1.5 Systemic and pulmonary circuits

Systemic Circulation Overview

• Definition: Systemic circulation refers to the movement of oxygenated blood from the heart to body tissues and the return of deoxygenated blood to the heart, excluding the lungs.

• Pathway of Blood:

  • Begins in the left ventricle of the heart.

  • Blood is ejected into the aorta.

  • Aorta branches into smaller arteries, eventually reaching capillaries.

  • At capillaries, oxygen is exchanged for carbon dioxide.

  • Deoxygenated blood returns through larger veins to the right atrium.

Hepatic Portal System

• Special part of systemic circulation that involves blood traveling from digestive organs to the liver before returning to the heart.

• Important for detoxification and nutrient processing.

Distribution of Blood

• Blood distribution in systemic circulation is parallel: all organs receive the same quality and quantity of blood simultaneously.

• Avoids scenarios where one organ receives oxygenated blood at the expense of others.

• Major recipients of blood at rest:

  • Kidneys - receive the most blood.

  • GI Tract - second most.

  • Followed by skeletal muscle, brain, skin, liver, bone, heart.

Pulmonary Circulation Overview

• Definition: Carries deoxygenated blood from the heart to the lungs and returns oxygenated blood to the heart.

• Pathway of Blood:

  • Blood is ejected from the right ventricle.

  • Travels through the pulmonary trunk into pulmonary arteries toward the lungs.

  • Capillary exchange occurs in the lungs: carbon dioxide is released, and oxygen is absorbed.

  • Oxygenated blood finally returns to the heart via pulmonary veins to the left atrium.

Distinction between Pulmonary and Systemic Circulation

• Pulmonary Veins: Carry oxygenated blood back to the heart.

• Aorta: Carries oxygenated blood away from the heart to systemic capillaries.

• Blood movement is continuous between these two systems, maintaining a cycle of oxygenation and circulation.

Key Mechanism of Blood Movement

• Blood flow is driven by pressure gradients, not gravity.

• Pressure differences cause blood to move from areas of high pressure to areas of low pressure, ensuring continuous circulation.

• This principle is similar for other physiological processes like gas exchange in the lungs and movement of nutrients.

Summary

• Systemic circulation delivers oxygenated blood to tissues and returns deoxygenated blood to the heart. The hepatic portal system is a specialized route.

• Pulmonary circulation moves blood between the heart and lungs for oxygenation.

• Continuous circulation is facilitated by pressure gradients governing blood flow throughout the body.