To some, digestion may seem like a simple process. However, it's actually a complex process with lots of different things happening all at once. It involves physical and chemical processes to break down food to gain the nutrients we need to survive! Digestion is just one of the processes that take place in our bodies. It takes place all along the digestive system, a series of organs including the mouth, stomach and intestines that work together to digest food. Other systems in the body include the respiratory system, nervous system, circulatory system and more! In this article, we'll focus on the digestive system, the process, and its function in humans!
Human Digestion System: Digestion
Digestion is the process of breaking down larger insoluble substances into smaller soluble substances that can be absorbed into the bloodstream and used across the body. Digestion is carried out by the digestive system. Digestion is an extremely important process in our bodies. It allows us to get the important nutrients we need to grow and gain energy.
Digestion takes place all along the digestive tract (the alimentary canal). This starts with the mouth and passes all the way through to the anus, with many different organs involved the whole way through. Each organ plays its own role in helping in the digestive process.
Human Digestive System Process
The first step of the digestive process is ingestion, the process by which food enters the digestive system through the mouth. This is essential as it allows food to enter the alimentary canal.
The following overview briefly outlines the remaining steps of the digestive process.
- Digestion directly follows ingestion, starting in the mouth with the enzyme amylase in the salivary glands. Digestion is the process of breaking down large insoluble molecules into small soluble molecules. This process continues all the way from the mouth through the stomach into the intestines.
- Absorption follows digestion. It is the process of moving digested molecules from the digestive system into the bloodstream. Absorption primarily occurs in the small intestine, more specifically in the ileum.
- Assimilation follows absorption. This is the process by which absorbed molecules present in the blood then travel from the bloodstream into the cells across the body that need them. This is a vital part of the process as it allows us to make use of the foods that we have eaten.
- Egestion is the process at the very end of the digestive system. It refers to the removal of 'waste' products that have not been absorbed by the body into the bloodstream through the anus.
Many of these processes sound similar, so make sure you do not get confused! Read more about them in our article Digestion.
Human Digestive System Diagram
As we have discussed above, many organs are involved in the process of digestion. Have a look at the organs involved below and a summary of their roles in the next section.
Before looking at their roles, have a look at their location in the human body. We describe food's route through the body as the alimentary tract, digestive tract or alimentary canal.
Fig. 1 - The digestive tract begins at the mouth and ends with excretion at the anus
Human Digestive System Parts and Functions
The human digestive system is a very complex system with many different parts and functions. These functions include enzyme production, mechanical digestion, absorption and more. It can be useful to consider the route that food takes once you eat it all the way to excretion, but it's important not to forget some organs that food doesn't actually pass through, like the pancreas and liver! Let's have a look at the different digestive system parts and their functions here:
Mouth - ingestion and digestion begins
Salivary glands - contain amylase for the digestion of carbohydrates
Oesophagus - moves food to the stomach from the mouth
Stomach - digestion continues
Pancreas - produces enzymes for digestion
Liver - produces bile
Gallbladder - Stores bile
Small intestine - absorption of nutrients
Large intestine - reabsorption of water and egestion
Enzymes of the Human Digestive System
Enzymes are proteins, a type of biological molecule! Enzymes function as biological catalysts (biocatalysts). This means that, like other catalysts, enzymes speed up chemical reactions by facilitating the interactions between the reactants or substrates. Enzymes do this by lowering the activation energy of important reactions in our bodies. As catalysts, they're also not used up in the reactions they facilitate. There are enzymes in our bodies for a variety of functions, including facilitating digestion.
Fig. 2 - The lock and key theory suggests that the enzyme and substrate perfectly fit into each other
Activation energy is the energy required for a chemical reaction to take place! Read more about it in our Enzymes article!
The lock and key theory explains how enzymes work. It unfolds in the following steps:
The substrate binds to the enzyme's active site, forming an enzyme-substrate complex.
The enzyme breaks down the substrate, and the reaction products are formed.
The enzyme remains unchanged in the reaction.
Enzyme's Role in Digestion
Enzymes play an essential role in digestion. Enzymes help to break down large insoluble molecules into small soluble molecules that can be used by our bodies. Many different enzymes are involved in digestion at different stages of the digestive process. After enzymes help break down molecules, these molecules then need to get into the bloodstream to be transported to where they are needed. This is the process of absorption.
Here are some examples of enzymes involved in the digestive process:
Factors Affecting Enzyme Activity
Many different factors affect enzyme activity. Temperature, in particular, can have a huge impact on enzyme activity. Every enzyme has an optimum temperature where its activity is highest. If we go too far above or below this temperature, the enzyme becomes denatured or inactivated and changes shape, leading to decreased enzyme activity.
Denaturation - Bond breakage in a protein affecting its activity.
pH also has a significant impact on enzyme activity. As with temperature, each enzyme has an optimum pH. Any movement above or below this pH leads to the enzyme being denatured and changing shape. This again decreases enzyme activity. Enzyme and substrate concentration also have an impact on enzyme activity. If we have more enzymes than substrates, then substrate concentration will limit enzyme activity.
The aspect that limits enzyme activity is called the limiting factor. If we have more substrates than enzymes, enzyme concentration will be the limiting factor!
Types of Digestive Systems
There are many different types of digestive systems. Different types of organisms have different digestive systems. The digestive system humans have, where we eat food using our mouth, then it passes through a long alimentary canal and then is excreted through the anus, is not the only type of digestive system! This is an example of a monogastric digestive system, where the organism only has one stomach. Other examples include the avian digestive system, found in poultry like chicken, and the ruminant digestive system found in cattle and other similar animals.
Carnivore vs Human Digestive System
What's the difference between a carnivore and human digestive systems? Well, let's start by reminding ourselves what a carnivore is.
A carnivore is an organism that only eats meat. An omnivore is an organism that can eat both meat and plant products. A herbivore is an organism that only eats plant-based products.
- Humans are omnivores, eating a mix of both meat and plant products. You might know some people that follow vegan diets, so they might technically be herbivores rather than omnivores. The same applies to those people who eat strictly meat-based diets, they may lean closer to carnivore diets.
There are a few differences between our digestive system and the digestive system of strict carnivores. However, there are more similarities than differences. The reason for this is that we, like carnivores, eat meat. As we eat the same foods, in some part, our digestive systems are similar. One area where we can find both similarities and differences is our teeth. If we look at a lion's teeth and then at our own teeth, we notice that some of our teeth have similar shapes, but others are very different. This difference is likely due to the meat that we eat. The meat we eat is often cooked softer, whereas a lion (or a similar animal) has to eat tougher, uncooked meat.
Another difference between the human digestive system and the digestive system of stricter carnivores is the length of our intestines. In humans, the digestive system contains longer intestines. This is needed to break down plant-based products in digestion.
As you can see there are many concepts to explore further related to the digestive system! Even though for us digestion might seem like just chewing and swallowing food, there are many processes that need to happen for us to be able to digest and absorb the nutrients in our food.
Human Digestive System - Key takeaways
- Digestion is the process of breaking down large insoluble molecules into smaller soluble molecules.
- Many different organs are involved in the digestive system
- Digestion, absorption and assimilation all help us to get the useful nutrients from foods into the cells that need them
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