How Your Body Processes Food and Air

The Digestive System

Role of Digestion

During the process of digestion, food is broken down. The broken molecules can then be used by cells.

Digestive Tract Structure

The digestive tract is a duct, a 9-meter long pipe through which food passes, extending from the mouth to the anus.

Glands: Glands pour their juices into the tube. The main glands are the salivary glands, liver, and pancreas.

Food is transported by a wave of contraction and relaxation called peristaltic movements.

Layers of the Digestive System

Internal or Mucosal Layer: This layer secretes digestive juices and mucus, protecting the surface. Nutrients are absorbed through this layer.

Muscularis: This layer consists of involuntary muscle fibers that contract. The anal sphincter muscles are under voluntary control.

Key Digestive Organs

• Buccal cavity (mouth)
• Liver
• Pyloric sphincter
• Anus
• Small intestine
• Large intestine
• Pancreas
• Stomach
• Cardiac sphincter
• Esophagus
• Pharynx

The Digestion Process

Mechanical Digestion: This process transforms large food particles into smaller ones. It begins in the mouth (food is crushed with teeth and mixed with saliva) and continues in the stomach.

Chemical Digestion: Digestive juices are produced, converting complex molecules into simpler ones. The food bolus passes to the pharynx and esophagus, then mixes with gastric juice in the stomach, forming chyme. The chyme then enters the small intestine, where it mixes with enzymes from pancreatic juice and the intestinal wall. Bile is also produced, which aids in nutrient absorption. In the large intestine, water and minerals are absorbed, making the residue more solid. The excrements are undigested materials and bacteria, which are expelled through the anus.

Nutrient Absorption

The small intestine is folded and has villi. These structures increase the surface area for absorption.

Common Digestive Condition: Diarrhea

Occurs when intestinal contents pass too quickly through the large intestine, resulting in liquid stools. Diarrhea leads to water and nutrient loss.

The Respiratory System

Function of Respiration

The respiratory system provides oxygen from the atmosphere and expels carbon dioxide. It is formed by the lungs and airways.

Airways and Lungs

Airways include:

• Nasal cavity
• Pharynx
• Larynx
• Trachea
• Bronchi
• Bronchioles

The lungs are two conical bodies located in the thoracic cavity. They are formed by the bronchi and bronchioles, which end in the alveoli. The lungs are covered by a double membrane called the pleura.

Pulmonary Ventilation

Pulmonary ventilation is the process of renewing the air in the lungs.

Inspiration: The lungs expand, the volume of the thoracic cavity increases, and air enters the respiratory tract.

Expiration: The volume of the thoracic cavity decreases, and air is expelled.

Common Respiratory Condition: Emphysema

A progressive destruction of the alveoli, often associated with smoking.