The Human Body Facts


Did you know the human body is made up of over 100 trillion cells, has 206 bones, 320 pairs of muscles and five vital organs? It is a remarkable biological machine with many systems working together to allow for life, movement, cognitive function, growth, repair, reproduction and so much more. These systems include the central nervous system, the circulatory system, the respiratory system, the digestive system, the immune system, the reproductive system, the skeletal structure and musculature

The human body is made up of a head, neck, torso, two arms and two legs. The average height of an adult human is about 5 to 6 feet tall. The human body is made to stand erect, walk on two feet, use the arms to carry and lift, and has opposable thumbs (able to grasp).

Systems in the Human Body

  • The human brain is the central command system for the whole body. It’s a mass of about 180-100 billion neurons. Neurons have multiple synapses that create a network of over 100 trillion connections!
  • Tiny electrical currents and chemical messengers send information around the brain at 268 miles per hour.
  • There’s enough electrical current in your brain to power an LED light, 12-25 watts.
  • An adult brain weighs about three pounds. If you hold your fists together with your thumbs touching, that’s the size of your brain.
  • The folds of the brain increase its area size. A baby’s brain is nearly smooth while an adult brain looks like a walnut with lots of folds.
  • Brain tissue needs oxygen and glucose to function. It uses 20% of the blood’s oxygen and glucose. Brain cells begin to die after five minutes of no oxygen.
  • Different parts of the brain have different functions. The main structures in the brain are the: Frontal lobe, parietal lobe, occipital lobe, cerebellum, temporal lobe and brainstem.
  • The brain connects to the rest of the body through the spinal cord, which branches out into smaller and smaller nerves throughout the body.
  • The nervous system is the body’s wiring system. It transmits messages to and from the brain that are both voluntary and involuntary.
  • The involuntary messages are things we can’t control, like our heart beat, feeling pain, and reflexes. Voluntary messages are things we’re aware of, like reaching for a pen and speaking.
  • A pins and needles sensation happens when a nerve is compressed and signal is disrupted.
  • Injury to nerves can cause permanent paralysis and numbness.
  • Nerve diseases can cause loss of memory, uncontrollable shaking, loss of feeling, muscle deterioration and seizures.
  • To examine and measure brain structure, activity and nerve function, doctors can perform an MRI, CT scan or EEG.
  • A healthy brain and nervous system needs a varied, healthy diet and vitamin B1, B9, zinc, calcium, magnesium and vitamin C in particular. Because the brain is over 70% water, it’s important to drink lots of water too.
  • The study of the brain is called neurology.

The Heart and Circulatory System

  • The heart is one big pump made of muscle fibres. Its job is to circulate blood around body so that oxygen and nutrients can be delivered to cells, carbon dioxide can be removed and infections fought.
  • A healthy adult heart beats about 60-80 times per minute. Children’s heartbeats are faster, around 100-120 bpm.
  • The heart has four chambers to pump blood: Deoxygenated blood enters the right atrium, then into the right ventricle where it goes to the lungs. Once oxygenated, it enters the left atrium, down into the left ventricle, and a big squeeze of the left ventricle pushes blood into various arteries.
  • Blood is transported around the body through blood vessels that are split into two functions, carrying oxygenated blood away from the heart, and carrying deoxygenated blood towards the heart.
  • Blood vessels carrying oxygenated blood in order of large to small are called: Aorta, arteries, arterioles and capillaries. Vessels carrying deoxygenated blood in order of large to small are called: Veins and capillaries.
  • There are so many blood vessels that, laid out end to end, would span 60 000 miles.
  • Red blood cells carry oxygen around the body. They’re so small that 2,5 million can fit on a pin head.
  • An average adult has around five quarts of blood and the heart pumps 83 gallons an hour, or 2 000 gallons worth every day.
  • It takes around 60 seconds for blood to leave the heart, circulate around the body and then return to the heart.
  • The heart is and is protected by the rib cage and sternum.
  • Because the heart is a muscle, physical exercise helps keeps it healthy and working well so you can live longer.
  • Heart disease is one of the biggest killers in America every year.
  • Eating too much fat and animal products can cause cholesterol to build up in blood vessels. When a blockage occurs, a heart attack happens.
  • Smoking, excessive alcohol, too much salt, drug abuse, stress, and high blood pressure can all lead to heart disease, heart attack and stroke.
  • Signs of a heart attack include difficulty breathing, pain in the left arm, heaviness on the chest, flu-like symptoms, sudden pain in the chest, turning blue.
  • Anxiety and acid reflux can sometimes feel like a heart attack but you should always call emergency services if someone thinks they’re having a heart attack.
  • The study of the heart is called cardiology.

