Have you ever wondered what happens to the food after you and swallow it? Once entering the body, the food is broken down and converted into energy and basic nutrients by a group of organs, call the digestive system. Although the Digestive system is one of the most overlooked body systems, it is also one of the most essential, in that it allows body to function, grow, and repair itself. The Digestive system can be divided into several categories. The anatomy of the digestive system (which includes the organs involved), the physiology of the digestive system (which includes the 6 major processes), and mechanical and chemical digestion.

Digestive System Anatomy

  • Mouth - Food begins the digestive process, as soon as it enters the mouth, also known as the oral cavity. The mouth contains 3 accessory organs that aid the digestive process. The teeth are designed to cut and grind food into smaller pieces. The tongue detects taste molecules in food and is used to push the food towards the pharynx. The salivary glands produce a watery secretion called saliva, which moistens and begins to digest the food chemically.

  • Pharynx and esophagus - the pharynx, or throat, is a funnel-shaped tube, connected to the mouth and is responsible for transferring the mechanically broken-down bits of food from the mouth to the esophagus. The esophagus is a muscular tube connected to the pharynx and the stomach and is responsible for the transfer and trapping of food in the stomach.

  • Stomach - The stomach is a muscular sac, about the size of two fists placed together, and acts as a storage tank for food. The stomach is also important for the use of the further breaking down of foods. The stomach mechanically digests the foods by acting as a mixer or grinder. The stomach also participates in the chemical digestion of foods by utilizing hydrochloric acid and digestive enzymes. Food is then reduced to nutritious liquid and small solid particles.

  • Small Intestine - The small intestine is a long, thin tube that is coiled like a hose and full of ridges and folds, which allow for the maximization of the digestion of food and absorption of nutrients. This digestion is supported by chemicals and enzymes produced by the pancreas. After leaving the small intestine, about 90% of all nutrients have extracted from the food.

  • Liver and Gallbladder - The liver produces bile and secretes into the small intestine to aid in chemical digestion, while the gallbladder stored and recycled excess bile so it can be reused for further digestion.

  • Large intestine - Absorbs water and contains bacteria that aid in the decomposing of wastes to extract small amounts of nutrients.

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Digestive System Physiology (Six primary processes)

  • Ingestion - First function of the digestive system. Ingestion involves the intake of food. The two primary organs involved in ingestion are the mouth and the stomach. The mouth serves as the orifice through which the food enters the body, while the stomach serves as the storage tank during digestion. This storage capacity is what causes humans to get full and inhibits them from constantly eating.

  • Secretion - The digestive system secretes about 7 liters of fluids, which involve saliva, mucus, hydrochloric acid, enzymes, and bile. Saliva moistens foods and contains amylase, an enzyme that begins the digestion of carbohydrates. Mucus serves as a protective barrier and lubricant, while hydrochloric acid aids in chemical digestion and protects the body by killing bacteria. Enzymes are like tiny biochemical machines that disassemble large macromolecules (proteins, carbs, lipids), and bile is used to emulsify lipids into smaller parts for easy digestion.

  • Mixing and movement of food and wastes - 3 main processes, swallowing, peristalsis, segmentation. During swallowing, the mouth and tongue are used to push food out of the mouth, through the pharynx, and into the esophagus. Peristalsis is the use of muscular waves to move partially digested food from the esophagus, through the stomach and the intestines. Segmentation occurs only in the small intestine and increases the absorption of nutrients through mixing and increased contact with intestine walls.

  • Digestion - a person's capacity to break down food into substances that can be used by the body, through mechanical and enzymatic means. Mechanical digestion involves physical breakdown of large pieces of food into smaller parts. Mechanical digestion involves mastication(chewing) and peristalsis. After chewing, the food continues to be digested by mixing in the stomach and intestines and bile breaks-down fats. While mechanical digestion occurs, chemical digestion begins. Chemical digestion begins in the mouth with salivary amylase, dissolving complex carbohydrates into simple carbohydrates. chemical digestion is continued in the stomach with the use of enzymes and acids. However, the majority of chemical digestion occurs in the small intestine with the help of pancreatic juice. At the end of both digestions, lipids, carbohydrates, proteins and nucleic acids have all been reduced to chemical building blocks (fatty acids, amino acids, monosaccharides, and nucleotides).

  • Absorption - After being reduced to building blocks (simpler molecules), food undergoes absorption. Water and alcohol are absorbed into the bloodstream, while digestion takes place in the stomach. In the small intestine the majority of food molecules are absorbed and carried throughout the body with the help of blood and lymphatic vessels. Large intestine is involved in absorption of water and vitamins B and K.

  • Excretion - Final process of the digestive system, in which waste is excreted through defecation. Defecation is the voluntary removal of indigestible substances from the body.

Appliance of chemistry

  • Basic/pure chemistry - Someone wants to learn what happens to the food after it is swallowed, and how energy is transferred from food to the muscles and organs. This may result in the exploration of and gaining of knowledge of digestive system.
  • Applied chemistry - The production of medicines, such as laxatives or Pepto-Bismol, after researching the processes of the digestive system.

  • Chemistry is used throughout the digestive system, especially during the phases of chemical digestion. Many chemical processes and reactions (mainly decomposition) are involved during digestion. In order to dissolve food molecules enzymes and very acidic substances, like hydrochloric acid are utilized. Enzymes are proteins that act as biological catalysts. This means that the enzymes increase the rates of chemical reactions in living things, but they themselves are not unchanged by the reaction. Introduction of an enzyme only changes the reaction speeds; it does not change the amount of product or reactant formed. Eight digestive enzymes are mainly responsible for chemical digestion. These enzymes include nuclease, protease, collagenase, lipase, amylase, elastase, trypsin, and chymotrypsin. Nuclease is a group of enzymes that split nucleic acids into nucleotides, while protease catalyzes the hydrolytic breakdown of proteins.


It has been made clear that barely any of the nutrients that is stored in food is used in the digestive process. Do you think there would be any way to harness any of the nutrients lost once the body turns food into waste product? If it is not possible to reuse any energy from this waste, are there any ways to reuse food waste produced by the body for practical application?
-Cole K.

Nicholas T. (To Cole). I did not find any ways that waste could be reused for some sort of nutrient source. However, in Japan, bricks made from sewage sludge. This sludge is heated to extreme temperature to create a solid brick and get rid of the smell. The bricks allows water to seep through to the ground, so there is no need for drainage systems.

Answering Cole: While there is a copious amount of chemical potential energy present in feces, one would have to separate out the usable material from the crap, literally, which would, on a small scale, be a waste of time and energy. However, there is a very fine green tea that is harvested in Sumatra. The luwak, a small, raccoon-like animal, eats the fine coffee beans and defecates them almost whole. The feces is collected and used to produce one of the world's finest green teas (no longer in production). It is called Kopi Luwak tea.

Zoe T- Nick, that's... gross :( Wait, wouldn't the sewage have a potential of decomposing since a significant amount of it is made from waste? And would the bricks not be able to be re-moistened from precipitation?

Cailey Cobb-A little while back i re watched a dirty jobs where they used cow manure to create bricks were made into a house the "waste bricks" were a great source of insulation, and was 100% natural and eco friendly!!!