Differences Between the Small and Large Intestines

The small and large intestine, as a whole, occupy several meters of surface and have an essential functionality in the digestion process. Do you want to know more about them?

Written and verified by el biólogo Samuel Antonio Sánchez Amador.

Last update: 05 July, 2023

The digestive system is a group of organs that process food and liquids to break them down into substances that the body uses as a source of energy, as a means of tissue repair, and as growth promoters. Knowing the differences between the small and large intestines is essential in order to understand this complex system.

In addition to the knowledge we obtain by understanding the differences between the organs that make up the body, it should be noted that this is also essential when it comes to detecting pathologies and establishing prognoses.

In the following lines, we’ll tell you all the differences that exist between both sections of the intestine. Keep reading, because at the end of the article, we’ll address the pathologies of each of these digestive tracts.

What are the differences between the small and large intestines?

As indicated by the National Cancer Institute, the digestive system is made up of the gastrointestinal tract, the liver, the pancreas, and the gallbladder. When we eat food, it enters through the mouth and mixes with saliva, goes down the esophagus and reaches the stomach, the part of the tract responsible for breaking down food through wave movements and gastric juices.

Once food has been processed in the stomach, it reaches the intestines, a portion of the digestive tract that ends in the anus. The main function of this tissue conglomerate is to absorb nutrients and water from the diet.

Before exploring the functioning and differences between the different sections of the intestinal tract, we’re interested in describing the main functions of the digestive system. We can highlight the following:

1. Food transportation: As we have said, what we eat must travel very broadly from the mouth to the anus. The digestive tract of an adult is about 9 meters (nearly 30 feet) long and food advances thanks to the peristaltic movements of the walls that compose it.
2. Secretion of digestive juices: Although it may not seem like it, the action of digestive enzymes begins in the mouth itself, since saliva contains compounds that initiate the transformation of sugars. There are more than 20 enzymatic proteins in the entire digestive tract that are responsible for transforming food into assimilable compounds.
3. Nutrient absorption: Most of this work is done in the small intestine, as we’ll see below. Nutrients are the fuel that cells need to carry out their metabolic reactions, grow, multiply, and replenish themselves.
4. Passing of stools: Food waste material and certain compounds must be passed through the anus each day.

As you can see, the functions of the digestive tract as a whole are multiple and shared between other organs. Now let’s see the differences between the small and large intestines.

1. Size and location

If we follow the digestive tract as if it were a highway, the small intestine would be the first stop right after the stomach. Its function is to connect the stomach cavity with the large intestine, but it also performs most of the absorption of nutrients. Each day, the small intestine receives 6 to 12 liters of predigested fluid from the stomach.

This structure lives up to its name, as its diameter ranges between 3.5-4.5 centimeters (1.5 to nearly 2 inches), and is 2.5 centimeters (1 inch) when it isn’t dilated. It’s a very long section of variable length, as it can go from 3 to 10 meters (10 to 33 feet), and it’s tightly rolled to fit on the abdomen. In any case, the average in a normal person is about 5 meters (16 feet) in length.

The large intestine communicates directly with the small intestine. As the term itself indicates, it has a diameter greater than its counterpart, about 4 to 6 centimeters (around 2 inches). On the other hand, its length is much shorter, around 1.5 meters, 5 feet. Each day about 1.5 liters of water (2.6 pints)  and nutrients reach this section of the digestive tract, and its absorption work is much less.

The differences between the small and large intestines are very easy to understand if we look at the anatomy of each. We summarize them in the following list:

1. The small intestine is longer than the large, but narrower.
2. The large intestine is shorter than the small intestine, but its diameter is considerably larger.
3. The stomach communicates with the small intestine and this in turn with the large one.

Different parts

As the Bio Differences portal indicates, the number of parts that each intestinal section has is another of its most obvious distinctions. The small intestine has 3 different parts, while the large has 4. We look at them separately below.

Parts of the small intestine

As we have said, this section of the digestive tract measures approximately 5 to 7 meters and is divided into 3 well-differentiated parts. These are the following:

• Duodenum: This is the section adjacent to the stomach and measures 20 to 25 centimeters (8 to 10 inches). It has a “C” shape and surrounds the head of the pancreas, a gland responsible for producing juices that help break down food and which are released into the duodenum.
• Jejunum: This is the middle part of the small intestine and measures about 2.5 meters (8.2 feet), about 2/5 of the total of this section of the digestive tract. It’s internally covered by mucous projections called villi, whose function is to increase the absorption surface. The products of digestion are absorbed in this section.
• Ileum: This final section is about 10 feet long and contains multiple villi, as does the jejunum. Its main function is to absorb vitamin B12, bile salts, and all the products that haven’t been “accepted” by the jejunum.

Although we always talk about 3 sections in the small intestine, it should be noted that at a histological level it isn’t always easy to make the distinction. For this reason, professionals sometimes prefer to use terms such as distal intestine or hindgut to refer to areas that include the jejunum and ileum.

Parts of the large intestine

Although shorter than the small intestine, the large has a total of 4 sections, one more than its counterpart. They are as follows:

1. Blind: This is the first section of the large intestine and is responsible for absorbing electrolytes –  mainly sodium and potassium.
2. Colon: This is the longest part of the large intestine and is responsible for extracting water and electrolytes from foods that have already been used and digested for the most part. In turn, this complex section is divided into the ascending, transverse, descending, and sigmoid colon.
3. Rectum: This is the last section of the large intestine and the digestive tract in general. It’s responsible for receiving waste materials (feces) and prepares them for ejection out of the body.
4. Anal canal: This is a very small tube (4 centimeters, nearly 2 inches) that has the anal sphincters; these are muscles responsible for preventing or enabling the passage of feces for excretion. When these relax, the stools are excreted.

