1. The Urinary System

2. Outline Introduction – Basic Anatomy & Function Kidneys
Nephrons
JGA Apparatus
Glomerular Filtration
Tubular Reabsorption
Tubular Secretion
Regulation of Urine Volume & Concentration
Renal Clearance
Kidney Stones
Ureter
Urinary Bladder
Urethra

3. Urinary System Organs
Figure 26.1a

4. Urinary System Organs
Figure 26.1a

6. Internal Anatomy
Figure 26.3b

7. Pyelitis & Pyelonephritis
Infection of the renal pelvis and calyces
Infections that affect the entire kidney are pyelonephritis

8. Blood and Nerve Supply
Approximately one-fourth (1200 ml) of systemic cardiac output flows through the kidneys each minute
Arterial flow into and venous flow out of the kidneys follow similar paths

9. The Nephron
Figure 26.4b

12. Renal tubule
Figure 26.4b

13. Renal tubule
Figure 26.4b

14. Capillary Beds
Figure 26.5a

15. Capillary Beds
Figure 26.5a

16. Vascular Resistance in Microcirculation
Figure 26.6

17. Juxtaglomerular Apparatus (JGA)

18. Filtration Membrane
Figure 26.8a

19. Filtration Membrane
Figure 26.8c

20. Mechanism of Urine Formation

21. Glomerular Filtration
Passive, nonselective process where hydrostatic pressure forces fluids and solutes through the membrane
The glomerulus is more efficient than other capillary beds

22. Net Filtration Pressure (NFP)
The pressure responsible for filtrate formation

23. Figure 14.08

24. Glomerular Filtration Rate (GFR)
The total amount of filtrate formed per minute by the kidneys
Factors governing filtration rate at the capillary bed
Normal GFR = 120ml/min

25. Thought Question

26. Renal Autoregulation
Under normal conditions, renal autoregulation maintains a nearly constant glomerular filtration rate
Autoregulation entails two types of control
Myogenic
Tubuloglomerular feedback

27. Myogenic Control
Responds to changes in pressure in the renal blood vessels
Reflects the tendency of vascular smooth muscle to contract when stretched

29. Tubuloglomerular Feedback
Senses changes in the JG apparatus
Directed by the macula densa cells and the JG apparatus
Cells of the macula densa respond to filtrate flow rate and osmotic signals
Intrinsic controls cannot handle extremely low systemic blood pressure

30. Sympathetic Nervous System
When the SNS is at rest:
Renal blood vessels are maximally dilated
Under stress:
Norepinephrine is released by the SNS
Epinephrine is released by the adrenal medulla
Afferent arterioles constrict and filtration is inhibited

31. Figure 14.20

32. Renin-Angiotensin Mechanism
Is triggered when the JG cells release renin
Renin acts on angiotensinogen to release angiotensin I
Angiotensin I is converted to angiotensin II by ACE
Angiotensin II:
As a result, both systemic and glomerular hydrostatic pressure rise

33. Figure 14.21

34. Regulation of GFR
Figure 26.11

35. Other Factors Affecting Glomerular Filtration
Prostaglandins (PGE2 and PGI2)
Nitric oxide
Adenosine
Endothelin

36. Anuria Low urine output
May indicate that glomerular blood pressure is to low to cause filtration
Usually results from situations where the nephrons cease to function

37. Thought Question

38. Tubular Reabsorption
A transepithelial process whereby most tubule contents are returned to the blood
Transported substances move through three membranes
Ca2+, Mg2+, K+, and some Na+ are reabsorbed via paracellular pathways
Organic Nutrients
Water and ions

39. Sodium Reabsorption: Primary Active Transport
About 80% of the energy used for active transport is used for sodium
Sodium reabsorption is almost always by active transport
From there it moves to peritubular capillaries
Na+ reabsorption provides the energy and the means for reabsorbing most other solutes

