Transportation of Oxygen : Respiratory physiology USMLE Step 1

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Transportation of Oxygen : Respiratory physiology USMLE Step 1

Oxygen is transported from the lungs to the tissues by the circulatory system. The oxygen-rich blood from the lungs enters the left atrium, then flows into the left ventricle and is pumped out into the systemic circulation via the aorta. The oxygen is then taken up by hemoglobin, the protein found in red blood cells that binds oxygen, and is transported to the tissues.

There are several factors that affect the binding of oxygen to hemoglobin. One of the most important factors is the partial pressure of oxygen in the blood, commonly known as the PO2. As the PO2 increases, more oxygen binds to hemoglobin, and as the PO2 decreases, less oxygen binds to hemoglobin. This relationship is described by the oxygen-hemoglobin dissociation curve.

Another factor that affects the binding of oxygen to hemoglobin is the presence of other molecules in the blood, such as carbon monoxide (CO) and hydrogen ions (H+). CO binds to hemoglobin with a much higher affinity than oxygen, so even small amounts of CO in the blood can displace oxygen from hemoglobin and reduce oxygen transport. High levels of H+ in the blood, as seen in conditions such as acidosis, can also reduce the affinity of hemoglobin for oxygen and impair oxygen transport.

In addition to binding to hemoglobin, a small fraction of oxygen is dissolved in the plasma and transported in the blood. This dissolved oxygen is important because it can diffuse across cell membranes and directly enter the tissues, providing oxygen to areas with poor blood flow.

Overall, understanding the mechanisms of oxygen transport is critical to understanding respiratory physiology and preparing for the USMLE Step 1 exam.

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