The Gut Guide: The digestive system part A

By Sakshi Khadiwala
April 29, 2025

Hey, ever wondered how does the body manage to provide us with the nutrients from the food we eat?

Let me help you take you through this journey of ingestion (food intake), digestion (food breakdown), absorption (nutrient absorption), assimilation (nutrient transport) and egestion (removal of waste).

The digestive system has two main parts: the gastrointestinal (GI) tract and the biliary tract.

GI Tract: This is the path food takes through your body and includes the mouth, esophagus, stomach, small intestine, large intestine, and anus. It’s often called the “gut” and is about 30 feet long! Even though we are only about 5 to 6 feet tall, the GI tract fits inside because it’s folded and packed tightly.
Biliary Tract: These are the organs that help the GI tract by making and sending enzymes needed to break down food. These organs include the bile duct, gallbladder, liver, and pancreas.
Both tracts work together to digest food and absorb nutrients.

Gastrointestinal tract (GI)

The GI tract is the primary site for ingestion, digestion, absorption, assimilation and egestion. It starts with the mouth → esophagus → stomach → small intestine → large intestine → rectum → anus.

Mouth

Digestion begins in the mouth, where two things happen: chewing and the action of saliva. Chewing breaks the food into smaller pieces (this is called mastication). At the same time, saliva contains enzymes that start breaking down the food. One enzyme, salivary amylase, breaks down starch into sugars, and another enzyme, lingual lipase, starts breaking down fats.
Once the food is soft enough, it forms a ball called a bolus, which you swallow, sending it down into your esophagus.

Image 1: Nursing Times – Gastrointestinal tract

2. Esophagus

No digestion happens in the esophagus, but it plays an important role in moving food from your mouth to your stomach. It does this by squeezing and relaxing in a wave-like motion called peristalsis, which pushes the food down into the stomach.

3. Stomach

Stomach is a J shaped organ that uses muscular contractions to mix the food with stomach juices, turning it into a thick liquid called chyme. This chyme is slowly sent to the small intestine.
The stomach has a layer of mucus that protects it from its own acid.
The stomach also makes hydrochloric acid (HCl) which kills bacteria, breaks down food, and activates an enzyme called pepsin to digest proteins.
It also produces a substance called intrinsic factor, which helps absorb vitamin B12 in the intestines.

Image 2: Neocate – Gut series

4. Small intestine

The small intestine is the longest part of your digestive system, about 20 feet long. It has tiny finger-like projections called villi and microvilli, which help increase the surface area to make digestion and absorption more efficient. These also have enzymes that help break down food even more.

The small intestine has three main parts:

Duodenum: This is where most digestion happens. Bile from the liver and pancreatic juices like amylase for carbohydrate digestion, trypsinogen and chymotrypsinogen for digestion of proteins and lipase for fat digestion enter here to help break down food. Carbs breakdown to glucose, proteins breakdown to amino acids and fats breakdown to fatty acids and triglycerides.
Jejunum: This is where most nutrients from the food get absorbed into the body.
Ileum: This part absorbs vitamin B12 and fat-soluble vitamins.

Image 3: MDPI

Large intestine

The large intestine is the last part of the digestive system, about 5 feet long. It has several sections: the cecum, ascending colon, transverse colon, descending colon, rectum, and anus.
It takes in the leftover, undigested food from the small intestine through a valve called the ileocecal valve. The large intestine mainly absorbs water and important minerals like sodium, potassium and chloride from the waste. It also helps break down carbohydrates, especially from foods like beans, using bacteria.
The waste is then stored in the rectum and eventually leaves the body through the anus.

Digestion summary:

Image 4: Fullscript- Digestive health

Image 6: Paul Wischmeyer

To wrap up our discussion on the digestive system, we’ve explored its intricate functions and how it aids in the breakdown, digestion, and absorption of food and nutrients. Understanding this process highlights the importance of maintaining a healthy digestive system, as it plays a key role in overall well-being.

In the next section of our blog, we will dive into essential nutrition tips and hygiene practices that can help optimise digestive health. From the right food choices to habits that promote gut balance, we’ll discuss actionable steps to ensure your digestive system functions smoothly. Stay tuned to discover how you can nourish your gut and support long-term digestive wellness!

Disclaimer: The information provided in this blog is sourced from research articles and reputable websites. However, as each individual’s body and health needs are unique, it is essential to consult with your doctor, dietitian, or healthcare provider for personalised advice and plans tailored specifically to your condition.

Acknowledgement: I would like to extend my heartfelt gratitude to our CEO, Purva Gulyani – Accredited Practising Dietitian, for providing me with the opportunity to contribute to this blog. Your valuable feedback, along with your time spent proofreading and editing, has greatly enhanced the quality of this work. Your guidance and support are truly appreciated.

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