The Pulmonary and Systemic Circuits: Functions and Diseases

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The Pulmonary Circuit

The pulmonary circuit begins in the right ventricle where deoxygenated blood is pumped through the pulmonary artery to each lung. The artery branches, finally becoming a network of capillaries that carry deoxygenated blood to the alveoli where gas exchange occurs. After gas exchange, oxygenated blood travels through the venous capillaries, the venules, and finally the pulmonary veins to the left atrium.

The Systemic Circuit

The systemic circuit begins in the left ventricle. Oxygenated blood is pumped through the aorta to the upper and lower body. It travels through the arteries, arterioles, and finally arterial capillaries to reach the cells. There, during cellular metabolism, nutrients and oxygen are collected while carbon dioxide and waste are removed. Afterwards, deoxygenated blood travels through the venous capillaries, venules, and finally the vena cava to the right atrium.

Cardiovascular Diseases

  • Arteriosclerosis
  • Hypertension (High Blood Pressure)
  • Myocardial Infarction (Heart Attack)

Diseases of the Blood

  • Anemia
  • Leukemia
  • Haemophilia


Excretion is the process by which the waste products from cell metabolism are eliminated from the blood.


  • Kidneys: They eliminate toxic substances resulting from cell metabolism through the urine.
  • Lungs: They expel carbon dioxide from cellular respiration.
  • Liver: It produces a liquid called bile that helps to eliminate waste from digestion through feces.
  • Sweat Glands: Exocrine glands of the skin are responsible for sweat excretion. Sweat is a liquid that is very similar to urine, but more diluted.

The Urinary System

The urinary system consists of the kidneys, two organs located along the posterior wall of the abdominal cavity, and the urinary tract, which includes the ureters, bladder, and urethra.

The Kidneys

The kidneys consist of the renal cortex (the outer part), renal medulla (the inner part that contains tissue called renal pyramids), and renal pelvis (this cavity collects urine and connects to the ureters).

Diseases of the Excretory System

  • Cystitis (Inflammation of the Bladder)
  • Renal Colic (Severe Pain Caused by Kidney Stones)

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