The Lungs and Respiratory System

  • The function of the lungs is to exchange oxygen from the air to the bloodstream (when you breathe in), and carbon dioxide from the bloodstream to the air (when you breathe out).
  • Humans have two lungs side by side, but they’re not the same size. The left lung is slightly smaller to make room for the heart.
  • Each lung is divided into lobes. The right lung has three lobes, the left, two.
  • When breathing, air enters the respiratory system through the nose or mouth. Hairs in the nose and mucus in the sinuses trap dust and germs. As air travels down the trachea it is warmed and moistened. The trachea branches into left and right bronchi. Each bronchus branches into smaller and smaller bronchi, bronchioles and finally into millions of alveoli.
  • A pair of lungs weighs 2,9lb. They have a spongy structure for lots of surface area for gas exchange. When laid out flat, they’d cover a tennis court!
  • Lungs can’t expand and contract on their own. This movement is controlled by the diaphragm under the rib cage and muscles between the ribs.
  • Lung capacity varies depending on a person’s size, fitness and even altitude. An average adult male has a 1,5 gallon lung capacity.
  • Most adults breathe 12-20 times per minute, which amounts to 2,900 gallons of air per day.
  • An average person can hold their breath for two minutes.
  • The epiglottis is a flap that protects the lungs from food and liquid when we swallow.
  • Coughing and sneezing is the respiratory system’s mechanism for getting rid of irritants like dust and pollen.
  • Asthma is a respiratory condition where the airways constrict as a result of an irritant. Breathing can become very difficult.
  • A person is still able to live with only one lung, but their ability to do physical activity is limited.
  • Because the lungs are the only organs that exchange oxygen and carbon dioxide, it’s very important to keep them healthy and clean. Smoking and air pollution damages lung tissue and leads to lung diseases like cancer and emphysema.
  • The study of the lungs is called pulmonology.

The Digestive System

  • The purpose of the digestive system is to break down food into components the body can use, like glucose for energy, protein for building and repairing cells, and extracting vitamins, minerals and amino acids for cell function.
  • The digestive system begins with the mouth, where teeth mash food, the tongue moves it around, and saliva lubricates it and begins digestion.
  • Upon swallowing, food travels down the oesophagus and into the stomach where acid kills bacteria and breaks down food further.
  • The liquid food then enters the small intestine where the acid is neutralized, and enzymes break down fat, protein and carbohydrates for absorption by tiny hairs called villi.
  • After travelling through 20 feet of small intestine, food passes into the large intestine, or colon, where water is absorbed and bacteria both extract and manufacture important vitamins. The colon is five feet long.
  • The final stop is the rectum, where indigestible food matter and gas are passed through the anus as faeces and flatulence.
  • The study of the digestive system is called gastroenterology.

Stomach Facts

  • The stomach is a muscular sac with hydrochloric acid.
  • To protect itself from the acid, it has a mucus lining.
  • An adult stomach can hold 0,5 gallons of food and liquid.
  • There are nerves in the stomach that tell your brain when it’s empty or full.
  • Vomiting is the body’s way of rejecting food and liquid that is bad.

Small Intestine Facts

  • After leaving the stomach, partially digested food called chyme enters the small intestine.
  • The small intestine is 16-20 feet long in an adult. It’s called ‘small’ because it is narrow – about the thickness of your thumb.
  • In the small intestine, the gallbladder secretes gall to break down fats and the pancreas secretes insulin to manage blood sugar levels.
  • Inside the small intestine, millions of tiny hairs call villi increase the surface area so that nutrients can be absorbed into the bloodstream. Laid out flat, the surface area would cover a tennis court!.
  • Food moves along the intestine through wave-like contractions called peristalsis.
  • Celiacs disease is a condition of the small intestine.

Large Intestine Facts

  • The large intestine, or colon, is about five feet in length and is called ‘large’ because it is wider than the small intestine.
  • Digestion creates up to 1,3 gallons of fluid. The main job of the colon is to reabsorb most of this fluid so things move slowly. It can take 18 – 24 hours for food to leave the digestive system.
  • The large intestine hosts billions of beneficial bacteria called gut flora or the microbiome. They manufacture and extract certain vitamins. Fermentation by gut bacteria creates gas.
  • Fibre is important for a healthy gut.
  • Diseases and disorders of the colon include IBS and colon cancer.

The Immune System

  • The human immune system is the military of the body. It is comprised of white blood cells and antibodies. These seek out and destroy foreign bodies including viruses, bacteria, parasites, fungi and abnormal cells.
  • White blood cells are created in bone marrow are carried in the bloodstream and lymphatic system.
  • A single drop of blood can have 25,000 white blood cells.
  • When white blood cells attack, they envelop the pathogen and destroy it. The remains are carried away in the lymph system.
  • The immune system is able to remember infections and fight them off better through antibodies.
  • Vaccines work by stimulating the immune system to create antibodies for a disease, like polio or measles without actually getting it. The person is then protected against the disease.
  • It’s important to get vaccines even if the disease is no longer common because of the “herd immunity” effect.
  • Stress, smoking, lack of sleep, poor diet and diseases like HIV/AIDS can weaken the immune system, making you vulnerable to infection.
  • Allergies and allergic reactions are a false alarm and the result of an overactive immune system. Allergic reactions can cause anaphylactic shock and swelling where a person can’t breathe.
  • Autoimmune diseases like Lupus mean that the immune system attacks its own body, not just germs.
  • Being too clean isn’t always a good thing. Without germs to develop antibodies, the immune system doesn’t develop or learn what’s harmful or not.
  • The study of the immune system is called immunology.

