Download The Lymphatic System

The Lymphatic System
Anatomy & physiology
Dr.Ryan G.AlGhanemi
Overview of the lymphoid immune system
Lymphocytes evolve from pluripotent stem cells located in
the bone marrow, and differentiate into two major
functional cell types:
1. B lymphocytes, comprising the humoral immune system,
whose ultimate function is the production of antibodies
2. T lymphocytes, comprising the cellular immune system,
whose functions include
a. Direct killing of foreign or intracellularly infected
cells, cytotoxic T cells,
b. Fine control of the immune response through the
secretion of cytokines, helper and suppressor T cells.
Overview of the lymphoid immune system
The anatomical organization of the lymphoid immune
system can also be divided into two major functional
groups:
1. The primary immune organs, which are the sites of
initial maturation from immature precursors into
immune competent cells:
a. B cells- bone marrow
b. T cells- thymus
Overview of the lymphoid immune system
2. The secondary immune organs, which are the sites of
antigen driven replication and differentiation into
committed effector cells
a. Lymph nodes
b. Spleen
c. Mucosal Associated Immune System (MALT)lymphoid cells lining the respiratory and
gastrointestinal tracts
d. Everywhere else
LYMPHATIC SYSTEM consists of:
complex capillary networks which collect the lymph in the
various organs and tissues.
collecting vessels which conduct the lymph from the
capillaries to the large veins of the neck at the junction of
the internal jugular and subclavian veins, where the lymph
is poured into the blood stream.
lymph glands or nodes which mainly filtering the lymph as
it passes through them and contributing lymphocytes to it.
Lymphatic System is developmentally an offshoot of the
venous system
In the human embryo the lymph sacs from which the
lymphatic vessels are derived are six in number; two paired,
the jugular and the posterior lymph-sacs; and two unpaired,
the retroperitoneal and the cisterna chyli. “ at the junction of
certain of the embryonic veins”
These lymph-sacs are developed by the confluence of
numerous venous capillaries.
Initially lose their connections with venous system, but
subsequently, on the formation of the sacs regain them.
The lining walls of its vessels are always endothelial.
Lymphatic System is Developmentally an Offshoot Of
The Venous System
From the lymph-sacs the lymphatic vessels bud out along
fixed lines corresponding more or less closely to the course
of the embryonic blood vessels.
Lymphatic vessels have been found in nearly every texture
and organ of the body which contains blood vessels.
Such non-vascular structures as cartilage, the nails, cuticle,
and hair have none, but with exceptions
Lymphatic System is Developmentally an Offshoot Of
The Venous System
Both in the body-wall and in the wall of the intestine, the
deeper plexuses are the first to be developed; by continued
growth of these the vessels in the superficial layers are
gradually formed.
All the lymph-sacs except the cisterna chyli are, at a later
stage, divided up by slender connective tissue bridges and
transformed into groups of lymph glands.
Lymphatic Capillaries
The complex capillary plexuses which consist of a single
layer of thin flat endothelial cells lie in the connectivetissue spaces in the various regions of the body to which
they are distributed and are bathed by the intercellular tissue
fluids.
That mode of covering help the physical process of
filtration, diffusion and osmosis, as well as active secretory
function.
lymph fluid is colorless plasma like fluid with more
lymphocytes & frequently red blood corpuscles.
Lymphatic Capillaries
The lymphatic capillary plexuses vary greatly in form:
Anastomoses are usually numerous
blind ends or cul-de-sacs are especially common in the
intestinal villi, the dermal papillae and the filiform
papillae of the tongue.
The plexuses are often in two layers: a superficial and a
deep, the superficial being of smaller caliber than the deep
and thery varies between micromillimeters to one
millimeter
The capillaries are without valves.
Distribution
The Skin:- Lymphatic capillaries are abundant in the dermis
where they form superficial and deep plexuses, the former
sending blind ends into the dermal papillae.
The plexuses are especially rich over the palmar surface and
plantar surface.
The epidermis and subcutaneous tissue without capillaries.
The Muscle:- The tendons of striated muscle and muscle
sheaths are richly supplied. In muscle, however, their
existence is still disputed.
The bone:- The periosteum of bone is richly supplied and
they have been described in the Haversian canals. They are
absent in cartilage and probably in bone marrow.
Lymphatic Vessels
The larger lymphatic vessels are each composed of three coats:
The internal coat: is thin, transparent, slightly elastic, and
consists of a layer of elongated endothelial cells with wavy
margins by which the contiguous cells are dovetailed into
one another; the cells are supported on an elastic membrane.
The middle coat: is composed of smooth muscular and fine
elastic fibers, disposed in a transverse direction.
Lymphatic Vessels
The external coat: consists of connective tissue, intermixed
with smooth muscular fibers longitudinally or obliquely
disposed; it forms a protective covering to the other coats,
and serves to connect the vessel with the neighboring
structures.
The thoracic duct has a more complex structure than the
other lymphatic vessels
Lymphatic Valves
The lymphatic vessels are formed of thin layers of fibrous
tissue covered on both surfaces by endothelium which
presents the same arrangement as on the valves of veins.
In form the valves are semilunar; they are attached by their
convex edges to the wall of the vessel, the concave edges
being free and directed along the course of the contained
current.
Usually two such valves, of equal size, are found opposite
one another; but occasionally exceptions occur, especially
at or near the anastomoses of lymphatic vessels. Thus, one
valve may be of small size and the other increased in
proportion.
Lymphatic Valves
In the lymphatic vessels the valves are placed at much
shorter intervals than in the veins.
They are most numerous near the lymph glands, and are
found more frequently in the lymphatic vessels of the neck
and upper extremity than in those of the lower extremity.
Lymphatic Valves
The wall of the lymphatic vessel immediately above the
point of attachment of each segment of a valve is expanded
into a pouch or sinus which gives to these vessels, when
distended, the knotted or beaded appearance.
They are interrupted at intervals by constrictions, which
give them a knotted or beaded appearance; these
constrictions correspond to the situations of valves in their
interior.
Lymph Glands (lymphoglandulae)
The lymph glands are small oval or bean-shaped bodies
Situated in the course of lymphatic and lacteal vessels so that the lymph
and chyle pass through them on their way to the blood.
Each generally presents on one side a slight depression—the hilus—
through which the blood vessels enter and leave the interior.
The efferent lymphatic vessel also emerges from the gland at this spot,
while the afferent vessels enter the organ at different parts of the
periphery.