Crash Course: The Heart and Circulatory System

Introduction

• The heart is an iconic organ, but essentially functions as a pump.
• Powers the circulatory system, moving nutrients, oxygen, waste, etc.
• The heart does not directly relate to emotions like love or heartbreak.
• Main function: maintain pressure to ensure blood flow.

Basic Physiology

• Fluid flow: High pressure to low pressure (e.g., squirt gun).
• Heart maintains pressure gradients for blood circulation.
• Blood pressure: strain on arteries by heart-moving blood.
• Heart beats about 60 times per minute, 100,000 times a day.

Heart Anatomy

• Size: like two fists clasped together.
• Hollow, cone-shaped, weighs 250-350 grams.
• Located in the mediastinum cavity, angled toward left hip/right shoulder.
• Surrounded by the pericardium: tough outer fibrous layer, inner serous layer.
• Layers of heart wall: Epicardium, Myocardium (cardiac muscle), Endocardium.

Function and Structure

• Heart divided into two sides by the septum: creates four chambers.
  • Superior atria: low-pressure receiving chambers.
  • Inferior ventricles: high-pressure discharging chambers.
• Valves ensure one-way blood flow (lub-DUB sound).
• Atria receive blood, ventricles pump it out.
• Arteries and veins: Arteries carry blood away, veins return it.

Circulatory Loops

• Pulmonary Circulation Loop: Right ventricle → lungs → left atrium.
  • Blood exchanges carbon dioxide for oxygen in lungs.
• Systemic Circulation Loop: Left ventricle → body → right atrium.
  • Oxygenated blood delivered to organs, returning deoxygenated.

Blood Pressure

• Ventricles’ contraction/relaxation creates systole/diastole.
• Systolic pressure: peak pressure from ventricle contraction.
• Diastolic pressure: pressure when ventricles relax.
• Blood pressure affects heart, lungs, brain, kidneys, etc.

Conclusion

• Heart creates pressure differences to circulate blood.
• Understanding systolic and diastolic pressure is important.
• Thanks to contributors and team at Crash Course.

Filmed at the Doctor Cheryl C. Kinney Crash Course Studio. Contributions by Kathleen Yale, Blake de Pastino, Dr. Brandon Jackson, Nicholas Jenkins, Nicole Sweeney, Michael Aranda, and Thought Cafe.