Question

All veins carry deoxygenated blood except (a) pulmonary vein (b) hepatic vein (c) hepatic portal vein (d) renal vein,

Short answer

The pulmonary vein is the exception; it carries oxygenated blood.

Step-by-step solution

Understanding the circulatory system

The circulatory system consists of the heart and blood vessels, which include arteries, veins, and capillaries. The main function of veins is to carry blood back to the heart. Typically, this blood is deoxygenated, having delivered its oxygen to the tissues of the body. However, there are exceptions to this rule.

Identifying the exceptions

To identify the vein that does not carry deoxygenated blood, understand that the pulmonary vein is the only vein in the list that carries oxygenated blood, as it brings blood back from the lungs to the heart after oxygenation. The hepatic vein, hepatic portal vein, and renal vein all carry deoxygenated blood from their respective organs back to the heart.

Selecting the correct option

Given the options, the pulmonary vein is the correct answer because it carries oxygenated blood from the lungs to the left atrium of the heart. Thus, the pulmonary vein is the only vein listed that does not carry deoxygenated blood.

Key concepts

Circulatory System

The essence of understanding the human body begins with grasping the complexities of the circulatory system. At its core, this system is like a vast network of highways, with the heart serving as the central hub from which all routes emanate. Blood vessels in the form of arteries, veins, and capillaries act as roads for the transportation of blood, which contains vital substances such as oxygen, nutrients, and waste products.

The arteries are blood vessels responsible for transporting oxygen-rich blood away from the heart to various body tissues. As the blood delivers oxygen and nutrients, it becomes deoxygenated, which is where veins play their part. They transport this deoxygenated blood back to the heart. However, there are exceptions to this pattern, such as the pulmonary veins, which defy the norm by carrying oxygenated blood. This unique exception is critical to understanding how oxygen flows through our bodies — a rare instance where veins reverse their usual role.

Understanding the circulatory system aids in comprehending broader physiological functions and underscores the importance of each component's role in maintaining homeostasis.

Veins and Oxygenation

Veins are traditionally defined as blood vessels that carry blood toward the heart, and in most cases, this blood is low in oxygen after having delivered it to the body's tissues. The notable exception to this convention is the pulmonary vein, which is the subject of the original exercise. It's essential to delve into this discrepancy to understand why the pulmonary veins are unique in the circulatory system.

The pulmonary veins' primary role is to transport freshly oxygenated blood from the lungs back to the left atrium of the heart. This is the only time in the circulatory journey where veins carry oxygen-rich blood. The process of oxygenation occurs in the lungs, where carbon dioxide is exchanged for oxygen. Once blood is oxygenated, it needs to be efficiently delivered to the heart so that it can then be pumped out to the rest of the body. This task falls to the pulmonary veins, making their role critical in the respiration and circulation processes.

Recognizing the special function of the pulmonary vein helps students understand the 'rule-breaker' of the vein family, supporting the body's vital requirement for oxygenated blood.

Blood Circulation

Blood circulation is a fundamental process necessary for life. The entire circulatory system's function hinges on the continuous flow of blood that nourishes all cells, tissues, and organs. This process is two-fold, involving both systemic and pulmonary circulation.

Systemic circulation describes the path of blood from the heart to the various parts of the body and back. During systemic circulation, oxygenated blood is pumped from the left ventricle into the aorta, dispersed through arteries to the entire body, and returns as deoxygenated blood via veins to the right atrium of the heart. Pulmonary circulation, on the other hand, refers to the movement of blood between the heart and lungs. Here, deoxygenated blood exits the right ventricle through the pulmonary artery, goes into the lungs for oxygenation, and then returns to the left atrium via the pulmonary vein—oxygen-rich and ready for systemic circulation.

Understanding the full cycle of blood circulation is crucial for students, as it illustrates how oxygen is transported to and from tissues, and pinpoints the special pathway of the pulmonary vein within this system.