Host responses
I.
II.
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
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 
Plasma
Fibrin
Material of which a clot is composed
Serum
Plasma minus fibrinogen
Serology important branch of medical microbiology
F.
G.
H.
I.
J.
K.
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
Lymphatic tissue includes
Liver
Spleen
Tonsils
Bone marrow
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
Phagocytosis
Major non-specific defense
Phagocytes are able to ingest and kill invading
microorganisms
Phagocytosis and Lymphatic system
Phagocytes in the reticuloendothelial system remove
foreign organisms from the lymph
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
III.
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
Lymphatic system
A.
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
B.
C.
D.
IV.
Beta lysine
Polypeptide released from blood platelets when blood clots
Kills some Gram positive bacteria
Disrupts plasma membrane
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
Small intestine
Intestinal enzymes
Bile
Pancreatic enzymes
Antibodies
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
G.
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
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