Khan Academy on a Stick

  • Meet the heart!

    Find out exactly where the heart rests in your body and what it does. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Flow through the heart

    Learn how blood flows through the heart, and understand the difference between systemic and pulmonary blood flow. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Two circulations in the body

    Learn the difference between the pulmonary and systemic circulatory systems in the body. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Lub dub

    Ever wonder why the heart sounds the way that it does? Opening and closing of heart valves makes the heart rhythm come alive with its lub dub beats... Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Layers of the heart

    Take a closer look at the heart, explore some of its interesting features and get to know the three layers that make up the heart. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Thermoregulation in the circulatory system

  • Arteries vs. veins - what's the difference?

    Learn some important differences between arteries (high pressure/low volume) and veins (low pressure/high volume). Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Arteries, arterioles, venules, and veins

    Learn the differences between these blood vessels! Rishi is a pediatric infectious disease physician and works at Khan Academy. 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 in seeking it because of something you have read or seen in any Khan Academy video.

  • Circulatory system and the heart

    Introduction to the circulatory system and the heart

Circulatory system introduction

No organ quite symbolizes love like the heart. One reason may be that your heart helps you live, by moving ~5 liters (1.3 gallons) of blood through almost 100,000 kilometers (62,000 miles) of blood vessels every single minute! It has to do this all day, everyday, without ever taking a vacation! Now that is true love. Learn about how the heart works, how blood flows through the heart, where the blood goes after it leaves the heart, and what your heart is doing when it makes the sound “Lub Dub.”

  • Meet the lungs

    Every time you take a breath, oxygen makes it way into your lungs. Follow along on that journey! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • People and plants

    Learn more about photosynthesis and cellular respiration through a classic story: Jack and the Beanstalk. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • The bronchial tree

    Follow the path of an oxygen molecule as it makes its way from your mouth down to an alveolus! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Inhaling and exhaling

    Find out exactly why air goes in and out of the lungs. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • How does lung volume change?

    Learn about how muscle contraction and lung recoil actually help the lungs change their volume with every breath! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Thermoregulation in the lungs

  • The lungs and pulmonary system

    The pulmonary system including the lungs, larynx, trachea, bronchi, bronchioles, alveoli and thoracic diaphragm

Respiratory system introduction

Did you know that your right lung is larger than your left? That’s because the majority of your heart is on the left side of your body, and your left lung is slightly smaller to accommodate it. The lungs take in oxygen and help you breathe out carbon dioxide. Humans have an intricate respiratory system, with hundreds of millions of tiny air sacs called alveoli, where all of the magic happens. These videos will introduce you to the lungs, and show how they help you survive.

Hematologic system introduction

Roughly 5 L of blood fill your arteries, veins, capillaries, and venules. What’s it good for you ask? It carries oxygen to help your cells carry out respiration in addition to a number of other substances like lipids and hormones throughout the body. In cases of blood loss, such as trauma situations, the physician must be wary of the different blood types. We will explore the intricacies of the hematologic system here.

Urinary system introduction

If you want to learn more about the renal system, then urine the right place! (Pun aside, the kidneys are about more than just making urine). Every thirty minutes, your kidneys filter the entire blood supply in your body. Imagine a dirty pool filled with algae. Placing a filter in this pool will cause the algae to be flushed out, and after a time you’ll have a clean, crisp blue pool to enjoy. Just like the filter for a pool, our kidneys filter the blood and remove toxic wastes. These paired organs are key to maintaining electrolyte and water homeostasis in your body.

Immunologic system introduction

Chances are, you’ve had a fever or a cough at least once in your life (unless you live in a bubble, in which case you should probably go out more!) Have you ever wondered why your body reacts this way? Your body has a deadly arsenal of weapons against microbial invaders, ranging from bacteria and viruses to protozoans and fungi. We have specialized cells that destroy foreign bodies through mechanisms such as consumption, expulsion, and degradation. You will become acquainted with the interplay of the numerous soldiers in your body’s army and how they keep you healthy!

Nervous system introduction

Neurons transmit information to one another through electrochemical signals. They make up the motor nerves that allow you to type an essay, the sensory nerves that let you feel a fluffy dog, and your brain, allowing to remember the content of this module. They have a number of helper cells, ranging from astrocytes, to microglia, to ependymal cells as well. You will come to appreciate the structure and function of neurons and the comrade cells which help to maintain the optimal function of the nervous system.

  • Myosin and actin

    How myosin and actin interact to produce mechanical force.

  • Tropomyosin and troponin and their role in regulating muscle contraction

    Tropomyosin and troponin and their role in regulating muscle contraction. How calcium ion concentration dictates whether a muscle is contracting or not.

