How many capillary beds must a red blood cell in the pulmonary artery pass before reaching the veins of the skin?

In the given scenario, a red blood cell in the pulmonary artery would journey through the circulatory system typically by passing through two distinct capillary beds before reaching the veins of the skin.

Initially, the red blood cell travels from the pulmonary artery to the lungs where gas exchange occurs in the pulmonary capillaries. Here, the cell picks up oxygen and releases carbon dioxide. After this exchange, the oxygenated red blood cell returns to the heart via the pulmonary veins and enters the left atrium, subsequently moving into the left ventricle.

Once the oxygen-rich blood is pumped from the left ventricle, it travels through the systemic circulation. As part of this journey, it reaches the capillary beds in tissues, such as those in the skin. This second capillary bed allows for interaction between the blood and the surrounding tissues, transferring oxygen to skin cells while collecting carbon dioxide and other waste products.

Thus, the answer to the question highlights the necessity of two capillary beds: the first in the lungs (pulmonary capillaries) and the second in the peripheral tissues (such as the skin). This systemic architecture provides essential functions of gas exchange and nutrient delivery throughout the body.