption Solute reabsorptionor secretion Variable solute reabsorptionor secretion Collecting duct Collecting duct Variable reabsorptionof water andreabsorption orsecretion of sodium,potassium, hydrogenand bicarbonate ions Papillary duct Delivery of urineto minor calyx Minorcalyx

45. Table 26-1 The Organization of the Nephron and Collecting System

46. 26-2 The Kidneys • Cortical Nephrons • 85% of all nephrons • Located mostly within superficial cortex of kidney • Nephron loop (Loop of Henle) is relatively short • Efferent arteriole delivers blood to a network of peritubular capillaries • Juxtamedullary Nephrons • 15% of nephrons • Nephron loops extend deep into medulla • Peritubular capillaries connect to vasa recta

47. Figure 26-7a The Locations and Structures of Cortical and Juxtamedullary Nephrons Corticalnephron Cortex Juxtamedullarynephron Medulla Collecting duct Papillary duct Renal papilla Minor calyx The general appearance and location ofnephrons in the kidneys

48. Figure 26-7b The Locations and Structures of Cortical and Juxtamedullary Nephrons Peritubularcapillaries Efferentarteriole Afferentarteriole Distalconvolutedtubule Renalcorpuscle Collectingduct Peritubularcapillaries Nephron loop The circulation to a cortical nephron

49. Figure 26-7c The Locations and Structures of Cortical and Juxtamedullary Nephrons Peritubularcapillaries Proximalconvolutedtubule (PCT) Glomerulus Distalconvolutedtubule (DCT) Vasa recta Collectingduct Vasa recta Nephronloop The circulation to ajuxtamedullary nephron

50. 26-2 The Kidneys • The Renal Corpuscle • Each renal corpuscle is 150–250 µm in diameter • Glomerular capsule • Is connected to initial segment of renal tubule • Forms outer wall of renal corpuscle • Encapsulates glomerular capillaries • Glomerulus • Knot of capillaries