MODULE 5
1|Page
Lymphatic system
Picks up fluid leaked from blood vessels and returns it to blood, disposes of
debris in the lymphatic stream, houses white blood cells involved in immunity
Lymphatic vessels
It forms an elaborate drainage system that picks up
this excess tissue fluid which is called the lymph
it is also called lymphatics, form a one-way system,
and lymph flows only to the heart
It forms an elaborate drainage system that picks up
this excess tissue fluid which is called the lymph
it is also called lymphatics, form a one-way system,
and lymph flows only to the heart
Lymph capillaries weave between the tissue cells
and blood capillaries in the loose connective tissues of the body and absorb the
leaked fluid.
2|Page
Lymphatic collecting vessels are larger lymphatic vessels which transports lymph
from lymphatic capillaries to the venous system through one of the largest ducts
in the thoracic regions
Lymph nodes
It help to protect the body by removing foreign material such as bacteria and
tumor cells from lymphatic stream and by producing lymphocytes that function in
the immune response.
Within the lymph nodes are macrophages which engulf and destroy bacteria,
viruses, and other foreign substances.
Collection of lymphocytes are also located in the lymph nodes and respond to
foreign substances
The center (germinal centers) enlarge when specific lymphocytes are generating
daughter cells called plasma cells which release antibodies.
Phagocytic macrophages are located in the central medulla.
3|Page
Other lymphoid organs
SPLEEN
Is a soft, blood rich organ that filters blood.
It filters and cleanses blood of bacteria, viruses and other debris
Provides a site for lymphocyte proliferation and immune response
Destroy worn out red blood cells and return some of their breakdown products to
the liver.
4|Page
Thymus gland
Functions at peak levels only during youth
It produces hormone- thymosin – that
function in the programming of certain
lymphocytes so they can carry out their
protective roles in the body.
TONSILS
small masses of lymphoid tissue that ring
the pharynx
They trap and remove any bacteria or other
foreign pathogens entering the throat
5|Page
Peyer’s patches
Found in the walls of intestine
It prevent bacteria from penetrating the intestine
Is part of collection of small lymphoid tissues –MALT (mucosa-associated
Lymphatic Tissue) which acts as sentinel to protect the upper respiratory
and digestive tracts from the attack of pathogens.
Body defenses
INNATE BODY DEFENSES
Also called the non-specific defense system
It refers to the mechanical barriers that cover the body surface and to the cells
and chemicals that act to protect the body from pathogens such as:
o Surface membrane barrier
* Intact skin
* The acidic pH of the skin secretions inhibits bacterial growth.
Sebum that contains chemicals that are toxic to the bacteria.
Vaginal secretions of adults in females
* The stomach mucosa secretes hydrochloric acid and protein
digesting enzymes
* Saliva and lacrimal fluid contains lysozyme
* Sticky mucus traps many microorganisms that enter Digestive and
Respiratory
o Internal defenses: cells and chemicals
* phagocytes (e.g. macrophage or neutrophil) that engulfs foreign
particles
* Natural killer cells which is consider the “police” the body in the
lymph, are unique group of lymphocytes that can lyse and kill
cancer cells and virus infected body cells .
o Inflammatory response: Is a non specific response that is triggered
whenever body tissues are injured. The four most common indicators of
inflammatory are redness, swelling, heat and pain.
o Antimicrobial proteins: Enhances the innate defenses either by attacking
microorganisms directly or by hindering their ability to reproduce.
* The most important of these is Complement protein and Interferon
6|Page
Complement: group of plasma proteins that lyses
microorganisms, enhances phagocytosis by
opsonization and intensifies inflammatory response
Interferon: protein released by virus infected cells that
protect uninfected tissue cells from viral takeover,
mobilize immune system
o Fever : Or abnormally high body temperature, is a systemic response to
invading microorganisms. It is regulated by a part of hypothalamus.
ADAPTIVE BODY DEFENSES
IMMUNE RESPONSE: it involves tremendously increased internal nonspecific
defenses and provides protection that is carefully targeted against specific
antigens
Sometimes referred as the third line of defense
Three important aspects of adaptive defenses:
o It is antigen specific- it recognizes and acts against particular pathogens
o It is systemic- immunity is not restricted to initial site of infection
o It has memory- it recognizes and mounts even stronger attacks on
previously encountered pathogens
The crucial cell of the adaptive system are lymphocytes and macrophages.
