Human Digestive System

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.

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.

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

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.

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.

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.

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.