Pulmonary Vein - The Definitive Guide | Biology Dictionary (2023)


The pulmonary vein(s) are vessels carrying oxygen- rich blood from the lungs to the left atrium of the heart, which is critical for proper respiration. There are two major pulmonary veins for each lung, leading to a total of four major vessels. As these veins are critical for ensuring proper respiration, blockages and disorders at these vessels can quickly become serious and lead to broader conditions such as pulmonary hypertension and heart failure.

The Circulatory System

Before leading into the specific vessels of the cardiac and pulmonary systems, lets first look at the overall system and vessels found throughout the body.

All vertebrates (as well as a few invertebrate species) have a closed circulatory system, where blood flows throughout the body in a continuous loop by a series of vessels. The heart facilitates blood flow through the circulatory system by pumping to create a forceful pressure that maintains a viable flow rate. The major vessels involved in a closed circulatory system include arteries, capillaries, and veins.


Arteries are thick- walled vessels that move blood away from the heart. They consist of mostly elastic fibers in addition to muscle fibers. The smooth muscle allows the arteries to contract, decreasing vessel diameter to slow down blood flow. However, the elastic fibers allow the arteries to return to a resting state so that diameter and blood flow can increase again. Very small arteries are called arterioles. These arterioles are needed to reduce blood pressure as blood prepares to pass through capillaries.

Capillaries are very thin vessels where gases and small molecules are exchanged from the blood to the tissues. These vessels are extremely thin, where the walls making up the vessels are only a single cell layer thick. Additionally, the capillary diameter is only wide enough to let red blood cells pass through one at a time. Large networks of capillaries are known as capillary beds. Once tissues use the oxygen and other molecules received, blood is brought back to the heart by flowing through venules and veins.

Veins are thin- walled vessels that move blood towards the heart. At this point, blood pressure is generally lower, allowing for veins to have larger diameters and thinner walls compared to arteries. Blood movement in veins is typically facilitated by skeletal muscle in the limbs. However, in large veins, valves are required to section the vessels into multiple segments, preventing blood from back-flowing. Very small veins are known as venules.

Sub-Circulatory Systems

The circulatory system is broken down into two parts- the pulmonary circuit and the systemic circuit. The pulmonary circuit is the loop that moves blood from the heart and into the lungs (or gills for aquatic species), while thesystemic circuit is the loop that moves blood from the heart and throughout the body. In fish species, gravity does not play a large role in maintaining blood flow, so blood pressure is consistently high throughout the body. However, in terrestrial vertebrates, gravity plays a larger role. Blood pressure must increase to overcome gravity while blood is traveling up towards elevated portions of the body. Therefore, separation of the two circulatory sub-systems allows for the overall system to remain balanced. Generally, the systemic circuit is high- pressured, while the pulmonary circuit in low- pressured. Specially, pulmonary blood pressure is only ~1/8th of systemic blood pressure.

The Heart

Chambers Within the Heart

The heart is broken down into at least two chambers in all vertebrates, where all species have at least one atrium and one ventricle. The atria(singular atrium) are responsible for collecting blood from the body, while the thick- walledventricles are responsible for pushing the blood out of the heart. The number of atria and ventricles diversifies with species, where fish have one of each, while amphibians and many reptiles have two atria and one ventricle, and other reptiles, birds, and mammals (including humans) have two atria and two ventricles.

The pulmonary and systemic circuits are only partially separated in species lacking four fully developed heart chambers. Because of this, oxygen-rich and oxygen- poor blood can mix. In species with four fully developed chambers- such as humans- the two sub-circuits are completed separated. This prevents oxygen-rich and oxygen-poor blood from mixing, allowing for better cellular efficiency as tissues are able to receive more oxygen. The increased available oxygen is also needed to maintain higher body temperatures, which is why bird and mammal species are known as endotherms.

