Download The Lymphoid System and Immunity Overview Chapter 22

Functions of the Immune
System
 Destroy pathogens (organisms that cause disease)
 Detect and kill abnormal cells such as cancerous cells
 Remove dead cells and debris from the body
Pathogens
 Can be classified according to size and where they live
in the body.
 Largest pathogens are the multicellular organisms such
as parasitic worms
 Others are microorganisms including fungi, protozoa
(such as the one that causes malaria), bacteria, and
viruses
Pathogens continued
Viruses
Must reproduce
inside cells
Bacteria
Protozoa
Fungi
Some hide inside
cells, but most
are extracellular
Parasitic worms
Always
extracellular
Three main lines of defense
1. Surface Barriers (Innate
External Defenses)
2. Innate Internal Defensesidentify enemies by
recognizing a limited number
of markers unique to
pathogens. When
overwhelmed, they secrete
chemical messengers to
mobilize adaptive defenses
Skin and mucous
membranes
Cells and chemicals
in body fluids
3. Adaptive Defenses- take
time to mobilize and train to
fight an identified enemy
Lymphocytes- T cells
and B cells
Innate and Adaptive Immunity
Innate immunity
 Nonspecific defense
mechanisms that come into
play immediately or within
hours of an antigen's
appearance in the body.
These mechanisms include
physical barriers such as skin,
chemicals in the blood, and
immune system cells that
attack foreign cells in the body.
The innate immune response
is activated by chemical
properties of the antigen.
Adaptive Immunity
 Antigen-specific immune
response. The adaptive immune
response is more complex than
the innate. The antigen first must
be processed and recognized.
Once an antigen has been
recognized, the adaptive immune
system creates an army of
immune cells specifically designed
to attack that antigen. Adaptive
immunity also includes a
"memory" that makes future
responses against a specific
antigen more efficient.
Adaptive defenses differ from
innate defenses in four ways:
1.
Are specific- directed against
an identified enemy
2.
Involve B and T lymphocytes
3.
Have memory
4.
Are systemic- can act
anywhere in the body
Adaptive Immunity-B cells and T
cells
 Recognize a shape on a pathogen called an antigenic determinant
and is formed by the 3D structure of a large molecule called an
antigen
 Antigens are usually proteins, but can also be large carbohydrates
or nucleic acids.
 The surface of a given pathogen is studded with many different
antigens, each having many different determinants.
Antigens
 Both B and T cells bind to
antigens. In addition,
protein molecules called
antibodies bind antigens.
These antibodies are
secreted by the clonal
descendants of B cells,
called plasma cells.
Humoral Immunity
 Aspect of specific immunity
which is mediated by B
lymphocytes and involves the
binding of antibodies to antigens
 Directed against extracellular
pathogens
Cellular Immunity
 The branch of adaptive
immunity involving T
lymphocytes that directly
attack infected, cancerous,
or that release chemicals
which regulate other
functions of the immune
system.
 Directed against pathogens
within the cells.
Circumstances that T cells
attack our own cells
 A cell has become
cancerous.
 A cell has been invaded by a
virus.
 A cell has been transplanted
from another individual.
Anatomy Review
 The immune system is strategically distributed
throughout the body, particularly at those points such
as the respiratory and digestive tract mucosae, where
pathogens can most easily gain entry to the body.
Two major parts of the immune
system:
 Specialized immune cells, many of which are
leukocytes (white blood cells) and their close relatives.
 Lymphoid organs and tissues including the bone
marrow, lymph nodes, spleen, and thymus.
 lymphocytes are produced, reside, and come into contact
with pathogens.
Immune Cells: Leukocytes
 Cells of the immune system:
 Originate in the bone marrow
 Migrate to tissues or circulate through the blood and
lymphatic system and enter tissues when needed.
 Are called leukocytes when traveling in the blood
 Have traditionally been classified according to their shape
and the colors of their granules, if any, when stained with
histological dyes.
Immune Cells besides
leukocytes
 Phagocytes- engulf and
destroy pathogens, dead
cells and debris.
 Antigen-presenting cells
(APCs) process and present
antigens to T cells
 Dendritic cells
 Macrophages
 B cells
 Effector Cells
 B cells
 T cells
 Mast cells
Lymphocytes and adaptive
immunity
 B cells mature in the bone
marrow
 T cells mature in the thymus
 Together the bone marrow
and the thymus are the
primary lymphoid organs
Lymphatic System
 A one way system of vessels
called lymphatic vessels.
 The fluid in those vessels,
called lymph
 Lymph nodes