2. The Urinary System
Chapter 26

3. Functions of the Urinary System
Removal of metabolic wastes (especially nitrogenous wastes e.g. urea & uric acid).
Water balance (and therefore blood pressure).
Control of electrolyte balance.
Control of pH.
Removal of toxins.

4. Anatomy of the Urinary System
The Kidneys: the functional heart of the urinary system.
The Ureters: pipeline from the kidneys to the bladder.
The Urinary Bladder: holding tank of urine.
The Urethra: avenue of relief
(word of the day “micturition” = voiding the bladder)

5. Urinary System Components

6. The Kidneys
Location: retroperitoneal against the dorsal wall of the abdominal cavity. The right kidney is slightly lower than the left.
Size & weight: approximately 150 grams (about 5 ounces) each and 12 cm x 10 cm x 4 cm.
Shaped like a bean (or are beans shaped like kidneys?)

7. The Position of the Kidneys
Figure 26–2

8. Gross Anatomy of the Urinary System
Figure 26–3

9. The Structure of the Kidney
Figure 26–4

10. Blood Supply to Kidneys
Kidneys receive 20–25% of total cardiac output
ml of blood flows through kidneys each minute
Kidney receives blood through renal artery

11. Blood Supply to the Kidneys
Figure 26–5

12. A slice of kidney
Cortex
Medulla
Glomeruli
Capsule

13. The Nephron: functional unit of the kidney
Interlobular artery
Afferent Arteriole
Glomeruli

14. Functional Anatomy of Nephron and Collecting System
Figure 26–6

15. Renal Corpuscle

16. The Nephron and Collecting System
Table 26–1

17. Filtrate & Urine flow

18. Cortical and Juxtamedullary Nephrons
Figure 26–7

19. The renal corpuscle and the Juxtaglomerular apparatus

20. The renal filtration membrane: Podocytes and fenestrated capillaries

21. Filtration slits
Pedicles

22. The filtration membrane

23. An Overview of Urine Formation
Figure 26–9 (Navigator)

24. Blood pressure drops due to peripheral resistance

25. Filtration pressures: NFP must be positive for U2P

26. GFR GFR is “Glomerular Filtration Rate”.
It is directly proportional to NFP.
It is a measurement of FLOW in milliliters per minute (ml/min).
If NFP drops more than 15% below 10 mmHg, GFR goes to 0.
If NFP goes up less than 30% above normal, the kidneys can handle it without major compensatory mechanisms kicking in.

27. Creatinine Clearance Test
Is used to estimate GFR
A more accurate GFR test uses inulin:
which is not metabolized

28. Response to Reduction in GFR
Figure 26–11

29. Tubular reabsorption
Reabsorption of filtered solutes occurs in the Proximal Convoluted Tubules.
Most solutes are reabsorbed by secondary active transport with Na+. Does this look familiar?

30. 4 Types of Carrier-Mediated Transport
Facilitated diffusion
Active transport
Cotransport
Countertransport

31. The Transport Maximum (Tm)
If nutrient concentrations rise in tubular fluid:
reabsorption rates increase until carrier proteins are saturated
Concentration higher than transport maximum:
exceeds reabsorptive abilities of nephron
some material will remain in the tubular fluid and appear in the urine
Determines the renal threshold

32. Transport Activities at the PCT
Figure 26–12 (Navigator)

33. Reabsorption of sodium

34. Reabsorption of glucose

35. Reabsorption of electrolytes and water

36. Reabsorption of ions in the Loop of Henle

37. Reabsorption 60–70% of filtrate volume produced at glomerulus:
is reabsorbed before tubular fluid reaches loop of Henle

38. The Loop of Henle
Reabsorbs about 1/2 of water, and 2/3 of sodium and chloride ions remaining in tubular fluid by the process of countercurrent exchange

39. Countercurrent Multiplication
Is exchange that occurs between 2 parallel segments of loop of Henle:
the thin, descending limb
the thick, ascending limb

40. Countercurrent
Refers to exchange between tubular fluids moving in opposite directions:
fluid in descending limb flows toward renal pelvis
fluid in ascending limb flows toward cortex

41. Multiplication Refers to effect of exchange:
increases as movement of fluid continues

42. Parallel Segments of Loop of Henle
Are very close together, separated only by peritubular fluid
Have very different permeability characteristics

43. Formation of dilute urine

44. Countercurrent Multiplication and Concentration of Urine
Figure 26–13a (Navigator)

45. Countercurrent Multiplication and Concentration of Urine
Figure 26–13b, c

46. Na+—K+/2 Cl— Transporter
Each cycle of pump carries ions into tubular cell:
1 sodium ion
1 potassium ion
2 chloride ions

