Although humans have lived with the same bodies for millennia, we are still exploring and uncovering new parts, processes, and functions every year.
Researchers continue to discover new organs; for example, mesentery, which was previously thought to be a fragmented series of tissues, was reclassified as a single organ in 2017. What's more, procedures to repair organs are also evolving rapidly. Just last March, doctors were able to perform groundbreaking brain surgery on a baby—while she was still in the womb.
There are 79 organs in the human body, spanning the muscular, nervous, endocrine, skeletal, cardiovascular, lymphatic, respiratory, digestive, urinary, and reproductive systems.
But not all organs are created equal. Of these, five are considered vital: the brain, heart, kidneys, liver, and lungs. While these heavy hitters keep us alive and functioning, there are plenty of organs we can live without. The appendix, spleen, reproductive organs, and colon are just a few of the many organs that, while helpful to our bodily processes, aren't necessary for survival.
Stacker compiled a quiz on what 25 major organs do for your body. Read on to see what you know about human anatomy.
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Clue 1: This organ detoxifies your blood
This cone-shaped organ rests in the upper right of the abdomen, between the diaphragm and the stomach.
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The liver processes all the blood that travels out of the stomach and intestines. During this process, the organ excretes bile, regulates chemical levels, creates nutrients, and metabolizes drugs. These are just some of the more than 500 vital functions the liver performs, which also include preventing blood from clotting and producing cholesterol.
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Clue 2: This organ digests your food
This organ is the longest piece of the gastrointestinal tract that food travels through on its way out of the body. It connects to a larger copy of itself, but the majority of digestion takes place here.
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It can take up to five hours for the small intestine to complete all of its digestive tasks, which include breaking food down, absorbing its nutrients, extracting water, and then passing food along to the large intestine. The small intestine is food's first stop immediately after leaving the stomach; most of the digestion process takes place here.
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Clue 3: This organ is often called useless, but may be important for immunity
Many people get this finger-shaped organ removed after experiencing inflammation—however, this hasn't been observed to have any negative side effects on the body.
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Also part of the gastrointestinal tract, the appendix is located in the lower abdomen and attached to the large intestine. However, it hasn't been observed to play any role in aiding digestion. It is thought that the appendix may promote immune system health by producing immunoglobulin A.
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Clue 4: This organ filters fluids leaking from blood vessels
Your immune system contains hundreds of these organs, which are small and shaped like a bean.
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The primary function of lymph nodes is to filter out lymphatic fluid, as well as to deploy white blood cells as part of the body's defense against infection. Lymph nodes are found grouped together in the neck, armpits, chest, abdomen, and groin.
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Clue 5: This organ produces insulin
Part of the digestive system, this organ is located in the back of the abdomen. It is a gland—that is, an organ that produces a substance.
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The two main functions of the pancreas are to produce enzymes that promote digestion and to release hormones that regulate sugar levels in the blood. Although it is technically possible to live without your pancreas, this would require taking enzyme supplements and insulin shots to regulate blood sugar in an alternative way.
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Clue 6: This organ pumps blood through your body
This is the primary organ of the circulatory system. It contains four main chambers and is about the size of one clenched fist for a child and two for an adult.
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The heart is controlled by electrical impulses sent by the brain and nervous system. Though its primary role is to pump blood throughout the body via valves and blood vessels, it also regulates blood pressure and heart rate.
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Clue 7: This organ transports eggs through the reproductive system
Only women have this organ, which comes in a pair and plays a central role in fertilization and pregnancy.
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The fallopian tubes act as pathways connecting the ovaries to the uterus. After eggs leave the ovaries each month during ovulation, they sit in the fallopian tubes, where they are fertilized if sperm makes its way into the reproductive system. Once fertilized, the embryo travels through the fallopian tubes to reach the uterus, where it will implant and remain for the rest of the pregnancy.
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Clue 8: This organ passes air through the lungs
We each have two of these organs, which sit inside the chest and connect to the left and right lungs. They are part of the respiratory system.
