Organs of the Digestive System and Their Functions

Introduction

Key Concepts

1. Mouth

The digestion process begins in the mouth, where mechanical and chemical breakdown of food occurs. Teeth chew and grind food into smaller pieces, increasing the surface area for enzymes to act upon. Salivary glands secrete saliva, which contains the enzyme amylase that initiates the breakdown of carbohydrates into simpler sugars. Additionally, saliva moistens food, making it easier to form a bolus for swallowing.

2. Salivary Glands

Located around the mouth, the salivary glands include the parotid, submandibular, and sublingual glands. These glands produce saliva, which not only aids in digestion but also maintains oral hygiene by flushing away food particles and bacteria. Saliva also contains mucus that lubricates food, facilitating its passage through the esophagus.

3. Pharynx and Esophagus

The pharynx serves as a passageway for both air and food. Once food is chewed and moistened, the tongue pushes it into the pharynx, propelling it towards the esophagus. The esophagus is a muscular tube connecting the pharynx to the stomach. Peristaltic movements—coordinated muscle contractions—propel the bolus downward, ensuring efficient transport to the stomach without regurgitation.

4. Stomach

The stomach is a sac-like organ located in the upper abdomen. It performs both mechanical and chemical digestion. Gastric glands in the stomach lining secrete hydrochloric acid (HCl) and the enzyme pepsin. HCl creates an acidic environment, denaturing proteins and activating pepsin, which begins protein digestion into peptides. The stomach's muscular walls churn food, mixing it with digestive juices to form chyme—a semi-liquid mixture ready for further digestion in the small intestine.

5. Small Intestine

The small intestine is a highly coiled organ where the majority of nutrient absorption occurs. It is divided into three sections: the duodenum, jejunum, and ileum. In the duodenum, chyme mixes with digestive enzymes from the pancreas and bile from the liver. The jejunum and ileum primarily absorb nutrients—such as amino acids, fatty acids, vitamins, and minerals—into the bloodstream. The inner surface of the small intestine is lined with villi and microvilli, which increase the surface area for absorption.

6. Liver

The liver is the body's largest internal organ and plays a crucial role in digestion and metabolism. It produces bile, a substance that emulsifies fats, breaking them into smaller droplets that are easier for enzymes to digest. Bile is stored in the gallbladder and released into the small intestine when needed. Beyond digestion, the liver detoxifies harmful substances, stores glycogen, and synthesizes essential proteins required for various bodily functions.

7. Gallbladder

The gallbladder is a small, pear-shaped organ located beneath the liver. Its primary function is to store and concentrate bile produced by the liver. Upon ingestion of fatty foods, the gallbladder releases bile into the duodenum through the common bile duct. This controlled release ensures that bile is available in adequate amounts to emulsify fats, facilitating their digestion and absorption.

8. Pancreas

The pancreas serves both endocrine and exocrine functions. In digestion, its exocrine role is paramount. It secretes a variety of enzymes into the small intestine via the pancreatic duct. These enzymes include amylase for carbohydrate digestion, lipase for fat digestion, and proteases like trypsin and chymotrypsin for protein digestion. Additionally, the pancreas releases bicarbonate ions to neutralize the acidic chyme entering the small intestine from the stomach, creating an optimal pH for enzyme activity.

9. Large Intestine

The large intestine, comprising the cecum, colon, rectum, and anal canal, is responsible for water and electrolyte absorption from indigestible food matter. As chyme moves through the colon, water is absorbed, and the remaining material is compacted into feces. Beneficial bacteria in the large intestine further break down some substances, producing vitamins like vitamin K. The rectum stores feces until they are excreted through the anal canal during defecation.

10. Accessory Organs

In addition to the primary organs, several accessory structures support the digestive process. The tongue aids in manipulating food within the mouth, the teeth facilitate mechanical digestion, and the epiglottis prevents food from entering the trachea during swallowing. These components work in harmony to ensure efficient digestion and nutrient absorption.

Comparison Table

Summary and Key Takeaways