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Pulmonary Circulation - Functions and Significance

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Pulmonary circulation comprises blood vessels that exchange blood between the heart and lungs. Read this article to learn about this function.

Written by

Dr. Sri Ramya M

Medically reviewed by

Dr. Kaushal Bhavsar

Published At December 1, 2022
Reviewed AtFebruary 12, 2024

Introduction:

Pulmonary circulation is a part of the circulatory system of the human body. The systemic circulation, which is the other component of the circulatory system, originates in the left atrium when oxygenated blood from the pulmonary circulation is received. The pulmonary arteries and the pulmonary veins take part in pulmonary circulation.

What Does Pulmonary Circulation Mean?

Oxygenated blood is moved from the lungs back to the heart and deoxygenated blood from the heart to the lungs is referred to as pulmonary circulation. The blood without oxygen from the heart is transported to the lungs by the pulmonary arteries, and the oxygenated blood from the lungs is transported to the systemic circulation by the pulmonary veins. Bronchial circulation is the separate system that supplies oxygenated blood to the larger airways of the lungs.

What Is the Difference Between Pulmonary and Systemic Circulation?

One significant similarity between these two systems is that they both carry blood to and from the heart via closed circuits. Numerous mammals also possess these two cardiovascular systems. Both of them aid in the transportation of nutrients, waste products from metabolism, and breathing gasses to all of the necessary locations. However, pulmonary and systemic circulation differ greatly, even though they both have equally significant functions in the organism.

The systemic and pulmonary circulations are involved in the general regulation of body temperature. Heat is moved from the body's center to its periphery when there is a reduction in blood flow to the lungs. Put another way, heat is transmitted from peripheral tissues to the core when there is a shortage of blood flow to the lungs. The body's systemic circulation transfers heat from the periphery to core tissues and vice versa, serving as a buffer against temperature fluctuations.

Nonetheless, a drop in blood flow is typically accompanied by a rise in perfusion pressure. Thus, it may be inferred that the vascular system is controlling both temperatures equally in these situations where the perfusion pressure is either normal or elevated.

How Does Pulmonary Circulation Develop?

The blood vessels form outside the implanted embryo fifteen days after fertilization to create the placenta. This delivers oxygen and nutrients to the developing fetus and removes the waste products. The pulmonary circulation loop is bypassed in the fetus. The placenta supplies oxygen-rich blood to the fetus via the umbilical vein.

This blood enters the inferior vena cava after passing through the ductus venosus along with the liver. The blood then enters the right atrium from the inferior vena cava. By bypassing the right ventricle and the lungs, blood from the right atrium reaches the left atrium immediately through the foramen ovale. The high lung resistance drops when the baby is delivered and takes its first birth. The blood enters the lungs for oxygenation. The oxygen relaxes the pulmonary vessels and eventually closes other portal shunts. After the shunts are closed, the neonatal pulmonary circulation is identical to the adult circulation.

How Does Pulmonary Circulation Work?

Deoxygenated blood is carried by the superior vena cava from the upside body to the right atrium, while deoxygenated blood from the lower body is carried by the inferior vena cava to the right atrium. The tricuspid valve allows the deoxygenated blood from the right atrium, to enter into the right ventricle, which then pumps the blood into the pulmonary artery via the pulmonary valve.

Pulmonary arteries carry oxygen-poor blood to the lungs, where carbon dioxide is released and oxygenated during respiration. The pulmonary veins transport this oxygenated blood to the left atrium. This forms the pulmonary cycle. Using the mitral valve, the left atrium's oxygenated blood flows into the left ventricle, which then circulates into the aorta via the aortic valve. The oxygenated blood is then transported to the body through systemic circulation, and pulmonary circulation continues. The lymphatic system prevents the accumulation of tissue fluid around pulmonary circulation. They are located close to the terminal bronchioles, and they drain the mediastinal lymphatics before emptying into the right lymphatic duct. The lung parenchyma receives oxygenated blood via bronchial and pulmonary circulation.

What Are the Functions of Pulmonary Circulation?

The major function of pulmonary circulation is the exchange of gasses, which eliminates carbon dioxide and supplies oxygenated blood to the body. The bronchial circulation transports oxygenated blood to the lung parenchyma. The pulmonary and bronchial circulation overlap in the central region. The low-pressure venous and lymphatic systems prevent the buildup of edematous fluid in the lungs.

What Is the Significance of Pulmonary Circulation?

Pulmonary circulation is vital for the supply of oxygenated blood. Any changes in pulmonary circulation can result in tissue dysfunction secondary to hypoxia. Pulmonary circulation disorders include the following:

Pulmonary Edema - Any changes in the starling forces in the pulmonary circulation can result in the accumulation of fluid in the alveoli. This impairs the gas exchange and causes respiratory distress. Pulmonary edema may be cardiogenic or noncardiogenic. Cardiogenic edema is associated with increased ventricular filling pressure. Noncardiogenic edema is associated with systemic inflammation. It occurs due to an increase in hydrostatic pressure, decrease in serum oncotic pressure, decrease in lymphatic clearance, increase in vessel permeability, and decrease in surfactant.

Pulmonary Embolism - A dislodged blood clot from a distant source, like a deep venous thrombosis, embolizes into the pulmonary circulation and results in ischemia. This impairs the gas exchange.

Pulmonary Hypertension - Pulmonary arterial hypertension is the increase in the mean pulmonary arterial pressure beyond 25 mmHg. It impairs gas exchange and causes exertional dyspnea. If it persists for a long time, it can result in right ventricular strain and right heart failure through cor-pulmonale.

