Nonspecific Defenses of the Host

The Immune SystemInnate (Nonspecific) Immunity Acquired

(Specific) Immunity

First line of defense (barriers at the body surface)

Second line defense Third line of defense

•Skin•Mucous membranes•Secretions•Reflexes•Normal microbiota

•Inflammation•Phagocytes•Fever•Complement system•Interferon

•T cell lymphocytes•B cell lymphocytes•Antibodies

The First Line of Defense

Surface Barriers

Epidermis (Skin)

• Intact surface is rarely penetrated by microbes

• Stratum Corneum is made of dead keratinized cells that form an armor plating

• Dead karatinized cells are constantly sloughing off

Epidermis

• Dry: Most areas of the skin are too dry for microbial growth.

• Acidic: (pH 5): The sebaceous glands produces sebum, an unsaturated fatty acid.

• Temperature: slightly cooler than 37 degrees• Resident microflora: The natural flora out

competes pathogenic organisms.

Mucous Membranes• Mucous membranes are surfaces areas

lining the Respiratory, G.I., and urogenital tracts.

• These membranes are considered to be outside the body.

• Mucous membranes are involved in either secretion or absorption and thus cannot be covered with an armor of dead cells.

• Membranes must be bathed in fluids (warm, wet environments that would readily colonize bacteria if they were not protected by a number of defenders.

Defense of the Mucous Membrane

• Goblet cells produce mucus, a thick sticky substance composed of polysaccharide and protein.

• Mucus contains carbohydrate structures similar to the ones on mucosal cells surfaces

• Mucus traps bacteria before they can reach membrane.

• Muco-ciliary escalator pushes microbes and debris outside the respiratory system

• M-cells funnel bacteria into waiting phagocyts

Eyes (lacrimal apparatus

• Washing action of tears along with the blinking action of the eyelid mechanically removes bacteria and debris

• Lysozyme attacks peptidoglycan layer of bacteria

Stomach

• Low pH and digestive enzymes kill microbes and endospores that enter the GI tract.

Reflexes

• Types: Coughing sneezing, blinking, vomiting

• Function: Expel microbes and toxins

Earwax

Antibacterial and insect repellent