The digestive system is responsible for the ingestion of food, secretion of enzymes, mixing and digesting food, absorption of the nutrients and defecation. The human digestive system consists of two major parts: the gastrointestinal tract and the accessory digestive organs.

Gastrointestinal tract:

1. Mouth: The mouth is the starting point of the digestive system. Its primary role is to mechanically break down food through chewing and mixing it with saliva, which contains enzymes that initiate the digestion of carbohydrates.
2. Pharynx: The pharynx, also known as the throat, is a muscular tube located behind the mouth and nasal cavity. It serves as a passage for both food and air. Its role in the digestive system is to help propel the chewed food from the mouth to the esophagus.
3. Esophagus: The esophagus is a muscular tube that connects the pharynx to the stomach. It lies posterior to the trachea and passes through the diaphragm before reaching the stomach. Its main function is to transport food from the mouth to the stomach through rhythmic contractions called peristalsis.
4. Stomach: The stomach is a J-shaped organ located in the upper abdomen, just below the diaphragm. Its primary role is to store and churn food, mixing it with digestive juices, including gastric acid and enzymes. The stomach also plays a crucial role in the initial breakdown of proteins.
5. Intestine: The intestine is divided into two parts: the small intestine and the large intestine.
   1. Small Intestine: The small intestine is a long, coiled tube located in the central and lower abdominal region. It is where the majority of digestion and nutrient absorption takes place. The walls of the small intestine are lined with tiny finger-like projections called villi, which increase the surface area for absorption.
   2. Large Intestine: The large intestine, also known as the colon, is a wider tube that follows the small intestine. Its primary function is to absorb water, electrolytes, and vitamins from the undigested food residue. It also houses beneficial bacteria that help with the final stages of digestion.
6. Anus: The anus is the terminal opening of the digestive system. It is located at the end of the rectum, and its role is to eliminate indigestible waste from the body in the form of feces.

Accessory Digestive Organs:

1. Liver: The liver is the largest gland in the body, located in the upper right side of the abdomen. It produces bile, which aids in the digestion and absorption of fats. The liver also plays a crucial role in detoxifying harmful substances and storing nutrients.
2. Pancreas: The pancreas is a glandular organ situated behind the stomach. It produces digestive enzymes that break down carbohydrates, proteins, and fats in the small intestine. The pancreas also secretes hormones, such as insulin and glucagon, which regulate blood sugar levels.
3. Gallbladder: The gallbladder is a small, pear-shaped organ located beneath the liver. Its main function is to store and concentrate bile produced by the liver. When fatty foods are consumed, the gallbladder releases bile into the small intestine to aid in digestion.

Understanding the anatomy and functions of these organs is essential for comprehending the complex process of digestion.