I’m not very philosophical, so strictly scientifically – what are we? It’s a complex thing the body, tiny but important parts all together making a pretty robust organism. There are a few different ways to look at this, it depends on how microscopic you want to go: systems, organs, tissues, cells, molecules, atoms. You could go smaller but it’s too small for me – quantum mechanics governs that stuff.
You could get roughly 160 billion helium atoms side-by-side in a centimeter but there’s a relatively huge gap between the middle (nucleus) and the electrons whizzing round the outside of the atom. If the Earth was an atom, the nucleus would be a football stadium. All the space adds up, so we are mostly empty space, but so is everything else! The atoms that make us are a little bigger than helium, but not hugely…
Oxygen ~65% Part of water (H2O) that’s in every cell in the main fluid of the body.
Carbon ~18.5% It’s in every carbohydrate, protein, fat, all the organic chemicals in the body.
Hydrogen ~9.5% The other part of water, and in your organic chemicals too, not very big or heavy, but very important.
Nitrogen ~3.3% It’s in all your proteins, the amino acids that make them have it and the nucleic acids your DNA is made of.
Calcium ~1.5% Bones and teeth: we all know how important they are! Also used in signaling to make muscles contract.
Phosphorous ~1% The major player in energy is something called ATP, the P being phosphorus, so very important! It’s in bones too.
There’s a lot more, like sodium, potassium, and magnesium that help electrical signals in the body, that’s those “electrolytes” you may have seen in sports drinks. There’s probably hundreds of elements inside you, including arsenic and uranium! But the top four make up over 95% of your body weight, so there aren’t much of the others but we need them!
Thinking bigger, we get cells. Cells are amazing: they’re the functional units that make us, the building blocks. We have trillions of them and they’re all specialized.
Cells of the same type grouping together give us tissues; like muscle, nerve and connective tissue. For example, muscle cells are built to contract, nerve cells are built to pass along electrical charges. A big tissue is epithelial, made from tightly packed cells forming sheets – barriers to separate bits.
Organs are when you’ve got tissues working together for something specific. The biggest is the skin. Skin is pretty amazing, it has plenty of functions with all the kind of sensors it has. The liver is the biggest internal organ and it too is amazingly complex with hundreds of vital functions.
Systems of the body are made of a group of organs like the digestive system from mouth, stomach, with a lot of intestines. There’s the respiratory system, cardiovascular, endocrine, immune, skeletal, muscular, lymphatic, reproductive, urinary, nervous… it’s a complex thing the body. This is a good site to learn more about all the different systems and their bits!