2.10 Path of Blood Through the Pulmonary and Systemic Circulation

The circulatory system is divided into two main circuits: the pulmonary circulation and the systemic circulation. The pulmonary circuit carries blood between the heart and the lungs for oxygenation. The systemic circuit carries oxygenated blood from the heart to the body tissues and returns deoxygenated blood back to the heart. Specialized circuits include the coronary, hepatic portal, and renal circulations.

Definition

Pulmonary Circulation: The pulmonary circulation is the portion of the circulatory system that carries deoxygenated blood from the right ventricle of the heart to the lungs for oxygenation, and returns oxygenated blood from the lungs to the left atrium of the heart.

Systemic Circulation: The systemic circulation is the portion of the circulatory system that carries oxygenated blood from the left ventricle of the heart to the body tissues, and returns deoxygenated blood from the body tissues to the right atrium of the heart.

Main Idea

• Pulmonary circulation = heart → lungs → heart (right side)
• Systemic circulation = heart → body → heart (left side)
• Coronary circulation = blood supply to the heart muscle itself
• Hepatic portal system = blood from digestive organs to the liver
• Renal circulation = blood supply to and from the kidneys

Core Concept

• Pulmonary circuit = right atrium → right ventricle → pulmonary trunk → pulmonary arteries → lungs → pulmonary veins → left atrium
• Systemic circuit = left atrium → left ventricle → aorta → body tissues → vena cavae → right atrium
• Coronary circulation = right and left coronary arteries → cardiac veins → coronary sinus → right atrium
• Hepatic portal system = digestive organs → hepatic portal vein → liver → hepatic veins → inferior vena cava
• Renal circulation = renal artery → kidney → renal vein → inferior vena cava

Detailed Explanation

Pulmonary Circulation

• The left atrium receives oxygenated blood from the lungs through two pairs of pulmonary veins.
• These veins open by a common aperture into the left atrium.
• From the left atrium, the blood flows into the left ventricle.
• The superior and inferior vena cavae bring deoxygenated blood and open into the right atrium.
• From the right atrium, blood flows into the lungs for oxygenation by a pulmonary arch or trunk.
• The pulmonary trunk divides into two pulmonary arteries, each going to the lung of its own side.

• This part of circulation is called pulmonary circulation or circuit.
• Pulmonary arteries carry deoxygenated blood.
• Pulmonary veins carry oxygenated blood.

Systemic Circulation

• The systemic circuit includes all the arteries and veins other than those involved in the pulmonary circuit.
• The largest artery in the systemic circuit is the aorta.
• The largest veins are the superior and inferior venae cavae.
• The path of systemic blood to any organ in the body begins in the left ventricle.
• The left ventricle pumps blood into the aorta.
• Branches from the aorta go to the organs and major body regions.
• The superior vena cava collects blood from the head, the chest, and the arms.
• The inferior vena cava collects blood from the lower body regions.
• Both enter the right atrium.
• The aorta and the vena cavae are the major pathways in the systemic circuit.

Key Points: - In most instances, the artery and the vein that serve the same organ are given the same name.

Coronary Circulation

The wall of the heart has its own supply of blood vessels to meet its vital needs.

• The myocardium is supplied with blood by the right and left coronary arteries.
• From the capillaries in the myocardium, the blood enters the cardiac veins.
• The course of these vessels parallels that of the coronary arteries.
• These cardiac veins converge to form the coronary sinus on the posterior surface of the heart.
• The coronary venous blood then enters the heart through an opening into the right atrium.

Hepatic Portal System

Definition: A portal system is a vascular system that begins and ends with capillary beds and has no pumping mechanism such as the heart.

• The portal system that begins with capillaries in the viscera and ends with the capillaries in the liver.
• The hepatic portal vein, the largest vein of the system, is formed by the union of all the veins coming from the digestive system.
• Within the liver, the blood flows through a series of dilated capillaries which empty into hepatic veins.
• The hepatic veins join the inferior vena cava.