Blood Flow Through the Heart

The general movement of blood through the heart in species such as humans that have four fully developed chambers is as follows:

  1. Oxygen-poor blood enters the heart by flooding into the right atrium via the superior and inferior venae cavae (both of which are veins).
  2. The oxygen-poor blood then flows past the tricuspid valve into the right ventricle.
  3. The right ventricle pushes the oxygen-poor blood past the pulmonary valve and into the pulmonary arteries.
  4. The right and left pulmonary arteries lead into the right and left lungs, respectively, where the blood becomes oxygen-rich. This gas exchange occurs as the blood flows through the capillary beds of the alveoli within the lungs.
  5. The now oxygen-rich blood flows from the lungs back to the heart through the pulmonary veins, flooding into the left atrium. Each lung has two large pulmonary veins, where all four lead directly into the left atrium.
  6. The oxygen-rich blood flows past the mitral (or bicuspid) valve into the left ventricle.
  7. The left ventricle pushes the oxygen-rich blood past the aortic valve, into the aorta.
  8. The oxygen-rich blood then flows out of the heart and spreads throughout the arteries of the body.

Steps 1-3 consist of pulmonary circulation, while steps 5-8 consist of systemic circulation. Therefore, despite both vessels having pulmonary in their name, only the pulmonary artery is technically part of the pulmonary circulation. The pulmonary vein is actually part of the systemic circulation.

Location of the Pulmonary Veins

Multiple vessels are required to ensure blood flows efficiently through the pulmonary and systemic systems. Therefore, it is important to properly locate the pulmonary veins in relation to the rest of the system. All four of the pulmonary veins are located at the superior (topmost) portion of the heart. The right pulmonary veins stem directly off of the right lung’s root and run behind the right atrium and superior vena cava into the left atrium. Meanwhile, the left pulmonary veins stem directly off of the left lung’s root and run in front of the descending aorta, directly into the left atrium.

Diseases and Dysfunctions

Pulmonary Vein Stenosis

Pulmonary vein stenosis is a rare dysfunction where at least one- but usually multiple- of the four pulmonary veins become blocked. This blockage prevents the oxygen-rich blood from entering the left atrium of the heart from the lungs. This may occur when the walls of the veins thicken, causing the vessels themselves to narrow. Patients can undergo surgery to widen the veins. However, this is typically a reoccurring condition within a patient, so this solution is only short-term. If left untreated, this condition can lead to advanced pulmonary diseases, such as pulmonary hypertension and pulmonary arterial hypertension. Despite its rarity, clinical studiesare ongoing to better understand this condition and applicable treatments.

Pulmonary Vein Thrombosis

Another rare dysfunction that can occur within the pulmonary veins is pulmonary vein thrombosis. Thrombosis- which is the formation of thrombi, or blood clots, within vessels- can decrease the available diameter of a blood vessel, thus restricting blood flow. When the thrombus is dislodged from its origin, it becomes a specific type of embolism (or intravascular mass) known as thromboembolism. The presence of these masses can lead to further pulmonary hypertension, blood clotting, and even sudden death.

Antecedent Heart Diseases

Additional antecedent heart diseases, such as mitral stenosis, can also increase blood pressure. As the mitral valve is on the left side of the heart separating the atrium and ventricle, pressure can buildup in the left atrium. The increase in pressure here can lead to increased pressure in the pulmonary veins pouring into the atrium. Similar to before, this can lead topulmonary hypertension and pulmonary arterial hypertension. It is reported that the pathophysiology leading to mitral stenosis is analogous to pulmonary vein thrombosis.

Resulting Conditions

As mentioned in the previous two disorders, pulmonary hypertension is a broad condition defined by increased pulmonary pressure. Specifically, pulmonary pressure increases to 1/4th or more of systemic pressure. (Reminder: pulmonary pressure should only be ~1/8th of systemic pressure). This condition consists of several subgroups that are categorized based on the dysfunction cause. Typically, however, pulmonary hypertension results when surrounding arteries narrow (or if vascular blood flow increases). In order to push blood through these narrowed vessels, the heart must pump harder. Over time, this causes the heart to weaken, and the chances of developing heart failure increases.There can be multiple causes of pulmonary hypertension, with pulmonary vein stenosis and thrombosis being just a few of them.Pulmonary arterial hypertension is a specific type of pulmonary hypertension, but its root cause is at the small arteries of the lung specifically.


Pulmonary veins are critical vessels in the pulmonary system need to ensure proper respiration is dispersed throughout the body. These veins carry freshly oxygenated blood from the lungs to the heart via the left atrium, where oxygen-rich blood can spread to all subsequent tissues. The evolution of multi-chambered hearts in select species have allowed for the complete separation between the pulmonary and systemic circuits, preventing the mixing of oxygen-rich and oxygen-poor blood. Though disorders found directly in the pulmonary veins tend to be rare, they can contribute to larger conditions and diseases that can quickly become fatal. Research is ongoing to better understand some of these diseases and improve available treatments.




