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URINARY SYSTEM
URINARY SYSTEM:
OVERVIEW
 Cellular
wastes are toxic if not removed
 Waste removal (from cells) is performed
by blood and lymph
 Elimination of wastes
- Urinary system: H2O, electrolytes,
nitrogenous wastes, drugs
- Respiratory system: CO2 and H2O
- Integumentary system: H2O,
electrolytes
URINARY SYSTEM:
FUNCTIONS
Waste removal
Maintenance of water/electrolyte
balance
Regulation of body fluid volume and
blood pressure
Control of RBC production
ANATOMY:
MACROSCOPIC
Kidneys (2): Filter, reabsorb, secrete
Ureters (2): Convey urine to bladder
Urinary bladder (1): Collects and stores
urine
Urethra (1): Conveys urine out of body
ANATOMY: KIDNEY
Red-brown, bean shaped
Enclosed in thin fibrous capsule
Retroperitoneal
Surrounded by adipose tissue
ANATOMY: KIDNEY continued
Hilum or Hilus (Indentation; Passage of
Vessels, Nerves, etc.)
Renal Cortex (Outer layer)
Renal medulla (Inner layer)
- Renal Pyramids (Conical Masses)
- Renal Columns? (Extensions of Cortical
Tissue between Pyramids)
ANATOMY: KIDNEY continued
Nephrons - Structural & Functional
Units
Renal Papillae (Tip of Pyramid)
Minor Calyces (“Cup” receives Urine
from Collecting Duct/Renal Papillae)
Major Calyces (Receives from Minor C.)
Renal Pelvis (Expanded Proximal End
Ureter)
ANATOMY: URETERS
Hollow tubes ~25cm (10”) in length
Extend from kidneys to urinary bladder
Retroperitoneal location
Muscular walls undergo peristalsis
Flaps of Mucosa at openings into
bladder; prevent backflow
ANATOMY: URINARY BLADDER
Hollow, muscular, distensible sac
In pelvic cavity; subperitoneal
Attached to pelvic floor at trigone
3 layers:
- Inner muscosa (Transitional E.T. allows
filling w/o pressure increase)
- Middle smooth (“detrusor”) muscle
- Outer Adventitia
Serosa (visceral peritoneum) covers only
superior surface
Urinary Bladder
ANATOMY: URETHRA
 Males
- Combined Urogenital System
- Long urethra (~18 cm) in three subdivisions
* Prostatic urethra
* Membranous urethra
* Penile or spongy urethra
 Females
- Separate reproductive and urinary systems
- Short urethra (~4 cm)
Male Urethra
ANATOMY: MICROSCOPIC
 Nephron: Functional unit of kidney
- Approximately 1 million/kidney
- Found Mostly in Renal Cortex
- Consists of :
* Glomerulus
* Renal Tubule (Bowman’s Capsule, Proximal &
Distal Convoluted Tubules + Loop of Henle)
- Collecting Duct – Receives from Multiple
Nephrons
URINE FORMATION
Three Processes:
- Filtration
- Reabsorption
- Secretion
GLOMERULAR
FILTRATION
 Depends on blood pressure (“Pressure
Filtration”)
 Afferent Arteriole carries blood to
Glomerulus
 Small molecules and water move through
Walls of Glomerulus into Bowman’s Capsule
 Fluid is filtrate
 Includes most substances found in urine
 Filtrate is similar to plasma (Water, Glucose,
Ions, Amino Acids, small Nitrogenous Wastes)
TUBULAR REABSORPTION
Selective Movement of molecules from
renal tubule back into blood
PCT Reabsorbs Water, Glucose, Amino
Acids, Ions (up to 80% of filtrate)
“Filtrate” changed to “tubular fluid”
Loop of Henle (& Collecting Duct)
Concentrates Urine/Reabsorbs Water
& Ions
Microvilli for High SA & Absorption
TUBULAR SECRETION
 Primarily in DCT
 Additional Molecules move: Blood  Renal
Tubules
 Active Transport or Osmosis
- Water
- Ions (H+, K+, Na+, Cl-)
- Some drugs, e.g., penicillin
- Creatinine (Nitrogenous waste)
Collecting Duct
Receives from
numerous nephrons
Now officially “urine”
Permeability altered by
ADH
Empties through renal
papillae into minor
calyces
REGULATION OF FLUID
VOLUME
Antidiuretic Hormone (ADH)
- Released when blood volume drops
- Increases permeability of collecting duct to
water
- Results in:
* Increase in Water Reabsorption (decreases
water loss)
* Increase in Blood Volume
URINE PATHWAY
Nephron  Collecting Duct (Out Renal
Papilla of Renal Pyramid)  Minor
Calyx  Major Calyx  Renal Pelvis 
Ureter  Urinary Bladder  Urethra
 Outside Body
COMPOSITION OF URINE:
NORMAL
95% water
pH 6.0 (avg.)
Urea: From proteins
Uric acid: From nucleic acids
Creatinine: From creatine phosphate
Amino acids: A trace
Electrolytes: Vary with diet
REGULATION OF FLUID
VOLUME
Relationship of blood pressure to urine
formation
- Blood pressure is required for glomerular
filtration
- If blood pressure falls below a certain
point, filtration stops
- Results in build-up of nitrogenous wastes
- Aldosterone & Renin, ADH, Plasma
proteins (i.e. albumin)  BP