Rachel
About

Khan Academy on a Stick

Health and medicine
  • What is blood pressure?

    Find out what a systolic and diastolic blood pressure mean. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Learn how a stethoscope can help determine blood pressure

    Learn how Dr. Korotkoff cleverly used a stethoscope to determine blood pressure, and that we still use his trick today! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Resistance in a tube

    Learn how the size of a tube (it's radius) is related to its resistance to something flowing through. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Adding up resistance in series and in parallel

    Learn about how resistance can be added up in series and in parallel (similar to electrical circuits!). Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Adding up resistance problem

    Here's a chance to see if you can combine what you know to add up resistance in series AND in parallel. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Flow and perfusion

    Learn the difference between blood flow (Volume/time) and perfusion (Volume/time/amount of tissue). Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Putting it all together: Pressure, flow, and resistance

    See how pressure, flow, and resistance relate to one another and how they each affect the human body. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Blood pressure changes over time

    See how increasing resistance in the blood vessels can cause blood pressure to rise over time. Rishi is a pediatric infectious disease physician and works at Khan Academy.

Blood pressure

Using the stethoscope to check blood pressure is a technique that’s been used for >100 years! Blood pressure is one of the major vital signs frequently measured by health care workers, and it tells us a lot about our blood circulation. Learn what blood pressure is, how it relates to resistance in a tube, why it is necessary to get oxygen to your cells, and how it can change as you age. We’ll finally put it all together by relating pressure, flow, and resistance in one awesome equation!

  • Regulation of blood pressure with baroreceptors

    Learn about how the arteries use nerve impulses to help regulate blood pressure. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Parts of a nephron

    Learn about the 5 major parts of the kidney's nephron. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • General overview of the RAAS system: Cells and hormones

    Learn the important cells and hormones that are working together to control your blood pressure! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Renin production in the kidneys

    Learn the three major triggers for Renin production by the Juxtaglomerular cells. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Activating angiotensin 2

    See how Renin and ACE work to cut Angiotensinogen down to size! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Angiotensin 2 raises blood pressure

    See how Angiotensin 2 effects 4 target "organs" to increase blood pressure. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Aldosterone raises blood pressure and lowers potassium

    See how Aldosterone effects the principal cells of the kidney to raise BP and lower potassium. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Aldosterone removes acid from the blood

    See how Aldosterone acts on the alpha-intercalated cell to remove protons (acid) from the blood. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • ADH secretion

    Learn the key triggers for ADH secretion. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • ADH effects on blood pressure

    See how ADH acts on blood vessels and the kidney to raise blood pressure. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Aldosterone and ADH

    Find out how Aldosterone and ADH cause changes in volume and osmolarity. Rishi is a pediatric infectious disease physician and works at Khan Academy.

Blood pressure control

The human body enjoys stability. For example, if your blood pressure changes, the body puts a couple of brilliant systems into motion in order to respond and bring your blood pressure back to normal. There are some quick responses using nerves and some slower responses using hormones. The system using hormones is sometimes called the renin-angiotensin-aldosterone-system (RAAS), which is the main system in the body for controlling blood pressure. When your blood pressure drops too low or gets too high, your kidneys, liver, and pituitary gland (part of your brain) talk to each other to solve the problem. They do this without you even noticing! Learn how the body knows when the blood pressure has changed, and how hormones like angiotensin 2, aldosterone, and ADH help return blood pressure to back to normal.

  • Meet the placenta!

    Learn how the needs of the fetus are met by the placenta, which is a special organ that belongs to both the mother and the fetus! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Umbilical vessels and the ductus venosus

    Watch as fetal blood goes through umbilical vessels and takes a shortcut through the Ductus Venosus to make it back to the heart. 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.

  • Hypoxic pulmonary vasoconstriction

    Watch how blood gets diverted away from alveoli with low oxygen levels. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Foramen ovale and ductus arteriosus

    Watch how the fetal heart allows blood to simply bypass the lungs altogether using the Foramen Ovale and the Ductus Arteriosus! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Fetal hemoglobin and hematocrit

    Although mom controls the oxygen source, the fetus has a couple of clever tricks to get the most oxygen possible! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Double Bohr effect

    Learn how there are two distinct Bohr effects happening at the same time in the placenta. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Fetal circulation right before birth

    Watch how the blood flows through the fetal circulation and compare it to what happens in the baby's body. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Baby circulation right after birth

    Watch how the blood flows through the baby's circulation and compare it to what happens in the fetus. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Fetal structures in an adult

    Find out what happens to those nifty fetal structures once we get older. Rishi is a pediatric infectious disease physician and works at Khan Academy.

