Pulmonary Artery: Hypertension, Functions, Significance & Anatomy

Introduction

A significant blood channel called the pulmonary artery transports deoxygenated blood from the right ventricle of the heart to the lungs, where it is exchanged for oxygen. In the human body, the pulmonary artery is special in terms of its anatomy, purpose, and importance. Additionally, it has an impact on a number of illnesses, including pulmonary arterial hypertension (PAH), an uncommon but potentially fatal disorder that affects the pulmonary circulation.

The pulmonary arteries' anatomy

The pulmonary trunk, also known as the pulmonary artery, emerges from the right ventricle of the heart as a single trunk. The pulmonary trunk measures 3 cm in diameter and 5 cm in length. The right and left pulmonary arteries split off from it after a modest ascent.

In comparison to the left, the right pulmonary artery is larger and longer. It crosses the upper chest and enters the right lung at the hilum after passing behind the ascending aorta and in front of the descending aorta. The superior, middle, and inferior lobes of the right lung are supplied by the right pulmonary artery's three lobar branches, which are divided into them.

Compared to the right one, the left pulmonary artery is shorter and narrower. It spreads out horizontally to the left side of the aorta before going through the hilum and into the left lung. The superior and inferior lobes of the left lung are supplied by the left pulmonary artery's two lobar branches.

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The segmental branches that are further divided into lobar branches within each lung supply each bronchopulmonary segment. In order to create a network around the bronchioles and alveoli, the segmental branches divide into smaller subsegmental arteries. The capillaries that finally emerge from the subsegmental arteries are in close proximity to the alveolar walls, where gas exchange takes place.

The tunica intima, tunica media, and tunica adventitia are the three layers that make up the pulmonary artery walls. The deepest layer, known as the tunica intima, is made up of endothelial cells and a thin layer of connective tissue. The middle layer, known as the tunica media, is made up of elastic fibres and smooth muscle cells. The outermost layer, known as the tunica adventitia, is made up of connective tissue and vasa vasorum, which are tiny blood vessels that supply the bigger ones.

Compared to systemic arteries, the pulmonary arteries have thinner walls and less smooth muscle. As a result, they can hold huge volumes of blood under low pressure and respond by expanding or contracting in reaction to variations in blood flow or oxygen levels.

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The Pulmonary Arteries Role

Transporting deoxygenated blood from the right ventricle of the heart to the lungs for gas exchange is the primary purpose of the pulmonary artery. Low partial pressures of oxygen (PO2) and high partial pressures of carbon dioxide (PCO2) characterise the blood in the pulmonary artery. It produces carbon dioxide when it passes through the pulmonary capillaries and absorbs oxygen from the alveoli. The blood subsequently travels through four pulmonary veins with high PO2 and low PCO21 to the left atrium of the heart.

Additionally, the pulmonary artery serves the following purposes:

• Controlling the pulmonary vascular resistance (PVR), which is influenced by the pulmonary arteriole diameter. The pressure gradient between the right ventricle and left atrium, which governs cardiac output, is impacted by PVR. Numerous factors, including acidosis, hypoxia, nitric oxide, prostacyclin, endothelin-, serotonin, angiotensin II, and norepinephrine, affect PVR. PVR typically falls off with physical activity, pregnancy, and high altitude.
• The pulmonary endothelium contains a variety of receptors and chemicals that regulate the inflammatory response, contributing to humoral and cellular immunity. Leukocytes, platelets, and blood coagulation factors all interact with the pulmonary endothelium .
• Releasing chemicals that control the tone of the pulmonary arteries, such as nitric oxide, prostacyclin, and endothelin-13. Vasodilators such prostacyclin and nitric oxide help to relax smooth muscle cells and reduce PVR3. Vasoconstrictor endothelin-1 makes smooth muscle cells contract and raises PVR3.
• Detecting mechanical forces produced by blood flow, such as shear stress and stretch. The pulmonary endothelium and smooth muscle cells are impacted by these factors in terms of their composition and operation. For instance, shear stress stimulates the formation of prostacyclin and nitric oxide. Stretch modifies calcium signalling pathways and ion channel activity, which in turn modifies smooth muscle cell contraction.

Important Functions of the Pulmonary Artery

The pulmonary artery is important for a number of causes, including:

It is necessary for the body's tissues and organs to receive oxygen. Without sufficient oxygenation, tissue hypoxia, organ failure, and death would result from reduced cellular metabolism and function.

It depicts the right hearts' hemodynamic condition. By measuring the pressure in the pulmonary artery using catheterization or echocardiography, it is possible to learn more about the right ventricles' preload, afterload, contractility, and compliance. The existence or severity of numerous cardiac or respiratory disorders, including heart failure, pulmonary embolism, chronic obstructive pulmonary disease (COPD), and interstitial lung disease (ILD), can also be determined by the pressure in the pulmonary artery.

It participates in a number of pathological processes that have an impact on the pulmonary circulation. One such is PAH, an uncommon form of pulmonary hypertension (PH) that causes the arteries in and around the lungs to constrict, stiffen, and thicken. Right heart failure, right ventricular hypertrophy, elevated PVR, and decreased survival are all caused by PAH. In addition to connective tissue diseases, congenital cardiac abnormalities, HIV infection, portal hypertension, and drug use, PAH can also be idiopathic or linked to other diseases and situations. By monitoring the pulmonary capillary wedge pressure (PCWP) (15 mmHg) and the mean pulmonary arterial pressure (mPAP) (>25 mmHg at rest or >30 mmHg during activity), catheterization can be used to diagnose PAH. Prostacyclin analogues, endothelin receptor antagonists, phosphodiesterase type 5 inhibitors, soluble guanylate cyclase stimulators, and tyrosine kinase inhibitors are just a few of the pharmacological medications that can be used to treat PAH.

Conclusion

The pulmonary artery, which connects the right heart with the lungs, is an essential part of the cardiovascular system. Its anatomy, purpose, and importance in the human body are all distinctive. Additionally, it affects a number of illnesses, including PAH, a chronic, progressive ailment marked by angioproliferative vasculopathy in the pulmonary arterioles.