Microbiology chapter 14- Defense Mechanisms of the Host

host defenses

The survival of the host depends upon an elaborate network of____ that keeps harmful microbes and other foreign materials from penetrating the body

innate, natural defenses

present at birth, provide nonspecific resistance to infection; it kills whatever it sees

adaptive immunities

specific, must be acquired

first line of defense

any barrier that blocks invasion at the portal of entry; nonspecific

second line of defense

protective cells and fluids; inflammation and phagocytosis; nonspecific

third line of defense

acquired with exposure to foreign substance; produces protective antibodies and creates memory cells; specific

physical or anatomical barriers at the body surface, chemical defenses, and genetic defenses

first line of defense is divided into 3 categories

physical or anatomical barriers

built in defenses in skin and mucous membranes

stratum cornuem

outermost layer of skin

built- in defenses in skin (physical or anatomical barriers)

outermost layer of skin with epithelial cells cemented together and impregnated with keratin; flushing effect of sweat

mucous membranes (physical or anatomical barriers)

coating of digestive, genitourinary and respiratory tracts; blinking and tear production; flow of saliva; flushing effect of urination, defecation, vomiting

mucous membranes

mucous coat impeded attachment and entry of bacterial. ciliary defense of respiratory tree: nasal hair traps larger particles

nonspecific chemical defenses

hydrochloric acid in stomach; digestive juices and bile of intestines; semen contains antimicrobial chemical; vagina has acidic pH

genetic defenses

some host are genetically immune to diseases of other host

immunology

study of the body’s 2nd and 3rd lines of defense

1. Surveillance of the body

2. Recognition and differentiation of normal versus foreign material 

3. Attack against and destruction of entities deemed to be foreign

primary functions of a healthy immune system

leukocytes

white blood cells: innate capacity to recognize and differentiate any foreign material

nonself

foreign material

self

normal cells of the body

pathogen-associated patterns (PAMPs)

molecules shared by mircoorganisms

Pathogen recognition receptors (PRRs)

receptors on WBCs for PAMPs

immune system

is a large, complex, and diffuse network of cells and fluids that penetrate into every organ and tissue

• Reticuloendothelial system (RES)    

• Extracellular fluid (ECF)

• Bloodstream        

• Lymphatic system

Body compartments that participate in immune function:

Reticuloendothelial System (RES)

network of connective tissue fibers that interconnects other cells and meshes with the connective tissue network surrounding organs; inhabited by phagocytic cells

mononuclear phagocyte system

macrophages ready to attack and ingest microbes that passed the first line of defense

whole blood

plasma and formed elements

serum

liquid portion of blood after a clot has formed

plasma

92% water, metabolic proteins, globulins, clotting factors, hormones, and other chemicals and gases to support normal physiological factors- carrier fluid element of blood

hemopoiesis or hematopoiesis

production of blood cells

stem cells

undifferentiated cells, precursor of new blood cells

platelets

thrombocytes

granulocytes

lobed nucleus

agranulocytes

unlobed, rounded nucleus

neutrophils, eosinophils, basophils

types of granulocytes

neutrophils

55-90% - lobed nuclei with lavender granules; phagocytes

eosinophils

1-3% - orange granules and bilobed nucleus; destroy eukaryotic pathogens

basophils

0.5% - constricted nuclei, dark blue granules; release potent chemical mediators

mast cells

nonmotile elements bound to connective tissue

lymphocytes, monocytes, macrophages, dendritic cells

types of agranulocytes

lymphocytes

20-35%, specific immune response

B cells and T cells

types of lymphocytes

B cells (humoral immunity)

produce antibodies

T cells (cell-mediated immunity)

modulate immune functions and kill foreign cells

monocytes and macrophages

3-7% - largest of WBCs, kidney shaped nucleus; phagocytic

macrophages

final differentiation of monocytes

dendritic cells

trap pathogens and participate in immune reactions

erythrocytes

develop from bone marrow stem cells, lose nucleus, simple biconcave sacs of hemoglobin  

platelets

formed elements in circulating blood that are not whole cells- this is what causes hemostasis 

Erythrocytes and Platelets

not part of the immune system

lymphatic system

Provides an auxiliary route for return of extracellular fluid to the circulatory system; Acts as a drain-off system for the inflammatory response; Renders surveillance, recognition, and protection against foreign material 

lymph

is a plasma-like liquid carried by lymphatic circulation; Made up of water, dissolved salts, 2-5% proteins

blood components move out of blood vessels into extracellular spaces

lymph are formed when ___

white blood cells, fats, cellular debris, and infectious agents 

lymph transports

lymphatic capillaries

Thin walls easily permeated by extracellular fluid which is then moved through contraction of skeletal muscles ; Functions to return lymph to circulation; flow is one-direction – towards the heart– eventually returning to blood stream

