Digestive System Processes: A Comprehensive Guide

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Digestive Phases

Cephalic Phase

The cephalic phase initiates digestion before food even reaches the stomach. Sensory cues like taste, smell, or even the thought of food trigger the central nervous system to stimulate gastric juice production.

Gastric Phase

Once food enters the stomach, receptors signal the brain, which in turn promotes further gastric juice secretion to break down the ingested food.

Intestinal Phase

As food moves into the duodenum, receptors detect its presence and signal the brain to increase the production of digestive juices for further processing.

Enterogastric Reflex

When the duodenum is full, the enterogastric reflex is activated, causing the pyloric sphincter to close and regulate the passage of chyme from the stomach to the duodenum.

Carbohydrate Digestion


Sucrase breaks down sucrose into glucose and fructose molecules.


Maltase breaks down maltose into two or three glucose molecules.


Lactase breaks down lactose into glucose and galactose molecules.

Sphincters in the Digestive System

Pyloric Sphincter

Located between the stomach and duodenum, the pyloric sphincter controls the flow of chyme into the duodenum.

Lower Esophageal Sphincter

Positioned between the esophagus and stomach, the lower esophageal sphincter allows the passage of the food bolus into the stomach.

Lipid Digestion and Bile

Bile, produced in the liver and stored in the gallbladder, emulsifies lipids in the duodenum, facilitating their digestion.

Hepatopancreatic Ampulla

Situated in the duodenal wall, the hepatopancreatic ampulla regulates the release of bile and pancreatic juice into the duodenum.

Small Intestine Functions

The small intestine plays a crucial role in both chemical and physical digestion, as well as absorption. Segmentation aids in mechanical digestion, while bile and pancreatic juice contribute to chemical digestion. Additionally, the small intestine absorbs carbohydrates, proteins, nucleic acids, and lipids.

Villi and Absorption

Villi, containing capillary blood vessels and lacteals (lymphatic capillaries), are responsible for nutrient absorption. Carbohydrates, proteins, and nucleic acids are absorbed into the capillaries, while lipids enter the lacteals.

Large Intestine Functions

The large intestine, comprising the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anal canal, absorbs water and vitamins, forms feces, and eliminates waste from the body.

Hormones Regulating Hunger and Appetite


Leptin is a hormone that helps regulate energy balance by suppressing hunger.


Ghrelin is a hormone that stimulates appetite, increasing hunger.

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