Chapter 30 - Urinary System Structure & Function

• the kidney functions to filter blood to produce urine
• the kidneys function in the excretion of metabolic waste products and toxins
• the kidneys function to maintain fluid balance which regulates blood volume and BP
• the kidneys regulate solute concentration in the body
• the kidneys function to maintain blood pH
• the kidneys are a multi-lobular structure
• each lobule of the kidney is composed of nephrons, the functional units of the kidney
• the kidneys are located outside the peritoneal cavity in the back of the upper abdomen
• there is one kidney on each side of the vertebral column at the level of the 12th thoracic to 3rd lumbar vertebrae
• the nephron functions in filtration where a filtrate of blood is pushed across the glomerulus into the glomerular capsule to form urine
• the nephron functions in reabsorption where it moves useful molecules from tubules back into blood so they are not excreted in urine
• the nephron functions in secretion where it transports undesirable molecules from blood into tubules so they can be excreted in urine
• the peritubular capillaries are located around the PCT and DCT
• the vasa recta are located around loops of nephron
• the ureters convey urine from the kidney to the bladder and are lined in transitional epithelium with a layer of smooth muscle
• the urinary bladder stores 500 mL to 1 L of urine
• the urethra drains the bladder and controls micturition
• the urethra is shorter in females than in males
• in males, the urethra is the common duct for semen and urine
• the internal urethral sphincter consists of smooth muscle which prevents leakage
• the external urethral sphincter consists of skeletal muscle which functions in voluntary control
• urine is formed by filtering the blood and has an output of 1 to 2 L per day
• normal components of urine:

  • 95% water
  • 5% solutes
  • nitrogenous waste (urea, creatinine, uric acid)
  • electrolytes
  • urobilin
  • hormones
• urea is formed from protein breakdown
• creatinine is formed by creatine-P breakdown
• uric acid is formed from nucleotide breakdown
• urobilin is the yellow pigment in urine from hemoglobin metabolism
• abnormal components of urine:

  • glucose
  • proteins
  • blood cells/hemoglobin
  • bile pigments
  • ketones
• glycosuria is a sign of diabetes
• proteinuria is asign of kidney disease/damage
• hematuria is a sign of inflammation, infection, kidney stones, and trauma
• bilirubinuria is a sign of liver disease
• ketonuria is a sign of starvation, diabetes, and low carb intake
• the specific gravity of urine varies with its concentration of solutes and provides a valuable index of the hydration status and functional ability of the kidneys
• healthy kidneys can produce concentrated urine with a specific gravity of 1.030 to 1.040
• during periods of marked hydration, specific gravity can approach 1.000
• the higher the number of specific gravity, the more dehydrated a person is
• serum creatinine is used in calculating GFR and in estimating the functional capacity of the kidneys
• if the value of serum creatinine doubles, the GFR (and renal function) has fallen approximately 50% of its normal state
• tests for renal function:

  • urinalysis (specific gravity)
  • glomerular filtration rate
  • blood tests (serum creatinine, blood urea nitrogen)
  • cystoscopy
  • ultrasonography
  • radiologic and other imaging studies