Structure of the Human Digestive System and Associated Structures

The human digestive system is a complex assembly of organs and structures, each with its specific functions.
The digestive system consists of the alimentary canal, a tube extending from the mouth to the anus, and its associated glands.
Digestion begins in the mouth, with the teeth grinding food into smaller pieces and salivary glands secreting saliva, which contains the enzyme amylase to break down carbohydrates.
The oesophagus is a muscular tube that transports chewed food from the mouth to the stomach through peristalsis, a wave-like muscle movement.
The stomach has thick muscular walls that churn food and mix it with digestive juices, including hydrochloric acid to kill bacteria and pepsin enzyme to digest proteins.
The small intestine, comprising the duodenum, jejunum, and ileum, is where most digestion and absorption occurs. Its inner surface is lined with millions of tiny finger-like protrusions called villi, which increase the area for nutrient absorption.
The pancreas, a gland located behind the stomach, secretes a juice containing enzymes that countinue the digestion of carbohydrates, fats, and proteins in the small intestine.
The liver, the largest internal organ, produces bile, which is stored in the gallbladder and released into the small intestine to emulsify fats and neutralise stomach acid.
The large intestine, consisting of the colon and rectum, absorbs water and salts from undigested food and converts it into faeces. Bacteria in the colon also help to synthesise certain vitamins.
The rectum holds the faeces until they can be expelled by the anus during defecation.
Accessory organs for digestion include the liver, the largest gland in the body, which produces bile to help digest fats and detoxifies harmful substances, and the pancreas, which releases digestive enzymes into the small intestine.
The digestive system also includes structures like the epiglottis, a flap of tissue that prevents food from entering the windpipe, and sphincters, rings of muscle that control the passage of material through the digestive tract.