40. Sodium Reabsorption or Excretion
Controlled by two hormones
Aldosterone – adrenal cortex (mineralocorticoid)
Atrial Natriuretic Peptide (ANP) – produced by the heart

41. Figure 14.22

42. Figure 14.23

43. Reabsorption by PCT Cells
Figure 26.12

44. Figure 14.17

45. Figure 14.17

46. Figure 14.29

47. Figure 14.30

48. Nonreabsorbed Substances
A transport maximum (Tm):
When the carriers are saturated, excess of that substance is excreted
Substances are not reabsorbed if they:
Urea, creatinine, and uric acid are the most important nonreabsorbed substances

49. Tubular Secretion Important for:
Essentially reabsorption in reverse, where substances move from peritubular capillaries or tubule cells into filtrate
Important for:

50. Regulation of Urine Concentration and Volume
Osmolality
Body fluids are measured in milliosmols (mOsm)
The kidneys keep the solute load of body fluids constant at about 300 mOsm
This is accomplished by the countercurrent mechanism

51. Countercurrent Mechanism
By the time the filtrate reaches the loop of Henle, the amount and flow are reduced by 65% but it is still isosmotic
The solute concentration in the loop of Henle ranges from 300 mOsm to 1200 mOsm
Loop of Henle functions as a countercurrent multiplier
Vasa Recta

52. Loop of Henle: Countercurrent Multiplier
Figure 26.14

53. Thought Question

54. Formation of Dilute Urine
Filtrate is diluted in the ascending loop of Henle
Dilute urine is created by allowing this filtrate to continue into the renal pelvis
Sodium and selected ions can be removed by active and passive mechanisms
Urine osmolality can be as low as 50 mOsm (one-sixth that of plasma)

55. Formation of Conc Urine
Antidiuretic hormone (ADH, Vasopressin) inhibits urine output
In the presence of ADH, 99% of the water in filtrate is reabsorbed
ADH is the signal to produce concentrated urine
The kidneys ability to respond depends upon the high medullary osmotic gradient

56. Loop of Henle: Countercurrent Multiplier
Figure 26.14

57. Figure 14.24

62. Diuretics Chemicals that enhance the urinary output include:
Any substance not reabsorbed
Substances that exceed the ability of the renal tubules to reabsorb it
Osmotic diuretics include:

63. Renal Clearance
The volume of plasma that is cleared of a particular substance in a given time
Renal clearance tests are used to:
Determine the GFR
Detect glomerular damage
Follow the progress of diagnosed renal disease
RC = UV/P
RC = renal clearance rate
U = concentration (mg/ml) of the substance in urine
V = flow rate of urine formation (ml/min)
P = concentration of the same substance in plasma

64. Renal Clearance
Measured using inulin, which is not reabsorbed, stored or secreted by the kidneys
Inulin’s renal clearance = GFR

65. Thought Questions
If renal clearance is less than that of inulin what does that mean?
If renal clearance is zero what does that mean?
If renal clearance is greater than that of inulin what does that mean?
If clearance is less than that of inulin the substance is partially reabsorbed
If the clearance value is zero reabsorption is complete or the substance is not filtered
If clearance is greater than that of inulin it means tubulin cells are secreting the substance

66. Table 14.02

67. Figure 14.11

68. Kidney Stones Kidney Stones
Calcium, magnesium or uric acids salts that crystalize in urine
Large stones  blockage  increasing pressure  excruciating pain
Predisposing conditions
Broken up using shock wave lithotripsy

70. Ureters

71. Urinary Bladder

73. Urethra
Figure 26.18a, b

74. Micturition

75. Summary Introduction – Basic Anatomy & Function Kidneys
Nephrons
JGA Apparatus
Glomerular Filtration
Tubular Reabsorption
Tubular Secretion
Regulation of Urine Volume & Concentration
Renal Clearance
Kidney Stones
Ureter
Urinary Bladder
Urethra