Mr. Johny Kutty
Lymph is the fluid that circulates throughout the
lymphatic system. The lymph is formed when the
interstitial fluid is collected through lymph capillaries.
It is then transported through larger lymphatic vessels to
lymph nodes, where it is cleaned by lymphocytes, before
emptying ultimately into the right or the left subclavian
vein, where it mixes back with the blood.
It is generally similar to blood plasma except that it also
contains white blood cells and some proteins.
Lymph may pick up bacteria and bring them to lymph
nodes, where they are destroyed.
Lymph also transports fats from the digestive system to
the lymph formed in the human digestive system called
Blood supplies nutrients and important metabolites to
the cells of a tissue and collects back the waste
products they produce, which requires exchange of
respective constituents between the blood and tissue
This exchange is not direct, but instead is effected
through an intermediary called interstitial fluid.
IDF is formed at capillary network and some plasma
leak out from arterial capillary end due to higher
pressure. This leaked out fluid is called lymph.
Lymph when formed is a watery clear liquid with the
same composition as the interstitial fluid.
It flows through the lymph nodes it comes in contact
with blood, and tends to accumulate more cells
Lymph nodes of the head are Occipital lymph nodes,
Mastoid lymph nodes and Parotid lymph nodes.
Lymph nodes of the neck are Cervical lymph nodes,
Deep cervical lymph nodes, Inferior deep cervical lymph
nodes and Supraclavicular lymph nodes
Lymph nodes of the lungs: are subsegmental,
segmental, lobar and interlobar lymph nodes.
Mediastinal lymph nodes: They consist of several lymph
node groups, especially along the trachea, esophagus and
In the mediastinal lymph nodes arises lymphatic ducts,
which drains the lymph to the left subclavian vein.
Lymph nodes of the arm; These drain the whole of the
arm, and are divided into two groups, superficial and deep.
Lower limbs have Superficial inguinal lymph nodes, Deep
Tubular vessels transport lymph back to the blood,
ultimately replacing the volume lost during the formation
of the interstitial fluid. These channels are the lymphatic
channels, or simply lymphatics.
Unlike the cardiovascular system, the lymphatic system
is not closed and has no central pump, or lymph hearts.
Lymph transport is slow and sporadic. Despite low
pressure, lymph movement occurs due to peristalsis ,
valves, and compression during contraction of adjacent
skeletal muscle and arterial pulsation.
Lymph that enters the lymph vessels from the interstitial
space usually does not flow backwards along the
vessels because of the presence of valves.
If excessive hydrostatic pressure develops within the
lymph vessels, though, some fluid can leak back into the
interstitial space and contribute to formation of oedema.
Water and solutes continually filter out from
capillary into interstitial space.
To balance this outflow fluid continually
reenters blood through lymphatic system.
Fluid that is forced out of the bloodstream
during normal circulation is filtered through
lymph nodes to remove bacteria, abnormal
cells and other matter.
This fluid is then transported back into the
bloodstream via the lymph vessels.
Lymph only moves in one direction, toward the
The immune system is a host defense system
comprising many biological structures and
processes within an organism that protects
In humans, the blood–brain barrier, blood–
cerebrospinal fluid barrier, and similar fluid–brain
barriers separate the peripheral immune system
from the neuroimmune system which protects the
T cells (thymus cells) and B cells (bone marrow derived
cells) are the major cellular components of the adaptive
The function of T cells and B cells is to recognize specific
“non-self” antigens, during a process known as antigen
Once they have identified an invader, the cells generate
specific responses that are tailored to maximally eliminate
specific pathogens or pathogen-infected cells.
B cells respond to pathogens by producing large
quantities of antibodies which then neutralize foreign
objects like bacteria and viruses.
Some T cells, called T helper cells, produce cytokines
that direct the immune response, while other T cells,
called cytotoxic T cells, produce toxic granules that
Following activation, B cells and T cells leave a lasting
legacy of the antigens they have encountered, in the form
of memory cells which will “remember” each specific
pathogen encountered, and are able to mount a strong
and rapid response if the pathogen is detected again.
The formation of these cells takes place through
The formation of lymphocytes is known as lymphopoiesis.
B cells mature into B lymphocytes in the bursa equivalent
(bome marrow equivalent), which in humans is the the
Peyer's patches of the intestine, while T cells migrate to
and mature in a distinct organ, called the thymus.
