The Innate Immune System

What is the innate immune system?

A group of natural barriers that resist infection.

How does the skin act as a barrier to resist infection?

• Keratin in epidermal cells makes the skin waterproof.

• Collagen in the connective tissue of the dermis, maintained by vitamin C, makes the skin tough.

How does skin flora act as a barrier to resist infection?

Skin microflora offer protection by outcompeting pathogenic bacteria.

Unlike the pathogens, they are not easily washed off and so regular washing remains an important way of resisting infection.

How does blood clotting act as a barrier to resist infection?

Blood clotting to seal wounds and prevent entry of microbes.

How does inflammation act as a barrier to resist infection?

Inflammation involves an increased blood flow to the area bringing large numbers of phagocytic cells; increased temperature is unfavourable to microbes and decreases their growth.

How do phagocytic cells act as a barrier to resist infection?

If microbes enter the bloodstream, phagocytic cells including macrophages and neutrophilis, engulf and digest them.

How does lysozyme act as a barrier to resist infection?

Lysozyme in tears and saliva is an enzyme that hydrolyses peptidoglycan in bacterial cell walls. The weakened cell wall breaks as water from the tears and saliva enters the microbe by osmosis, causing the cells to lyse, killing the bacteria.

How does mucus act as a barrier to resist infection?

Inhaled air is a source of micro-organisms and their spores. Mucus traps them and the cilia of the epidermal cells lining the respiratory passage brin g them up to the opening of the oesophagus, from where they are swallowed.

How does stomach acid act as a barrier to resist infection?

Stomach acid kills ingested bacteria.