The lymphatic system acts as a filter against microbes and other debris. It comprises lymph fluid, lymph corpuscles like lymphocytes, and lymphoid organs like lymph nodes and the spleen. Lymph nodes filter lymph and mount immune responses, while the spleen filters blood and produces immune cells. Together they defend the body against infection.
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Lymphatic system by yogesh patel GRYIP borawan
1. 6.
Lymphatic system
Lymph and lymphatic system,
composition, function and its
formation.
Structure and functions of spleen
and lymph node.
2. Composition, function and formation
of Lymph
Lymph is a colourless fluid that circulates throughout the lymphatic
system. The main role of the lymphatic system is to act as a filter
against microbes, organic wastes, toxins and other debris. It carries
lymphocytes throughout the body that fight against infections.
Composition of Lymph
The lymphatic system comprises lymph plasma, lymph corpuscles and
lymphoid organs. The composition of lymph is described below:
1. Lymph Plasma
Lymph is the interstitial fluid. It has similar mineral content as in
plasma. It consists of less calcium, few blood proteins, less
phosphorus, and high glucose concentration. Globulin proteins which
are actual antibodies are found in lymph plasma. Other substances
include organic and inorganic substances. The exchange of nutrients
and gases between the blood and cells of tissues occurs through the
lymph.
3. 2. Lymph Corpuscles
These comprise leucocytes and amoeboid cells. It contains
specialised lymphocytes that are involved in eliciting immune
responses in the human body.
3. Lymphoid Organs
The lymphatic system consists of numerous lymph nodes deep
inside the body. These lymph nodes are connected to
lymphatic vessels which circulate the lymph throughout the
body. The lymph gets filtered at the lymph nodes.
The spleen, tonsils, adenoids and thymus all form a part of the
lymphatic system. The spleen is considered the largest
lymphatic organ in the system, which is located under the
ribcage, above the stomach, and exactly in the left upper
quadrant of the abdomen. Other parts of the lymphatic system
– tonsils, adenoids and thymus are located on either side of the
throat and neck.
4. Other Components of Lymph in Humans
• Carbohydrates
• Lymphocytes
• Creatinine
• Water – 94%
• Urea
• Chlorides
• Enzymes
• Proteins – Albumin, globulin, and fibrinogen
• Non-protein nitrogenous substances.
6. Function of Lymph: Lymph performs many important
functions. A few major functions of lymph are mentioned
below:
Nutritive:
It supplies nutrition and oxygen to those parts where blood
cannot reach.
Drainage:
It drains away excess tissue fluid and the metabolites and in
this way tries to maintain the volume and composition of
tissue fluid constant.
Transmission of Proteins:
Lymph returns proteins to the blood from the tissue spaces.
Absorption of Fats:
Fats from the intestine are also absorbed through the
lymphatics.
7. Defensive: The lymphocytes and monocytes of lymph act as
defensive cells of the body. The lymphatics also remove
bacteria from tissues.
• It keeps the body cells moist.
• It transports oxygen, hormones and nutrients to different
parts of the body and removes metabolic waste from the
cells.
• It transports antibodies and lymphocytes to the blood.
• Maintaining the composition of tissue fluid and the
volume of blood.
• Absorption of fats from the small intestine occurs through
lymphatic vessels.
• Prevents invasion of microbes and foreign substances
inside the lymph nodes.
8. Formation of Lymph: lymph is formed from tissue fluid,
anything that increases the amount of tissue fluid will increase
the rate of lymph formation. Lymph formation depends upon
physical factors. The following factors are responsible for lymph
formation:
1. Capillary Pressure:
If the capillary pressure is raised, the rate of lymph formation
increases. This is seen in venous obstruction. [But after some
time, the rate slows down due to increased accumulation of fluid
in the tissue spaces and the consequent rise of hydrostatic
pressure of the tissue fluid.]
9. 2. Permeability of the Capillary Wall:
Under any condition, where the permeability of the capillary
wall is increased, more tissue fluid will be formed and
consequently more lymph.
3. Substances that Alter the Osmotic Pressure:
Anything that reduces the colloidal osmotic pressure of
blood will increase the formation of tissue fluid and lymph.
Normal or hypotonic saline, when given intravenously, will
dilute the plasma colloids and reduce the osmotic pressure.
Moreover, blood pressure will be raised. Both these factors
will favour formation of tissue fluid and lymph. Hypertonic
solutions will exert the same effect in a better way.
10. 4. Increased Metabolic Activity of an Organ:
Increased activity of a particular area increases the flow of lymph
in the locality
It is due to:
• Formation of more metabolites which increase the osmotic
pressure of the tissue fluid.
• Local vasodilatation and increased capillary pressure and
permeability.
11. Spleen
The spleen is a large, encapsulated, bean-shaped organ that is
situated on the left side of the body below the diaphragm. The
spleen contains T and B lymphocytes as well as many
phagocytes and is a major component of the mononuclear
phagocyte system.
