1. The Urinary System
Dr. Holly Nash-Rule

2. The Urinary System Important functions of the kidneys
Maintain the chemical consistency of blood
Filter many liters of fluid from blood
Send toxins, metabolic wastes, and excess water out of the body
Main waste products
Urea
Uric acid
Creatinin
Dr. Holly Nash-Rule

3. Organs of the Urinary System
Kidneys
Ureters
Urinary bladder
Urethra
Dr. Holly Nash-Rule

4. Location and External Anatomy of Kidneys
Located retroperitoneally
Lateral to T12–L3 vertebrae
Average kidney is 12 cm tall, 6 cm wide, 3 cm thick
Hilum
On concave surface
Vessels and nerves enter and exit
Fibrous capsule surrounds the kidney
Perirenal fat—external to renal capsule
Renal fascia—external to perirenal fat

5. Internal Gross Anatomy of the Kidneys
Frontal section through the kidney
Renal cortex
Renal pyramids
Renal pelvis
Major calicies
Minor calicies
Gross vasculature
Renal arteries branch into segmental arteries
Segmental arteries branch into interlobar arteries
Arcuate arteries branch from interlobar arteries
Dr. Holly Nash-Rule

6. Internal Gross Anatomy of the Kidneys
Nerve supply—renal plexus
A network of autonomic fibers
An offshoot of the celiac plexus
Supplied by sympathetic fibers from
Lowest thoracic splanchnic nerve
First lumbar splanchnis nerve

7. Mechanisms of Urine Production
Filtration
Filtrate of blood leaves kidney capillaries
Reabsorption
Most nutrients, water, and essential ions reclaimed
Secretion
Active process of removing undesirable molecules

8. Nephron Structure
Nephron is composed of
Renal corpuscle
Renal tubule

9. The Nephron Renal corpuscle—first part of nephron
Glomerulus and glomerular capsule
Glomerulus—tuft of capillaries
Capillaries of glomerulus are fenestrated
Glomerular (Bowman’s) capsule
Parietal layer—simple squamous epithelium
Visceral layer—consists of podocytes

10. Filtration Membrane The filtration membrane
Filter that lies between blood in the glomerulus and capsular space
Consists of three layers
Endothelium of the capillary
Slits between foot processes of podocytes
Basement membrane

11. Filtration Membrane Basement membrane and slit diaphragm
Hold back most proteins
Allow through
Water
Ions
Glucose
Amino acids
Urea

12. Renal Tubule Filtrate proceeds to renal tubules from glomerulus
Proximal convoluted tubule
Nephron loop
Descending limb
Thin segment
Thick segment
Distal convoluted tubule
Collecting ducts
Receive urine from several nephrons
Play an important role in conserving body fluids

13. Classes of Nephron Cortical nephrons Juxtamedullary nephrons
85% of nephrons
Juxtamedullary nephrons
15% of nephrons
Contribute to kidney’s ability to concentrate urine

14. Blood Vessels Associated with Nephrons
Nephrons associate closely with two capillary beds
Glomeruli
Peritubular capillaries in cortical nephrons or vasa recta in juxtamedullary nephrons

15. Blood Vessels Associated with Nephrons
Glomeruli
Produce filtrate that becomes urine
Fed and drained by arterioles
Afferent and efferent arteriole
Efferent arteriole has a smaller diameter than afferent arteriole
Generate 1 liter of fluid every 8 minutes
99% of filtrate is resorbed by tubules

16. Blood Vessels Associated with Nephrons
Peritubular capillaries
Arise from the efferent arterioles
Are adapted for absorption
Low-pressure, porous capillaries
All molecules secreted by nephrons into urine are from peritubular capillaries

17. Blood Vessels Associated with Nephrons
Vasa recta
Continue from efferent arterioles of juxtamedullary nephrons
Are thin-walled looping vessels
Descend into the medulla
Are part of the kidney’s urine concentrating mechanism

18. Juxtaglomerular Apparatus
Functions in regulating blood pressure
An area of specialized contact between terminal end of the ascending limb and afferent arteriole
Granular cells—modified smooth muscle cells with secretory granules
Contain the hormone renin
Renin—secreted in response to falling BP in afferent arteriole

19. Juxtaglomerular Apparatus
Macula densa—end of nephron loop
Adjacent to granular cells
Tall, closely packed epithelial cells
Monitor solute concentration in the filtrate
Signal granular cells to secrete renin
Initiates renin-angiotensin mechanism

20. Juxtaglomerular Apparatus
Mesangial cells
Located around base of the glomerulus
Regulated blood flow within the glomerulus
Extraglomerular mesangial cells
Interact with macula densa and granular cells
Help regulate blood pressure

21. Ureters Carry urine from the kidneys to the urinary bladder
Oblique entry into bladder prevents backflow of urine
Histology of ureter
Mucosa—transitional epithelium
Muscularis—two layers
Inner longitudinal layer
Outer circular layer
Adventitia—typical connective tissue

22. Urinary Bladder A collapsible muscular sac Stores and expels urine
Full bladder—spherical
Expands into the abdominal cavity
Empty bladder—lies entirely within the pelvis

23. Urinary Bladder Urachus—closed remnant of the allantois Prostate gland
In males
Lies directly inferior to the bladder
Surrounds the urethra
Dr. Holly Nash-Rule

24. Urinary Bladder Urinary bladder is composed of three layers
Mucosa—transitional epithelium
Thick muscular layer—detrusor muscle
Fibrous adventitia

25. Urethra Epithelium of urethra Transitional epithelium
At the proximal end (near the bladder)
Stratified and pseudostratified columnar—mid urethra (in males)
Stratified squamous epithelium
At the distal end (near the urethral opening)

26. Urethra Internal urethral sphincter External urethral sphincter
Involuntary smooth muscle
External urethral sphincter
Voluntarily inhibits urination
Relaxes when one urinates

27. Urethra In females In males—20 cm in length; three named regions
Length of 3–4 cm
In males—20 cm in length; three named regions
Prostatic urethra
Passes through the prostate gland
Membranous urethra
Through the urogenital diaphragm
Spongy (penile) urethra
Passes through the length of the penis

28. Disorders of the Urinary System
Urinary tract infections
More common in females
Burning sensation during micturition
Renal calculi
Kidney stones
Bladder cancer
3% of cancers—more common in men
Kidney cancer
Arises from epithelial cells of uriniferous tubules

29. The Urinary System Throughout Life
Embryo develops three pairs of kidneys
Pronephros
Mesonephros
Metanephros
Only metanephros persists to become the adult kidneys
Metanephric kidney produces urine by fetal month 3
Contributes to the volume of amniotic fluid

30. Development of the Urinary Organs
Week 8
Gonad
Kidney
Urinary
bladder
Urethra
Anus
Ureter
Rectum
Urogenital
sinus
(developing
urinary
bladder)
Metanephros
(kidney)
Week 7
Figure 24.17c, d

31. The Urinary System Throughout Life
Kidney and bladder function declines with advancing age
Nephrons decrease in size and number
Tubules less efficient at secretion and reabsorption
Filtration declines
Recognition of desire to urinate is delayed
Loss of muscle tone in the bladder

32. The End
Dr. Holly Nash-Rule