1. Chapter 26
Urinary System

2. Urinary System Functions
Filtering of blood
Regulation of
blood volume
concentration of blood solutes
pH of extracellular fluid
blood cell synthesis
Synthesis of Vitamin D

3. Urinary System Anatomy:

5. Location and External Anatomy of Kidneys
Renal capsule
Surrounds each kidney
Perirenal fat
Engulfs renal capsule and acts as cushioning
Renal fascia
Anchors kidneys to abdominal wall
Hilum
Renal artery and nerves enter and renal vein and ureter exit kidneys
Location
Lie behind peritoneum on posterior abdominal wall on either side of vertebral column
Lumbar vertebrae and rib cage partially protect
Right kidney slightly lower than left

6. Internal Anatomy of Kidneys:
Cortex: Outer area
Renal columns
Medulla: Inner area
Renal pyramids
Calyces
Major: Converge to form pelvis
Minor: Papillae extend
Nephron: Functional unit of kidney
Juxtamedullary
Cortical

8. The Nephron:

9. Histology of the Nephron

10. Internal Anatomy of Kidneys
Renal corpuscle
Bowman’s capsule
Parietal layer
Visceral layer
Glomerulus
Network of capillaries
Arterioles
Afferent
Blood to glomerulus
Efferent
Drains
Tubules
Proximal (convoluted) tubule
Loops of Henle
Descending limb
Ascending limb
Distal (convoluted) tubules
Collecting ducts

11. Renal Corpuscle

12. Kidney Blood Flow:

13. Ureters and Urinary Bladder
Tubes through which urine flows from kidneys to urinary bladder
Urinary bladder
Stores urine
Urethra
Transports urine from bladder to outside of body
Difference in length between males and females
Sphincters
Internal urinary
External urinary

14. Ureters and Urinary Bladder

17. Urine Formation

18. Filtration Filtration Filtration membrane Filtration pressure
Renal filtrate
Plasma minus blood cells and blood proteins
Most (99%) reabsorbed
Filtration membrane
Fenestrated endothelium, basement membrane and pores formed by podocytes
Filtration pressure
Responsible for filtrate formation
Glomerular capillary pressure (GCP) minus capsule pressure (CP) minus colloid osmotic pressure (COP)
Changes caused by glomerular capillary pressure

21. Filtration Pressure

24. Tubular Reabsorption Reabsorption Substances transported
Passive transport
Active transport
Cotransport
Specialization of tubule segments
Substances transported
Active transport moves Na+ across nephron wall
Other ions and molecules moved by cotransport
Passive transport moves water, urea, lipid-soluble, nonpolar compounds

26. Reabsorption in Proximal Nephron:

27. Reabsorption in Loop of Henle

28. Reabsorption in Loop of Henle

30. Tubular Secretion
Substances enter proximal or distal tubules and collecting ducts
H+, K+ and some substances not produced in body are secreted by countertransport mechanisms

31. Secretion of Hydrogen and Potassium

32. Urine Production In ascending limb of loop of Henle
Na+, Cl-, K+ transported out of filtrate
Water remains
In distal tubules and collecting ducts
Water movement out regulated by ADH
If absent, water not reabsorbed and dilute urine produced
If ADH present, water moves out, concentrated urine produced
In Proximal tubules
Na+ and other substances removed
Water follows passively
Filtrate volume reduced
In descending limb of loop of Henle
Water exits passively, solute enters
Filtrate volume reduced 15%

33. Filtrate and Medullary Concentration Gradient

34. Medullary Concentration and Urea Cycling

35. Urine Concentration Mechanism
When large volume of water consumed
Eliminate excess without losing large amounts of electrolytes
Response is kidneys produce large volume of dilute urine
When drinking water not available
Kidneys produce small volume of concentrated urine
Removes waste and prevents rapid dehydration

36. Urine Concentrating Mechanism I:

37. Urine Concentrating Mechanism II:

39. Hormonal Mechanisms ADH Renin Atrial natriuretic hormone Aldosterone
Secreted by posterior pituitary
Increases water permeability in distal tubules and collecting ducts
Aldosterone
Produced in adrenal cortex
Affects Na+ and Cl- transport in nephron and collecting ducts
Renin
Produced by kidneys, causes production of angiotensin II
Atrial natriuretic hormone
Produced by heart when blood pressure increases
Inhibits ADH production
Reduces ability of kidney to concentrate urine

40. Effect of ADH on Nephron

41. Aldosterone Effect on Distal Tubule

42. Autoregulation and Sympathetic Stimulation
Involves changes in degree of constriction in afferent arterioles
As systemic BP increased, afferent arterioles constrict and prevent increase in renal blood flow
Sympathetic stimulation
Constricts small arteries and afferent arterioles
Decreases renal blood flow

43. Clearance and Tubular Load
Plasma clearance
Volume of plasma cleared of a specific substance each minute
Used to estimate GFR
Used to calculate renal plasma flow
Used to determine which drugs or other substances excreted by kidney
Tubular load
Total amount of substance that passes through filtration membrane into nephrons each minute
Normally glucose is almost completed reabsorbed

44. Tubular Maximum Tubular maximum
Maximum rate at which a substance can be actively absorbed
Each substance has its own tubular maximum

45. Urine Flow and Micturition Reflex
Hydrostatic pressure forces urine through nephron
Peristalsis moves urine through ureters
Micturition reflex
Stretch of urinary bladder stimulates reflex causing bladder to contract, inhibiting urinary sphincters
Higher brain centers can stimulate or inhibit reflex

46. Micturition Reflex

47. Effects of Aging on Kidneys
Gradual decrease in size of kidney
Decrease in kidney size leads to decrease in renal blood flow
Decrease in number of functional nephrons
Decrease in renin secretion and vitamin D synthesis
Decline in ability of nephron to secrete and absorb

48. Kidney Dialysis