VN 201 Immunity and inflammation Notes

Skin and Mucous Membranes

 The body’s first line of defense
o Protective covering; secretes substances that inhibit the growth of
microorganisms
 Skin acts as a physical barrier preventing entry of pathogens into the body.
 Mucous membranes line various cavities and secrete mucus that traps
microorganisms and debris.
o Sweat glands secrete lysozyme, an antimicrobial enzyme
 Lysozyme breaks down bacterial cell walls, reducing bacterial growth on
the skin.
o Sebaceous glands secrete sebum, which has antimicrobial and antifungal
properties
 Sebum creates a slightly acidic environment on the skin's surface,
inhibiting bacterial growth.
o Acidic secretions from skin and mucosa of GI and GU systems inhibit growth
of many pathogenic organisms
 Gastric acid in the stomach and vaginal acidity prevent colonization by
pathogens.
 Secretions from mammary glands and the respiratory and GI tracts contain
immunoglobulin; also clean up phagocytes
o Breast milk contains secretory IgA that provides passive immunity to infants.
o Respiratory and GI tract secretions contain immunoglobulins that neutralize
pathogens.

Phagocytosis and Inflammation

 The second line of defense
o Helps rid body of invading microorganisms
 Phagocytosis involves white blood cells (phagocytes) engulfing and
digesting pathogens.
 Macrophages and neutrophils are key phagocytic cells in the immune
system.
o White blood cells (leukocytes): colorless cells that can phagocytose (ingest)
bacteria that can cause infection when they invade the body
 Neutrophils are the most abundant type of white blood cell and are first
responders to infection.
 Monocytes differentiate into macrophages that engulf and digest
pathogens.
 Measuring the number of these cells indicates severity of infection
o Increased white blood cell count (leukocytosis) often indicates an ongoing
infection.

Immunity

,  Provides resistance to invading organisms; enables body to fight off invaders once
they have gained access
o If our immune systems are intact and functioning properly, adequate
protection from most infections and diseases is provided
 Immunocompetence allows the body to recognize and respond to specific
pathogens.
o Antigen
 Any substance capable of stimulating an immune response.
 Antigens are usually foreign and recognized as non-self by the immune
system.
 Antibodies
o Also known as immunoglobulins
 Proteins produced by B lymphocytes in response to specific antigens.
 Antibodies neutralize antigens and mark them for destruction by
phagocytes.
 Innate (natural) immunity
o Present at birth; not dependent on a specific immune response or previous
contact with an infectious agent
 Includes physical barriers (skin), chemical barriers (acids, enzymes), and
cellular defenses (phagocytes).
 Acquired immunity
o Develops after birth as a result of the body’s natural immune responses to
antigens
 Dependent on B and T lymphocytes and involves memory cells that
provide long-term protection.
o Active acquired immunity
 Developed after direct exposure to an antigen through infection or
vaccination.
 Memory cells allow for a rapid response upon subsequent exposure.
o Passive acquired immunity
 Conferred by transfer of antibodies from another source, providing
temporary immunity.
 Occurs naturally (maternal antibodies via placenta or breast milk) or
artificially (administration of immune globulins).

Organs of the Immune System

 Leukocytes (white blood cells)
o Key role in immune responses to infectious organisms and other antigens
 Include granulocytes (neutrophils, eosinophils, basophils) and
nongranulocytes (lymphocytes, monocytes).
o Thymus and bone marrow
 Sites of T and B lymphocyte maturation, respectively.
 Lymph nodes
o Attack antigens and debris in the interstitial fluid and produce and circulate
lymphocytes