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Once air is breathed in, it moves through the bronchi, which direct it to either the left or right lung. Besides carrying air to the lungs, the bronchi (singular: bronchus) also moisturize the air and clear it of mucus and particles each time you cough or swallow.
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Clue 9: This organ distributes oxygenated blood
Part of the cardiovascular system, this organ exists in many varieties throughout the body, serving everything from the heart to the brain to the legs to the spine, and much more.
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Arteries transport blood from the heart to every other part of the body, thus distributing oxygen, nutrients, and hormones that keep the cells healthy and working. Elastic arteries act as receptacles, blood's first stop once it leaves the heart; muscular arteries then take this blood and spread it around the body's systems.
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Clue 10: This organ communicates with everything in your body
This organ makes up one-half of the central nervous system. It weighs about three pounds for adults and is made up of fat, water, proteins, carbohydrates, and salts.
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Through receiving and sending chemical and electrical signals, the brain controls everything from pain to memory to fatigue to speech. It has four main parts: the frontal lobe dictates smell, decision-making, personality, speech, and movement; the parietal lobe controls spatial understanding, pain, touch, understanding speech, and identifying objects; the occipital lobe creates vision; and finally, the temporal lobe is involved in short-term memory and musical rhythm.
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Clue 11: This organ regulates metabolism
This organ is shaped like a butterfly and located at the front of the neck. It is part of the endocrine system.
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By making and distributing certain hormones throughout the body, the thyroid gland affects every system in the body. The thyroid's main function is to control your metabolic rate, which is the speed at which your body turns food into energy. It also affects your heart rate, breathing, body temperature, digestion, fertility, and mental health, among many other functions.
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Clue 12: This organ exchanges oxygen for excess carbon dioxide
This organ is part of the respiratory system. We each have a pair and can strengthen them and improve their performance through regular exercise.
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Twelve to 20 times per minute, the lungs take inhaled air, cleanse it of carbon dioxide, and release it into the rest of the body. Through this process, oxygen travels to the heart, from where it is then distributed to all other organs.
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Clue 13: This organ absorbs water and expels waste
When unravelled, this organ stretches to six feet long. It is the last stop for food being digested along the gastrointestinal system.
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After being processed in the small intestine, food enters the large intestine, where it is solidified into waste and stored until it is excreted. The large intestine—also known as the colon—carries this out by dehydrating liquefied food and breaking it down via internal bacteria.
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Clue 14: This organ helps us breathe and speak
This piece of the respiratory system is larger in females than in males. It connects the pharynx to the trachea.
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Also known as a voice box, the larynx contains the vocal cords. Its primary function is to create sounds to form speech, but it also aids in breathing and catching food and other substances from getting caught in the lungs. Generally, the larger a larynx is, the deeper the person's voice will be.
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Clue 15: This organ filters blood and produces antibodies
Roughly the size of an avocado in adults, this organ rests within the left rib cage above the stomach. It is part of the lymphatic system.
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Your spleen performs a variety of functions that keep the body healthy, including storing and filtering blood; producing white blood cells and antibodies; and maintaining internal fluid levels. The spleen is particularly susceptible to injury and disorders, and some individuals may have to have the organ removed via a splenectomy.
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Clue 16: This organ holds intestines in place
When inflamed, this organ could be affected by Crohn's Disease, in which individuals can suffer diarrhea as well as difficulties absorbing the nutrients from food.
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The mesentery is a series of tissues that secure the intestines to the walls of the abdomen. Though previously thought to be separate organs, researchers recently redefined it as a single organ. Besides preventing the intestines from collapsing into the pelvic region, the mesentery also stores lymph nodes and produces proteins.
Clue 17: This organ transports food into your digestive system
You might mistake this organ for the trachea, which looks and is situated similarly. However, while the trachea operates within the respiratory system, this organ plays a function within the digestive system.
