If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Course: Health and medicine > Unit 3

Lesson 5: Hypertension
Science
Health and medicine
Circulatory system diseases
Hypertension
© 2024 Khan AcademyTerms of usePrivacy PolicyCookie Notice

What is hypertension?

Google Classroom

What is hypertension?

Each time your heart beats, blood is pumped through your arteries and veins, the blood vessels of your circulatory system. Arterial blood pressure is created by the force exerted by the blood against the artery walls, as they carry blood around your body.
  • Hypertension, also known as high blood pressure, is when the pressure of the blood being pumped through your arteries is higher than it should be.
High blood pressure, or hypertension has been called the "silent killer", because it often has no warning signs or symptoms, and many people do not even know they have it. Over time, the constant pressure overload causes accumulating damage that eventually becomes more than your circulatory system can handle, often leading to serious health problems.

Your circulatory system, blood pressure, and what can go wrong

Your circulatory system is made up of three main parts: blood, which carries substances such as nutrients, oxygen and waste products around your body; your blood vessels, a network of tubes that carry the blood; and your heart, a muscular organ, located in the centre of your chest, whose job is to pump your blood throughout the circulatory system.
image of the circulatory system
Blood is made of a pale yellow fluid, called plasma that contains red and white blood cells, and platelets. The red blood cells contain hemoglobin, a chemical that can combine with oxygen.
You have different types of blood vessels, the tubes through which your blood travels, with different jobs. Blood flows away from your heart through strong, thick-walled vessels, called arteries, which branch into networks of tiny, thin-walled tubes, called capillaries. Oxygen and other substances can easily diffuse out of your capillaries into the cells of your tissues and organs, where they are needed, while carbon dioxide and waste products can easily diffuse back into the bloodstream, for disposal. The capillaries eventually join up again to form veins, which are the tubes that transport blood back to your heart.
Your heart is divided into four chambers. The two upper chambers are the atria (singular atrium) and the two lower chambers are the ventricles. As your heart pumps, one way valves between the chambers keep the blood flowing in a specific direction. Blood passes through your heart twice as it makes a complete tour of your body. Starting from your heart, it is pumped from the right ventricle to your lungs, where it picks up oxygen. It then returns to the left atrium, flows into the left ventricle, and is pumped out of there to the rest of your body. With this done, the blood returns to the right atrium, flows into the right ventricle, and the cycle starts again.
diagram of the heart
Blood pressure is set by:
  • cardiac output - the amount of blood pumped by each ventricle in one minute; and
  • peripheral resistance - the resistance that the heart has to overcome to make the blood flow through the blood vessels of your circulatory system.
Your body uses multiple complicated, overlapping processes to control blood pressure. Together, these systems do this by regulating vasodilatation and vasoconstriction, the widening and narrowing of blood vessels, as well as rates of excretion of salt and water, which is how your body adjusts blood volume. Around 5-10% of people have a specific underlying medical condition that causes a malfunction in one or more of the physiological processes that maintain blood pressure; for example, chronic kidney disease or thyroid disease. However, the majority of people with high blood pressure have what is known as essential hypertension, meaning the cause is unknown.
Regardless of whether you have essential hypertension, or hypertension due to an underlying condition, it can increase cardiac output, the resistance to blood flow caused by the muscle tone and diameter of the blood vessels, known as peripheral resistance, or both. High blood pressure is dangerous because the higher your blood pressure gets, the harder your heart has to work to pump blood around your body, and the more likely your heart and blood vessels will be damaged. Without treatment, hypertension can cause a heart attack, enlargement of your heart, and/or heart failure. Your blood vessels may start to bulge, burst, or clog, and excessive pressure inside the vessels in your brain may cause a brain bleed leading to a stroke. In some cases, high blood pressure can also bring on kidney failure, blindness, and even cognitive impairment.

Does hypertension have symptoms?

Although sometimes hypertension causes nosebleeds, headaches, shortness of breath, or dizziness, these types of symptoms are nonspecific, and generally only occur if your blood pressure has increased to a dangerous or life threatening level. In fact:
  • most people with hypertension don’t have any signs or symptoms, even when their blood pressure is extremely high.

What are the risk factors for hypertension?

Although for most people there is no identifiable cause of hypertension, there are known risk factors that increase the likelihood that you will become hypertensive. Several of these are things that you can’t do anything about, including:
  • Genetics
    • having family members with hypertension increases the likelihood that you will too.
  • Race
    • high blood pressure is more common in people with dark skin than in people with pale skin.1
  • Age
    • your blood vessels become more rigid as you age, preventing them from opening as effectively as when you were younger, which increases peripheral resistance.
Other risk factors are known as modifiable risk factors, because many people can reduce their blood pressure by changing their diet and lifestyle. The most common risk factors include being overweight and inactive, eating a high salt diet, and smoking.
Image of modifiable risk factors (obesity, excessive alcohol consumption, smoking, certain medications, and vitamin D deficiency)

How likely are you to become hypertensive?

