Urinary system

• Urinary System


  The body's vital system for filtering and expelling waste
• Functions of the Urinary System

  • Filter blood
  • Process waste and excess ions
  • Eliminate wastes, toxins, and drugs
  • Regulate blood volume and chemical makeup
  • Produce renin to regulate blood pressure
  • Produce erythropoietin to stimulate red blood cell production
  • Convert vitamin D to its active form
• The Kidneys


  • Maintain purity and constancy of internal fluids
  • Located in the superior lumbar region
  • Right kidney positioned slightly lower than left
  • Size of a large bar of soap
  • Adrenal gland atop each kidney
  • Enclosed in a fibrous capsule and perirenal fat capsule
  • Renal cortex and renal medulla
  • Renal pyramids and renal columns
  • Renal pelvis and calyces
  • Renal artery, segmental arteries, arcuate arteries, and cortical radiate arteries
• Nephrons


  • Structural and functional units of the kidneys
  • Glomerulus - knot of capillaries
  • Renal tubule - with Bowman's capsule, podocytes, and foot processes
  • Proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct
  • Cortical nephrons and juxtamedullary nephrons
  • Afferent arteriole and efferent arteriole
  • Peritubular capillaries
• Ureters


  • Slender tubes 25-30 cm long and 6 mm in diameter
  • Run behind the peritoneum from the renal hilum to the posterior aspect of the bladder
• The ureters play an active role in urine transport
• The urinary bladder and urethra are also part of the urinary system
• Understanding the anatomy and physiology of the urinary system is crucial for nurses to provide the best patient care
• Cortical nephrons


  Most nephrons are located almost entirely within the cortex
• Juxtamedullary nephrons


  Nephrons situated next to the cortex-medullary junction, with loops of Henle dipping deep into the medulla
• Afferent arteriole


  The "feeder vessel" that arises from a cortical radiate artery
• Efferent arteriole


  Receives blood that has passed through the glomerulus
• Peritubular capillaries


  Arise from the efferent arteriole that drains the glomerulus
• Ureters


  • They play an active role in urine transport
• The ureters are two slender tubes each 25 to 30 cm (10 to 12 inches) long and 6 mm (1/4 inch) in diameter
• Location of ureters


  Each ureter runs behind the peritoneum from the renal hilum to the posterior aspect of the bladder, which it enters at a slight angle
• Function of ureters

  Carry urine from the kidneys to the bladder through contraction of the smooth muscle layers in their walls that propel urine into the bladder by peristalsis, and is prevented from flowing back by small valve-like folds of bladder mucosa that flap over the ureter openings
• Urinary bladder


  A smooth, collapsible, muscular sac that stores urine temporarily
• The urinary bladder is located retroperitoneally in the pelvis just posterior to the symphysis pubis
• Function of urinary bladder


  The detrusor muscles and the transitional epithelium both make the bladder uniquely suited for its function of urine storage
• Trigone


  The smooth triangular region of the bladder base outlined by the three openings, where infections tend to persist
• Detrusor muscles


  The three layers of smooth muscle in the bladder wall, collectively called the detrusor muscle
• Transitional epithelium


  The special type of epithelium that makes up the bladder mucosa
• Urethra


  A thin-walled tube that carries urine by peristalsis from the bladder to the outside of the body
• Internal urethral sphincter


  A thickening of the smooth muscle at the bladder-urethral junction that forms an involuntary sphincter to keep the urethra closed when urine is not being passed
• External urethral sphincter


  A second sphincter fashioned by skeletal muscle as the urethra passes through the pelvic floor, which is voluntarily controlled
• The female urethra is about 3 to 4 cm (1 1/2 inches) long, with the external orifice lying anteriorly to the vaginal opening
• The male urethra is approximately 20 cm (8 inches) long and has three named regions: the prostatic, membranous, and spongy (penile) urethrae, opening at the tip of the penis
• Urine formation

  1. Glomerular filtration - Water and solutes smaller than proteins are forced through the capillary walls and pores of the glomerular capsule into the renal tubule

  2. Tubular reabsorption - Water, glucose, amino acids, and needed ions are transported out of the filtrate into the tubule cells and then enter the capillary blood

  3. Tubular secretion - Hydrogen, potassium, creatinine, and drugs are removed from the peritubular blood and secreted by the tubule cells into the filtrate
• In 24 hours, the kidneys filter some 150 to 180 liters of blood plasma through their glomeruli into the tubules
• In 24 hours, only about 1.0 to 1.8 liters of urine are produced
• Components of urine

  Urine contains nitrogenous wastes and unneeded substances
• Freshly voided urine is generally clear and pale to deep yellow
• When formed, urine is sterile and slightly aromatic, but if allowed to stand, it takes on an ammonia odor caused by the action of bacteria on the urine solutes
• Urine pH is usually slightly acidic (around 6), but changes in body metabolism and certain foods may cause it to be much more acidic or basic
• The specific gravity of urine usually ranges from 1.001 to 1.035, whereas the specific gravity of pure water is 1.0
• Solutes normally found in urine include sodium and potassium ions, urea, uric acid, creatinine, ammonia, bicarbonate ions, and various other ions
• Micturition (voiding)


  1. Ordinarily, the bladder continues to collect urine until about 200 ml have accumulated

  2. At about this point, stretching of the bladder wall activates stretch receptors

  3. Impulses transmitted to the sacral region of the spinal cord and then back to the bladder via the pelvic splanchnic nerves cause the bladder to go into reflex contractions

  4. As the contractions become stronger, stored urine is forced past the internal urethral sphincter into the upper part of the urethra

  5. Because the lower external sphincter is skeletal muscle and voluntarily controlled, we can choose to keep it closed or it can be relaxed so that urine is flushed from the body
• The function of the kidney decreases with age but is still able to carry out excretory functions unless a disease process intervenes
• Complaints of urinary urgency and frequency are common in older people because the capacity of the bladder and its ability to completely empty diminish with age