Host responses I. Host responses during infection



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Host responses

I. Host responses during infection

A. Two general types

1. Nonspecific defenses

2. Specific defenses (Immune response)

B. Nonspecific defenses

Act against all invading pathogens

C. Specific defenses (Immune response)

Humoral immunity
Cellular immunity

II. Non-specific defenses

A. Act against any type of damage to the host body

Response is always the same

No matter what the agent

B. Blood and lymphatic circulatory systems

Many innate resistance mechanisms based in the blood and lymphatic circulatory systems

C. Blood and lymph

Two kinds of components

1. Cellular components

2. Noncellular components

D. Cellular components

Originate in the bone marrow

1. Erythrocytes [red blood cells (RBC)]

Carry O2 from lungs to tissues

5.5 million/ml3 of blood in males

4 - 5 million/ml3 of blood in females

No known function in host defense

2. Leukocytes [white blood cells (WBC)]

7000 - 8000/m3 blood

Several different types

Phagocytes

Involved in nonspecific host defenses


3. Lymphocytes

Involved in cellular and humoral immunity

4. Thrombocytes

Produce platelets

Involved in blood clotting

E. Noncellular blood components

Water Salts

Sugar (glucose) Proteins

Fibrinogen (clotting factor)

Fibrinogen Fibrin

Plasma

Fibrin

Material of which a clot is composed

Serum

Plasma minus fibrinogen

Serology important branch of medical microbiology

F. Lymph

Similar to blood

Lacks red blood cells

Contains WBC

About half the protein in blood

Bathes the intercellular spaces

Carries nutrients

Picks up wastes

Passes through lymphatic tissue way back to heart

G. Lymphatic tissue includes

Liver

Spleen

Tonsils

Bone marrow

H. Reticuloendothelial system

Major non-specific defense

Composed of lymphatic tissue and associated WBC

Collection of various types of phagocytes

Monocytes

Macrophages

Associated cells

Cells of the reticuloendothelial system located in

Liver

Spleen

Lymph glands

Pathogens in blood or lymph pass through these cells and are phagocytized and destroyed

I. Phagocytosis

Major non-specific defense

Phagocytes are able to ingest and kill invading microorganisms

J. Phagocytosis and Lymphatic system

Phagocytes in the reticuloendothelial system remove foreign organisms from the lymph

K. Phagocytosis Process

Phagocytes chemically attracted to bacteria

Bacteria attach to cell membrane of phagocyte

Bacteria are taken into cell

Killed and digested

Digestion

Lysosomes fuse with food vacuoles

Contain hydrolytic enzymes

Enzymes kill and digest bacteria

L. Phagocytes types

Phagocytes originate in bone marrow

Released into the blood

Two major types and many sub-types

1. Granulocytes

2. Macrophages

M. Granulocytes

Also called polymorphonuclear leucocytes or polymorphs

Granular cytoplasm

Granules contain hydrolytic enzymes

Kill bacteria

Nucleus divided into 3 - 5 lobes

Short lived cells

Appear in large numbers during acute stages of infection

N. Macrophages

Also called monocytes

Few granules in cytoplasm

Kidney shaped nucleus

Two types of macrophages

1. Wandering macrophages

Free in blood and tissues

2. Fixed histocytes

Embedded in lymphatic tissue

Lymph passes through lymphatic tissue on its way back to

heart

Liver

Spleen

Tonsils

Thymus

Lymph glands

III. Lymphatic system

  1. Attacks

Bacteria

Viruses

Other foreign material

B. Antimicrobial Substances

Lysozyme

Lytic enzyme

Dissolves Gram positive cell wall

Found in

Saliva Nasal secretions

Tears Skin

Mucus Various organs

  1. Beta lysine

Polypeptide released from blood platelets when blood clots

Kills some Gram positive bacteria

Disrupts plasma membrane

C. pH of stomach

pH of stomach is between 2 and 3

Low pH kills most bacteria

Food particles sometimes protect bacteria

Pass through stomach unharmed

Enter small intestine where pH is higher and conditions for growth are somewhat more favorable

D. Small intestine

Intestinal enzymes

Bile

Pancreatic enzymes

Antibodies

IV. Inflammatory response

A. Series of defense mechanisms

Isolate and destroy pathogens and other injurious materials

B. Signs of the Inflammatory Response

Redness

Heat

Swelling

Pain

Loss of function

C. Inflammatory Response responds to

Bacteria

Viruses

Cuts

Burns

Chemicals

D. Inflammatory response

Histamine is released when tissue is injured

Causes the inflammatory response

E. Inflammatory response location

May be

Localized

Systemic

F. Localized response

Red

Swollen

Hot

Painful

Histamine acts on capillary walls

Causes dilation

Capillaries increase in diameter

Increases blood flow

injured area becomes red and hot

Capillary wall becomes more permeable

Fluid leaves blood

Enters the tissues

Causes swelling

Permeable capillary wall

Phagocytes move through capillary walls into the tissues

Destroys invading pathogens and

Damaged or dead host cells

Lymphocytes - Antibody forming cells enter the injured area

Produce antibodies against specific pathogens

G. Systemic inflammatory response

Similar to local response

In addition increased number of white blood released from the bone marrow

Systemic inflammatory response

Fever occurs

Enhances phagocytosis

Inhibits growth of certain microorganisms

May cause tissue damage

Antihistamines used to control inflammatory response



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