ANAPHY

• Functions of the urinary system


  • Filter blood
  • Dispose of waste products in urine (nitrogenous wastes, toxins, drugs, excess ions, water, etc.)
  • Regulate blood pressure (produce renin)
  • Stimulate red blood cell production (produce erythropoietin)
  • Convert vitamin D to its active form

  
• Organs of the urinary system

  • Kidneys
  • Ureters
  • Urinary bladder
  • Urethra

  
• Kidneys

  • Located against the dorsal body wall in a retroperitoneal position
  • Situated at the level of the T12 to L3 vertebrae
  • Right kidney is slightly lower than the left

  
• Renal hilum

  Medial indentation where several structures enter or exit the kidney (ureters, renal blood vessels, and nerves)

  
• An adrenal gland sits atop each kidney
• Protective layers of the kidney

  • Fibrous capsule
  • Perirenal fat capsule
  • Renal fascia

  
• Regions of the kidney

  • Renal cortex
  • Renal medulla (renal pyramids, renal columns)
  • Renal pelvis (calyces)

  
• Blood supply to the kidneys


  • One-quarter of the total blood supply of the body passes through the kidneys each minute
  • Renal artery divides into segmental arteries, interlobar arteries, arcuate arteries, and cortical radiate arteries
  • Cortical radiate veins, arcuate veins, interlobar veins, and renal vein return blood to the inferior vena cava

  
• Nephron


  Structural and functional units of the kidneys, each kidney contains over a million nephrons

  
• Parts of the renal corpuscle


  • Glomerulus
  • Glomerular (Bowman's) capsule

  
• Subdivisions of the renal tubule


  • Proximal convoluted tubule
  • Nephron loop (loop of Henle)
  • Distal convoluted tubule

  
• Types of nephrons


  • Cortical nephrons
  • Juxtamedullary nephrons
• Glomerulus

  • Specialized for filtration, high pressure forces fluid and solutes out of blood and into the glomerular capsule
• Peritubular capillary beds


  • Arise from the efferent arteriole of the glomerulus, low-pressure and porous, adapted for absorption instead of filtration
• Urine formation


  1. Glomerular filtration

  2. Tubular reabsorption

  3. Tubular secretion

  
• Glomerular filtration


  Nonselective passive process where water and solutes smaller than proteins are forced through glomerular capillary walls
• Tubular reabsorption

  Peritubular capillaries reabsorb useful substances from the renal tubule cells (water, glucose, amino acids, ions)
• Tubular secretion


  Materials move from the blood of the peritubular capillaries into the renal tubules to be eliminated in filtrate (hydrogen ions, potassium ions, creatinine)
• Nitrogenous waste products are poorly reabsorbed and tend to remain in the filtrate and are excreted from the body in the urine (urea, uric acid, creatinine)
• In 24 hours, about 1.0 to 1.8 liters of urine are produced
• Filtrate


  Contains everything that blood plasma does (except proteins and blood cells)
• Urine


  Contains substances that were not reabsorbed or secreted
• Creatinine


  Produced by muscles from the breakdown of creatine
• One of the sources of ATP is by getting the phosphate group in Creatine phosphate and attaching it to Adenosine diphosphate to become ATP
• Secretion of substances


  • Getting rid of substances not already in the filtrate
  • Removing drugs and excess ions
  • Maintaining acid-base balance of blood
• Materials left in the renal tubule move toward the ureter

  
• Nitrogenous waste products


  • Urea—end product of protein breakdown
  • Uric acid—results from nucleic acid metabolism
  • Creatinine—associated with creatine metabolism in muscles
• Filtrate


  Contains everything that blood plasma does (except proteins)
• Urine


  What remains after the filtrate has lost most of its water, nutrients, and necessary ions through reabsorption
• Urine characteristics


  • Clear and pale to deep yellow in color
  • Yellow color is normal and due to the pigment urochrome (from the destruction of hemoglobin, done by liver) and solutes
  • Dilute urine is a pale, straw color
  • Sterile at the time of formation
  • Slightly aromatic, but smells like ammonia with time
  • Slightly acidic (pH of 6)
  • Specific gravity of 1.001 to 1.035
• Solutes normally found in urine

  • Sodium and potassium ions
  • Urea, uric acid, creatinine
  • Ammonia
  • Bicarbonate ions
• Solutes NOT normally found in urine


  • Glucose (can be an indication of diabetes)
  • Blood proteins
  • Red blood cells
  • Hemoglobin
  • WBCs (plus) (can be a sign of infection)
  • Bile
• Abnormal Urinary Constituents


  • Glucose (Glycosuria)
  • Proteins (Proteinuria)
  • Pus (WBCs and bacteria) (Pyuria)
  • RBCs (Hematuria)
  • Hemoglobin (Hemoglobinuria)
  • Bile pigment (Bilirubinuria)
• Ureters


  • Slender tubes 25–30 cm (10–12 inches) attaching the kidney to the urinary bladder
  • Continuous with the renal pelvis
  • Enter the posterior aspect of the urinary bladder
  • Run behind the peritoneum
  • Peristalsis aids gravity in urine transport
• Urinary bladder

  • Smooth, collapsible, muscular sac situated posterior to the pubic symphysis
  • Stretchable
  • Stores urine temporarily
  • Trigone—triangular region of the urinary bladder base based on three openings (two from the ureters and one to the urethra)
  • In males, the prostate surrounds the neck of the urinary bladder
  • Wall has three layers of smooth muscle collectively called the detrusor muscle
  • Mucosa made of transitional epithelium
  • Walls are thick and folded in an empty urinary bladder
  • Can expand significantly without increasing internal pressure
  • Capacity of about 500 ml, capable of holding twice that amount

  
• Urethra


  • Thin-walled tube that carries urine from the urinary bladder to the outside of the body by peristalsis
  • Females—carries only urine
  • Males—carries urine and sperm
  • Release of urine is controlled by two sphincters (internal urethral sphincter and external urethral sphincter)
  • Females: 3 to 4 cm long
  • Males: 20 cm long
  • Females—anterior to the vaginal opening
  • Males—travels through the prostate and penis (prostatic urethra, membranous urethra, spongy urethra)
• Micturition


  1. Bladder collects urine to 200 ml

  2. Stretch receptors transmit impulses to the sacral region of the spinal cord

  3. Impulses travel back to the bladder via the pelvic splanchnic nerves to cause bladder contractions

  4. When contractions become stronger, urine is forced past the involuntary internal sphincter into the upper urethra

  5. Urge to void is felt

  6. The external sphincter is voluntarily controlled, so micturition can usually be delayed
• Blood composition


  • Depends on diet, cellular metabolism, and urine output
  • Kidneys have four roles: excreting nitrogen-containing wastes, maintaining water balance, maintaining electrolyte balance, ensuring proper blood pH

  
• Water occupies three main fluid compartments


  Intracellular fluid (ICF), Extracellular fluid (ECF), Plasma (blood)
• Regulation of water intake and output


  1. Water intake must equal water output

  2. Sources of water intake: ingested foods and fluids, water produced from metabolic processes

  3. Thirst mechanism is the driving force for water intake

  4. Sources of water output: lungs, perspiration, feces, urine