Anatomy/Excretory System

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The excretory system is a topic of the event Anatomy. It is part of the 2012 Division C event.


The urinary system consists of the kidneys, two ureters, the urinary bladder, and the urethra. Blood flows through the kidneys as they filter out waste such as urea. The urine produced by the kidneys goes through the ureters. It then waits in the urinary bladder, until it goes out through the urethra.


Anatomy of the Kidney

Anatomy Kidney midsagital.jpg

  • The tissue is divided into two parts
    • Cortex- outer layer
    • Medulla- inner layer, the renal pyramids collectively
  • Renal Columns- extensions of the cortex that divide the medulla into pyramids
  • Renal Pyramids- point toward the renal pelvis
    • Terminate at a minor calyx
      • Minor Calyx- connective and muscular tissue which collects urine (extension of the ureter)
    • Striped appearance results from the straight segments of the nephrons that spans the pyramids
  • Renal Pelvis- leads out of kidney to ureter

Anatomy of the Nephron

The nephron is the functional unit of the kidney. It is a tube-like structure that spans the renal cortex and medulla. The average human kidney contains 800,000- 1.5 million nephrons. The nephron is the site of ion and water reabsorption, and where urine is produced.

F27-5 nephron structure c.jpg

The nephron has five regions.

  • Glomerular (Bowman's) capsule
  • Proximal Convoluted Tubule (PCT)
    • The PCT is a highly coiled region, which is closely associated with the peritubular capillary bed.
    • It is the site of early reabsorption of water, ions, glucose, and amino acids
    • Nitrogenous wastes and blood pollutants such as medications are secreted
    • By the end of the PCT, 60% of the original water is reabsorbed, and 65% of original ions
  • Loop of Henle
    • The descending segment is the site of water reabsorption. This is a passive process, which occurs via osmosis due to the ion gradient created by the ascending segment.
    • The ascending segment is the site of ion reabsorption, which occurs via active transport.
    • By the end of the Loop of Henle, 80% of the original water is reabsorbed, and 90% of the original ions.
  • Distal Convoluted Tubule (DCT)
    • This is the site of the secretion of any extra wastes.
  • Collecting Duct
    • The main function is absorption of more water. It relies on the solute gradient created by the Loop of Henle.

Collectively, the PCT, Loop of Henle, and DCT comprise the renal tubule.

Associated Vessels

  • Afferent arteriole transports blood into the...
  • Glomerulus (capillary bed), where it then moves into the...
  • Efferent arteriole, which leaves the nephron. It is much narrower than the afferent arteriole, causing high pressure and encouraging filtration.
  • Peritubular capillaries are any of the capillaries that surround the nephron.
  • Vasa recta capillaries are the portions of the peritubular capillaries that surround the Loop of Henle.


  • Excretion- remove waste products from the blood
  • Regulation of blood volume and pressure- kidneys control amount of extracelluar fluid, can make dilute or very concentrated urine
  • Regulation of the concentration of solutes in the blood- kidneys regulate molecules and ions like glucose, sodium, hydrogen carbonate
  • Regulation of red blood cell synthesis- kidneys secrete erythropoietin, which regulates blood cell production in bone marrow
  • Vitamin D synthesis- kidneys control blood levels of calcium by regulation synthesis of vitamin D.

Substances Removed by Kidneys

Most of the substances removed are metabolic wastes, produced as by products from normal body function. Some of the most toxic include the nitrogenous wastes.

  • Urea- produced in liver by protein metabolism
  • Uric Acid- produced in liver by metabolism by nucleic acid metabolism
  • Creatinine- produced in muscles by protein metabolism


  • (Re)Absorption- movement of a solute across a membrane and incorporation into the body
  • Secretion- release of a solute across a membrane, out of the body, in this case from the peritubular capillaries into the tubule.
  • Excretion- filtration and removal of solutes out of the body
  • Solute- a substance that is dissolved in the blood plasma (ions, waste chemicals, toxins, etc.)
  • Clearance- the rate at which a solute is filtered from the blood plasma
2019 Anatomy and Physiology Topics
Cardiovascular System · Lymphatic System · Excretory System