The circulatory system is divided into two main circuits: the pulmonary circulation and the systemic circulation. Each circuit has a specific path that blood follows throughout the body.
1. Pulmonary Circulation
The primary function of pulmonary circulation is to carry deoxygenated blood from the heart to the lungs and return oxygenated blood back to the heart. Here’s the step-by-step path:
- Right Atrium: Deoxygenated blood from the body returns to the heart via the superior and inferior venae cavae and enters the right atrium.
- Right Ventricle: From the right atrium, blood flows through the tricuspid valve into the right ventricle.
- Pulmonary Arteries: When the right ventricle contracts, blood is pumped through the pulmonary valve into the pulmonary arteries.
- Lungs: The pulmonary arteries transport the blood to the lungs, where it passes through the capillary networks surrounding the alveoli (tiny air sacs). Here, carbon dioxide is exchanged for oxygen through the process of respiration.
- Pulmonary Veins: The now oxygenated blood returns to the heart via the pulmonary veins.
- Left Atrium: The pulmonary veins empty into the left atrium.
2. Systemic Circulation
Systemic circulation is responsible for delivering oxygenated blood from the heart to the rest of the body and returning deoxygenated blood back to the heart. The path is as follows:
- Left Atrium: The oxygenated blood from the lungs enters the left atrium through the pulmonary veins.
- Left Ventricle: Blood flows from the left atrium through the mitral (bicuspid) valve into the left ventricle.
- Aorta: When the left ventricle contracts, blood is pumped into the aorta, the main artery that distributes oxygenated blood throughout the body.
- Arteries and Arterioles: The aorta branches into smaller arteries and arterioles, which deliver blood to various tissues and organs.
- Capillaries: In the tissues, oxygen and nutrients are exchanged for carbon dioxide and metabolic wastes through the thin walls of the capillaries.
- Veins and Venules: The deoxygenated blood collects into venules, which merge to form larger veins.
- Venae Cavae: Ultimately, deoxygenated blood returns to the heart via the superior and inferior venae cavae, entering the right atrium, where the cycle begins anew.
Summary
In summary, the path of blood flow can be condensed into two main routes:
- Pulmonary Circulation: Right atrium → Right ventricle → Pulmonary arteries → Lungs → Pulmonary veins → Left atrium.
- Systemic Circulation: Left atrium → Left ventricle → Aorta → Body tissues → Veins → Superior/Inferior venae cavae → Right atrium.
This continuous cycle ensures that the body receives the oxygen and nutrients it needs while disposing of carbon dioxide and other waste products.
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