The stress hormones released by the endocrine system act on the digestive and urinary systems to slow them down — energy is needed elsewhere.
DNA is a long molecule that provides all the information necessary for an organism to develop, survive, and reproduce. It is like a twisted ladder with rungs made of a pari of chemical bases. These bases form long sequences called genes that are coded instructions for building proteins. When a cell needs to duplicate its DNA or make a new protein, the two halves of the ladder unzip so that a copy of the gene can be made. Humans have more than 3 billion bases in their DNA and nearly 20,000 genes.
Humans have a relatively low number of genes. We have more than a chicken (16,000) but fewer than an onion (100,000) or an amoeba (200,000). This is because we lose unwanted genes faster from our DNA than they do.
If our DNA is the body’s recipe book, then a gene within that DNA is equivalent to a single recipe in the book; it is the instructions for building a single chemical or protein. It’s estimated that humans have around 20,000 genes that code for different proteins.
The skin uses UV light to synthesize vitamin D — but too much UV light can cause skin cancer. A skin pigment called melanin helps maintain a balance between the two.
Scalp hair can grow for years, but hair found elsewhere on the body only grows for weeks or months. That’s why body hair is usually short — it falls out before it can grow very long.
Because nails are nonessential structures, blood and nutrients are diverted away from the nails beds in times of deficiency. Nails are therefore a good indicator of your general health and diet.
Bone is 5 times stronger than a steel bar of the same weight, but it is brittle and can fracture on impact.
Tooth enamel is the hardest substance in the body, but readily dissolved in acid, exposing the underlying parts of the tooth to bacteria and infection.
When you are relaxed an not focusing on the world around you, your brain shows a specific pattern of activity; this is called the default mode network. It is thought that this network helps generate thoughts as you mind wanders, and may be linked with creativity, self-reflection, and moral reasoning.
Pressure over a nerve, such as from a tight sock, can cut off its blood supply. This causes numbness by preventing the nerve from sending messages. When pressure is relieved, blood flow returns. As the nerve and its receptors become active again, a tingling sensation, which an be unpleasant, occurs.
Your stomach is instructed to bring digestion to a halt. In times of true terror, you may vomit to stop digestion. A full stomach can slow you down if running.
The muscles that usually keep the bladder shut tend to relax if you are anxious, unfortunately resulting in frequent trips to the toilet.
The sensation of butterflies before a stage performance or big interview is due to the reduction of blood flow to the stomach when readying the body for danger.
What we think of as our sense of touch is actually composed of signals from several different receptors in our skin. Some receptors are concentrated in certain areas, such as the sensitive fingertips.
Local anesthetic blocks conduction of electrical impulses along the A and C nerve fibers, so these impulses never reach the spinal cord.
Opioids such as morphine mimic your body’s natural opioids, binding to the nerve cells in order to reduce or even block pain’s chemical message. It can erase the feeling of pain altogether, which is useful during medical emergencies.
The iris is the colored part of the eye with a central opening called the pupil. It contains muscles that contract or relax to alter the size of the pupil and so let more or less light into the eye.
We are used to seeing objects in a variety of lighting conditions and our brain takes this into account to cancel out the effects of shadows and lighting. This means we always see a banana as yellow, no matter how it is illuminated.
Cataracts are cloudy lenses that disturb vision and are the cause of half the cases of blindness worldwide.
Our ears don’t help much in pinning down the height of sound sources, though. Left and right localization is easier — a sound from the left is louder in the left ear than in the right, particularly at high frequencies. It also reaches our left ear a few milliseconds before our right.
Our brains can “tune in” to a single conversation over the babble of noise at a party by grouping sounds into separate streams, based on frequency, timber, or source. It might seem as though you don’t hear any other conversations — but you will notice if someone mentions your name. That’s because your ears still send signals from the other conversations to the brain, which will override the filtering if something important comes up elsewhere.
When shown these shapes and asked to name one Bouba and the other Kiki, most people call the spiky shape Kiki because of its spiky sound, while deciding the softer Bouba fits the rounded shape.
Taste is a simple sense, made up of crude sensations such as “sweet” or “salty”. Most of what you think of as flavor is actually what you are smelling. Smell can also influence the crude sense of taste itself. Smelling vanilla can make food or drink taste sweeter, but only in parts of the world where vanilla is a common flavor for sweet foods.
The best liars convince themselves they are telling the truth — if you truly believe your lie, your body language can’t give you away.
Blood transports oxygen to every single cell in the body. Each cell uses oxygen in a chemical reaction to break down the sugars ingested from food to produce energy. This process is called cellular respiration, and is happening constantly throughout your body. A byproduct of this reaction is carbon dioxide, which is carried back to the lungs by veins and breathed out as we exhale.
Exerting yourself in a short space of time causes your body to make energy inefficiently, which releases a lot of lactic acid, causing the “burn.”
During strenuous exercise, your body demands energy more quickly than you can provide oxygen to make it. Muscles can continue to break down glucose without oxygen in a process known as anaerobic respiration. It is great for short bursts of energy, but it generates excessive lactic acid in your muscles and is unsustainable. Now, oxygen is needed, not to help burn glucose, but to convert the build up of lactic acid into glucose — for future energy. This is known as paying the oxygen debt and leaves your out of breath for some time after an intense sprint.
There are 6 essential types of nutrient that the body needs to get from the diet in order to function properly: fats, proteins, carbohydrates, vitamins, minerals, and water. The last 3 are small enough to be absorbed directly through the lining of the gut, but fats, proteins, and carbohydrates need to be broken down chemically into smaller particles before they can be absorbed. Theses particles are sugars, amino acids, and fatty acids respectively.
90% of all the cells in our bodies are bacterial rather than human.
Probiotics are the opposite of antibiotics. They are live bacteria that are consumed — in yogurts or tablets — to fortify gut bacteria that have been damaged by antibiotics or disease.
Calories are equal in terms of the amount of energy the contain, but where they come from — fat, protein, or carbohydrate — determines how they are used by the body. Some foods give us a steady source of energy; others can take us on a hormone roller-coaster ride.
Sugar is now thought to be more addictive than cocaine.
Exercising when your body is naturally burning fat may give your workout more punch. A run before breakfast, for example, takes advantage of the fact that your body is already burning fat after fasting all night. A run in the evening, however, is more likely to be fueled by blood glucose supplied by the day’s food. For this reason, morning exercise is generally more effective for losing weight.
The formation of pus is an indication that bacteria have gotten into the wound — pus is the accumulated remains of dead immune cells.
Shivering raises your body temperature — rapid contractions from your muscles generates heat, helping to speed up reactions that fight off infection.
Sometimes the immune system is too reactive — launching attacks on things that aren’t harmful and even attacking the body’s own cells. Allergies, hay fever, asthma, and eczema are all caused by an oversensitive immune system.
2 hours: the estimated total time you spend dreaming each night.