The Journey of Erythrocytes: From Heart to Lungs and Back
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Entering the Heart: Erythrocytes (RBCs)
begin their journey returning from the body through the superior vena cava (from the upper body) or inferior vena cava (from the lower body), which are large veins that carry deoxygenated blood into the heart. The blood enters the right atrium of the heart.
2. Right Atrium to Right Ventricle: From the right atrium, the RBCs pass through the tricuspid valve (a one-way valve) into the right ventricle.
3. Right Ventricle to Pulmonary Circulation:
When the right ventricle contracts, the RBCs are pushed through the pulmonary valve into the pulmonary trunk. The pulmonary trunk splits into the right and left pulmonary arteries, which carry deoxygenated blood to the lungs. The RBC travels through these arteries to the lungs for oxygenation.
4. In the Lungs: In the lungs, the RBCs exchange carbon dioxide for oxygen in the capillaries surrounding the alveoli. The hemoglobin carried by the RBCs becomes oxygenated.
5. Returning to the Heart: After oxygenation, the RBCs travel through the pulmonary veins (two on the left and two on the right) back to the heart. The blood enters the left atrium of the heart.
6. Left Atrium to Left Ventricle: From the left atrium, the RBCs pass through the bicuspid (mitral) valve into the left ventricle.
7. Left Ventricle to Aorta: When the left ventricle contracts, the RBCs are pushed through the aortic valve into the ascending aorta. From the ascending aorta, the RBCs move into the aortic arch and then through various branches (like the brachiocephalic artery, left common carotid artery, and left subclavian artery) depending on the body region that will receive oxygenated blood.
8. Systemic Circulation: The RBCs enter the systemic arteries, which distribute oxygenated blood to the body tissues. They will travel through progressively smaller arteries and arterioles until they reach the capillaries of the organs and tissues, where they deliver oxygen and pick up carbon dioxide. Once the RBC has delivered its oxygen, it will start its journey back to the heart.