A pulmonary artery is an

artery An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pu ...

in the

pulmonary circulation The pulmonary circulation is a division of the circulatory system in all vertebrates. The circuit begins with deoxygenated blood returned from the body to the right atrium of the heart where it is pumped out from the right ventricle to the lung ...

that carries deoxygenated

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in th ...

from the right side of the

heart The heart is a muscular organ found in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon diox ...

to the lungs. The largest pulmonary artery is the ''main pulmonary artery'' or ''pulmonary trunk'' from the

, and the smallest ones are the

arteriole An arteriole is a small-diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries. Arterioles have muscular walls (usually only one to two layers of smooth muscle cells) and are the pri ...

s, which lead to the

capillaries A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the body: ...

that surround the

pulmonary alveoli A pulmonary alveolus (plural: alveoli, from Latin ''alveolus'', "little cavity"), also known as an air sac or air space, is one of millions of hollow, distensible cup-shaped cavities in the lungs where oxygen is exchanged for carbon dioxide. Al ...

Structure

The pulmonary arteries are

blood vessel Blood vessels are the structures of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away from ...

s that carry systemic venous blood from the right ventricle of the heart to the microcirculation of the lungs. Unlike in other organs where arteries supply oxygenated blood, the blood carried by the pulmonary arteries is deoxygenated, as it is venous blood returning to the heart. The main pulmonary arteries emerge from the right side of the heart, and then split into smaller arteries that progressively divide and become

s, eventually narrowing into the capillary microcirculation of the lungs where gas exchange occurs.

Pulmonary trunk

In order of blood flow, the pulmonary arteries start as the pulmonary trunk that leaves the fibrous pericardium (

parietal pericardium The pericardium, also called pericardial sac, is a double-walled sac containing the heart and the roots of the great vessels. It has two layers, an outer layer made of strong connective tissue (fibrous pericardium), and an inner layer made o ...

) of the

ventricular outflow tract A ventricular outflow tract is a portion of either the left ventricle or right ventricle of the heart through which blood passes in order to enter the great arteries. The right ventricular outflow tract (RVOT) is an infundibular extension of t ...

right ventricle A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood towards the peripheral beds within the body and lungs. The blood pumped by a ventricle is supplied by an atrium, an adjacent chamber in the upper ...

(also known as infundibulum or conus arteriosus. The outflow track runs superiorly and to the left, posterior to the

pulmonary valve 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 ...

. The pulmonary trunk bifurcates into right and left pulmonary arteries below the arch of aorta and in front of the left main bronchus. Pulmonary trunk is short and wideapproximately in length and - in diameter. The pulmonary trunk splits into the right and the left main pulmonary artery. The left main pulmonary artery is shorter than the right, passes behind and downwards the descending aorta and above the left main bronchus to the root of the left lung. Above, the left main pulmonary artery is connected to the concavity of the proximal descending aorta by the ligamentum arteriosum. The right pulmonary artery pass across the midline of the body, below the carina of trachea, and comes in front of the right main bronchus.

Branches

The left main pulmonary artery then divides into two lobar arteries, one for each lobe of the left lung. At the right root of the lung, it bifurcates into artery that supplies the right upper lobe of the lung, in front of the right upper lobe bronchus, and interlobar artery that supplies the right middle and inferior lobes of the lung, running together with bronchus intermedius. The right and left main pulmonary (lungs) arteries give off branches that supplies the corresponding lung lobes. In such cases it is termed lobar arteries. The lobar arteries branch into segmental arteries (roughly 1 for each segment). Segmental arteries run together with segmental bronchi, at the posterolateral surfaces of the bronchi. These in turn branch into subsegmental pulmonary arteries. These eventually form intralobular arteries. The pulmonary arteries supply the alveoli of the lungs. In contrast, bronchial arteries, that has different origins, supply the bronchi of the lungs.

Development

The pulmonary arteries originate from the truncus arteriosus and the sixth pharyngeal arch. The truncus arteriosus is a structure that forms during the development of the heart as a successor to the conus arteriosus. By the third week of development, the endocardial tubes have developed a swelling in the part closest to the heart. The swelling is known as the bulbus cordis and the upper part of this swelling develops into the truncus arteriosus. The structure is ultimately mesodermal in origin. During development of the heart, the heart tissues undergo folding, and the truncus arteriosus is exposed to what will eventually be both the left and right ventricles. As a

septum In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interat ...

develops between the two ventricles of the heart, two bulges form on either side of the truncus arteriosus. These progressively enlarge until the trunk splits into the

aorta The aorta ( ) is the main and largest artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries (the common iliac arteries). The aorta distributes ...

and pulmonary arteries. During early development, the ductus arteriosus connects the pulmonary trunk and the aortic arch, allowing blood to bypass the lungs.

