How the Heart Works: The Science of Pumping Blood
Ever wonder how the heart pumps blood? It’s a complex organ, but here’s the short version: Electrical impulses trigger the heart’s pumping action, and many moving parts help oxygen-rich blood circulate.
For students pursuing health careers, understanding heart function isn’t just fascinating — it’s foundational for the MCAT and professional programs. In honor of American Heart Month, we’re unpacking the complicated process of how the heart works.
How the Heart Works
The heart is one big muscle: a dedicated pump. It uses powerful muscular contractions to push about 2,000 gallons of blood through the body per day. But those contractions don’t happen randomly. The heart has its own built-in electrical system that controls every beat.
Every Heartbeat Starts With Electricity
Did you know that the heart has its own electrical power supply? It’s the sinus node, a tiny clump of specialized cells found in the right atrium.
The sinus node fires about 60 to 100 rhythmic electrical signals every minute. It generates these signals as charged sodium, calcium and potassium ions flow in and out. This electrical stimulus triggers both atria to contract.
The electrical impulse shoots down to the ventricles as the atrial blood is pushed into them. The ventricles then contract, pumping blood out of the heart while the atria get a blood refill. This sequence is one “pump” or heartbeat.
Because the heart pumps blood with each contraction they cause, electrical impulses are key to healthy heart function. This is why medical teams use a defibrillator: a quick electric shock that stops cardiac arrhythmia (irregular heartbeat). The heart can then reset, letting the sinus node take back over and restore a regular rhythm.
The Sinus Node: How Your Heart Keeps a Steady Beat
When the sinus node works properly, it creates a steady pattern called the cardiac cycle: the pattern of the heart’s chambers tightening and relaxing to pump blood, from the start of one beat to the next. The heart’s rhythm is regulated by the sinus node — the heart’s own pacemaker.
Each heartbeat has a relaxation phase (diastolic) when the chambers fill with blood and a contraction phase (systolic) when they pump it out. (This is where those two numbers in your blood pressure reading come from.) The atria and ventricles take turns — while one relaxes, the other contracts.
The heart’s mechanical functions, from pumping blood to keeping pressure steady, depend on its electrical system, and it all starts with the sinus node.
What Are the 12 Steps of Blood Flow Through the Heart?
How is blood pumped away from the heart and brought back in? The process is complex, involving a crucial detour through the lungs.
The heart has four chambers: two upper chambers (atria) and two lower chambers (ventricles). Blood flows through these chambers in 12 coordinated steps. Here’s the step-by-step flow:
- Deoxygenated blood flows into the heart through the vena cava.
- The blood enters the right atrium.
- The blood is propelled through the tricuspid valve.
- The blood flows into the right ventricle.
- It’s then pushed through the pulmonary valve.
- The pulmonary artery carries blood to the lungs for oxygenation.
- Oxygenated blood returns from the lungs to the heart through the pulmonary veins.
- The blood enters the left atrium.
- It then passes through the mitral valve.
- The blood enters the left ventricle.
- Blood is pushed through the aortic valve into the aorta.
- The aorta sends oxygenated blood out to the body.
All of this happens in a second or less with a normal heart rate. Here’s a video illustrating the process.
The heart’s one part of a larger body system devoted to getting blood where it needs to go, but it doesn’t work alone. Once blood leaves the heart, the circulatory system takes over. This network of blood vessels delivers oxygen and nutrients throughout your entire body.
What Is the Circulatory System?
The circulatory system is a network dedicated to moving oxygen-rich blood through the body and waste products out. This “blood highway” has two components:
- The heart: the hub and traffic control center
- Blood vessels: about 60,000 miles of veins, arteries and capillaries that form the routes for blood to travel outside the heart
Veins transport blood to the heart, while arteries move it away. Capillaries trade oxygen and nutrients for carbon dioxide and waste throughout the body.
Study Heart Function and Physiology With UF Online
Understanding how the heart pumps blood — and how to keep it healthy — is central to many meaningful health careers. Thinking about heading in that direction?
UF’s online medical sciences degrees prepare you for your next step, whether that’s a new career path or more advanced training. Pick the option that fits your interests and goals:
- MS in Medical Physiology and Pharmacology
- MS in Medical Physiology and Aging
- MS in Medical Anatomy and Physiology
- MS in Anatomical Sciences Education
Fascinated by how the heart works? These programs let you dive deeper into the cardiovascular system, cardiovascular physiology and circulation.
Not looking for a degree right now? UF also offers online graduate certificates you can finish in as little as 9 credits, including a cardiovascular/renal physiology specialization.
Learn more about UF’s online medical sciences graduate programs here.
Sources:
https://www.hopkinsmedicine.org/health/wellness-and-prevention/facts-about-blood
https://quartzmountain.org/article/how-blood-travels-through-the-cardiovascular-system
https://my.clevelandclinic.org/health/articles/17060-how-does-the-blood-flow-through-your-heart
https://www.ncbi.nlm.nih.gov/books/NBK537194/
https://www.nhlbi.nih.gov/health/heart/blood-flow
https://www.news-medical.net/health/How-the-Heart-Pumps-Blood.aspx
https://medlineplus.gov/ency/imagepages/19612.htm
https://myhealth.alberta.ca/Health/pages/conditions.aspx?hwid=tx4097abc
