Urinary System and Kidney Anatomy

Organs of the Urinary System

• Left and Right Kidneys
  • Filter blood to produce urine.
• Left and Right Ureters
  • Carry urine to the urinary bladder.
• Urinary Bladder
  • Stores urine until urination.
• Urethra
  • Expels urine from the body in males and females.
  • In males, it also expels semen during ejaculation.

Basic Functions of the Urinary System

• Constantly filters blood to maintain blood composition and remove wastes.
  • Excess fluid, molecules, and wastes are collected in urine.
  • By filtering blood, the kidneys can regulate:
    • Blood ion/electrolyte concentrations
      • Regulates elimination of Na^+, K^+, Cl^-, HCO3 ^-, Ca2^+, etc., in urine.
    • Blood/body fluid pH
      • Regulates elimination of H^+ and HCO3 ^- in urine.
    • Blood volume
      • Lower blood volume by losing more water to urine.
      • Increase blood volume by preventing water loss to urine.
• Storage and Elimination of Urine from the body
  • Via ureters, urinary bladder, and urethra.

The Kidneys

• Basic functions
  • Constantly filter blood to maintain blood composition and remove wastes.
  • Excess fluid, molecules, and wastes are collected in urine.
• Location of the Kidney
  • In the abdominal cavity
    • Retroperitoneal
  • Left Kidney
    • Between the 10th and 12th ribs.
  • Right Kidney
    • Slightly lower than the left kidney to make room for the liver.
  • Surrounded by a layer of adipose tissue called perirenal/perinephric fat.
• Internal Gross Anatomy
  • Hilum
    • Indentation on the medial side of the kidney.
    • Where blood vessels, nerves, lymphatics, and renal pelvis are attached.
  • Renal Sinus
    • Space in the center of the kidney containing adipose tissue and urine collection tubes.
  • The kidney is surrounded by a thin fibrous capsule/renal capsule made of dense connective tissue.
  • Two distinct regions of tissue:
    • The Renal Cortex
      • An outer layer of kidney tissue that is lighter in color.
    • The Renal Medulla
      • Inner, darker layer.
      • Contains cone-shaped structures called renal pyramids.
        • The base of each pyramid faces the cortex, and the point or renal papilla of each pyramid faces internally.
        • Each papilla drains the final urine product into a urine collection tube called a minor calyx.
      • Between each renal pyramid is a region of cortex tissue that dips down into the medulla called a renal column.
  • Urine Collection Tubes
    • Tubes in the center of the kidney that drain urine from the renal papillae into the ureters:
      • Minor Calyces
        • Singular = minor calyx
        • Attached to the renal papilla, drain urine from the renal papilla.
        • One or more merge to form a major calyx.
      • Major Calyces
        • Singular = major calyx
        • Formed by the merging of one or more minor calyces.
        • Drain urine from minor calyces into renal pelvis.
        • All the major calyces merge to form the renal pelvis.
      • Renal Pelvis
        • Flat, funnel-shaped tube in the center of the kidney that bends inferiorly out of the hilum of the kidney into the ureter.
  • Blood Vessels of the Kidney
    • The kidney filters the entire blood volume about 6 times every day, so blood flow through the kidney is essential to understanding its function.
      • Renal Artery
        • Carries blood into the kidney and immediately branches into 5 segmental arteries.
      • The segmental arteries branch into interlobar arteries that pass between the renal pyramids.
      • The interlobar arteries branch into arcuate arteries that arch over the bases of the renal pyramids between the cortex and medulla.
      • The arcuate arteries branch into small arteries that radiate out into the cortex called cortical radiate arteries.
      • In the cortex, branching off the cortical radiate arteries are small afferent arterioles, which carry blood to a ball of capillaries called the glomerulus or the glomerular capillaries.
        • The glomerulus is the blood filter in the kidney and filters fluid from the blood into the functional unit of the kidney called the nephron.
      • Blood is drained from the glomerulus by the efferent arterioles into capillaries surrounding the nephron called peritubular capillaries or vasa recta capillaries.
      • These nephron capillaries drain into cortical radiate veins adjacent to the cortical radiate arteries.
      • The cortical radiate veins drain into arcuate veins adjacent to the arcuate arteries.
      • The arcuate veins drain into interlobar veins adjacent to interlobar arteries.
      • There are no segmental veins; the interlobar veins drain directly into the renal vein.