1. The Urinary System: Modified by Dr. Par Mohammadian25
The Urinary System: Modified by Dr. Par Mohammadian

2. Kidney Functions
Regulating total water volume and total solute concentration in water
Regulating ECF ion concentrations
Ensuring long-term acid-base balance
Removal of metabolic wastes, toxins, drugs
Endocrine functions
Renin - regulation of blood pressure
Erythropoietin - regulation of RBC production
Activation of vitamin D
Gluconeogenesis during prolonged fasting

3. Urinary System Organs
Kidneys - major excretory organs
Ureters - transport urine from kidneys to urinary bladder
Urinary bladder - temporary storage reservoir for urine
Urethra transports urine out of body

4. Figure 25.1 The urinary system.
Hepatic veins (cut)
Esophagus (cut)
Inferior vena cava
Renal artery
Adrenal gland
Renal hilum
Aorta
Renal vein
Kidney
Iliac crest
Ureter
Rectum (cut)
Uterus (part of female
reproductive system)
Urinary
bladder
Urethra
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5. Kidney Anatomy
Retroperitoneal, in the superior lumbar region; ~ T12 to L5
Right kidney crowded by liver  lower than left
Adrenal (suprarenal) gland atop each kidney
Convex lateral surface, concave medial surface; vertical renal hilum leads to renal sinus
Ureters, renal blood vessels, lymphatics, and nerves enter and exit at hilum
12th rib

6. 2. Simple Cuboidal Epithelium
Description: Single layer of
cubelike cells with large, spherical central nuclei.
Simple cuboidal epithelial cells
Nucleus
Function: Secretion and absorption.
Basement membrane
Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface.
Connective tissue
Photomicrograph: Simple cuboidal epithelium in kidney tubules (430x).
Figure 4.2b
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7. Layers of surrounding supportive tissue
Kidney Anatomy
Layers of surrounding supportive tissue
Renal fascia
Anchoring outer layer of dense fibrous connective tissue
Perirenal fat capsule
Fatty cushion
Fibrous capsule
Prevents spread of infection to kidney

8. Figure 25.2a Position of the kidneys against the posterior body wall.
Anterior
Inferior
vena cava
Aorta
Peritoneum
Peritoneal cavity
(organs removed)
Supportive
tissue layers
Renal
vein
• Renal fascia
anterior
posterior
Renal
artery
• Perirenal
fat capsule
• Fibrous
capsule
Body of
vertebra L2
Body wall
Posterior
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9. Internal Anatomy Renal cortex Renal medulla
Granular-appearing superficial region
Renal medulla
Composed of cone-shaped medullary (renal) pyramids
Pyramids separated by renal columns
Inward extensions of cortical tissue

10. Internal Anatomy Papilla
Tip of pyramid; releases urine into minor calyx
Lobe
Medullary pyramid and its surrounding cortical tissue; ~ 8/kidney
Renal pelvis
Funnel-shaped tube continuous with ureter
Minor calyces
Drain pyramids at papillae
Major calyces
Collect urine from minor calyces
Empty urine into renal pelvis

11. Figure 25.3 Internal anatomy of the kidney.
Urine flow: Renal pyramid  minor calyx  major calyx  renal pelvis  ureter
Renal
hilum
Renal cortex
Renal medulla
Major calyx
Papilla of
pyramid
Renal pelvis
Minor calyx
Ureter
Renal pyramid in
renal medulla
Renal column
Fibrous capsule
Photograph of right kidney, frontal section
Diagrammatic view
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12. Figure 25.4a Blood vessels of the kidney.
Cortical radiate
vein
Cortical radiate
artery
Arcuate vein
Kidneys cleanse blood; adjust its composition  rich blood supply
Renal arteries deliver ~ ¼ (1200 ml) of cardiac output to kidneys each minute
Arterial flow into and venous flow out of kidneys follow similar paths
Nerve supply via sympathetic fibers from renal plexus
Arcuate artery
Interlobar vein
Interlobar artery
Segmental arteries
Renal vein
Renal artery
Renal pelvis
Ureter
Renal medulla
Renal cortex
Frontal section illustrating major blood vessels

13. (no segmental veins!)

14. Nephrons Structural and functional units that form urine
> 1 million per kidney
Two main parts
Renal corpuscle
Renal tubule
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15. Two parts of renal corpuscle
Glomerulus
Knot of capillaries; fenestrated endothelium  highly porous  allows filtrate formation
Glomerular capsule (Bowman's capsule)
Cup-shaped, hollow structure surrounding glomerulus
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16. Glomerular capsule: parietal layer
Renal cortex
Renal medulla
Renal pelvis
Glomerular capsule: parietal layer
Basement
membrane
Ureter
Podocyte
Kidney
Fenestrated endothelium
of the glomerulus
Renal corpuscle
• Glomerular capsule
Glomerular capsule: visceral layer
• Glomerulus
Distal
convoluted
tubule
Apical
microvilli
Mitochondria
Highly infolded basolateral
membrane
Proximal
convoluted
tubule
Proximal convoluted tubule cells
Cortex
Apical side
Medulla
Basolateral side
Thick
segment
Thin segment
Distal convoluted tubule cells
Nephron loop
• Descending limb
• Ascending limb
Nephron loop (thin-segment) cells
Collecting
duct
Principal
cell
Intercalated cell
Collecting duct cells
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17. Renal Corpuscle Glomerular capsule
• Glomerulus
Glomerular capsule
Parietal layer - simple squamous epithelium
Visceral layer - branching epithelial podocytes
Extensions terminate in foot processes that cling to basement membrane
Filtration slits between foot processes allow filtrate to pass into capsular space