Pleural Effusion - Changes in the starling forces of the pleural circulation can result in fluid accumulation in the pleural space, known as pleural effusion. It causes pleuritic chest pain and respiratory distress.

Pulmonary Shunt - The deoxygenated blood from the right side of the heart enters the left side without undergoing oxygenation in the pulmonary capillaries in the pulmonary shunt due to the presence of fluid in the alveoli of the lungs. This results in the reduction of oxygen in the blood, causing hypoxemia.

Vascular Resistance - Pulmonary vascular resistance is the resistance created by pulmonary circulation to force the blood into the circulatory system to create flow. It is caused by hypoxic vasoconstriction that occurs due to pulmonary emboli, pulmonary edema, and cardiovascular diseases. Vascular resistance is the main causative factor for pulmonary hypertension.

Cardiac Shunt - A shunt is a deviation in the blood flow pattern to the heart. It can occur as a right-left shunt, left-right shunt, bidirectional shunt, systemic-pulmonary shunt, or pulmonary-systemic shunt. A cardiac Shunt can be caused by congenital or acquired causes.

Conclusion:

Pulmonary circulation constitutes a wide network of arteries, veins, and lymphatics. They perform unique functions like the gas exchange and exchange of blood and tissue fluids between the heart and the lungs. Pulmonary circulation is vital for the continuous supply of oxygenated blood—disruption in the pulmonary circulation results in pulmonary circulation diseases.

Frequently Asked Questions

1.

What Are the Stages of Pulmonary Circulation?

Pulmonary circulation is the blood flow that bridges the heart and lungs. It enables the blood to refill the oxygen molecules and eliminate the gathered carbon dioxide molecules. The blood from diverse body areas finally reaches the upper right heart chamber (right atrium) by specific blood vessels called inferior and superior vena cava. From the right atrium, the blood flows into the corresponding lower chamber (right ventricle). From there it is picked up by the pulmonary artery, which presents the blood to the lungs, where the intended gas exchange happens. The oxygen-loaded blood then returns to the upper left heart chamber (left atrium) via the pulmonary vein, creating access for the blood to enter the systemic circulation. 

2.

What Are the Three Forms of Circulation and What Do They Do?

- Pulmonary Circulation: This portion of the cycle transports oxygen-depleted blood from the heart to the lungs and then back to the chambers of the heart.
- Systemic Circulation: This portion of the cycle transports oxygenated blood from the heart to various body parts.
- Coronary Circulation: The heart muscles need oxygenated blood for functioning and it is supplied by coronary arteries. This blood flow to the heart muscles is called coronary circulation. 

3.

What Is the Importance of Double Circulation?

The distinction between oxygenated and deoxygenated blood is supported by double circulation. As a result, this circulation guarantees that the body has a constant supply of oxygen and also enhances physiological efficiency. Blood circulates to bodily tissues by means of systemic circulation and to the lungs by pulmonary circulation.

4.

What Is the Location of the Pulmonary Circulation?

The pulmonary circulatory system consists of a complex network of arteries, veins, and lymphatics that transport blood and other tissue fluids between the heart and the lungs. It carries deoxygenated blood to the lungs, where it absorbs oxygen and excretes carbon dioxide. The oxygenated blood is subsequently returned to the heart.

5.

What Are the Two Forms of Lung Circulation?

The lung is the only organ that has two types of circulation: 
- Pulmonary Circulation - This is responsible for gas exchange.
- Bronchial Circulation - A systemic circulatory supply that distributes oxygenated blood to the walls of the conducting airways, pulmonary arteries, and veins.

6.

Name the Blood Vessels That Carry Oxygenated Blood.

Arteries are the blood vessels that are concerned with the distribution and circulation of oxygenated blood throughout the body. However pulmonary artery is an exception for that. Though it is coined as an artery, the pulmonary artery ships deoxygenated blood. Similarly, the pulmonary vein irrespective of its name, conveys oxygen-loaded blood to the heart chamber. All the arteries (excluding the pulmonary artery) and pulmonary veins are the chief blood vessels that are responsible for the conveyance of oxygenated blood. 

7.

What Is the Distinction Between Open and Closed Circulation?

- The Open Circulatory System: There are no arteries to transmit the blood here. Therefore, blood flows freely across the cavities and is most commonly observed in invertebrates. 
- The Closed Circulatory System: Blood is confined within the blood vessels in a closed circulatory system and flows in a single direction from the heart around the systemic circulatory route before returning to the heart. The closed circulatory system is seen in vertebrates and a few invertebrates, such as earthworms.

8.

What Is the Volume of Blood in the Pulmonary Circulation?

Pulmonary circulation contains around 250 to 300 milliliters of blood per square meter of body surface area. Around 84 percent of total blood volume is in the systemic circulation, 7 percent in the heart, and 9 percent in the pulmonary circulation.

9.

What Are the Purposes of the Pulmonary and Bronchial Circulations?

Pulmonary circulation transports deoxygenated blood away from the heart to the lungs and supplies oxygenated blood from the lungs to the heart. 
Bronchial circulation is a distinct system that delivers blood to the tissue of the major airways of the lung.

10.

What Is the Importance of Pulmonary Circulation?

Pulmonary circulation serves numerous important roles. Its principal role is gaseous exchange across the alveolar membrane, supplying oxygenated blood to the rest of the body and eliminating carbon dioxide from circulation.
Dr. Kaushal Bhavsar
Dr. Kaushal Bhavsar

Pulmonology (Asthma Doctors)

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