immune system .

Epithelial Cells and Structures

• Epithelial cells have hair-like structures on their surface, which help trap dust and pathogens.

• These structures are found in mucous membranes, particularly in the lungs, nose, and eyes.

Damage to Epithelial Structures

• Smoking is known to be harmful as it introduces carcinogenic substances that can damage these protective hair-like structures in the lungs.

Goblet Cells

• Goblet cells are specialized epithelial cells that produce and secrete mucus.

• Their structure resembles a goblet—narrow at the bottom and wider at the top.

• Goblet cells help trap pathogens and facilitate movement through the digestive system.

Vesicles and Mucus Function

• Vesicles in the digestive tract transport contents, trapping foodborne illnesses and aiding their movement through the intestines.

• Mucus forms a protective layer around pathogens, supporting digestive health.

Peristalsis

• Peristalsis is the coordinated contraction and relaxation of intestinal muscles that moves contents through the digestive tract.

• This mechanism prevents pathogens from invading the intestinal walls.

Skin vs. Mucous Membranes

• The outer layer of skin is primarily composed of dead cells and is rich in keratin, making it tough and resilient.

• In contrast, mucous membranes have living cells that secrete mucus and do not have a keratinized outer layer.

Chemical Defenses

• Defensins: Chemicals present in skin and mucous membranes that have antimicrobial properties.

• Lysosomes: Enzymes present in skin cells and mucous membranes that can break down bacterial walls.

• Sebum: Oil produced by sebaceous glands that keeps the skin moisturized and can trap pathogens.

• Peroxidase: Enzymes that help in breaking down harmful peroxides.

Normal Flora and Microbial Antagonism

• The skin and mucous membranes host a vast community of normal flora (microbiota) that outnumber pathogenic bacteria.

• Normal flora compete for space and nutrients against pathogens, helping to prevent opportunistic infections.

• They also alter local pH levels, making environments less hospitable for pathogenic bacteria (e.g., the skin is slightly acidic).

Mutualistic Benefits of Normal Flora

• Normal microbiota play a role in digestion and synthesis of essential vitamins and nutrients.

• An imbalance or absence of these microbes can hinder proper digestion and nutrient absorption.

Defensive Mechanisms in the Body

• Physical defenses include actions like sneezing, which is an innate response to expel irritants and pathogens.

• Saliva and stomach acid, along with lysozymes, contribute to the breakdown of pathogens.

• Other mechanisms like vomiting can help clear the digestive tract of unwanted substances, including pathogens.