  • Freeman, S., Quillin, K., Allison, L. A., Black, M., Podgorski, G., Taylor, E., & Carmichael, J. (2017). “Biological science (Sixth edition.).” Boston: Pearson Learning.
  • Kato H, Fu YY, Zhu J, et al. (2014). “Pulmonary vein stenosis and the pathophysiology of “upstream” pulmonary veins.”J Thorac Cardiovasc Surg. 148(1):245‐253.
  • Kumar, V., Abbas, A., Aster, J. (2013). “Robbins Basic Pathology (Ninth Edition).” Philadelphia: Elsevier Inc.


What is the pulmonary vein quizlet? ›

Pulmonary veins are responsible for carrying oxygenated blood from the lungs back to the left atrium of the heart. This differentiates the pulmonary veins from other veins in the body, which are used to carry deoxygenated blood from the rest of the body back to the heart. ...

What is correct about pulmonary vein? ›

The lung veins sometimes referred to as the pulmonary veins, are blood vessels that transfer freshly oxygenated blood from the lungs to the left atria of the heart.

What is pulmonary vein explanation? ›

Pulmonary veins are blood vessels that carry oxygen-rich blood from your lungs to your heart. Your pulmonary veins are part of your body's pulmonary circuit. This is a system of blood vessels that moves blood between your heart and your lungs.

What blood do the pulmonary veins carry to the ____? ›

The pulmonary veins bring oxygen-rich blood to the left atrium.

Where is the pulmonary vein quizlet? ›

The pulmonary veins are large blood vessels that receive oxygenated blood from the lungs and drain into the left atrium of the heart. There are four pulmonary veins, two from each lung. The pulmonary veins are among the few veins that carry oxygenated blood.

Where is the pulmonary vein? ›

The pulmonary veins are fixed to the pericardium travel alongside the pulmonary arteries. The right superior pulmonary vein passes in front of and a tad below the pulmonary artery at the root of the lung, and the inferior pulmonary vein is situated at the lowest part of the lung hilum.

Does pulmonary vein have high pressure? ›

Anomalous connection of the pulmonary veins (to the right atrium, systemic or hepatic veins, or the coronary sinus) can occur with or without obstruction to egress of blood from the veins. In the former, pulmonary vein pressure is usually elevated, and PH can be severe after birth.

Does pulmonary vein have valves? ›

The pulmonary valve (sometimes referred to as the pulmonic valve) is a valve of the heart that lies between the right ventricle and the pulmonary artery and has three cusps. It is one of the four valves of the heart and one of the two semilunar valves, the other being the aortic valve.

What is the pressure in the pulmonary vein? ›

A normal value for pulmonary vascular resistance using conventional units is 0.25–1.6 mmHg·min/l. Pulmonary vascular resistance can also be represented in units of dynes/sec/cm5 (normal = 37-250 dynes/sec/cm5).

What is the left pulmonary vein simple definition? ›

: a vein that returns oxygen-rich blood from the lungs to the left side of the heart.

Does pulmonary vein have low blood pressure? ›

The pulmonary circulation is a relatively low pressure system compared to the systemic circulation because the pulmonary arteries are not as muscularized as their systemic counterparts. Thinner, less muscular vessels are more easily distended.

What is pulmonary vein issues? ›

Pulmonary vein stenosis (PVS) is a rare condition in which the veins that carry blood from the lungs back to the heart are narrowed. This is a different condition than pulmonary valve stenosis and peripheral pulmonary stenosis. Sometimes, PVS can occur as a complication of another heart or lung problem.

Where does the pulmonary vein return blood to? ›

The blood that comes back from the lungs is oxygen-rich, and it moves through the pulmonary veins to the left atrium. The left side of the heart pumps oxygen-rich blood to the rest of the body through the aorta.

Does the pulmonary vein carry oxygenated blood or oxygenated blood? ›

Pulmonary vein is the only vein that carries oxygenated blood as they carry blood from lungs to the heart and, pulmonary artery is the only artery that carry deoxygenated blood.

Where does the pulmonary vein get blood from? ›

The main pulmonary veins receive blood from three or four feeding veins in each lung, and drain into the left atrium. The peripheral feeding veins do not follow the bronchial tree. They run between the pulmonary segments from which they drain the blood.

