Physiology_الفصل الثاني

The Nature of Disease

Pathogenic Organisms Genetic Disorders Toxic Chemicals Other Environmental Factors Physical Damage to Organs Nutritional Disorders

Types of Pathogenic Organisms

Viruses Bacteria Protozoan Fungi Animal Parasites

Mechanisms of Disease by Pathogens

Utilization of host nutritional resources Physical damage to host tissues Production of toxic substances Chromosomal and gene damage Body cells behave abnormally

Viruses

nucleic acid
capsid
envelope

Bacteria

cell wall
plasma membrane
cytoplasm
circular DNA

Defense Mechanisms

External defense Internal Defense Immune Defense


Skin acts as barrier to microbes and viruses - sweat has a low pH Mucus traps foreign particles Tears - Lysozyme has antimicrobial action Gastric stomach acid
1st Line of Defense

Body Coverings: The Skin

sebaceous glands
sweat gland
epidermis

Body Coverings: Mucous Membranes

mucus
cilia
columnar epithelium



Phagocytic cells (WBCs) N L M E B Natural Killer (NK) Cells: attack virus infected cells Inflammatory Response Antimicrobial proteins Lysozyme Interferon Antibodies
2nd Line of Defense

Nonspecific Phagocytosis

Neutrophils Monocytes Eosinophils

Mechanism of Phagocytosis

Mechanism of Phagocytosis
Macrophage

Lymphatic System

Inflammatory Response
Histamine & prostaglandins released
Capillaries dilate Clotting begins
Chemotactic factors attract phagocytic cells
Phagocytes consume pathogens & cell debris

Characteristics of Immunity

Recognition of self versus non-selfResponse is specificRetains a “memory” allowing an accelerated second responseCan respond to many different materialsInvolves lymphocytes and antibodies

Types of Immunity

Active Immunity Naturally-Acquired Active Immunity Artificially-Acquired Active Immunity Passive Immunity Naturally-Acquired Passive Immunity Artificially-Acquired Passive Immunity

Types of Acquired Immunity

The production of antibodies against a specific disease by the immune system. Naturally acquired through disease Artificially acquired through vaccination Vaccines include inactivated toxins, killed microbes, parts of microbes, and viable but weakened microbes. Active immunity is usually permanent
Active Immunity


A vaccinated person has a secondary response based on memory cells when encountering the specific pathogen. Routine immunization against infectious diseases such as measles and whooping cough, and has led to the eradication of smallpox, a viral disease. Unfortunately, not all infectious agents are easily managed by vaccination. HIV vaccine in the works


Passive Immunity- Protection against disease through antibodies produced by another human being or animal. Effective, but temporary Ex. Maternal antibodies Colostrum.
Passive Immunity



Passive immunity can be transferred artificially by injecting antibodies from an animal that is already immune to a disease into another animal. Rabies treatment: injection with antibodies against rabies virus that are both passive immunizations (the immediate fight) and active immunizations (longer term defense).

Immune System Response to Antigens

Humoral Immunity Involves antibodies (secreted from B cells) dissolved in the blood plasma. Demonstrated as a immune response using only the blood serum. Defense against bacteria, bacterial toxins, & viruses.


Cell-Mediated Immunity Involves the activities of specific white blood cells (T cells). Defense against cancer cells, virus-infected cells, fungi, animal parasites, & foreign cells from transplants.
Immune System Response to Antigens

Lymphocyte Formation

B Cells
Mature in bone marrow Involved in humoral immunity Once activated by antigen, proliferate into two clones of cells: plasma cells that secrete antibodies and memory cells that may be converted into plasma cells at a later time

B Cells

antibodies

Clonal Selection

plasma cells
memory cells
antibodies

Humoral Immune Response

time (days)
antibody concentration
first exposure to antigen A

Humoral Immune Response

time (days)
antibody concentration
first exposure to antigen A
primary response: concentration of anti-A antibody
second exposure to antigen A



Humoral Immune Response
time (days)
antibody concentration
secondary response: concentration of anti-A antibody
second exposure to antigen A
first exposure to antigen B

Humoral Immune Response

time (days)
antibody concentration
primary response: concentration of anti-B antibody
first exposure to antigen B


Antibodies constitute a group of globular serum proteins called immunoglobins (Igs). A typical antibody molecule has two identical antigen-binding sites specific for the epitope that provokes its production.

Antibody Molecule

antigen binding sites
antigen
light chains
heavy chains

Mechanisms on Antibody Action

Precipitation of soluble antigens Agglutination of foreign cells Neutralization Enhanced phagocytosis Complement activation leading to cell lysis Stimulates inflammation


The binding of antibodies to antigens to form antigen-antibody complexes is the basis of several antigen disposal mechanisms.

Immunoglobin Classes

IgM1st response to antigenEffective in agglutinationCan’t cross placenta IgG Most common form Crosses blood vessels Crosses placenta (passive immunity to fetus)
IgA Secreted from mucus membranes Prevents attachment of bacteria to epithelial surface In colostrum
IgDB cell activationCan’t cross placenta IgE Histamine reactions and allergies

Overview of Immune System Responses

T Cells
Mature in thymus Involved in cell-mediated immunity Activated when another cell presents antigen to them Several types of T cells: cytoxic T cells, helper T cells, suppressor T cells, and memory T cells

There are two main types of T cells, and each responds to one class of MHC molecule.Cytotoxic T cells (TC) have antigen receptors that bind to protein fragments displayed by the body’s class I MHC molecules.Helper T cells (TH) have receptors that bind to peptides displayed by the body’s class II MHC molecules. T Cells

Cytotoxic T Cell

perforin
pores in target cell

Helper T Cells

interleukin 1
macrophage
helper T cell
bacterium
bacterial antigens
T cell receptor

The central role of helper T cells

The central role in Helper T cells in an infected cell



T-independent antigens T cells activated by binding to certain antigens No memory cells generated Weaker response than t-dependent T-dependent antigens Most antigens require co-stimulation to evoke a B-cell response Antibody production stimulated with help from TH Most antigens are t-dependent


T-dependent antigens- can trigger a humoral immune response by B cells only with the participation of helper T cells.

Tissue/Organ Transplants

Major Histocomatibility Complex (MHC) Bone marrow Organs


Malfunctions of the immune system can produce effects ranging from the minor inconvenience of some allergies to the serious and often fatal consequences of certain autoimmune and immunodeficiency diseases.
Abnormal immune function can lead to disease

Abnormal Immune Function

Autoimmune Disease Allergy Immunodeficiency

Autoimmune Disease

Rheumatoid arthritisType I DiabetesMS(multiple sclerosis)LupisCrohn’s diseaseGrave’s disease


Allergy (Immune Hypersensitivity)
Hypersensitive response to certain environmental allergens Food, pollen, pet dander, asthma, bee sting Anaphylactic shock - epinephrine

Mast cells, IgE, and the allergic response.

AIDS
Acquired Immunodeficiency Syndrome HIV (virus) attacks T-cells Weakens or eliminates immune system Susceptible to many fatal diseases
Problems


Transmission of HIV requires the transfer of body fluids containing infected cells, such as semen or blood, from person to person. Unprotected sex Nonsterile needles HIV transmission among heterosexuals is rapidly increasing as a result of unprotected sex with infected partners. HIV in Africa and Asia- primarily by heterosexual sex

AIDS

AIDS