Physical & Chemical Defenses

Physical and Chemical Defenses

Introduction

The human body has developed a remarkable array of defenses to protect itself against pathogens, such as bacteria, viruses, and other harmful microorganisms. These defenses can be broadly categorised into physical and chemical mechanisms. This section explores how epithelial cells create a physical barrier and how chemical secretions work to fend off invading pathogens.

Epithelial Cells as a Physical Barrier

• Epithelial cells play a crucial role in forming a physical barrier against pathogens.
• They are closely packed together, forming tight junctions that prevent pathogens from entering the body.
• These cells are found in various parts of the body, including the skin, as well as the inner linings of the digestive and respiratory systems.

Examples of Epithelial Barriers

1. Skin

The skin is the body's first line of defence. It consists of multiple layers of closely packed epithelial cells that create a formidable physical barrier. Additionally, the skin's outermost layer, the epidermis, is constantly shedding, removing potential pathogens along with it.

2. Respiratory System

The respiratory tract is lined with epithelial cells that produce mucus. This mucus traps pathogens, preventing them from reaching the lungs. Cilia, tiny hair-like structures on the surface of these cells, move the mucus and trapped pathogens upwards, where they can be expelled through coughing or sneezing.

3. Digestive System

The digestive tract, from the mouth to the stomach and intestines, is also lined with epithelial cells. These cells produce digestive enzymes and stomach acid, which can kill or neutralise many ingested pathogens.

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Physical & Chemical Defenses

Chemical Secretions Against Pathogens

• In addition to physical barriers, the body employs a range of chemical secretions to combat invading pathogens.
• These secretions create an inhospitable environment for pathogens, making it difficult for them to survive and reproduce.

Examples of Chemical Defenses

1. Tears

The eyes produce tears that contain enzymes and proteins with antimicrobial properties. These components help protect the eyes from infections.

2. Saliva

Saliva contains enzymes, such as lysozyme, which can break down the cell walls of bacteria, rendering them harmless.

3. Mucus

Mucus, found in the respiratory and digestive tracts, is a sticky substance that can trap pathogens. It also contains antimicrobial proteins and enzymes.

4. Stomach Acid

The stomach secretes hydrochloric acid, creating an extremely acidic environment that can kill many pathogens, including bacteria and viruses.

Pathogens and Disease

• It's important to note that a pathogen is any bacterium, virus, or other organism capable of causing disease.
• Pathogens can enter the body through various means, such as inhalation, ingestion, or contact with contaminated surfaces.

Summary

The human body employs both physical and chemical defenses to protect itself from invading pathogens. Epithelial cells form a physical barrier by closely packing together and lining various parts of the body. Chemical secretions, such as tears, saliva, mucus, and stomach acid, create an environment that is hostile to pathogens, making it challenging for them to establish infections. Together, these defenses help maintain the body's health and prevent the onset of diseases caused by harmful microorganisms.