As humans, we are constantly gaining the necessary nutrients and energy from the things we consume, food. The digestive system is there to break it into smaller components so that the nutrients which the body requires is absorbed. This may include vitamins, proteins, fats and carbohydrates, which is then used for growth, replacement and repair of cells.
How is food digested in our body?
The process begins in the mouth, where starch is broken down by saliva due to the presence of the enzyme, amylase. Food is made easier to chew as it becomes moistened by saliva produced by the salivary glands, and this then passes through the pharynx into the oesophagus. The oesophagus is a long tube located in your throat and helps transport food to the stomach. Unlike the mouth, its function does not involve any further breaking down of food. The food is delivered to the stomach by involuntary, wave-like contractions of the muscles called peristalsis, which propels food along the digestive tract and occurs in a sequence to produce a wave that prevents the food from travelling backwards.
The main digestion takes place in the stomach, which holds the food while it is broken down. Hydrochloric acid is released along with enzymes to kill any bacteria that is present and complete the breakdown of food. The acid provides the low optimum pH needed for the enzymes to work best in, including pepsin which is involved in the digestion of proteins into polypeptides. The movements caused by the strong muscular walls within the stomach help mix the digestive fluids and enzymes with the food, before it is sent to the small intestine.
The process of digestion continues in the small intestine which also plays a key role in absorption of nutrients. About 90% of the nutrients are absorbed in the small intestine and its inner walls are covered with villi to provide the large surface area, so that diffusion of the digested food can take place quickly. The small intestine is composed of three segments: the duodenum, jejunum and ileum.
The food first enters the duodenum, where most of the chemical digestion occurs using enzymes produced by the pancreas and bile from the liver. Bile causes fat molecules to emulsify into smaller components, so that they can be digested by enzymes more efficiently due to their larger surface area. It is also important in increasing the pH of the food coming from the acidic stomach, so that the enzymes can function properly since they work best in neutral environments. Most of the key nutrients are absorbed by the jejunum and then absorbed even further as they pass into the ileum. The large intestine then absorbs any water left in the food, causing the waste to turn into stool. Peristalsis also takes place here helping to move the stool into your rectum where it is stored until it is pushed of your anus during bowel movement.
How are the processes controlled?
The digestive system does not only rely on the organs to break down the food. The body’s hormones can be used to help control the processes. When your body has enough food and energy, a hormone called leptin made by fat cells is secreted into the bloodstream, activating the hypothalamus in the brain to decrease your appetite, causing the person to feel the sensation of being full. Leptin levels are usually linked to the individual’s body fat amount, which are energy stores. Therefore, when a person increases their body fat, leptin levels will increase as well since they do not require as much energy. On the other hand, when your stomach is empty, a hormone called ghrelin is produced by the stomach and small intestine which triggers the hypothalamus to instead stimulate hunger so that the body can receive more food and energy.
In a simple summary, the digestive system breaks down all the food as it travels through the body and absorbs what is simply needed, removing what is then left. It is formed from a network of organs that work simultaneously to carry out its function and without it, our bodies wouldn’t be able to absorb the nutrients and energy from the foods we eat. Like all the other systems in the body, it plays a small, yet fundamental role within life so that our body can work smoothly and without fail.
- Cleveland Clinic (2018) “The structure and function of the digestive system” [online] Last accessed: 09/13 2018 https://my.clevelandclinic.org/health/articles/7041-the-structure-and-function-of-the-digestive-system
- National Institute of Diabetes and Digestive and Kidney Disease (2017) “Your digestive system and how it works” [online] Last accessed December 2017 https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-system-how-it-works#whatis
- Wikipedia (2020). “Peristalsis” [online] Last accessed 09/04/2020 https://en.wikipedia.org/wiki/Peristalsis
- Verywell Fit (2020) “The hormones that regulate hunger and digestion” [online] Last accessed 30/03/2020 https://www.verywellfit.com/hormones-that-regulate-hunger-and-digestion-2507054