Urinary System: Kidneys Overview

Location of the Kidneys

  • Shape and Size:
    • Bean-shaped organs, approximately 11 to 14 cm in length, 6 cm wide, and 4 cm thick
  • Anatomical Position:
    • Located in the posterior wall of the abdominal cavity
    • Right kidney is lower than the left due to the liver\'s position
    • Positioned between vertebrae T12 and L3
  • Protection:
    • Upper portion protected by the 11th and 12th ribs
    • Surrounded by connective tissue and abdominal fat

Structure of the Kidneys

  • Major Structures:

    • Renal Hilum:
    • Entry point for blood vessels and nerves into the kidney (circled in red)
    • Renal Pelvis:
    • Internal cavity where blood vessels and nerves branch off (circled in purple)

  • Layers of the Kidney:

    • Cortex:
    • Outer layer of the kidney (green box)
    • Medulla:
    • Inner layer containing renal pyramids (green box)
    • Triangular structures with tips known as renal papillae
    • Project into renal pelvis via minor and major calyx (circled in purple)
    • Separated by renal columns (grayish color)

  • Renal Capsule:

    • Tough outer protection made of collagen fibers (yellow color)

Nephrons

  • Functional Unit of Kidney:
    • Microscopic tubular structures responsible for urine production
  • Blood Supply:
    • Kidneys receive ~25% of cardiac output (1,200 mL/min)

Blood Supply to the Kidneys

  • Renal Artery:
    • Delivers blood to the kidney
  • Segmental Arteries:
    • Branch from the renal artery in the renal pelvis
    • Leads to interlobar arteries that extend into renal columns
  • Arcuate Arteries:
    • Located along the medulla-cortex border
    • Supply cortical radiate arteries and continue to afferent arterioles

Nephron Blood Flow

  • Afferent Arteriole:
    • Brings blood into the nephron
  • Glomerulus:
    • A network of tiny capillaries where filtration occurs
  • Efferent Arteriole:
    • Takes blood away from the glomerulus
  • Peritubular Capillaries:
    • Surround nephron, facilitating exchange between nephron and blood

Blood Return from the Nephron

  • Cortical Radiate Veins:
    • Collect blood from capillaries
  • Arcuate Veins:
    • Receive blood from cortical radiate veins
  • Interlobar Veins:
    • Drain into the renal vein
  • Match of Arteries and Veins:
    • Structures tend to have corresponding names except for segmental artery (no segmental vein)

Summary of Important Blood Vessels

  • Renal Artery
  • Segmental Arteries (no corresponding veins)
  • Interlobar Artery & Vein
  • Arcuate Artery & Vein
  • Cortical Radiate Artery & Vein
  • Afferent Arteriole: brings blood to glomerulus
  • Efferent Arteriole: carries blood away
  • Peritubular Capillaries: surround the nephron

Upcoming Topics

  • Focus on nephrons and their role in urine formation, regulation, and control in the urinary system.