If you have high blood pressure, you are certainly not alone. More than one in three adults worldwide have high blood pressure, and it is credited with contributing to half of all deaths due to heart disease and stroke.1 High blood pressure is more common in men during middle-age, around 45 years, with women catching up after age 65. Worryingly, children can also become hypertensive for many of the same reasons as adults - inactivity, unhealthy diet, and obesity. Although it is common in both economically developed and developing countries and regions, many people in developing countries go undiagnosed, and miss out on treatment that could significantly reduce cardiovascular problems.
graph showing prevalence of high blood pressure in adults aged 20 and older

Steps you can take to lower your blood pressure

Lifestyle changes can really help to lower your blood pressure. For example, you can work on eating a healthy diet with lots of fruits and vegetables to take care of any nutritional deficiencies, and to eat less salt. This, together with reducing high fat, and calorie laden foods can help you reach and maintain a healthy weight. Another way to lower your blood pressure is to increase the amount of exercise you do. Routinely exercising not only helps to lower your blood pressure, but may give you more energy, and is a great way to reduce stress. Finally, reducing or better still quitting smoking, and limiting your daily amounts of alcohol (2 drinks for men, 1 drink for women), are also great ways to get your blood pressure heading into the healthy range.
As an adult, it is a good idea to ask your doctor to check your blood pressure one or two times a year if you think you may be at increased risk for any of the reasons described above. That way, you will know early on in the course of the disease, and be able to take steps to minimize your risk for other illnesses.

How do you diagnose and treat hypertension?

Diagnosing hypertension: Blood pressure is usually measured using a pressure cuff or an electronic device placed on your upper arm. A blood pressure reading is written as two numbers, representing the maximum pressure in the circulatory system when the heart pumps blood out (systolic pressure), and the minimum pressure when the heart refills (diastolic pressure). Blood pressure is measured in millimeters of mercury (mm Hg). Normal resting blood pressure in an adult is approximately 120 / 80 mm Hg. However, your blood pressure can fluctuate from minute to minute, and readings are generally higher in the afternoon and lower at night.
Doctors often classify blood pressure into four categories:
  • Normal blood pressure
    • below 120 / 80 mm Hg.
  • Prehypertension
    • 120-139 / 80-89 mm Hg.
  • Stage 1 hypertension
    • 140-159 / 90-99 mm Hg.
  • Stage 2 hypertension
    • 160 / 100 mm Hg or higher.
Both numbers in a blood pressure reading are important, and an increase in either number (systolic or diastolic pressure) indicates you are hypertensive. It is worth noting that a blood pressure below 90 / 60 mm Hg is considered outside the normal range, and is known as hypotension, or low blood pressure.

Treating hypertension

Treatment typically involves lifestyle changes and medications when necessary. If you are prehypertensive, but otherwise healthy, your doctor is most likely going to encourage lifestyle changes, such as eating a healthier diet, quitting smoking, getting more exercise, and managing stress, as a first step to lowering your blood pressure. However, if this doesn’t work, or you are already hypertensive, you may need medications.
If you are healthy, blood pressure medications are recommended when your blood pressure is 160 / 100 mm Hg or higher, but if you have other cardiovascular risk factors such as atherosclerosis, diabetes, or obesity, your doctor is likely to recommend medication earlier so as to protect your kidneys, heart, and other organs from potential damage.3 Generally, the treatment goal is to lower blood pressure to less than 140 / 90 mm Hg in people younger than 60, and less than 150 / 90 in people older than 60.
Many different classes of drugs are used to treat high blood pressure. The most common ones are:
  • Diuretics - these promote the production of urine, which removes excess fluid from the bloodstream. This reduces the volume of blood in your circulatory system, and your blood pressure.
  • Beta-blockers - these make your heart beat slower and with less force, and your blood vessels open up. This reduces blood pressure, and improves blood flow.
  • Angiotensin-converting enzyme inhibitors, (ACE inhibitors) - these block the action of a hormone that causes your blood vessels to constrict and that thickens and stiffens the walls of your blood vessels and heart, as well as triggering the release of another hormone that increases the amount of sodium and water in your body. Together, this has the effect of lowering blood pressure.
  • Angiotensin II receptor blockers - these affect similar biochemical pathways as ACE inhibitors, for similar effects.
  • Alpha blockers - these block the action of hormones that trigger vasoconstriction of the smaller arteries and veins, improving blood flow and lowering blood pressure.
  • Calcium channel blockers - these relax and widen blood vessels by preventing calcium from entering heart cells and the muscle cells within the blood vessel walls. This slows your heart rate and vasodilates your arteries, resulting in lower blood pressure.
Diuretics are often recommended as the first line of therapy for most people who have high blood pressure, and no other medical conditions. If you do have a medical condition, then your doctor may choose a medication from one of the other drug classes to suit your individual needs. For example, if you have diabetes, your doctor may prescribe an ACE inhibitor rather than a diuretic, as diuretics sometimes interfere with blood sugar levels. The good thing is that if one drug doesn’t work, there are plenty more to choose from. And, if your blood pressure is extremely high, your doctor may prescribe combinations of two or more medications to bring it under control.
After you start antihypertensive medication, your doctor will want to follow your blood pressure regularly for a few months to make sure you reach your treatment goal. You may also need blood tests to check the health of your kidneys, which are sometimes affected as a side effect of blood pressure medicine.

Consider the following:

People with vitamin D deficiency tend to have higher blood pressure than average. Why do you think this is? Vitamin D inhibits the secretion and activity of a hormone that triggers a cascade of hormonal activity that ultimately increases blood pressure, by constricting blood vessels throughout your body, and stimulating reabsorption of sodium and water, which increases blood volume, and also raises blood pressure. One possible mechanism is that a vitamin D deficiency leads to increased renin secretion.

Want to join the conversation?

Log in