Human Digestive System: Structure, Function and Digestion Process

Digestive System: Stages and Organs

Digestive Process Phases

The digestive process includes ingestion, digestion, absorption and egestion.

Mouth (Oral Cavity)

• Mechanics: Teeth chew food.
• Chemistry: Saliva contains the enzyme amylase, which begins breaking down starch into maltose.
• Lysozyme: Destroys bacteria.
• Labial glands: Work on moistening food.
• Result: Food is formed into a bolus (food bolus).

Esophagus

Food passes from the mouth to the stomach through the esophagus, using peristaltic movements.

Stomach

• Mechanics: Peristaltic movements mix food into chyme.
• Chemistry: Gastric juice acts through enzymes.
• Gastric juice: Produced by gastric cells, with a pH of 2 to 3 (acidic). Ingredients: water, hydrochloric acid (HCl), mucin and enzymes.
• Pepsin: Breaks down proteins into peptones. It is secreted as pepsinogen, which is activated by HCl.
• Renin: Works on milk protein (casein). It is produced in inactive form.
• Gastric lipase: Breaks down lipids (fats).
• Alcohol: Is absorbed in the stomach.

Pylorus and Small Intestine

The pylorus controls the passage of chyme into the small intestine.

Liver and Bile

• The liver produces bile, which is stored in the gallbladder.
• Bile is composed of bile salts, bile pigments, cholesterol and minerals.
• Function: Emulsifies fats, breaking them into small droplets so lipase can act on them.

Pancreas

• The pancreas is a mixed gland because it has two types of tissue: the exocrine tissue, formed by acinar cells, and the endocrine tissue, formed by the islets of Langerhans.
• Pancreatic juice enzymes: Trypsin, lipase and amylase.
• Insulin: Lowers blood sugar levels.

Small Intestine

• Length: About 7 meters, divided into the duodenum, jejunum and ileum.
• Mechanics and chemistry: Intestinal enzymes complete digestion. Sucrase breaks down sucrose into glucose and fructose.
• Function: Absorbs nutrients through the action of enzymes.
• Internal surface: The mucosa has villi and microvilli, which increase the absorption surface to approximately 250 m².

Large Intestine

• Length: About 2 meters.
• Sections: Cecum, colon, rectum and anus.
• Functions: Absorbs water and minerals, eliminates waste, forms feces and produces vitamin B complex.
• Rectum: Stores feces.

Teeth and Glands

• An adult has 32 teeth.
• Accessory digestive glands: salivary glands, liver and pancreas.