The Circulatory System – Keeping Your Body in Motion

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The Circulatory System – Keeping Your Body in Motion

Introduction

Your heart may be the size of your fist, but it’s got the strength and endurance to keep you alive every second of your life. The circulatory system—also called the cardiovascular system—is your body’s internal transport network. It delivers oxygen and nutrients to your cells, removes waste like carbon dioxide, and powers every process in between.

The Heart: Your Body’s Central Pump

The heart has four main chambers:

  • Right atrium: Receives deoxygenated blood from the body via the superior and inferior vena cava.

  • Right ventricle: Pumps that blood to the lungs via the pulmonary artery.

  • Left atrium: Receives oxygenated blood back from the lungs via the pulmonary veins.

  • Left ventricle: Pumps oxygen-rich blood to the rest of the body through the aorta.

Each chamber has its own set of valves to prevent backflow:

  • Tricuspid valve (between right atrium and ventricle)

  • Pulmonary valve (to the lungs)

  • Bicuspid valve (between left atrium and ventricle)

  • Aortic valve (to the rest of the body)

Blood Flow Pathway (In Order)

  1. Body → Vena Cava (Superior Vena Cava & Inferior Vena Cava)

  2. → Right Atrium

  3. → Tricuspid Valve

  4. → Right Ventricle

  5. → Pulmonary Valve

  6. → Pulmonary Arteries

  7. → Lungs (oxygenation happens here!)

  8. → Pulmonary Veins

  9. → Left Atrium

  10. → Bicuspid Valve

  11. → Left Ventricle

  12. → Aortic Valve

  13. → Aorta

  14. → Body Again (to deliver oxygen)



Blood Vessels 101

  • Arteries carry blood away from the heart (mostly oxygenated).

  • Veins carry blood to the heart (mostly deoxygenated).

  • Capillaries are where gas exchange happens at the tissue level.

Blood Pressure: Systolic vs Diastolic

  • Systolic pressure (120 mmHg) – When the heart contracts and pushes blood out.

  • Diastolic pressure (80 mmHg) – When the heart relaxes and refills with blood.

  • Heart rate (65 bpm average) – Number of heartbeats per minute.


Pulmonary vs. Systemic Circuits:

One of the most important but often overlooked details in the circulatory system is this: every organ has its own blood circuit. That means your kidneys, liver, stomach, and even your toes all get blood delivered directly from the heart and returned straight back again.

This is essential because each organ has unique needs. Your lungs require a circuit to exchange gases (oxygen in, carbon dioxide out), while your kidneys filter waste from blood, and your liver metabolizes nutrients and toxins. If these organs all shared the same path before blood got filtered and re-oxygenated, some would never get what they need.

  • Pulmonary Circuit: Blood flows from the heart to the lungs and back to the heart (for oxygen exchange).

  • Systemic Circuit: Blood is pumped from the heart to the rest of the body—organs, muscles, tissues—and returns deoxygenated.




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