Following maturation, the lymphocytes enter the
circulation and peripheral lymphoid organs (e.g. the
spleen and lymph nodes) where they survey for invading
Immunity or resistance is the ability to ward off
damage or diseases through our defence. The
different types of immunity are
Adaptive immunity: Two types.
a. Cell mediated immunity
b. Antibody mediated immunity
The innate immune system, also known as the non-
specific immune system or in-born immunity
Innate immune systems provide immediate defence
It includes external physical/anatomical barriers and
internal defences such as antimicrobial substances,
natural killer cells, phagocytes, inflammation and fever.
Anatomical barrier: Skin (Sweat), Gastrointestinal tract
(Peristalsis, gastric acid, bile acids, digestive enzyme,
Respiratory system (mucous, surfactant, saliva) and
Anatomical barriers include physical, chemical and
The epithelial surfaces form a physical barrier that is
Antimicrobial Substances: it include interferons
(prevents viral replication), transferrin (prevents
bacterial replication) etc.
Natural Killer Cells and Phagocytes: This is a form of
lymphocytes which are activated by the intrusion of
microorganisms. They are present lymphatic system.
Phagocytes such as neutrophils and macrophages
migrate to the infected area.
Inflammation:The process of acute inflammation is
initiated by cells already present in all tissues, mainly
resident macrophages, dendritic cells, and
mastocytes. Chemical factors produced during
inflammation (histamine, bradykinin, serotonin, and
prostaglandins) sensitize pain receptors, cause local
vasodilation of the blood vessels, and attract
phagocytes, especially neutrophils.
The adaptive immune system, also known as
the acquired immune system or, more rarely, as
the specific immune system.
Adaptive immunity creates immunological
memory after an initial response to a specific
pathogen, and leads to an enhanced response
to subsequent encounters with that pathogen.
This process of acquired immunity is the basis
Substances that provoke immune responses
are called antigens.
Adaptive immunity includes both T-cells and B
There are two types of T-cells such as helper T
cells (CD4) and cytotoxic T cells (CD8). CD4
Clonal Selection is the process by which a
lymphocyte proliferates and differentiates in
response to a specific antigen.
The clonal selection give rise to two types of
cells called effecter cells and memory cells.
Cell Mediated Immunity: This begins same as the
clonal selection by the activation of T cells. the
result of clonal selection is the formation of
clone of cells that recognize the antigen as the
original lymphocyte. (effectors an memory
Antibody Mediated immunity: The response B
cells in response to an antigen. In response to
antigen the B cells undergo clonal selection
forming a clone of plasma cells and memory
An antigen is a molecule capable of inducing an
immune response on the part of the host
Exogenous antigens are antigens that have
entered the body from the outside, for example
by inhalation or ingestion.
Endogenous antigens are generated within
normal cells as a result of normal cell
metabolism, or because of viral or intracellular
An auto-antigen is usually a normal protein or
protein complex (sometimes DNA or RNA) that
is recognized by the immune system of patients
suffering from a specific autoimmune disease.
An antibody (Ab), also known as an
immunoglobulin (Ig), is a large, Y-shaped
protein produced mainly by plasma cells that
is used by the immune system to identify and
neutralize pathogens such as bacteria and
Antibodies are secreted by B cells of the
adaptive immune system, mostly by
differentiated B cells called plasma cells.
Antibodies can come in different varieties
known as isotypes or classes.
IgA: Found in mucosal areas, such as the gut,
respiratory tract and urogenital tract, and
prevents colonization by pathogens. Also
IgE: Binds to allergens and triggers histamine
release from mast cells and basophils, and is
involved in allergy. Also protects against
IgG: The only antibody capable of crossing the
placenta to give passive immunity to the fetus.
IgM: Eliminates pathogens in the early stages
of B cell-mediated (humoral) immunity before
there is sufficient IgG.
Cytokines are a broad and loose category of
small proteins that are important in cell
Cytokines modulate the balance between
humoral and cell-based immune responses,
and they regulate the maturation, growth, and
responsiveness of particular cell populations.
Each cytokine has a matching cell-surface
Cytokines are often involved in several
developmental processes during
Cytokines are crucial for fighting off