Lymphocytes exist in two “flavors”:
o The B lymphocytes or B cells which produce antibodies
o The T lymphocytes or T cells oversee the humoral immunity- non-antibody-
producing lymphocytes that constitute the cell-mediated arm of the
adaptive defense system
Lymphocyte
Originates from hematocytoblast
T cells arise from lymphocytes that migrate to thymus where they undergo
maturation process for 2 to 3 days directed by thymosin
B cells develop immunocompetence in bone marrow but is less is known about
the factors that regulate B cell maturation
Macrophages
widely distributed in lymphoid organs and connective tissues
Arise from monocytes formed in the bone marrow
7|Page
The major role is to engulf foreign particles and rid them from the area.
they also present the fragments of those antigens like signal flags on their own
surface where they can be recognized by immuno-competent T cells.
They also secrete cytokines proteins that is important in the immune response.
Humoral (antibody-mediated) immune response
Is provided by antibodies present in the body’s “humors” or fluids.
An immunocompetent but as yet immature B lymphocyte is stimulated to
complete its development when antigens bind to its surface receptors.
This binding event sensitizes or activates, the lymphocyte to switch on and
undergo clonal section
The lymphocytes begins to grow and then multiplies rapidly to form an army of
cells all exactly like itself and bearing the same antigen specific receptors
The resulting family of identical cells descended from the same ancestor cell is
called a clone, and clone formation is the primary humoral response to that
antigen
Most of the B cell clone members, or descendants become plasma cells.
B cell clone members that do not become plasma cells become long-lived memory
cells capable of responding to the same antigen. It is responsible for the
immunologic memory. This later immune responses called secondary humoral
response, are produced much faster, are more prolonged and more effective
Active and passive humoral immunity
Active Immunity
- Is naturally acquired during bacterial and viral infection
- Artificially acquired through vaccine
- two benefits from vaccines:
- They spare us most of the signs and symptoms of the disease that would
otherwise occur during the primary response
- The weakened antigens are still able to stimulate antibody production and
promote immunological memory
passive immunity
- It is conferred naturally on fetus when the mother’s antibodies cross the placenta
and enter the fetal circulation and after birth during breastfeeding.
8|Page
- Is artificially conferred when one receives immune serum or gamma globulin
- Gamma globulin is commonly administered after exposure to hepatitis. Other
immune sera are used to treat poisonous snake bites, botulism, rabies and
tetanus
Antibodies
Also referred to as immunoglobulins, constitute the gamma globulin part of blood
proteins
Are soluble proteins secreted by a activated B cells or by their plasma-cell
offspring in response to antigen.
Immunoglobin Classes
IgD
- Virtually always attached to B cell
- Believed to be cell surface receptor of immunocompetent B cell
- Important in activation of B cell
IgM
- Attached to B cell; free plasma
- When bound to the B cell membrane, serves as antigen receptor,
first Ig released to plasma cells during primary response
- Fixes complement
9|Page
IgG
- Most abundant antibody in plasma
- Main antibody of both primary and secondary responses, crosses
placenta and provides passive immunity to fetus.
- Fixes complement
IgE
- Secreted by plasma cells in skin, mucosae of GI and respiratory
tract and tonsils
- Binds to mast cells and basophils, and triggers release of histamine
and other chemicals that mediate inflammation and certain allergic
response
Antibody function
Complement
- Is the chief antibody ammunition
- It is fixed during innate defenses.
- It is activated very efficiently when it binds to antibodies attached to
cellular targets.
Neutralization
- Occurs when antibodies bind to specific site on bacterial exotoxins or on
virus that can cause cell injury
10 | P a g e
Agglutination
-the process causes clumping of the foreign cells
- This type of antigen-antibody reaction occurs when mismatched blood is
transfused
Precipitation
- when the cross-linking reaction involves soluble antigenic molecules, the
resulting antigen-antibody complexes are so large that they may become
insoluble and settle out of solution.
Cellular (cell mediated) immune response
When lymphocytes themselves defend the body
Immunocompetent T cells are activated to form a clone by binding with a
recognized antigen
T cells are not able to bind with free antigens instead the antigens must be
presented by a macrophage and double recognition must occur.
A macrophage engulf an antigen and process it internally.
Different classes of T cell clones
Cytotoxic (Killer) T cells
- Cells that specialize in killing virus infected, cancer or foreign graft cells
Helper T cells
- T cells that act as the directors or managers of the immune system
Regulatory T cells
- Formerly called the suppressor T cells
- Releases chemicals that suppress the body activity of both T and B cells
11 | P a g e
- They are vital in winding down and finally stopping the immune response after
an antigen has successfully inactivated
Memory Cells
- Provide the immunological memory for each antigen encountered and enable the
body to respond quickly to subsequent invasion.
12 | P a g e
