Urinary System Study Notes

Urinary System Notes

Main Functions of the Urinary System

  • Removes Waste Products: The urinary system eliminates waste products such as urea and creatinine from the body.
  • Regulates Fluid Balance: It maintains the appropriate amount of fluid in the body.
  • Maintains Electrolyte Balance: Essential ions like sodium (Na+) and potassium (K+) levels are regulated.
  • Controls Acid–Base Balance: The system helps maintain the body’s pH by regulating the concentration of hydrogen ions.

Organs of the Urinary System

  • Kidneys: These are the primary organs that filter blood and form urine.
  • Ureters: Tubes that carry urine from the kidneys to the bladder.
  • Bladder: A muscular sac that stores urine until it is excreted.
  • Urethra: The duct through which urine is expelled from the body.

Structure of the Kidney

  • Cortex: The outer layer of the kidney.
  • Medulla: The inner layer where renal pyramids are located.
  • Renal Pelvis: The structures that collects urine before it passes to the ureters.

Nephron (Functional Unit of the Kidney)

  • Glomerulus: A network of capillaries that filters blood, allowing water and small molecules to pass while retaining larger proteins and cells.
  • Bowman’s Capsule: A cup-like sac that surrounds the glomerulus and collects the filtrate.
  • Proximal Convoluted Tubule (PCT): The first segment of the nephron that reabsorbs water, ions, and organic nutrients.
  • Loop of Henle: A U-shaped portion of the nephron that further concentrates urine, consisting of a descending limb and an ascending limb.
  • Distal Convoluted Tubule (DCT): The segment where additional salt and water reabsorption occurs, as well as secretion of ions.
  • Collecting Duct: The duct that collects urine from multiple nephrons and drains it into the renal pelvis.

Urine Formation (3 Steps)

  1. Filtration: Occurs in the glomerulus, where blood is filtered to remove excess substances and waste.
  2. Reabsorption: The process whereby useful substances (such as glucose and certain ions) are reabsorbed back into the bloodstream, primarily occurring in the PCT.
  3. Secretion: The final step where additional wastes and excess ions are secreted into the tubular fluid, primarily in the DCT.

Fluid Balance Regulation

  • Hormonal Control: Fluid balance is primarily regulated by the hormone Antidiuretic Hormone (ADH).
    • More ADH: Leads to increased water reabsorption in the kidneys, resulting in less urine production.
    • Less ADH: Results in decreased water reabsorption, leading to increased urine production.

Cram Summary

  • Kidneys filter blood and produce urine.
  • Nephron is identified as the functional unit of the kidney.
  • Three Processes of Urine Formation: filtration, reabsorption, and secretion.
  • Regulates fluids, electrolytes, and pH within the body.