first line of defence

Question 1

define: first line of defence

Answer 1

consists of physical, chemical and microbiological barriers that prevent pathogens from entering the body.

Question 2

describe physical barriers

Answer 2

Intact skin:
• Outermost layer of epidermis is constantly being shred – barrier against pathogens
• Skin’s sebaceous glands produce sebum – barrier against pathogens
• Passed through cuts, punctures, burns, bites…
Mucous membranes
• Line the gut, airways and urogenital tract.
• Mucous cells in mucous membranes secrete mucus, which trap pathogens
• In airways, many cells of mucous membranes contain cilia, which move mucus and trapped pathogens to the back of the throat, where they are either swallowed and destroyed by stomach acid or are expelled through coughing/sneezing
• Hairs in nose trap bacteria
Saliva and urine: washes mouth/bladder and urethra, preventing establishment of pathogens

Question 3

describe chemical barriers

Answer 3

Intact skin:
• Sweat contains protein dermcidin acts as an agent against pathogens.
Saliva and tears: contains lysozyme, which causes bacteria to lyse
Urine and stomach acid: acidic, kills bacteria.

Question 4

describe microbiological barriers

Answer 4

Presence of normal flora (commensals)
• Def: non-pathogenic bacteria which are normal residents of particular body regions (particularly gut, airways and urogenital tract)
• They compete for physical space and nutrients, which inhibits growth of pathogenic bacteria.