Function

The pulmonary artery carries deoxygenated blood from the

to the lungs. The blood here passes through

adjacent to alveoli and becomes oxygenated as part of the process of respiration. In contrast to the ''pulmonary arteries'', the bronchial arteries supply nutrition to the lungs themselves.

Pressure

The pulmonary artery pressure (PA pressure) is a measure of the

blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressur ...

found in the main pulmonary artery. This is measured by inserting a

catheter In medicine, a catheter (/ˈkæθətər/) is a thin tube made from medical grade materials serving a broad range of functions. Catheters are medical devices that can be inserted in the body to treat diseases or perform a surgical procedure. Cat ...

into the main pulmonary artery. The mean pressure is typically 9–18 mmHg, and the wedge pressure measured in the

left atrium The atrium ( la, ātrium, , entry hall) is one of two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular valves. There are two ...

may be 6–12 mmHg. The wedge pressure may be elevated in

left heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...

mitral valve stenosis Mitral stenosis is a valvular heart disease characterized by the narrowing of the opening of the mitral valve of the heart. It is almost always caused by rheumatic valvular heart disease. Normally, the mitral valve is about 5 cm2 during ...

, and other conditions, such as

sickle cell disease Sickle cell disease (SCD) is a group of blood disorders typically inherited from a person's parents. The most common type is known as sickle cell anaemia. It results in an abnormality in the oxygen-carrying protein haemoglobin found in red b ...

Clinical significance

The pulmonary artery is relevant in a number of clinical states. Pulmonary hypertension is used to describe an increase in the pressure of the pulmonary artery, and may be defined as a mean pulmonary artery pressure of greater than 25 mmHg. As can be measured on a

CT scan A computed tomography scan (CT scan; formerly called computed axial tomography scan or CAT scan) is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers ...

, a diameter of more than 29 mm diameter is often used as a cut-off to indicate pulmonary hypertension. In chest X-rays, diameter of descending pulmonary artery more than 16 mm indicates pulmonary hypertension. This may occur as a result of heart problems such as

heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, ...

, lung or airway disease such as

COPD Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...

scleroderma Scleroderma is a group of autoimmune diseases that may result in changes to the skin, blood vessels, muscles, and internal organs. The disease can be either localized to the skin or involve other organs, as well. Symptoms may include areas o ...

, or thromboembolic disease such as

pulmonary embolism Pulmonary embolism (PE) is a blockage of an artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism). Symptoms of a PE may include shortness of breath, chest pain particularly upon breathing ...

or emboli seen in sickle cell anaemia. Most recently, computational fluid based tools (non-invasive) have been proposed to be at par with the current clinical tests (invasive) of pulmonary hypertension. Pulmonary embolism refers to an embolus that lodges in the pulmonary circulation. This may arise from a deep venous thrombosis, especially after a period of immobility. A pulmonary embolus is a common cause of death in patients with cancer and stroke. A large pulmonary embolus that becomes lodged in the bifurcation of the pulmonary trunk with extensions into both the left and right main pulmonary arteries is called a ''saddle embolus''. Several animal models have been utilized for investigating pulmonary artery related pathologies. Porcine model of pulmonary artery is the most frequently used and it was recently found that their mechanical properties vary with every subsequent branching.

Additional images

File:Relations of the aorta, trachea, esophagus and other heart structures.png, Image showing ''main pulmonary artery'' coursing ventrally to the aortic root and

trachea The trachea, also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends from th ...

, and the ''right pulmonary artery'' passes dorsally to the ascending aorta, while the ''left pulmonary artery'' passes ventrally to the descending aorta. File:Illu pulmonary circuit.jpg, Pulmonary circuit File:Gray503.png, Transverse section of thorax, showing relations of pulmonary artery. File:Slide16444 (1).jpg, alt=Original image from Anatomist 90, Pulmonary artery File:Slide44uru.JPG, Pulmonary artery.Deep dissection.Anterior view. File:Computed tomograph of pulmonary vessels.jpg,

of a normal lung, with different levels of pulmonary arteries. File:Bronchial anatomy.jpg, Bronchial anatomy

References

External links

* – "Heart: The Pericardial sac and

Great vessels Great vessels are the large vessels that bring blood to and from the heart. These are: * Superior vena cava *Inferior vena cava * Pulmonary arteries * Pulmonary veins *Aorta Transposition of the great vessels is a group of congenital heart de ...

" * – "Heart: Openings of Great Vessels into the Pericardial Sac" * – " Mediastinal surface of the right lung" * – "Mediastinal surface of the left lung" * {{DEFAULTSORT:Pulmonary Artery Arteries of the thorax