Human Digestive System: Organs, Processes and Functions
The Digestive System: Organs and Processes
The main organs and processes of the digestive system are:
- Ingestion: the intake of food to be digested.
- Digestion: the transformation of food into nutrients, through mechanical and chemical processes.
- Absorption: the passage of nutrients from the intestine into the circulation.
- Egestion: the elimination of undigested substances.
The digestive system consists of 2 main components:
1. The digestive tube
The digestive tube is approximately 10 to 12 m long and has 2 openings: the entry (mouth) and the exit (anus).
- Mouth: contains the teeth, the salivary glands and the tongue.
- Pharynx: a short tube that is the common passage for air and food.
- Esophagus: a conduit that connects the pharynx to the stomach.
- Cardia: a valve that connects the esophagus to the stomach.
- Stomach: a J-shaped cavity with two openings, the cardia (connecting it to the esophagus) and the pylorus (connecting it to the intestine). Its walls are thin and muscular, allowing peristaltic movements (contraction and relaxation) that mechanically digest food.
- Intestine: a tube about 6 m long, divided into approximately 3 parts:
- Duodenum: the part attached to the stomach.
- Jejunum: the part that follows the duodenum and represents the majority of the small intestine.
- Ileum: the part that connects to the large intestine.
The intestinal walls contain intestinal glands that produce intestinal juices, which chemically contribute to digestion. The folds of the intestine increase its surface area, facilitating absorption, and the intestinal villi further increase this absorptive surface.
Large Intestine
The final part of the gut has 3 sections:
- Cecum: the initial section, located below the small intestine.
- Colon: forms a curved, inverted U-shape.
- Rectum: where feces are stored before being eliminated through the anus.
2. Digestive glands
Glands pour their contents into the digestive tube:
- Salivary glands: produce saliva, which contains amylase, salts, water, bacteria and other substances.
- Pancreas: a factory of pancreatic juice that flows into the duodenum and contributes to chemical digestion.
- Liver: manufactures bile, which is accumulated in the gallbladder and poured into the duodenum, where it emulsifies fats.
The Digestion Process
- Mouth: chewing (mastication) breaks food into smaller pieces. Insalivation mixes the food with saliva, and amylase begins chemical digestion, forming the food bolus.
- Swallowing: the food bolus passes from the pharynx into the esophagus.
- Stomach: peristaltic movements mechanically mix and churn the food. Chemically, gastric juices containing acids and enzymes act mainly on proteins, forming a mixture called chyme that passes into the small intestine.
- Small intestine: peristalsis continues mechanical digestion, bile emulsifies fats, and intestinal juices complete chemical digestion. Digested nutrients such as monosaccharides, amino acids, minerals, vitamins and fatty acids are absorbed through the intestinal wall into the blood and lymph. Undigested substances pass on.
- Large intestine: water and some substances are absorbed, and the undigested material is compacted into feces, which accumulate in the rectum until defecation (elimination).
Key Terms
- Egestion: the expulsion of undigested waste from the body.
- Digestion: the process of breaking down food into absorbable substances.
- Ingestion: the process by which food enters the digestive system.
- Food bolus: a soft, moistened mass of chewed food mixed with saliva.
- Enzyme in saliva: amylase, which begins breaking down starches.
- Salivary glands: glands that secrete saliva into the mouth.
- Gastric juice: a substance containing enzymes and hydrochloric acid that digests food in the stomach.
- Liver: an organ responsible for detoxifying the blood and storing glucose.
- Pancreas: a glandular organ that produces pancreatic juice.
- Bile: a substance that emulsifies fats, making them easier to digest.