Our Chemical Composition

Upon examining our physical makeup, we discover that a significant portion of our bodies is formed from just seven chemical elements: oxygen, carbon, hydrogen, nitrogen, calcium, phosphorus, and potassium. These elements are the fundamental building blocks of chemistry, remaining unchanged during chemical reactions.

Atoms represent the smallest units of these elements, and they can combine to create stable structures known as molecules. According to scientists like Bill Bryson and Herbert Zeng, out of the 118 known chemical elements, about 59 are utilized in the human body, with approximately 21 classified as essential for life.

For an average individual weighing about 70.0859 kg, the essential elements contribute approximately 70.0832 kg (99.9962%), while the remaining 38 non-essential elements collectively weigh around 0.0027 kg (0.0038%). Notably, merely one-third of the 21 essential elements make up 99.5% of our body, centering around seven key constituents: oxygen (43 kg), carbon (16 kg), hydrogen (7 kg), nitrogen (1.8 kg), calcium (1 kg), phosphorus (0.8 kg), and potassium (0.1 kg).

This leads us to ponder: how do we grow physically when atoms do not multiply or change size? The answer lies in our consumption of food and water. By obtaining the necessary nutrients, we increase the number of atoms within our bodies, facilitating physical growth over time.

Next, let’s explore the origins and roles of these seven essential elements.

Section 1.1: Oxygen

Importance in the Human Body

Oxygen serves two primary purposes: respiration and metabolism. Approximately 21% of the air we breathe is oxygen, with the remainder largely being nitrogen. Oxygen enters our bloodstream through the lungs, where it is transported by red blood cells to support metabolic processes, including energy production.

Around 20% of our oxygen intake is utilized by the brain, which relies on this element for both neuronal function and energy metabolism. This metabolic process encompasses the construction and repair of tissues, energy conversion, waste removal, and cell reproduction.

The energy we derive originates from oxidation, wherein cells combust nutrients—this process is facilitated by enzymes, which expedite chemical reactions. As a result, energy carriers like ATP transport the energy to various cellular locations for different functions.

Cosmic Origins of Oxygen

Oxygen was first identified in the universe approximately 600 million years after the Big Bang (13.8 billion years ago) within interstellar dust of the A2744_YD4 galaxy. Most heavier elements, including oxygen, were formed outside galaxies, predominantly in intergalactic space.

Heavier elements, including oxygen, are created through stellar nucleosynthesis in the cores of massive stars. This process involves merging lighter atomic nuclei into heavier ones, particularly during supernova events.

Section 1.2: Carbon

Importance in the Human Body

The 16 kg of carbon within our bodies serves as a critical building block for carbohydrates, proteins, and fats. Along with oxygen, carbon plays a significant role in cellular metabolism, converting glucose into ATP through cell respiration, while releasing carbon dioxide as a waste product.

Moreover, carbon is integral to the formation of nucleic acids, such as DNA and RNA, which store genetic information and guide protein synthesis.

Cosmic Origins of Carbon

Carbon exists in various forms in the interstellar medium, primarily in atomic and molecular arrangements. The creation of carbon occurs in stars as they evolve and burn helium, especially in more massive stars, which are also responsible for dispersing carbon throughout space upon their demise.

Section 1.3: Hydrogen

Importance in the Human Body

Hydrogen is found in carbohydrates, proteins, and fats, and is essential for maintaining bodily fluids. It lubricates joints, facilitates nutrient transport, removes toxins, and helps regulate internal temperature.

Hydrogen also plays a crucial role in immune function and protects vital organs from shocks, ensuring proteins and DNA maintain their functional shapes.

Cosmic Origins of Hydrogen

Hydrogen, the simplest and most abundant element in the universe, was formed shortly after the Big Bang, when the universe cooled enough for neutral atoms to emerge.

Section 1.4: Nitrogen

Importance in the Human Body

Nitrogen, primarily sourced from plant-based foods and proteins, is vital for tissue health, DNA and RNA synthesis, and metabolic enzyme function. It constitutes about 2.6% of our body, influencing neurotransmitter activity and overall bodily functions.

Cosmic Origins of Nitrogen

Nitrogen is produced by both intermediate-mass and massive stars, with its distribution occurring through planetary nebulae rather than supernovae explosions.

Section 1.5: Calcium

Importance in the Human Body

Calcium, the most prevalent mineral in our bodies, is essential for maintaining strong bones and teeth. It also plays a role in muscle function, blood clotting, and hormone regulation.

Cosmic Origins of Calcium

Calcium is primarily created during the explosive deaths of massive stars, dispersing into space through supernova events.

Section 1.6: Phosphorus

Importance in the Human Body

Phosphorus, often found in conjunction with oxygen as phosphate, is crucial for bone health and cellular functions, including energy metabolism and DNA structure.

Cosmic Origins of Phosphorus

Phosphorus is formed during the final stages of massive star evolution and supernova events.

Section 1.7: Potassium

Importance in the Human Body

Potassium is vital for maintaining fluid balance, supporting nerve and muscle functions, and regulating blood pressure.

Cosmic Origins of Potassium

This element is synthesized in massive stars during the process of supernova nucleosynthesis.