Body Defenses Immune System

Microbes and You Microorganisms are widely distributed in the environment and carry out many beneficial functions. Decomposition Nitrogen fixation Breakdown environmental toxins Normal flora protect you against some pathogens Skin, vagina, mouth, gut E. coli in your gut produce vitamin K - you cannot make this substance yourself and without it your blood won’t clot properly

Pathogens Bacteria Viruses Fungi Protozoans Parasites Prions

Pathogens Bacteria See previous notes on prokaryotic cell structure Damage host by Exotoxins – toxins produced by bacteria  Shigella toxin, Staphylococcus aureus toxin Endotoxins and non-specific immunity  From cell wall of E coli and related bacteria Effects of the body’s specific humoral and cell mediated immunity

Eukaryotic Pathogens Fungi: examples Althlete’s foot Nail fungus Histoplasmosis Protozoans: examples PCP: Pneumocystis carinii pneumonia Amoebic dysentery Parasites: examples Tapeworms Roundworms, pinworms

Viruses Acellular – not quite a living organism Obligate parasites Virus always has two parts: Some viruses have an outer envelope – HIV, Influenza Outer capsid composed of protein units Inner core of nucleic acid, which can be either DNA or RNA Virus relies on the host’s enzymes and ribosomes for its own reproduction.

Prions Proteinaceous infectious particles Proteins of unknown function in the brains of healthy individuals Disease occurs when certain prion proteins change their shape into a “rogue” form that converts other normal prion proteins into the rogue configuration. Cause a group of degenerative diseases of the nervous system Bovine and human Spongiform Encephalopathy

transmissible spongiform encephalopathies

The Lymphatic System Consists of lymphatic vessels and the lymphatic organs Four main functions; Lymphatic capillaries absorb excess tissue fluid and return it to the bloodstream; Lacteals absorb fats in the form of lipoproteins from the small intestines and transport them to the bloodstream; Lymphatic system produces, maintains, and distributes lymphocytes; Defends the body against pathogens.

Fig. 7.5

Lymphatic Vessels & Organs Form a one-way system of capillaries, vessels, and ducts Lymphatic vessels take up excess tissue fluid called lymph to cardiovascular veins in the shoulders. Lymphatic Organs Primary organs (red bone marrow and thymus) Secondary organs (lymph nodes and spleen)

Lymphatic Organs The Primary Lymphatic Organs Red bone marrow is the site of stem cells that divide and produce blood cells. B cells mature in the bone marrow T cells mature in the thymus, located in the thoracic cavity. The thymus also produces thymic hormones, and is absolutely critical to immunity.

Primary Lymphatic Organs Red Bone Marrow

Thymus

Lymphatic Organs Secondary Lymphatic Organs The spleen contains white pulp and red pulp. White pulp contains a concentration of lymphocytes Red pulp is involved in filtering the blood.  Removes damaged, dying red blood cells In the case of infection or a blow, the spleen can burst.

Spleen

Lymphatic Organs Secondary Lymphatic Organs Lymph nodes occur along lymphatic vessels. Each node is packed with B lymphocytes. Lymph is filtered through the lymph nodes. Lymphocytes react with pathogens present in the filtered blood and lymph. They fight infections and attack cancer cells.

Lymph nodes

Tonsils The tonsils are patches of lymphatic tissue located around the pharynx.

Immune Defenses Immunity involves innate and acquired defenses. Innate defenses protect against any pathogen, Acquired defenses are effective against a particular infectious agent.

Innate Immune Defenses Barriers to Entry Physical Intact skin and mucous membranes Ciliated cells that line upper respiratory tract  Sweep mucus and trapped particles up into the throat where they can be swallowed or coughed out Chemical barriers – kill or inhibit growth of microbes Secretions of the sebaceous glands of the skin, Antibacterial enzyme lysozyme in perspiration, saliva and tears Acid pH of the stomach and vagina Normal flora

Innate Immune Defenses Inflammatory Response Redness, heat, swelling, and pain Histamine released from damaged tissue cells and mast cells brings about redness and swelling. The swollen area stimulates free nerve endings, causing the sensation of pain. Rise in temperature increases phagocytosis by neutrophils and macrophages. Cytokines - chemical mediators Attract white blood cells to the area.  Monocytes become macrophages - attract lymphocytes, that are part of the specific arm of the immune system.

Inflammatory Response

Innate Immune Defenses Protective Proteins The complement system Includes various plasma proteins Assists innate immunity.  Amplifies the inflammatory reaction by attracting phagocytes and promoting phagocytosis.  Some complement proteins form pores in the surface of bacteria and thereby cause them to burst. Interferons Proteins produced by virus-infected cells  Help noninfected cells prepare for possible viral attack.  Used to treat certain viral infections.

Fig. 7.9