The Reproductive System

  • The reproductive system’s function is to create new life so that genes can be passed along to future generations.
  • A woman’s reproductive organs include a pair of ovaries that form eggs and the uterus, where a baby gestates until it’s ready to be born.
  • A man’s reproductive organs include the testes, where sperm is formed, and a penis for delivering sperm into the uterus.
  • When an egg and sperm cell fuse as a result of sexual intercourse, conception occurs and a baby begins to grow.
  • Gestation of a baby is 40 weeks, or nine months, during which it grows from a few cells into a fully formed baby.
  • Humans reach reproductive age around 13 years old. With good nutrition, puberty is arriving sooner with each generation.
  • A woman produces one egg every 28 days. If it is not fertilized, menstruation sheds the uterine lining.
  • A man’s ejaculate can have as many as 300 million sperm cells.
  • Sexually transmitted diseases include HIV/AIDS, chlamydia, syphilis and HPV, which can cause cervical cancer.
  • The most common cancers of the reproductive organs include ovarian and cervical cancer in women, and testicular and prostate cancer in men.
  • The study of women’s reproductive organs is called gynaecology, the study of men’s reproductive organs is called andrology.

The Skeleton

  • Humans are vertebrates, meaning they have a backbone or spinal column.
  • An adult skeleton has 206 bones. A baby has 300 bones at birth and some fuse together as they grow. Half of these bones are in your hands and feet!
  • The largest and strongest bone in the body is the femur. The smallest bones are in the middle ear.
  • Where bones meet is a cushion of cartilage. Bones are held together by tough ligaments.
  • Bones consist of hard bone gives structure, spongy bone, which is still hard, but has more air pockets, and bone marrow, where blood and stem cells are produced.
  • A healthy human bone can withstand three times your bodyweight in force.
  • Arm and leg fractures and breaks are more common in growing children because the growth plates are vulnerable.
  • When a bone fractures or breaks, it is able to repair itself. Special bone cells will surround the injury, form a callus, break down injured bone and replaces it. Even healthy bones are continually maintained.
  • Bone is made mostly of calcium for strength and collagen for flexibility, which is why it’s important to eat lots of green leafy vegetables.
  • An adult reaches their full height in their 20s, and maximum bone density in their 30s.
  • Bones can be seen with an X-ray.
  • Diseases of the bone include osteoporosis and arthritis.
  • The study of bones is called osteology.


  • The human body is incredibly flexible and able to move in thousands of ways, all thanks to 320 pairs of skeletal muscles.
  • Muscles are made when muscle proteins form strands of muscle fibre. These then form bundles which make up larger skeletal muscles.
  • Skeletal muscles occur in pairs, when one muscle group contracts, the opposing pair relaxes. Example: To raise your forearm, your bicep contracts and your tricep relaxes.
  • Bones cannot move by themselves, that’s the work of muscles. Where ligaments connect bones to each other, tendons connect muscle to bone.
  • Electrical signals carried by nerves to and from the brain instruct muscles to contract or relax.
  • Muscles are responsible for creating body heat. They twitch so slightly you don’t even feel it. This generates heat necessary for metabolism.
  • Muscles are built and repaired when tiny tears in the muscle fibre are filled in with new muscle cells.
  • Muscles need oxygen and glucose to function, and protein to repair and regenerate.
  • The body has three kinds of muscle: Skeletal, for movement, cardiac, for the heart, and smooth in the digestive system.
  • Some 40% of a person’s weight is comprised of muscle mass. It’s also denser than fat, which is why two people of the same size can have different weights.
  • The largest muscle in the body is the gluteus maximus. Jaw muscles can exert 200lbs of force.
  • The study of muscles is called myology.

More interesting facts about the human body

  • The adult body is made up of: 100 trillion cells, 206 bones, 600 muscles, and 22 internal organs.
  • Every square inch of the human body has about 19 million skin cells.
  • Every hour about 1 billion cells in the human body must be replaced.
  • The average human head has about 100,000 hairs.
  • The circulatory system of arteries, veins, and capillaries is about 60,000 miles long.
  • The heart beats more than 2.5 billion times in an average lifetime.
  • There are about 9,000 taste buds on the surface of the tongue, in the throat, and on the roof of the mouth.
  • The strongest muscle in the body is the tongue.
  • The human heart creates enough pressure when it pumps out to the body to squirt blood 30 feet.
  • You blink over 10,000,000 times a year.
  • The human brain weighs about 3 pounds.
  • It takes about 20 seconds for a red blood cell to circle the whole body.
  • Only 10% of the population are left handed.
  • One fourth of the bones in your body are in your feet.
  • Children tend to grow faster in the spring.
  • The most sensitive finger on the human hand is the index finger.
  • More men are color-blind than women.
  • More people have brown eyes than any other color


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