Understanding the Mechanics of Human Digestion and Metabolism

Human Body Systems: Core Functions

The human body relies on several interconnected systems to maintain life and process energy.

The Digestive System

This system is responsible for taking in solid and liquid foods, preparing and transforming them so that nutrients can be distributed to every cell in the body.

The Respiratory System

The respiratory system captures the oxygen necessary for cells and removes carbon dioxide produced during cellular metabolism.

The Circulatory System

The circulatory system transports nutrients and oxygen to cells and removes waste substances.

The Excretory System

This system expels the waste products of cellular metabolism, which are carried by the circulatory system, outside the body.

Components of the Digestive Tract

The gastrointestinal tract includes the following organs:

• Oral cavity
• Pharynx
• Esophagus
• Stomach
• Small intestine
• Large intestine

Accessory Digestive Glands

These glands aid the digestive process:

• Pancreas
• Liver

Mechanical Digestion: Chewing

Chewing is a mechanical process that involves grinding food into smaller pieces to facilitate the overall digestive process.

Types of Teeth and Their Functions

Teeth are specialized for different tasks:

• Incisors: Used to cut food.
• Canines: Also called tusks, they are used for tearing food.
• Premolars and Molars: Known as grinding wheels, their function is to grind food.

The tongue is involved in moving the food between the teeth during chewing.

Chemical Digestion: Salivation

Saliva has several crucial functions:

• It facilitates the passage of the food bolus into the pharynx and esophagus.
• It aids digestion (chemical breakdown).
• It destroys some bacteria present in food.

Swallowing (Deglutition)

During swallowing, the food bolus passes through the pharynx and esophagus, ending its journey in the stomach.

Digestion in the Stomach

The gastric juice remains in the stomach for 3 to 4 hours, mingling with the partially digested food (chyme).

Gastric juice contains:

• Pepsin: An enzyme that initiates the digestion of proteins.
• Hydrochloric Acid: This acid serves two main purposes:
  1. It activates pepsin and promotes its action, facilitating the breakdown of food fibers.
  2. It destroys bacteria that may be present in the food.

Key Accessory Organs

The Role of the Liver

The Liver produces bile, which is poured into the duodenum through the ampulla of Vater. Bile does not contain digestive enzymes, but it contains substances called bile salts, which aid the digestion of fats by emulsifying them.

The Role of the Pancreas

The Pancreas produces hormones that regulate the amount of glucose in the internal environment and its accumulation in the liver. It also secretes pancreatic juice, which contains enzymes capable of digesting all types of molecules present in food.