Which one among the following statements about arteries and veins in humans is NOT correct ?

In the human circulatory system, arteries are defined as vessels that carry blood away from the heart, while veins bring blood toward the heart [3]. Generally, systemic arteries carry oxygenated blood and systemic veins carry deoxygenated blood [1]. However, the pulmonary circuit is a notable exception to this rule [1]. The pulmonary artery carries deoxygenated (oxygen-poor) blood from the right ventricle of the heart to the lungs for gas exchange [4]. Conversely, the pulmonary veins carry freshly oxygenated blood from the lungs back to the left atrium of the heart [1]. Therefore, the statement that pulmonary arteries 'always' carry oxygenated blood and pulmonary veins 'always' carry deoxygenated blood is incorrect. Additionally, arteries have thicker, more elastic walls to withstand high pressure, whereas veins have thinner walls and contain valves to prevent the backflow of blood [1].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > The tubes – blood vessels > p. 93
2. [3] https://www.nhlbi.nih.gov/health/heart/blood-flow
3. [2] https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/circulatory-system
4. [4] https://training.seer.cancer.gov/anatomy/cardiovascular/blood/classification.html