Urinary System Notes
The Urinary System
 Produces and secretes urine
 Maintains normal blood composition
 Uremia (uremic poisoning) – accumulation of toxic levels of wastes in the blood
Kidneys
• Internal structure
 Cortex—outer layer of “skin”
 Medulla—inner portion
 Pyramids—triangular divisions of medulla
 Papilla—narrow, innermost end of pyramid
 Pelvis—upper end of ureter inside kidney
 Calyces—divisions of renal pelvis
• Nephrons - microscopic units of kidneys:
 Renal corpuscle—Bowman’s capsule with its glomerulus
• Bowman’s capsule—the cup-shaped top
• Glomerulus—network of blood capillaries surrounded by
Bowman’s capsule
 Renal tubule
• Proximal convoluted tubule—extension of ascending limb of loop
of Henle
• Collecting tubule—extension of distal tubule
• Functions
 Excretes toxins and nitrogenous wastes
 Regulates levels of chemicals in blood
 Maintains water balance
 Helps regulate blood pressure via secretion of renin
Formation of Urine
• Three processes that take place in successive parts of nephron
 Filtration— continually in renal corpuscles
 glomerular blood pressure causes water and dissolved substances
to filter out of glomeruli into Bowman’s capsule

Reabsorption—substances move from renal tubules into peritubular
capillaries
 water, nutrients, & ions osmose from proximal tubules
 Sodium and some ions are actively transported back into urine
 Secretion— substances move into urine in distal and collecting tubules
from peritubular capillaries
 hydrogen ions, potassium ions, & certain drugs secreted by active
transport
 ammonia secreted by diffusion
• Posterior pituitary hormone, ADH, decreases urine
Glycosuria – glucose in urine
•
high concentrations of glucose cannot be reabsorbed by the kidney
tubule cells
Ureters
• Narrow long tubes with renal pelvis in kidney & lined with mucous membrane
• Drain urine from renal pelvis to urinary bladder
Urinary Bladder
• Structure
 Elastic muscular organ, capable of great expansion
 Lined with rugae of mucous membrane
• Functions
 Storage of urine before voiding
 Voiding
Urethra
• Structure
 Narrow tube from urinary bladder to exterior
 Lined with mucous membrane
 Urinary meatus - opening of urethra to the exterior
• Functions
 urine from bladder to exterior of body
 semen from the body
Micturition
• Urination or voiding - Passage of urine from body
• Regulatory sphincters
 Internal urethral sphincter (involuntary)
 External urethral sphincter (voluntary)
• Bladder - storage of urine with little increase in pressure
• Emptying reflex
 Initiated by stretch reflex in bladder wall
 Bladder wall contracts
 Internal sphincter relaxes
 External sphincter relaxes and urination occurs
• Urinary retention—urine not voided
• Urinary suppression—no urine produced
• Incontinence—urine voided involuntarily
 May be caused by spinal injury or stroke
 Retention of urine may cause cystitis
• Cystitis—bladder infection
 Overactive bladder— frequent urination
 Called interstitial cystitis
 Amounts voided are small
 Extreme urgency and pain are common