Health and medicine

The medical world can be a confusing place. Patients and their families might feel overwhelmed by the large vocabularies and complicated explanations they get from their health care providers. Students entering health care also struggle to grasp the complexity of health sciences, and are forced to memorize huge amounts of information. We hope to make understanding the medical world a bit easier. Look around! These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay seeking it because of something you have read or seen in any Khan Academy video.
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Human anatomy and physiology

Get introduced to all of the major organ systems of the body. You'll learn some general anatomy (roadmap for your body), and how the organs work to keep you alive! Watch some videos, read some articles, try some flashcards, and then quiz yourself!

Advanced circulatory system physiology

Your heart sits in the middle of your chest and pumps blood from about 4 weeks after conception until the day that you die. It never stops, and over your lifetime it will pump ~175 million liters of blood. To visualize that, imagine the amount of water that falls over Niagara falls in a few minutes. Remarkable! This little pump is the size of your clenched fist and in an adult can weigh about 300 grams. Watch these videos to learn more about how the heart works, blood flow in arteries and veins, blood pressure, and lymphatics.

Circulatory system diseases

With the heart pumping 24 hours a day, 7 days a week, it’s absolutely vital to make sure things are flowing smoothly (pun intended!). Unfortunately, this isn’t always the case, and different parts of the circulatory system can cause problems: your heart, your blood vessels, and even the fluid in your tissues and blood itself can be the issue. To further complicate things, the underlying reasons for circulatory system problems vary from your genes (nature) to your lifestyle habits (nurture). An understanding of how different diseases can affect your circulatory system is important to combat this growing problem in the world.

Advanced respiratory system physiology

Place your hand on your ribs and inhale deeply. You’ll notice that your chest expands and your back straightens. As this occurs, air is rushing through your windpipe and branches off to either your left or right lung. After 20 to 30 more branch points, oxygen in the air ends up in the alveoli where it diffuses into the liquid that surrounds the alveoli, and slips into the blood. This microscopic gas exchange occurs rapidly, oxygen is taken into the body and carbon dioxide is removed from the body, and then you exhale. Learn more about the intricate and fascinating respiratory system in these videos!

Respiratory system diseases

Our lungs are composed of a bronchial tree (think of an upside down tree with millions of leaves), blood vessels bringing blood in and out, and a protein-rich fluid that forms a matrix holding everything together! If any part of this well-balanced organ isn’t working properly, a person can be left feeling short of breath. The lungs are also exposed to the outside environment, making them prone to infections. To counter infections, the lungs are lined with cells that have tiny protein bristles which wave back and forth and can literally sweep away dangerous bacteria. Learn more about diseases of the lungs and how modern medicine helps to keep them healthy!

Advanced hematologic system physiology

It takes between 30 seconds to a minute for your blood to travel from your heart, to your body, and back to the heart again - perhaps a bit longer if the trip is out to your big toe! Our blood is incredibly important for transporting oxygen throughout the body. Hemoglobin, the protein that fills our blood cells, has wonderful mechanisms to allow it to bind to both oxygen and carbon dioxide. This is important for effective and quick transport of the gases around our body. Our blood is about 45% cells and 55% plasma, so the old adage “blood is thicker than water” quite literally holds true in scientific terms! Learn more about how this amazing system works in the following videos.

Hematologic system diseases

Blood is incredibly important in combating disease and the healing process after an injury. It acts as a highway for medicine, stops bleeding, fights infections, controls cells from multiplying too fast, and so much more. But things can go wrong with blood too! What if your blood couldn’t clot and stop you from bleeding, or started to clot uncontrollably? What if your red blood cells or white blood cells suddenly disappeared? Blood contains many different types of tissues doing very different jobs, making diseases of the blood produce a variety of symptoms, including continuously feeling tired and bone pain. Learn about the different blood diseases, how they are diagnosed, and the cool ways health professionals treat these conditions.

Advanced endocrine system physiology

When you’re nervous before an important speech, or asking someone out on a date, you might feel butterflies in your stomach. This is actually the result of your endocrine system releasing hormones! You can’t really point to any single organ as “the endocrine system”, because it’s actually a family of glands that secrete hormones into the body. Hormones seep into the blood (imagine putting a tea bag into hot water), and as the blood flows around the body, it carries with it these important hormone molecules that interact with specific target cells and organs. This signaling system helps to keep the entire body well-balanced and on the same page.

Endocrine system diseases

Advanced nervous system physiology

There are billions and billions of neurons in your brain (about 85 billion), and they’re all sending electrical signals throughout your body right now! They tell your eyes to move across this page, how to interpret the words that you read, how to maintain your posture, your heart rate, and your breathing...all of it in a fraction of a second. In this section, we’ll explore the nature of this vast, complex system, from the cellular level to how it operates at a sensory level. A common misconception is that we only have 5 senses (see, smell, taste, hear, and feel), but we have many more that are nuanced but equally important. Learn more about how our bodies are designed to interact with the world.

Nervous system diseases

Advanced gastrointestinal physiology

Advanced muscular-skeletal system physiology

Muscular-skeletal diseases

Executive systems of the brain

Aristotle asserted that what separates humankind from non-human animals is our ability to engage in high reasoning. This reasoning includes solving problems, making decisions, recalling and recording memories, and expressing complex emotions. We’ll explore different states of consciousness, and how our brain adapts and responds to stimuli. Learn all about the higher-order executive functions of the brain, which help you remember your friend’s name, learn a new language, and even fall asleep at night.