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The esophagus' main role is to move food and liquids down the throat and to the stomach. It does this through a series of muscular contractions: after you swallow, food moves to the throat, and the esophagus begins to push it downwards, while other muscles close to prevent it from travelling up the nose or towards the windpipe.
Clue 18: This organ breaks down food with acid
This organ is shaped like a J and sits along the gastrointestinal tract. It connects to the small intestine.
The stomach plays a key role in digestion by storing and breaking down food. It does this by producing a mixture of enzymes and acids that mix and disintegrate food. The stomach then holds this mixture until it is ready to move on to the small intestine.
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Clue 19: This organ stores urine
This organ makes up one-fourth of the urinary tract. It is balloon-shaped and can store around two cups of liquid before emptying.
The bladder first receives urine from the kidneys. Once the bladder is full, a person will feel an urge to urinate, at which time the bladder helps expel the liquids by contracting and pushing urine into the urethra. The bladder is particularly sensitive to infection and irritation.
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Clue 20: This organ produces T-cells
This organ is most active during childhood. It starts working even while you're still in utero, and starts slowing its work and decreasing in size post-puberty.
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The thymus is part of the lymphatic system and is a gland. Its main function is to process and specialize T-cells, which are a type of white blood cell. After T-cells are passed from the bone marrow to the thymus, they mature there before entering the blood and playing a central role in the body's immune system. The thymus also creates and releases many hormones, all of which support the immune system.
Clue 21: This organ removes excess fluids
Everyone is born with two of these organs, which are commonly donated between individuals. People in high-impact accidents, or who have diabetes or high blood pressure, are at risk of losing one.
The kidneys are a central part of the urinary system, receiving and filtering around 200 quarts—or a large bathtub's worth—of fluid daily. After you swallow liquids, the kidneys extract waste from them and turn them into urine, passing them on to the bladder to eventually be expelled. The kidneys also play a role in balancing the body's levels of water and electrolytes.
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Clue 22: This organ helps us chew and swallow
This organ is mostly made up of muscles. It is one of the most visible parts of the digestive system.
The tongue plays an essential part in allowing a person to chew, speak, and breathe. It does this by moving food around the mouth, working with the larynx to form vocal sounds, and keeping the airways of the lungs accessible. The tongue is also covered in taste buds, which are nerve cells that transmit the five basic taste sensations to our brain: sweet, salty, bitter, sour, and savoury.
Clue 23: This organ protects our internal organs, muscular, and skeletal systems
This is the body's largest organ. It has three layers. Along with our hair, nails, and oil and sweat glands, it makes up the integumentary system.
The skin is the body's first defense against bacteria, injury, and temperature fluctuations. The outer layer, the epidermis, works as a protective barrier and continually produces new skin cells throughout the day. The middle layer, the dermis, grows hair, allows you to feel touch and temperature, and produces sweat. Finally, the bottom layer, the hypodermis, provides a fatty cushion for organs and regulates body temperature.
Clue 24: This organ transports air, food, and water
This organ connects the mouth and nose to the lungs. It is shaped like a tube and is made up of muscle.
The throat is comprised of the pharynx and larynx. When air, food, or liquids enter the mouth or nose, they travel immediately to the throat, which then sends them on to either the lungs or the esophagus. Besides eating, drinking, and breathing, the throat also helps the larynx produce speech sounds.
Clue 25: This organ kills bacteria in your mouth
If you open your mouth wide enough, you'll be able to see this organ, which sits in a pair at the back of the throat. It is part of the immune system.
When bacteria enter the body through the nose or mouth, they are filtered out by the tonsils, which act as a barrier and repel infection. Tonsils contain many white blood cells that help them kill germs. If the tonsils become infected and are removed via a tonsillectomy, the body will still be able to find other ways to fight off infection and germs.
Data reporting by Emma Rubin. Story editing by Brian Budzynski. Copy editing by Robert Wickwire. Photo selection by Abigail Renaud.