What are the 4 pulmonary veins? ›

There are typically four pulmonary veins, two draining each lung:
  • right superior: drains the right upper and middle lobes.
  • right inferior: drains the right lower lobe.
  • left superior: drains the left upper lobe.
  • left inferior: drains the left lower lobe.
Mar 14, 2023

Why does the pulmonary vein have oxygen? ›

Recall that in internal respiration, oxygen diffuses from the alveoli to the deoxygenated blood. When this happens, the blood then becomes oxygenated. The function of the pulmonary veins is to transport that oxygenated blood from the lungs to the heart.

What is the function of pulmonary artery? ›

The main pulmonary artery and the subsequent right and left pulmonary arteries sit within the middle mediastinum. They arise from the right ventricle of the four-chambered heart and transport blood to the lungs.

What is the order of the pulmonary veins? ›

Pulmonary circulation is ordered from the right ventricle to the pulmonary arteries, through the lungs, to the pulmonary veins, and reenters the heart in the left atrium.

What is the top pulmonary vein? ›

Results: Right top pulmonary vein (RTPV) is a supernumerary vein arising from the roof of the right part of the left atrium separately from the orifice of the right superior pulmonary vein.

What does pulmonary mean in biology? ›

(PUL-muh-NAYR-ee) Having to do with the lungs.

Does the pulmonary vein have a pulse? ›

Flow velocities in the extraparenchymal pulmonary veins typically demonstrate two major antegrade flow pulses, one during ventricular systole (VS) (S wave) and one during diastole (D wave).

Are pulmonary veins oxygen rich? ›

Oxygen-rich blood flows from the lungs back into the left atrium (LA), or the left upper chamber of the heart, through four pulmonary veins. Oxygen-rich blood then flows through the mitral valve (MV) into the left ventricle (LV), or the left lower chamber.

Does the pulmonary vein have the most oxygen? ›

The pulmonary vein carries oxygen around the body back to the heart. It, therefore, has the greatest oxygen content.

What is the largest artery in the body? ›

The aorta is the largest artery of the body and carries blood from the heart to the circulatory system.

Does pulmonary vein have thick walls? ›

The walls of the pulmonary arteries are thick and elastic. The walls of the pulmonary veins are thinner compared to pulmonary arteries.

Is the pulmonary vein in the left ventricle? ›

Your main pulmonary artery (pulmonary trunk) leaves your right ventricle at your pulmonary valve. It soon splits into your right and left pulmonary arteries, which carry blood to each of your lungs.

What causes pulmonary venous pressure to increase? ›

Pulmonary venous hypertension (PVH).

This form is caused by diseases of the left side of the heart, such as heart failure or mitral valve disease. This can increase pulmonary artery blood pressure but usually doesn't become severe PAH.

What happens when pulmonary venous pressure increases? ›

Increases in pulmonary capillary pressures over a long period lead to smooth muscle hypertrophy and fibrosis of pulmonary vasculature. These changes, in turn, cause pulmonary arterial hypertension and eventually cor pulmonale.

What are the symptoms of pulmonary venous pressure? ›

Pulmonary hypertension signs and symptoms include:
  • Blue lips and skin (cyanosis)
  • Chest pressure or pain.
  • Dizziness or fainting spells (syncope)
  • Fast pulse or pounding heartbeat (palpitations)
  • Fatigue.
  • Shortness of breath (dyspnea), initially while exercising and eventually while at rest.
Apr 13, 2022

Why is pulmonary vein called a vein? ›

The right pulmonary veins pass behind the right atrium and superior vena cava while the left part passes in front of the descending thoracic aorta. Despite carrying oxygenated blood this is considered a vein because it carries blood towards the heart.

Why pulmonary veins do not have valves? ›

The pulmonary veins do not have valves because the pressure exerted by the heart is strong enough to keep the blood flowing in one direction.

What is the best position to sleep in with pulmonary hypertension? ›

Sleeping in a position with your upper body raised may help you breathe easier. You can use foam wedges or elevate the head of your bed. There are many devices that you can buy to help raise your upper body while in bed. Use a device that will tilt your whole body, or bend your body at the waist.

How long can you live with pulmonary hypertension? ›

For patients treated by experts in PAH, the average survival now exceeds 7 years and may be closer to 10 years. We now have many patients that are alive and well more than 10 years after they were first formally diagnosed (often 15 years since they first started having symptoms).

