1. Host Defence Mechanism

Front 1

What are the physical/chemical barriers present within the skin?

Back 1

Skin is composed of epidermis (keratin) that is virtually impregnable
-Infections occur where there are breaks in the epidermis
(abrasions, puncture wounds)
-Skin lacks moisture and also has high salt concentration
-Sebaceous glands secrete fatty acids, and lactic acids that decrease pH of the skin and inhibit growth of microorganisms
-Genes encoding antimicrobial peptides (Dermcidin) are expressed in sweat glands, and the antimicrobial peptides are secreted into sweat and transported to the epidermal surface

Front 2

What are the physical/chemical barriers to infection in the URT?

Back 2

Major barriers include the mucous membranes
-Which contains mucous secreting cells and ciliated cells (Mucociliary system)
-Mucous traps the bacteria and the cilia beating sweeps them up and out of the URT
-Also, the area is heavily colonized with normal flora
-This may include opportunistic pathogens and this area is partly protected by antimicrobial peptides in the body secretions (Tongue and throat)

Front 3

What is the LRT

Back 3

Includes
Trachea
Bronchial Tubes
Alveoli in the lungs
-This is normally sterile and it does not contain bacteria such as normal flora

Front 4

What host defence mechanisms are present in the LRT

Back 4

1) Mucociliary system which moves particles up toward throat where they are swallowed (or coughing expels them) Smoking, alcohol consumption and old age affect the functioning of the ciliated epithelium and may increase susceptibility to infections
2) The lungs (the alveoli lack a ciliated membrane and are protected by alveolar macrophages and Ab)
3) Antimicobial proteins (lactoferrin, lysozyme) and peptides (defensins, LL-37) are evident

Front 5

What are the physical/chemical barriers in the GI tract?

Back 5

Stomach acidity
Peristaltic movements of the intestinal contents (which tends to expel potential pathogens before they can colonize)
Microbial antagonism from the normal flora

Front 6

What are key features of the non-specific immune defences?

Back 6

1) Effective against a variety of potential pathogens by recognizing features shared by all bacteria (peptidoglycan)
2) Innate - not dependent on prior exposure to a pathogen but can be up-regulated upon pathogen exposure
3) Effective immediately or rapidly (0-4) hours this is in contrast to the specific immune response which takes days

Front 7

WHat are the antimicrobial compoents of the body fluids?

Back 7

Tears, saliva, mucus, blood and lymph all contain antimicrobial substances
-Main ones are
-Anti-microbial enzyme called lysozyme
-Iron binding proteins such as lactoferrin
-Enzymes such as lactoperoxidase that generate oxygen to kill bacteria
-Antimicrobial peptides (B-defensins, LL-37)

Front 8

What kind of antimicrobial componets do blood contain?

Back 8

Blood and lymph contain phagocytic cells (neutorphils. monocyes) that can move into the tissues to phagocytose infecting bacteria
-Many organs also contain resident phagocytes in the form of macrophages. lung contains alveolar macrophages

Front 9

What is the major antimicrobial component of the body fluids?

Back 9

COmplement
-Complement makes up 10% of the protein content of the serum and also present in tissues

When activated
1) Attract phagocytic cells to the infection site
2) Stimulate the release of histamine during inflammation
3) Promote the binding of bacteria to phagocytes by a process known as opsonisation
4) Can cause cell lysis of certain bacteria