18. Renal Tubule Three parts
Proximal convoluted tubule (Functions in reabsorption and secretion) Confined to cortex
Proximal  closest to renal corpuscle
Nephron loop (loop of Henle)
Descending and ascending limbs
Distal convoluted tubule
Distal  farthest from renal corpuscle
Confined to cortex

19. Collecting Ducts Two cell types Principal cells Intercalated cells
Sparse, short microvilli
Maintain water and Na+ balance
Intercalated cells
Cuboidal cells; abundant microvilli; two types
A and B; both help maintain acid-base balance of blood
Receive filtrate from many nephrons
Run through medullary pyramids  striped appearance
Fuse together to deliver urine through papillae into minor calyces

20. Cortical radiate artery Distal convoluted tubule
Cortical nephron
Juxtamedullary nephron
• Short nephron loop
• Glomerulus further from the cortex-medulla junction
• Efferent arteriole supplies peritubular capillaries
• Long nephron loop
• Glomerulus closer to the cortex-medulla junction
• Efferent arteriole supplies vasa recta
Renal
corpuscle
Glomerulus
(capillaries)
Efferent
arteriole
Cortical radiate vein
Cortical radiate artery
Glomerular
capsule
Afferent arteriole
Collecting duct
Proximal
convoluted
tubule
Distal convoluted tubule
Afferent
arteriole
Efferent
arteriole
Classes of Nephrons
Peritubular
capillaries
Cortical nephrons—85% of nephrons; almost entirely in cortex
Juxtamedullary nephrons
Long nephron loops deeply invade medulla
Ascending limbs have thick and thin segments
Important in production of concentrated urine
Ascending
limb of
nephron loop
Cortex-medulla
junction
Arcuate vein
Kidney
Arcuate artery
Vasa recta
Nephron loop
Descending
limb of
nephron loop
Renal tubules associated with two capillary beds
Glomerulus
Peritubular capillaries
Juxtamedullary nephrons also associated with
Vasa recta

21. Juxtaglomerular Complex (JGC)
One per nephron
Involves modified portions of
Distal portion of ascending limb of nephron loop
Important in regulation of rate of filtrate formation and blood pressure
Three cell populations:
Macula densa, granular cells, extraglomerular mesangial cells
1) Macula densa
Chemoreceptors; sense NaCl content of filtrate
2) Granular cells (juxtaglomerular, or JG cells)
Enlarged, smooth muscle cells of arteriole
Secretory granules contain enzyme renin
Mechanoreceptors; sense blood pressure in afferent arteriole
3) Extraglomerular mesangial cells
Between arteriole and tubule cells
Interconnected with gap junctions
May pass signals between macula densa and granular cells

22. Figure 25.8 Juxtaglomerular complex (JGC) of a nephron.
capsule
Glomerulus
Foot
processes
of podocytes
Efferent
arteriole
Parietal layer
of glomerular
capsule
Podocyte cell body
(visceral layer)
Capsular
space
Afferent
arteriole
Red blood cell
Efferent
arteriole
Proximal
tubule cell
Juxtaglomerular
complex •
Macula densa
cells
of the ascending
limb of nephron loop
Lumens of
glomerular
capillaries
• Extraglomerular
mesangial cells
• Granular
cells
Endothelial cell
of glomerular
capillary
Afferent
arteriole
Glomerular mesangial
cells
Juxtaglomerular complex
Renal corpuscle
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23. Mechanisms of Urine Formation
Urine formation and adjustment of blood composition involves three major processes
Glomerular filtration
Tubular reabsorption
Secretion

24. Ureters
- Slender tubes that convey urine from the kidneys to the bladder
- Ureters enter the base of the bladder through the posterior wall
This closes their distal ends as bladder pressure increases and prevents backflow of urine into the ureters
- Ureters have a trilayered wall:
transitional epithelial mucosa
Smooth muscle muscularis
Fibrous connective tissue adventitia
Ureters actively propel urine to the bladder via response to smooth muscle stretch

25. Figure 4.3f Epithelial tissues.
Transitional epithelium
Description: Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamouslike, depending on degree of organ stretch.
Transitional epithelium
Function: Stretches readily, permits stored urine to distend urinary organ.
Basement membrane
Location: Lines the ureters, bladder, and part of the urethra.
Connective tissue
Photomicrograph: Transitional epithelium lining the bladder, relaxed state (360x); note the bulbous, or rounded, appearance of the cells at the surface; these cells flatten and elongate when the bladder fills with urine.

26. Urinary Bladder
Smooth, collapsible, muscular sac that temporarily stores urine
It lies retroperitoneally on the pelvic floor posterior to the pubic symphysis
Trigone – triangular area outlined by the openings for the ureters and the urethra
Clinically important because infections tend to persist in this region
The bladder wall has three layers:
Transitional epithelial mucosa
A thick muscular layer
A fibrous adventitia
The bladder is distensible and collapses when empty

27. Urinary Bladder
Figure 25.18a, b

28. Urethra Muscular tube that: Drains urine from the bladder
Conveys it out of the body
Sphincters keep the urethra closed when urine is not being passed:
Internal urethral sphincter – involuntary sphincter at the bladder-urethra junction
External urethral sphincter – voluntary sphincter surrounding the urethra as it passes through the urogenital diaphragm

29. Urethra
1. The female urethra is tightly bound to the anterior vaginal wall
Its external opening lies anterior to the vaginal opening and posterior to the clitoris
2. The male urethra has three named regions:
Prostatic urethra – runs within the prostate gland
Membranous urethra – runs through the urogenital diaphragm
Spongy (penile) urethra – passes through the penis and opens via the external urethral orifice