LYMPHATIC SYSTEM
Lymphatic system is a closed system of
lymph channels or lymph vessels, through which lymph flows. It
is a one-way system and
allows the lymph flow from tissue spaces toward the blood.
ORGANIZATION OF LYMPHATIC
SYSTEM
Lymphatic system arises from tissue
spaces as a meshwork of delicate vessels. These vessels are
called
lymph capillaries. Lymph capillaries
start from tissue spaces as enlarged blind-ended terminals called capillary bulbs. These
bulbs contain valves, which allow flow of lymph in only
one direction. There are some muscle fibers around these
bulbs. These muscle fibers cause contraction of bulbs
so that, lymph is pushed through the vessels. Lymph capillaries are
lined by endothelial cells. Capillaries unite to form large lymphatic
vessels.
Lymphatic
vessels become larger and larger because of the joining of many
tributaries along their course. The structure of lymph
capillaries is slightly different from that of the blood
capillaries. Lymph capillaries are more porous and the cells lie
overlapping on one another.
This allows the fluid
to move into the lymph capillaries and not in the opposite direction.
DRAINAGE OF LYMPHATIC
SYSTEM
Larger lymph vessels ultimately form
the right
lymphatic duct and
thoracic
duct. Right
lymphatic duct opens into right subclavian vein and the thoracic duct opens into left
subclavian vein. Thoracic duct drains the lymph from more
than two third of the tissue spaces in the body.
SITUATION OF LYMPH
VESSELS
Lymph vessels are situated in the
following regions:
1. Deeper layers of
skin
2. Subcutaneous
tissues
3. Diaphragm
4. Wall of abdominal
cavity
5. Omentum
6. Linings of
respiratory tract except alveoli
7. Linings of
digestive tract
8. Linings of urinary
tract 9. Linings of genital tract
10. Liver
11. Heart.
Lymph vessels are not present in the
following structures:
1. Superficial layers
of skin
2. Central nervous
system
3. Cornea
4. Bones
5. Alveoli of lungs.
LYMPH NODES
Lymph nodes are small glandular
structures located in the course of lymph vessels. The lymph nodes are
also called
lymph glands or lymphatic nodes.
STRUCTUTRE OF LYMPH
NODES
Each lymph node constitutes masses of
lymphatic tissue, covered by a dense connective tissue capsule.
The structures are arranged
in three layers namely cortex, paracortex and medulla Cortex Cortex
of lymph node consists of primary and secondary lymphoid follicles. Primary
follicle develops first. When
some antigens enter the body and reach
the lymph nodes, the cells of primary follicle proliferate. The active proliferation of the
cells occurs in a particular area of the follicle called the
germinal center. After proliferation of cells, the primary follicles become the
secondary follicle. Cortex also contains some B lymphocytes, which
are usually aggregated into the primary follicles. Macrophages
are also found in the cortex.
Paracortex
Paracortex is in between
the cortex and medulla. Paracortex contains T lymphocytes.
Medulla
Medulla contains B and
T lymphocytes and macrophages. Blood vessels of lymph node pass through
medulla.
Lymphatic Vessels to
Lymph Node
Lymph node receives lymph by one or
two lymphatic vessels called afferent vessels. Afferent vessels divide into
small channels. Lymph passes through afferent vessels and small channels
and reaches the cortex. It circulates through cortex, paracortex and medulla
of the lymph
node. From medulla, the lymph leaves the node via one or two efferent vessels.
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