Infectious diseases

There's an intricate dance between humans and viruses, bacteria, molds, and even tiny worms! They want to survive and replicate just like humans do... and this is why they cause infections.

Lab values and concentrations

Ever wonder about your lab values and what they mean? Lab values measure amounts of electrolytes or cells in your blood and occasionally tell you about how hormones and enzymes are working! Dive deeper and get a good understanding of concentrations as well!

Current events in health and medicine

Learn more about some of the current issues in health and medicine. Dr. Rishi Desai is a pediatric infectious disease physician and former epidemiologist with the Centers for Disease Control and Prevention (CDC)

Health care system

The health care system in the United States is rapidly changing. To better understand these changes, we review the health care insurance, drug pricing, physician compensation, and much more! join us as we explore the basics about the Health Care system in the US, including a comparison with European healthcare.



Circulatory system diseases

With the heart pumping 24 hours a day, 7 days a week, it’s absolutely vital to make sure things are flowing smoothly (pun intended!). Unfortunately, this isn’t always the case, and different parts of the circulatory system can cause problems: your heart, your blood vessels, and even the fluid in your tissues and blood itself can be the issue. To further complicate things, the underlying reasons for circulatory system problems vary from your genes (nature) to your lifestyle habits (nurture). An understanding of how different diseases can affect your circulatory system is important to combat this growing problem in the world.
Community Questions
All content in “Circulatory system diseases”

Coronary artery disease

Coronary artery disease - clogging of the arteries supplying the heart- is the cause of about 30% of all deaths globally, making it the leading cause of death. Stroke is a similarly debilitating condition that results from lack of perfusion to the brain. Unfortunately, patients with heart disease are more likely to suffer from heart disease and vice versa. You will come to an understanding of the pathophysiology behind these common diseases and how they relate to one another.

Atherosclerosis, arteriosclerosis, and arteriolosclerosis

The ancient Greeks thought blood vessels actually carried air throughout the body. Although we know better today, many people are still often confused with the specifics! We now know that the vessels carry blood instead, and we are able to distinguish between two different types: arteries and veins. Learn about how arteries differ from veins and how vessels can get damaged over time.


Nearly one billion people in the world have high blood pressure. That’s 1 in every 7 people! With the amount of unhealthy foods becoming increasingly available to everyone, it makes sense that this number is climbing. This set of videos will explore high blood pressure, also known as hypertension. Learn more about it, what it does to different parts of the body, symptoms of hypertension, and what you can do with your everyday life to manage it!

Aortic dissection and aneurysm

When a patient with hypertension and chest pain radiating to the back presents to the hospital, one should suspect aortic dissection, which is a tear of the inner lining (tunica intima) of the aorta, with dissection of blood through its middle layer (tunica media). And when an elderly male presents with a pulsatile abdominal mass, one should suspect a rupturing abdominal aortic aneurysm. An aneurysm is simply a balloon-like dilation of a vessel wall. You will come to an understanding of the pathophysiology of these life-threatening diseases in addition to their surgical and medical management.

Myocarditis and pericarditis

Inflammation of the heart muscle and the fibrous sac surrounding the heart are called myocarditis and pericarditis, respectively. Each of these disorders present with specific signs and symptoms. For instance, pericarditis sometimes presents with a subtle finding when listening to the heart with the stethoscope, termed the friction rub. You will come to appreciate the clinical differences between these diseases as well as their therapeutic management.Hell


Cardiomyopathy encompasses a group of diseases in which the myocardium (heart muscle) is unable to contract, leading to cardiac dysfunction. These flavors come in three flavors - dilated, restrictive, and hypertrophic. Patients unfortunately are at risk for heart failure, arrhythmias, and sudden cardiac death. We will discuss the signs and symptoms of the cardiomyopathies as well as what clinicians can do to treat these conditions.

Cardiac dysrhythmias and tachycardias

Your heart is an electrical organ, and it produces a rather rhythmic music - lub-dub, lub-dub. We are able to measure its music through the electrocardiogram (EKG), which is able to pick up pathological rhythms - supraventricular tachycardias, atrial fibrillation, and ventricular tachyardia for instance- through electrical leads placed on the chest. We will discover how to identify these dysrthymias as well as how these conditions are treated, such as through the use of anti-arrhythmic drugs and pacemakers.

Acyanotic heart diseases

Acyanotic means, quite simply “not blue.” When deoxygenated blood is pumped out by our heart into our vessels. Fortunately, not all congenital heart diseases result in cyanosis. In this module, we will discuss these acyanotic heart diseases, from atrial septal defect to patent ductus arteriosus as well as the embryological defects that lead to them.


Shock is a rather common clinical situation, especially in the emergency room. Quite simply, circulatory shock refers to poor perfusion of organs with blood. For example, shock may result from loss of blood (hemorrhage), a poorly functioning heart (heart failure), or dilated blood vessels (sepsis and anaphylactic shock). We will explore how to differentiate the many different causes of shock here.


Inflammation of the blood vessel wall is termed “vasculitis,” though the etiology of these diseases are rather nebulous. They present with nonspecific symptoms like fever, fatigue, weight loss. Large, medium, and small vessels can all be involved. We will explore the specific differences between the various vasculitides, which range from Takayasu arteritis to microscopic polyangitis.