Understanding Human Nutrition: Digestive System Essentials

Human Nutrition: The Digestive System

Human nutrition involves several key systems: digestive, respiratory, circulatory, and excretory.

Preparation for Digestion

This phase consists of three main parts:

Insalivation

Insalivation involves saliva, a watery substance containing amylase enzymes that break down simple carbohydrates. Saliva is produced in three salivary glands: sublingual, submandibular, and parotid. The tongue, a muscular organ covered in taste buds, helps mix food with saliva, allowing us to taste food.

Mastication

Mastication consists of breaking down food into smaller pieces to ease digestion. Types of teeth include incisors, canines, molars, and premolars. Humans have 20 milk teeth and 32 adult teeth.

Swallowing

Swallowing involves two movements:

1. Voluntary: The tongue moves, squeezing the food bolus into the pharynx.
2. Involuntary: The epiglottis closes the trachea, and the food bolus moves down to the stomach. The esophagus produces peristalsis movements that move the food bolus downward.

Digestive Process

The stomach is a crescent-shaped organ connected to the small intestine via the pylorus, a valve that is usually closed. The cardia, a valve at the entrance of the stomach, is always open. Food boluses remain in the stomach with gastric juice for about 3 to 4 hours, resulting in chyme. Gastric juice contains pepsin, an enzyme that begins protein digestion, and hydrochloric acid. The stomach wall is made of special muscles that prevent acid damage. Once chyme is formed, the pylorus opens, allowing it to pass into the small intestine.

Small Intestine

The small intestine is approximately 6 to 7 meters long and has three parts:

Duodenum

The first section, U-shaped and about 25 cm long.

Jejunum

The second and longest part.

Ileum

The final section, leading to the large intestine.

The Liver

The liver is a large organ located on the right side of the body. It produces bile, which enters the duodenum via the ampulla of Vater and is stored in the gall bladder. Bile does not contain enzymes but has substances called bile salts, which help emulsify fats. It also destroys toxic substances.