47. Tubular Fluid at DCT Arrives with osmotic concentration of 100 mOsm/L:
1/3 concentration of peritubular fluid of renal cortex
Rate of ion transport across thick ascending limb:
is proportional to ion’s concentration in tubular fluid

48. Regional Differences More Na+ and Cl— are pumped into medulla:
at start of thick ascending limb
than near cortex
Regional difference in ion transport rate:
causes concentration gradient within medulla

49. Normal Maximum Solute Concentration
Of peritubular fluid near turn of loop of Henle:
1200 mOsm/L

50. The Concentration Gradient of the Medulla
2/3 (750 mOsm/L) from Na+ and Cl—:
pumped out of ascending limb
Remainder from urea

51. Urea and the Concentration Gradient (1 of 2)
Thick ascending limb of loop of Henle, DCT, and collecting ducts:
are impermeable to urea
As water is reabsorbed:
concentration of urea rises

52. Urea and the Concentration Gradient (2 of 2)
Tubular fluid reaching papillary duct:
contains 450 mOsm/L urea
Papillary ducts are permeable to urea:
concentration in medulla averages 450 mOsm/L

53. 2 Benefits of Countercurrent Multiplication
Efficiently reabsorbs solutes and water:
before tubular fluid reaches DCT and collecting system
Establishes concentration gradient:
that permits passive reabsorption of water from tubular fluid in collecting system

54. In the collecting duct

55. Reabsorption in the Distal Convoluted Tubule & Collecting Duct

56. Differences between Solute Composition in Urine and Plasma
Table 26–2

57. Summary of tubular reabsorption/excretion

58. Renal autoregulation

59. Compensatory Mechanisms to maintain GFR

60. A Pyelogram
Figure 26–17

61. After the Kidneys: the bladder & urethra

62. Male
Figure 26–18a

63. v
Female
Figure 26–18c

64. The Human Bladder: It can hold a maximum of 800 – 1000 ml!

65. Histology

66. Physical characteristics of Urine
Color - Clear to deep yellow, almost rusty, depending on concentration.
Odor - Fresh urine is slightly aromatic, stale urine smells like downtown Tacoma on a Sunday morning.
pH – range of 4.5 – 8 depending on diet. High protein leads to low pH (acid ash diet), vegetarian (alkaline ash) diet leads to high pH. Heavy vomiting and bacterial infection can also lead to alkaline urine.
Specific gravity – Normal range is – Distilled water has a s.g. of Anything solutes cause the specific gravity of a liquid to go up. Concentrated urine has a higher s.g. than dilute urine.

67. General Characteristics of Normal Urine
Table 26–5

68. Typical Values Obtained from Standard Urinalysis
Table 26–6

69. Composition of Urine Normal Urea Uric acid Creatinine Na K Phosphates
Sulfates
Bicarbonate Ca Mg
Abnormal
Glucose “glycosuria”
Proteins “proteinuria” or
“albuminuria”
Ketones “ketonuria”
Hemoglobin “hemoglobinuria”
Erythrocytes “hematuria”
Bile pigments “bilirubinura”
Leukocytes “pyruia”
Abnormally low output = oliguria
No output = anuria
Abnormally high output = polyuria
Diuresis = increased urine output
Diuretic = substance that leads to diuresis

70. A Summary of Renal Function
Figure 26–16a

71. A Summary of Renal Function
Figure 26–16b

72. The Micturition Reflex
Figure 26–20 (Navigator)

73. Incontinence Is the inability to control urination voluntarily
May be caused by trauma to internal or external urethral sphincter

74. Age-Related Changes in Urinary System
Decline in number of functional nephrons
Reduction in GFR
Reduced sensitivity to ADH
Problems with micturition reflex

75. Stages of Renal Disease
Stage 1: signs of kidney damage w/ GFR ≥ 90.
Stage 2: signs of kidney damage w/ GFR 60 – 89.
Stage 3: GFR 30 – 59.
Stage 4: GFR 15 – 29.
Stage 5: < 15

76. Renal Clearance RC = UV/P
The volume of plasma that is cleared of a particular substance in a given time (usually one minute).
RC = UV/P
U = concentration of the substance in urine (mg/ml)
V = flow rate of formation (ml/min)
P = concentration of the substance in the plasma (mg/ml)
High renal clearance values means that the substance is being effectively cleared, low values means that more is being reabsorbed. For some solutes low is good (glucose should be 0). For others, high RC would be expected (creatinine should be complete, urea should be about 80%).

77. The Excretory System
Includes all systems with excretory functions that affect body fluids composition:
urinary system
integumentary system
respiratory system
digestive system

78. Kidney stones
Renal Calculi

79. “Well Mr. Osborne, I don’t think that it’s kidney stone after all”