Excretion and Circulatory System Overview

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Elimination of waste substances from blood is performed by the urinary system and other organs.

Urinary System

  • Kidneys: bean-shaped organs behind the abdomen, filtering blood to form urine.
  • Ureter: thin tubes transporting urine to the bladder.
  • Urinary bladder: elastic bag storing urine.
  • Urethra: duct transporting urine outside.

Other organs involved in excretion are lungs, liver, and sweat glands.

The Circulatory System

Function: Transporting O2, nutrients, and collecting CO2 and waste substances.


  • Blood Plasma: 55% of blood, transporting nutrients, waste substances, and CO2.
  • Blood Cells: red blood cells, white blood cells, and platelets.

Blood Vessels

Arteries, veins, and blood capillaries carry blood around the body.


Hollow muscular organ pumping blood through the blood vessels.

Heartbeat and Blood Circuits

The heart pumps blood through the body in different stages of the cardiac cycle.

  • Atrial Systole: Atria contract, propelling blood into the ventricles.
  • Ventricular Systole: Ventricles contract, blood exits the heart through arteries.
  • Diastole: Atria and ventricles relax, blood enters the atria.

The circulation of blood in humans is double and complete, describing two circuits: pulmonary and systemic.

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