Fetal circulation

At one stage or another in development, every friend you know had gill slits and a tail. Pretty crazy thought, huh? Fetal development is incredible, and it’s important to understand exactly how it happens. The structure and function of the circulatory system is incredibly complex, and fetuses are no exception. Find out how the heart and circulatory system work in the fetus!

  • Layers of a blood vessel

    Remember the 3 key layers of a blood vessel (Tunica intima, Tunica media, and Tunica externa) and how arteries, veins, and capillaries are all different from one another. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Three types of capillaries

    Learn the differences between continuous, fenestrated, and discontinuous capillaries, and how they affect the movement of molecules. 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.

  • Pre-capillary sphincters

    Find out how the body controls how much blood flows through a capillary bed. 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.

Blood vessels

Where does your blood go after it leaves the heart? Your body has a fantastic pipeline system that moves your blood around to drop off oxygen and food to those hungry cells, and removes cell waste. Learn how arteries carry blood away from the heart, how veins bring blood back to the heart, and about the different layers of cells that make up these blood vessels.

  • Compliance and elastance

    Learn about compliance (and elastance) of arteries, veins, and lead pipes! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Bernoulli's equation of total energy

    Learn how total energy of a fluid helps explain why fluids can move from low pressure to high pressure! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Stored elastic energy in large and middle sized arteries

    See how arteries behave like sling shots, shooting blood (not rocks) onwards! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Compliance - decreased blood pressure

    Find out how compliance allows arteries to store elastic energy (and lower pressure). Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Compliance - increased blood flow

    Learn how compliant arteries allows for a "Constant Pressure System" like a modern water gun! Rishi is a pediatric infectious disease physician and works at Khan Academy.

Arterial stiffness

Believe it or not, the arteries are elastic and when they recoil they actually push blood along when the heart is relaxing (diastole). This is known as the windkessel effect and is the same basic principle used by some water guns. Unfortunately, with all the work that the circulatory system has to do, our arteries can become rigid with age. When the arteries get stiff like lead pipes, the problem is quite different then when the arteries actually get clogged up, but just as important.

  • Three types of muscle

    Understanding the structure of a muscle cell.

  • Heart cells up close!

    Get a close-up view of the cardiac cells and see what makes them different from the other (skeletal and smooth) muscle cells. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • 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.

  • Calcium puts myosin to work

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

  • Sympathetic nerves affect myosin activity

    Check out how the amount of Myosin that is tugging on your heart can change depending on your activity level! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Why doesn't the heart rip?

    Understand LaPlace's law to see the effect that pressure, radius, and wall thickness each have on the "wall stress" in the left ventricle. Rishi is a pediatric infectious disease physician and works at Khan Academy.

Heart muscle contraction

Your heart is made of a special type of muscle, found nowhere else in the body! This unique muscle is specialized to perform the repetitive task of pumping your blood throughout your body, from the day you’re born to the day you die. We’ll take an in-depth look of how the heart accomplishes this on a cellular level, and learn about the proteins actin and myosin that are the workhorses that tug and pull on one another to create every single muscle contraction. You’ll appreciate the fact that your heart beat is a fairly sophisticated process!

  • Membrane potentials - part 1

    Find out how a cell that is permeable to one ion can become charged (either positive or negative) if there is permeability and a concentration gradient. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Membrane potentials - part 2

    Find out how a cell that is permeable to one ion can become charged (either positive or negative) if there is permeability and a concentration gradient. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Permeability and membrane potentials

    Find out why a cell that is permeable to multiple ions has a membrane potential that is influenced by the ion with the highest permeability. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Action potentials in pacemaker cells

    Find out how the pacemaker cells use the movement of sodium, calcium, and potassium to get your heart beating! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Action potentials in cardiac myocytes

    See how muscle cells in the heart contract by allowing Calcium to flow inside and bringing along some positive charge with it! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Resetting cardiac concentration gradients

    Watch as the heart cells use energy to reset the concentration gradients for all of the ions after the action potential has gone through. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Electrical system of the heart

    See where the pacemaker cells start the electrical wave of depolarization, and how it gets all the way to the ventricles of the heart. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Depolarization waves flowing through the heart

    Get a clearer idea of what a "Depolarization Wave" means and how it goes from cell to cell through the entire heart! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • A race to keep pace!

