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