CNS, bone, placenta, and thymus

lymphatic capillaries permeate al parts of the body except

primary organs

Sites of lymphocytic origin and maturation

thymus gland and bone marrow

primary organs

secondary organs

Circulatory-based locations 

Lymph nodes and Spleen 

secondary organs

MALT

mucosal-associated lymphoid tissue

SALT

skin-associated lymphoid tissue

GALT

gut-associated lymphoid tissue

thymus, lymph nodes, spleen

lymphoid organs

thymus

High growth and activity until puberty, then begins to shrink

lymph nodes

Small, encapsulated, bean shaped organs along lymphatic channels and large blood vessels of the thoracic and abdominal cavities

spleen

Nestled below the diaphragm and left of the stomach; Structurally similar to lymph node; filters circulating blood to remove worn out RBCs and pathogens

• Recognition

• Inflammation  

• Phagocytosis

• Interferon 

• Complement

mechanisms that play important roles in host defenses

inflammatory

Reaction to any  traumatic event in the tissues that attempts to restore homeostasis; Helps to clear away invading microbes and cellular debris left by immune reactions

redness, warmth, swelling, pain

stages of inflammation

redness

increased circulation and vasodilation in response to chemical mediators

warmth

heat given off by the increased blood flow

swelling

increased fluid in the tissue as blood vessels dilate(edema) ; WBC’s, microbes, debris, and fluid collect to form pus; prevents spread of infection

pain

stimulation of nerve ending

injury/ immediate reactions

Blood vessels narrow (vasoconstriction); blood clots; and mast cells release chemokines(chemicals that stimulate WBC) and cytokines  into injured area.

vasoconstriction

Blood vessels narrow

vascular reactions

Nearby blood vessels dilate; increased blood flow; increased vascular permeability; increased leakage of fluid forms exudate.

edema and pus formation

Collection of fluid; edema/swelling; infiltration by neutrophils and formation of pus.

resolution/ scar formation

Macrophages lymphocytes, and fibroblasts migrate in; initiate immune response and repair of injury; scar and loss of normal tissue.

diapedesis

migration of cells out of blood vessels into the tissues

chemotaxis

migration in response to specific chemicals at the site of injury or infection

fever

Initiated by circulating pyrogens  which reset the hypothalamus to increase body temperature; signals muscles to increase heat production and vasoconstriction

exogenous pyrogens

products of infectious agents; endotoxin

endogenous pyrogens

liberated by monocytes, neutrophils, and macrophages during phagocytosis; interleukin-1 (IL-1) and tumor necrosis factor (TNF)

benefits of fever

inhibits multiplication of temperature, impedes nutrition of bacteria by reducing the available iron, increases metabolism and stimulates immune reaction and protective physiological processes

second-line of defenses

phagocytosis is a form of

phagocytosis

1. To survey tissue compartments and discover microbes, particulate matter, and dead or injured cells 

2. To ingest and eliminate these materials

3. To extract immunogenic information from foreign matter

neutrophils, eosinophils, macrophages

major categories of phagocytes

neutrophils

react early to bacteria and other foreign materials, and to damaged tissue- primary component of pus.

eosinophils

attracted to sites of parasitic infections and antigen-antibody reactions

macrophages

scavenge and process foreign substances to prepare them for reactions with B and T lymphocytes

Toll-like receptors (TLRs)

Protein receptors within cell membrane of macrophages; Detect foreign molecules and signal the macrophage to produce chemicals to stimulate an immune response

chemotaxis, binding and ingestion

• Phagocytes migrate to inflammation following a   gradient of stimulant products 

• Using TLRs they bind pathogen-associated molecular pattern (PAMPs) receptorsdestruction and elimation

phagolysosome formation

• Phagocyte extends pseudopods(arm-like projection) that enclose pathogen in a vacuole called a phagosome

• In a short time, lysosomes with antimicrobial substances fuse with the phagosome  to form a phagolysosome  and digest the pathogen

destruction and elimination

• Oxygen-dependent system(respiratory burst)

• Liberation of lactic acid, lysozyme, and nitric oxide

• Indigestible debris are released from the macrophage by exocytosis

respiratory burst

oxygen-dependent system

interferon

Small protein produced by certain WBCs and tissue cells; All three types bind to cell surfaces and induce                   of antiviral proteins and inhibit antiviral proteins and inhibit expression of cancer genes

interferon alpha, interferon beta, interferon gamma

3 major types of interferons

interferon alpha

product of lymphocytes and macrophages

interferon beta

product of fibroblast and epithelial cells

interferon gamma

• product of T cells