At the diameter level, the cecum is the widest of all the components of the large intestine, at about 9 centimeters (nearly 4 inches). It’s very important to know the standard measurements of each of the sections of the large intestine, since megacolon is a relatively common pathology in the general population.

3. Functions

Another clear difference between the small and large intestines lies in their general functions. We’re going to look at them separately in the following lines, making comparisons when relevant.

Small intestine functions

As indicated by the Statpearls portal, carbohydrates, proteins, and lipids are absorbed in the small intestine. Due to its work, this section of the digestive tract has specialized absorbent cells: the enterocytes.

However, for the enterocytes to be able to absorb the macronutrients, they need to have been metabolized previously. For example, carbohydrates undergo enzymatic processes and are split into simple monosaccharides that can pass directly into the bloodstream. We summarize the functions of the small intestine in the following list:

1. 90% of nutrient absorption takes place in the small intestine, as indicated by the Canadian Cancer Society.
2. By passive diffusion, 1 to 2 liters of food fluid (with plenty of water) are reabsorbed each day by the small intestine. It’s estimated that 90% of the water reabsorbed throughout the digestive tract has been collected in the small intestine.
3. Certain hormones, such as cholecystokinin, are produced in this section of the intestine. Its main function is to promote gallbladder contraction and pancreatic secretion.

So, in summary, the small intestine has 3 essential functions: digesting and assimilating nutrients, reabsorbing water that could be lost in the stools, and secreting certain hormones involved in the process of digestion. For this reason, it has multiple folds that increase its absorption surface up to 30 square meters (322 square feet).

Functions of the large intestine

The large intestine is also essential for the body, but it doesn’t have as many functions as the small intestine. For example, it doesn’t secrete hormones and it isn’t responsible for the absorption of macronutrients. We summarize its main tasks in the following list:

1. Absorption of water and electrolytes, especially sodium and potassium. Water passes into the bloodstream by osmosis, while sodium is actively reabsorbed through the use of sodium channels. Potassium is absorbed or secreted into the intestinal lumen, depending on the electrolyte concentrations at the time.
2. Production and absorption of vitamins. Vitamins K and B12 are synthesized in the colon by the symbiotic bacteria that inhabit it.
3. Formation and excretion of feces out of the body. Thanks to peristaltic movements and muscle sphincters, stool can safely exit the body once the digestion process is complete.

The differences between the small and large intestines in terms of their functionality are easy to understand if they’re reduced to their basic functions. Quickly and simply put, the former is responsible for the absorption of essential nutrients (carbohydrates, fats and proteins), while the latter obtains water and certain micronutrients, forms the stool, and expels them.

4. Associated pathologies

As indicated by the National Library of Medicine of the United States, there are multiple pathologies that can affect the small intestine. The large intestine isn’t exempt from harmful conditions, but some are shared with the other section and others are considered more typical of it. Again, we’ll analyze them separately, making distinctions when necessary.

Small intestine diseases

In the following list, you’ll find many diseases located in the small intestine that are sure to be familiar to you, since they have quite high prevalences in the general population:

• Celiac disease: To do a quick summary, people with celiac disease can’t consume gluten because it damages their small intestine. It’s a condition closely associated with genetics and its prevalence ranges from 1/71 in the child population to 1/357 in the adult population. 70% of people with this pathology don’t know they have it and haven’t yet been diagnosed.
• Crohn’s disease: This is one of the pathologies shared between the small and large intestines, as it can appear in any part of the digestive tract. It’s an inflammation of the lining of any of the aforementioned structures and affects 3 to 20 people per 100,000 inhabitants.
• Peptic ulcer: Ulcers are lesions that don’t heal and arise as a result of friction after exposure to gastric acids. They can appear in the stomach and small intestine.

Diseases of the large intestine

The group of diseases of the large intestine is somewhat more extensive and includes certain conditions of its own that cannot occur in the rest of the digestive tract. Among all of them, we highlight the following:

• Colorectal cancer: A type of malignancy that manifests as a tumor in any of the sections of the large intestine. It is estimated that 1 in 23 men (4.3%) will suffer from it throughout their lives, as indicated by the Cancer.org portal.
• Polyps: Polyps can grow on the inner lining of the colon. Most of them are not dangerous, but some can turn carcinogenic over time and spread to other parts of the body.
• Ulcerative colitis: Ulcers can appear in the large intestine, but these aren’t the result of corrosion by the action of gastric juices. They’re typical of inflammatory conditions such as Crohn’s disease.
• Diverticulitis: This pathology is characterized by the appearance of small “bags” or diverticula in the colon. It’s quite common in the adult population and especially in women, affecting 98.6 per 100,000 inhabitants.

We can’t establish clear differences between the small and large intestines with regard to the epidemiology of the pathologies, since the prevalence of each condition depends on the place and the population analyzed. However, pathologies in the large intestine are likely to be somewhat more prevalent than their counterparts.

Two sections of the intestine as similar as they are variable

As you can see, the differences between the small and large intestines are many. Not only do they have different functions, but their own histology, dimensions, and pathological conditions are also different. In any case, the most important difference of all those mentioned is the following: the small intestine absorbs the vast majority of the nutrients, and the large intestine, the electrolytes.

Although they’re different sections of the digestive tract, it’s always necessary to emphasize that certain diseases and functions are combined and shared. Both structures are necessary to achieve a correct digestion, either for the absorption or for the excretion of substances.