  • Role of the sarcoplasmic reticulum in muscle cells

    The role of the sarcoplasmic reticulum in controlling calcium ion concentrations within the muscle cell.

  • Anatomy of a muscle cell

    Understanding the structure of a muscle cell. By Raja Narayan.

  • Three types of muscle

    Understanding the structure of a muscle cell.

  • Motor neurons

    How do neurons help us move? Learn about how motor neurons send signals to muscle cells and what happens when we damage this precious neurons. By Raja Narayan.

  • Neuromuscular junction, motor end-plate

    How do neurons talk directly to muscle cells? Learn about how a neuronal message is translated into a muscular action at the neuromuscular junction. By Raja Narayan.

  • Type 1 and type 2 muscle fibers

    What's the difference between type 1 and type 2 muscle fibers? Learn one golden rule that will help you easily distinguish between them. By Raja Narayan.

  • Calcium puts myosin to work

    See exactly how Calcium binds Troponin-C and allows Myosin to do some work.

  • Muscle innervation

    Which muscles do we voluntarily control? Which muscles do we have NO control over? What's the difference between sympathetic and parasympathetic innervation? Learn about how our brain splits its control over the body into autonomic and somatic nervous systems.  By Raja Narayan.

  • Autonomic vs somatic nervous system

    Understand the different divisions of the brain that control our muscles.  By Raja Narayan.

  • Thermoregulation by muscles

    Why do we shiver when it's cold? How do our muscles make sure we don't freeze or have a heat stroke? Learn how the skin, brain, blood vessels, and muscles work together to maintain our core body temperature.  By Raja Narayan.

Muscular system introduction

Muscles never sleep (literally). If you have ever taken a breath, you have benefited from the work of the diaphragm, which contracts to create an area of low pressure within your thoracic cavity, allowing air in. How exactly are some weightlifters able to support 717 lbs without breaking anything more than a little sweat? Fun fact: the largest muscle in your body is the gluteus maximus (that’s your butt) while the smallest skeletal muscle is the stapedius (it stabilizes the smallest bone, the stapes, which is in your middle ear).

Skeletal system introduction

Were it not for your skeleton, you and I would be a mere sack of flesh. You will come to appreciate that the bones, together with muscles, are a scaffolding for your body. We will also explore their endocrine function, especially with regards to calcium and phosphate homeostasis. Fun fact: the bone most broken is the clavicle (AKA collar bone).

Endocrine system introduction

Glands are special organs that secrete chemical messages called hormones, which seep into the blood - it’s like putting a tea bag in hot water. As the heart pumps, this blood carries these chemical messages throughout the body, allowing the hormones to interact with specific target cells and organs. Endocrine glands help us to maintain our appetites, grow up, metabolize molecules, concentrate urine,- and oh, so much more! We will examine how these variegated hormones play a role in homeostasis as the body responds to a changing environment.

Integumentary system introduction

There is really more than meets the eye with skin. Yes, it does make us look nicer than a bag of bones, muscles, and organs. But it also serves other important purposes which range from guarding the body against infection to sensation to allowing for metabolism of vitamin D. We will explore the structure and function of skin from the macroscopic to the microscopic level in this tutorial.

  • Why we need a lymphatic system

    Welcome to the lymphatic system! Find out why we need it, and how it interacts with our blood vessels. By Patrick van Nieuwenhuizen.

  • How lymphatic vessels move fluid

    Find out how the body's mysterious second circulatory system works. Learn how it can move fluid even when it has no heart of its own. By Patrick van Nieuwenhuizen.

  • The lymphatic system's role in immunity

    Learn about how B and T cells reside in lymph nodes. Find out how that enables them to get a preview of what they need to be prepared to fight. By Patrick van Nieuwenhuizen.

  • Lipid and protein transport in the lymphatic system

    Learn about a third function of the lymphatic system. See how it finds a sneaky way to get fats and proteins into your bloodstream. By Patrick van Nieuwenhuizen.

  • What is actually in lymph

    Learn about the differences between lymph and blood. Find out what is actually in lymph, and how it might be different across your body. By Patrick van Nieuwenhuizen.

Lymphatic system introduction

Your heart pumps roughly 20 L of blood throughout the day to your tissues. The plasma component of blood (not containing blood cells) leaks out through capillaries (the tiniest of blood vessels) and is mostly reabsorbed. However, about 3L of the plasma is left behind in fluid surrounding tissues, and it is the job of the hard-working lymphatic system to bring back this fluid to the circulatory system. The lymphatic system moves fluid in one direction, but without the force of a pump like the heart.