Although the structure resembles that of the large lymph nodes,
the spleen differs from a lymph node in having no lymphatic
drainage, and also in containing large numbers of red cells.
12. Structure of Spleen
• It is a dark purple-coloured organ, which lies in the left
hypochondriae region of the abdomen, between the
fundus of the stomach and the diaphragm.
• It varies in size and weight during the lifetime of an
individual but in an adult is usually about 12 cm long,
8cm broad and 3-4 cm thick weighing about 200gm.
• The spleen has diaphragmatic and visceral surfaces.
The diaphragmatic surface is in contact with the inner
surface of the diaphragm.
• The spleen has an outer coat of peritoneum which is
firmly adherent to the internal fibro-elastic coat or
splenic capsule that dips into the organ, forming
trabeculae.
13. The spleen has a spongy interior called splenic pulp. The
splenic pulps are of two kinds:
White Pulp:
• It consists of periarteriolar sheaths of lymphatic tissue with
enlargements called splenic lymphatic follicles containing
rounded masses of lymphocytes.
• These follicles are center of lymphocytes production called
primary lymphoid follicles, composed mainly of follicular
dendritic cells (FDC) and B cells.
• They are visible to the naked eye in freshly cut surface of
the spleen as whitish dots against the dark red background
of red pulp.
• The white pulp forms ‘islands’ within a meshwork of
reticular fibers containing red blood cells, macrophages and
plasma cells (red pulp).
14. Red Pulp:
• It consists of numerous sinusoids containing blood, separated
by a network of perivascular tissue which is referred to as the
splenic cords.
• The splenic cords contain numerous microphages abd are the
site of intense phagocytes activity.
• They also contain numerous lymphocytes, which are derived
from the white pulp.
17. Functions of Spleen
1. The main immunological function of the spleen is to filter the blood by
trapping bloodborne microbes and producing an immune response to
them. It is particularly important for B cell responses to polysaccharide
antigens.
2. The spleen is formed partly by lymphatic tissue which produces T
lymphocytes and B lymphocytes.
3. Due to the presence of lymphoid reticulo-endothelial tissue, the spleen
is involved in producing antibodies and antitoxin.
4. In the foetus, the spleen acts as an important haemopoitic organ.
5. It also removes damaged red blood cells and immune complexes.
6. It can act as an erythropoietic organ which acts as a reservoir of
erythrocytes or a reservoir for blood.
7. Those individuals who have had their spleens removed
(splenectomized) have a greater susceptibility to infection with
encapsulated bacteria, and are at increased risk of severe malarial
infections, which indicates its major importance in immunity.
18. Lymph node
Lymph nodes are small solid structures placed at varying points
along the lymphatic system such as the groin, armpit and
mesentery.
• They contain both T and B lymphocytes as well as accessory
cells and are primarily responsible for mounting immune
responses against foreign antigens entering the tissues.
• Lymph nodes are situated at strategic positions throughout the
body and serve to filter the lymph.
19. Structure of Lymph Nodes
• They range in size from 2 to 10 mm, are spherical in shape
and are encapsulated.
• Lymph node is surrounded by a fibrous capsule which dips
down into the node substance forming partition or
trabeculae.
• The node is made by reticular and lymphatic tissues
containing mainly lymphocytes and macrophages.
• Beneath the capsule is the subcapsular sinus, the cortex, a
paracortical region and a medulla.
• The cortex contains many follicles and on antigenic
stimulation becomes enlarged with germinal centers.
20. • The follicles are comprised mainly of B cells and follicular
dendritic cells.
• The paracortical (thymus-dependent) region contains large
numbers of T cells interspersed with inter digitating cells.
• Each lymph node has 4-5 afferent vessels that bring lymph to
the node while only one efferent vessel draining lymph away
from the node.
• It also has a concave surface called the hilum where an artery
enters, a vein and the efferent lymph vessel leave.
• Depending upon the position, the lymph nodes may be
superficial or deep lymph nodes. Groups of lymph nodes are
present in the neck, collarbone, under the arms (armpit), and
groin.
22. Lymph Circulation in Lymph Nodes
1. Lymph arriving from the tissues or from a preceding lymph
node in the chain, passes via the afferent lymphatics into the
subcapsular sinus and then into the cortex, around the
follicles, into the paracortical area and then into the medulla.
2. Lymph in the medullary sinuses then drains into efferent
lymphatics and hence through larger lymphatic vessels back
into the bloodstream.
23. Functions of Lymph Nodes
1. The primary role of the lymph node is to filter the lymph
and then produce an immune response against trapped
microbes/antigens.
2. Filtering of the lymph helps in removal of particles not
normally found in the serum.
3. The lymphoide tissues in the nodes break down materials
which have been filtered off such as microorganisms,
tumor cells and cells damaged by inflammation.
4. Lymphocyte develops from the reticular and lymphoid
tissue in the nodes.
5. Antibodies and antitoxins are also formed by the cells of
lymph nodes.