VMC 221: Veterinary Immunology and Serology (1+1)

PHYSICAL AND CHEMICAL BARRIERS

• Intact epithelial surfaces form physical barriers from microbial invasion. The skin, mucous membrane of the respiratory tract and gastrointestinal tract are the three main interfaces between the environment and the host.
• Skin
• The intact skin is effective mechanical barrier.
• Keratinized layer of skin is impermeable to microorganisms.
• Microbial growth is less in dry environment of the skin.
• Sweat contains lactic acid, salts that inhibit the growth of many bacteria and fungi.
• Normal microorganisms present in the skin inhibit the growth of super infecting microorganisms.
• Sebaceous glands liberate sebum, which protect the skin.
• Epithelia produce some peptides, which have natural antibiotic function.
• Mucous membrane 
  • Stratified squamous epithelium of mucous membrane and mucous secretions of respiratory, digestive and urogenital tract trap and prevent the entry of micro organisms.
  • Gastric secretions (HCl, enzymes etc.) with acidic pH kill the microorganisms. The epithelium of the intestine secretes antimicrobial peptides called cryptocidins. These natural antibiotics kill the microorganisms.
  • Acidic pH of vagina kills microorganisms.
  • Tears - Contain lysozymes that prevent the entry of pathogens.