• Digestive organs → capillaries
• Hepatic portal vein
• Liver → capillaries
• Hepatic veins
• Inferior vena cava
• Right atrium

Renal Circulation

• Renal artery enters into the kidney.
• Gives branches which pass through the medulla.
• In the cortex, they give rise to afferent arterioles.
• Afferent arterioles → glomerulus → efferent arterioles.
• Efferent arterioles → peritubular capillaries.
• Peritubular capillaries → renal vein.
• Renal vein exits the kidney and connects to the inferior vena cava.

Summary Table of Circulations

Intermediate Level

Comparison of Pulmonary and Systemic Circulation

Path of Blood Through Pulmonary Circulation

Path of Blood Through Systemic Circulation

Special Circulations

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Pulmonary circulation carries blood between heart and lungs.
• 2. Systemic circulation carries blood between heart and body.
• 3. Pulmonary arteries carry deoxygenated blood.
• 4. Pulmonary veins carry oxygenated blood.
• 5. Coronary circulation supplies the heart muscle.
• 6. Hepatic portal system carries blood from digestive organs to liver.
• 7. Renal circulation supplies the kidneys.
• 8. Aorta is the largest artery in the systemic circuit.
• 9. Superior and inferior vena cavae are the largest veins.
• 10. Coronary sinus opens into the right atrium.
• 11. Hepatic portal vein is formed by union of veins from digestive system.
• 12. Renal artery enters the kidney.
• 13. Renal vein exits the kidney.
• 14. Portal system begins and ends with capillary beds.
• 15. The heart is a double pump.

Remember

• - Pulmonary circulation = heart → lungs → heart
• - Systemic circulation = heart → body → heart
• - Coronary circulation = heart muscle
• - Hepatic portal system = digestive organs → liver
• - Renal circulation = kidneys
• - Pulmonary arteries = deoxygenated blood
• - Pulmonary veins = oxygenated blood
• - Aorta = largest artery
• - Vena cavae = largest veins
• - Coronary sinus = opens into right atrium
• - Hepatic portal vein = digestive organs to liver
• - Renal artery = enters kidney
• - Renal vein = exits kidney

Common Mistakes

• 1. Thinking pulmonary arteries carry oxygenated blood — They carry deoxygenated blood.
• 2. Thinking pulmonary veins carry deoxygenated blood — They carry oxygenated blood.
• 3. Confusing pulmonary and systemic circuits — Pulmonary = lungs; systemic = body.
• 4. Forgetting the coronary circulation — The heart has its own blood supply.
• 5. Mixing up the hepatic portal system — It carries blood from digestive organs to liver.
• 6. Confusing renal artery and renal vein — Renal artery enters kidney; renal vein exits.
• 7. Believing the portal system has a pump — It has no pump; it begins and ends with capillaries.
• 8. Mixing up the vena cavae — Superior vena cava drains upper body; inferior vena cava drains lower body.
• 9. Confusing the coronary sinus — It opens into the right atrium.
• 10. Thinking the heart only pumps blood to the body — It also pumps blood to the lungs.

Quick Revision

The circulatory system is divided into pulmonary and systemic circuits. Pulmonary circulation carries deoxygenated blood from the right ventricle to the lungs for oxygenation and returns oxygenated blood to the left atrium. Systemic circulation carries oxygenated blood from the left ventricle to the body tissues and returns deoxygenated blood to the right atrium. Specialized circuits include the coronary circulation (supplies the heart muscle), hepatic portal system (carries blood from digestive organs to the liver), and renal circulation (supplies the kidneys). Pulmonary arteries carry deoxygenated blood; pulmonary veins carry oxygenated blood. The aorta is the largest artery; the vena cavae are the largest veins.

60-Second Revision

• Pulmonary circulation = heart → lungs → heart
• Systemic circulation = heart → body → heart
• Coronary circulation = heart muscle
• Hepatic portal system = digestive organs → liver
• Renal circulation = kidneys
• Pulmonary arteries = deoxygenated blood
• Pulmonary veins = oxygenated blood
• Aorta = largest artery
• Vena cavae = largest veins
• Coronary sinus = opens into right atrium
• Warning: Pulmonary arteries carry deoxygenated blood; pulmonary veins carry oxygenated blood

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• 2. Blood Circulatory System of Man

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• 2.11 RATE OF BLOOD FLOW IN BLOOD VESSELS

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