What is the most common cause of pulmonary hypertension? ›

In the United States, the most common type of pulmonary hypertension is caused by left-sided heart disease, such as left heart failure. Several other medical conditions and environmental factors can raise your likelihood of developing pulmonary hypertension.

What happens when your pulmonary vein is blocked? ›

Pulmonary vein stenosis is often a progressive disease. This means that over time, the disease can spread to other veins that were previously healthy. A severe narrowing or blockage of the pulmonary veins can ultimately result in pulmonary hypertension and/or heart failure.

What happens if a pulmonary vein is blocked? ›

Pulmonary vein stenosis (PVS) is when there is a narrowing or blockage in the pulmonary veins. It is a rare disease and if it progresses, it can lead to pulmonary hypertension and right heart failure.

What is the survival rate for pulmonary vein stenosis? ›

The spectrum of PVS is broad. Single vessel stenosis is well tolerated; however, 2-year survival for infants and children with progressive PVS is approximately 50% to 60%.

Is the pulmonary vein oxygenated or deoxygenated quizlet? ›

The pulmonary arteries carry deoxygenated blood and the pulmonary veins carry oxygenated blood.

Where are the pulmonary arteries? ›

The pulmonary artery is located at the exit of the right ventricle. This main arterial branch is located above the heart to the left of the ascending aorta. These vessels go through the connective tissue covering around the heart (pericardium ).

Why are pulmonary veins called arteries? ›

The function of the pulmonary arteries is to transport the deoxygenated blood to the lungs where it can be reoxygenated through diffusion. They are still called arteries because they transport blood away from the heart, regardless of whether or not the blood is deoxygenated or oxygenated.

Does the pulmonary vein carries deoxygenated blood to the heart? ›

Generally, veins carry deoxygenated blood from the body to the heart, where it can be sent to the lungs. The exception is the network of pulmonary veins, which take oxygenated blood from the lungs to the heart.

Does pulmonary carries deoxygenated blood? ›

Your pulmonary arteries carry blood from your heart to your lungs. They're the only arteries in your body that carry oxygen-poor (deoxygenated) blood. Your main pulmonary artery (pulmonary trunk) leaves your right ventricle at your pulmonary valve.

Does oxygenated blood go to the pulmonary vein? ›

The oxygenated blood is brought back to the heart by the pulmonary veins which enter the left atrium.

Why are the four pulmonary veins? ›

The pulmonary veins are the veins that transfer oxygenated blood from the lungs to the heart. The largest pulmonary veins are the four main pulmonary veins, two from each lung that drain into the left atrium of the heart. The pulmonary veins are part of the pulmonary circulation.

What color is blood without oxygen? ›

Furthermore, the blood in human veins is also not blue. Blood is always red. Blood that has been oxygenated (mostly flowing through the arteries) is bright red and blood that has lost its oxygen (mostly flowing through the veins) is dark red.

How many pulmonary veins are there? ›

In normal conditions, the four pulmonary veins carry oxygenated blood from both lungs and drain into the left atrium, as follows: (a) the right superior pulmonary vein drains the right upper and middle lobes; (b) the left superior pulmonary vein drains the left upper lobe and lingula; and (c) the two inferior pulmonary ...

What connects the heart to the lungs? ›

The pulmonary artery is a big artery that comes from the heart. It splits into two main branches, and brings blood from the heart to the lungs. At the lungs, the blood picks up oxygen and drops off carbon dioxide. The blood then returns to the heart through the pulmonary veins.

What is the root of the lung? ›

The hilum (root) is a depressed surface at the center of the medial surface of the lung and lies anteriorly to fifth through seventh thoracic vertebrae. It is the point at which various structures enter and exit the lung. The hilum is surrounded by pleura, which extends inferiorly and forms a pulmonary ligament.

What are the 5 pulmonary veins? ›

1: Five pulmonary veins entering left atrium (LSPV=Left superior pulmonary vein, LIPV=Left inferior pulmonary vein, RSPV=Right superior pulmonary vein, RMPV=Right middle pulmonary vein, RIPV=Right inferior pulmonary vein).

Why are pulmonary veins red? ›

The pulmonary vein carries oxygenated blood from the lungs to the heart and therefore, the pulmonary vein is conventionally shown in red colour.


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