    Find out how the various pacemaker cells in the heart actually race against the clock to try to keep pace for the heart, and how the heart has not one but two back up systems! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Thinking about heartbeats

    Find out what happens when things move very slowly through the AV Node! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • New perspective on the heart

    Take a look at the heart in cross section, looking down at it from the top! Rishi is a pediatric infectious disease physician and works at Khan Academy.

Heart depolarization

Your heart relies on the flow of electricity to maintain a steady, consistent beat - like an automatic pump that maintains a regular rate and rhythm throughout your life! There are specialized heart cells that allow positive current to travel quickly throughout the heart muscle. In these videos, we’ll check out the flow of this positive charge on a macroscopic and microscopic level.

  • Changing the AV node delay - chronotropic effect

    Find out exactly how your autonomic nervous system has a chronotropic effect (i.e. timing) that changes the delay between the contraction of the atria and the ventricles! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Changing the heart rate - chronotropic effect

    Find out exactly how your autonomic nervous system has a chronotropic effect (i.e. timing) that changes speed of your heartbeat! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Increasing ventricular contractility - inotropic effect

    Find out how the sympathetic nerves increase the heart's force of contraction and speed of relaxation! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Autonomic nervous system effects on the heart

    Carefully go through each of the four major effects that the sympathetic and parasympathetic system has on your heart: Chronotropy, Dromotropy, Inotropy, and Lusitropy. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Getting a new heart

    Think through the result of getting a new heart, and how the heart can still maintain homeostasis when the nerves are no longer around. Rishi is a pediatric infectious disease physician and works at Khan Academy.

Nerve regulation of the heart

Although your heart can beat independently, your nervous system is important as an external regulator. Your brain can tell your heart to speed up or slow down, depending on the scenario. For example, when you’re falling asleep, your nervous system will cause your heart to slow down, and 8 hours later when your phone alarm goes off, your nervous system will speed up your heartbeat! So even though your heart muscle beats by itself, the nerves can ramp up or down the speed. Check out the videos to learn more about how the nerves help to regulate the heart.

  • Why doesn't the heart rip?

    Understand LaPlace's law to see the effect that pressure, radius, and wall thickness each have on the "wall stress" in the left ventricle. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • What is preload?

    Some say Preload = End-Diastolic Pressure, others say Preload = End-Diastolic Volume, so which one is it? Watch and find out! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Preload and pressure

    Find out how left ventricular end-diastolic pressure helps you make an educated guess about preload. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Preload stretches out the heart cells

    Find out why stretching a heart cell in diastole affects how forcefully it contracts in systole. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Frank-Starling mechanism

    Carefully follow 5 different preload scenarios to see how each one will have a different effect on how actin and myosin line up. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Sarcomere length-tension relationship

    Find out why the length of a sarcomere (in diastole) affects the amount of force that it can generate (in systole), and how that would look on a graph. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Active contraction vs. passive recoil

    Go through the similarities and differences between the sarcomere and a slingshot! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • What is afterload?

    Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Increasing the heart's force of contraction

    Find out exactly how stretch increases force of contraction in end-diastole, whereas more calcium increased force of contraction in end-systole. Rishi is a pediatric infectious disease physician and works at Khan Academy.

Preload and afterload

After using your jeans for a while, you’ll begin to notice small tears and rips developing in the fabric. Why doesn’t this happen to your heart as well? Well, your heart manages to stay healthy despite all of the “wall stress” that pulls on the heart walls. During different parts of the heart cycle (afterload vs. preload) the mechanics of “wall stress” change dramatically. Learn exactly what preload and afterload mean, and how we can use pressure-volume loops to estimate their values.

  • Pressure in the left heart - part 1

    Watch the pressure in the left heart go up and down with every heart beat! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Pressure in the left heart - part 2

    Watch the pressure in the left heart go up and down with every heart beat! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Pressure in the left heart - part 3

    Watch the pressure in the left heart go up and down with every heart beat! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Left ventricular pressure vs. time

    Ever wonder exactly how the left ventricle's pressure changes over time? Find out in this color-coded video! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Left ventricular volume vs. time

    Left ventricular volume changes over time in a way that makes a curious looking graph. Learn more in this video! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Drawing a pressure-volume loop

    Use the left ventricular pressure and volume information to put together a cool new graph. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Understanding the pressure-volume loop

    Figure out how all of those physiology terms: end-systolic, end-diastolic, pulse pressure, stroke volume, and ejection fraction, can be easily figured out using the pressure-volume loop. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • End diastolic pressure-volume relationship (EDPVR)

    Find out what happens when the left ventricle is not allowed to contract, and instead you simply add and take away blood from it. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • End systolic pressure-volume relationship (ESPVR)

    Find out what happens when the left ventricle is not allowed to relax, and instead you simply add and take away blood from it. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Reimagine the pressure volume relationship

    Understand what is happening at the cellular level to cause two identical left ventricular volumes to have such different pressures! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • What is preload?

    Some say Preload = End-Diastolic Pressure, others say Preload = End-Diastolic Volume, so which one is it? Watch and find out! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Why doesn't the heart rip?

    Understand LaPlace's law to see the effect that pressure, radius, and wall thickness each have on the "wall stress" in the left ventricle. Rishi is a pediatric infectious disease physician and works at Khan Academy.

Pressure volume loops

The pressure volume loop is one of the classic figures that helps us to conceptualize and understand the mechanics of the left ventricle of the heart. In addition to a filling up with blood and squeezing out blood there is a (very short) period of time when the heart muscle is contracting and relaxing with no volume change! As the left ventricle moves around the PV loop with each lub dub you get a sense for the amazing amount of work it does as pressures and volumes go up and down, all day, every day. This is a fascinating area where physics and biology meet to produce something miraculous.

  • What is preload?

    Some say Preload = End-Diastolic Pressure, others say Preload = End-Diastolic Volume, so which one is it? Watch and find out! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • What is afterload?

    Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Increasing the heart's force of contraction

    Find out exactly how stretch increases force of contraction in end-diastole, whereas more calcium increased force of contraction in end-systole. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Reimagine the pressure volume relationship

    Understand what is happening at the cellular level to cause two identical left ventricular volumes to have such different pressures! Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • What is contractility?

    Contractility tells us how many myosin heads are working at the end of systole; a number that goes up or down with the level of sympathetic nerve stimulation. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Getting Ea (arterial elastance) from the PV loop

    Find out how to use the PV loop to draw the Ea (Arterial Elastance) line, and what it represents. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Arterial elastance (Ea) and afterload

    First, learn the difference between arterial elastance (Ea) and afterload. Then, understand how Ea is affected by changes in afterload, and in turn, how the PV loop can shift. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Arterial elastance (Ea) and preload

    Understand how Ea is affected by changes in preload, and in turn, how the PV loop can shift. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Stroke work in PV loops and boxes

    Watch how PV loops can be "morphed" into PV boxes to make drawing them and thinking about them much simpler. Rishi is a pediatric infectious disease physician and works at Khan Academy.

  • Contractility, Ea, and preload effects on PV boxes

    See how contractility, Ea (arterial elastance), and preload each have an effect on PV Boxes. Rishi is a pediatric infectious disease physician and works at Khan Academy.

Changing the PV loop

Once you’ve learned about the PV loop, a natural question arises - Does it ever change shape? It turns out that there are precisely three things that can change the shape of the loop: 1. Preload, 2. Afterload, and 3. Contractility. That’s it! The tricky part comes when you try to change one and you realize that the body begins to change the other two as well as a natural consequence. In order to simplify, you’ll find that PV loops are sometimes even described as PV boxes. You’ll get to learn about PV loops, PV boxes, and even play around with them yourself in this tutorial!