Download lymphatic vessels

Practical histology
The lymphatic system
is a network of tissues and organs that primarily consists of lymphatic
vessels, which transport interstitial fluid (lymph) back to the blood
circulation, and the lymphoid organs which house lymphocytes and other
cells of the body’s immune defense system.
Primary lymphoid organs are the bone marrow and thymus, where B and
T lymphocytes are formed respectively.
The secondary lymphoid organs include the lymph nodes, mucosa—
associated lymphoid tissue (MALT), and spleen.
The lymphatic vascular system is closely associated with the circulatory
system. Its composed of vascular channels that drain extracellular fluid
called lymph from the tissues.
The walls of lymph vessels show more permeability than the walls of blood
capillaries because the endothelium in the lymph capillaries is extremely
thin.
Lymph node
Each L.N contain an outer cortex and an inner medulla.
The lymph node is surrounded by a pericapsular adipose tissue that contain
blood vessels.
A dense connective tissue capsule surround the node.
Inferior to the capsule is the subcapsular (marginal) sinuses that continue on
both sides of the trabecula as trabecular sinuses.
From the capsule , connective tissue trabeculaeextend into the node initially
between the lymphatic nodules.
The trabeculae connective tissue contain the major blood vessels of the
lymph node.
Afferent lymphatic vessels with valves in the capsule penetrate it to enter a
narrow space called subcapsular sinus from here, the sinuses(cortical
sinuses) extend along the trabeculae to pass into medullary sinuses.
The cortex of the L.N. contains numerous lymphocytes aggregations called
lymphoid nodule.
Some lymphoid nodule exhibit lighter-staining central area called germinal
center represent the active sites of lymphocyte proliferation.
The medulla consist of medullary cords and medullary sinuses.
medullary cords are networks of reticular fibers filed with plasma cells,
macrophages, and lymphocytes separated by capillary-like channels called
medullary sinuses.
Nerves, blood vessels and efferent lymphatic vessels are located in the hilus.
Regions of a lymph node. A low—magnification section of a lymph node showing the
three functional regions: the cortex (C), the paracortex (P), and the medulla (M).
Connective tissue of the capsule (CT) completely surrounds each lymph node and
extends as several trabeculae (T) throughout the lymphoid tissue. Major spaces for
lymph flow are present in this tissue under the capsule and along the trabeculae.
The lymphatic system
Lymphoid nodules (LN) are normally restricted to the cortex and the medulla is
characterized by sinuses (MS) and cords (MC) of lymphoid tissue. X40.
The thymusgland
is a lobulated lymphoid organ enclosed by a
connective tissue capsule from which arise connective tissue trabeculae
The trabeculae extend into the interior of the organ and subdivided the
thymus gland into numerous incomplete lobules .
Each lobule contain of outer cortex (dark staining) and inner medulla
(light staining) because the lobules are incomplete, the medulla shows
continuity between the neighboring lobules
The thymus, an encapsulated, bilateral organ in the mediastinum, is subdivided by connective tissue
(CT) septa into connected lobes. Lobes of an active thymus shown have peripheral regions of cortex
(C), where basophilic lymphocytes are fairly dense, and more central medulla (M) regions with fewer
lymphocytes. Besides the differences in location and cell density, the medulla region is characterized
by the scattered presence of distinct thymic corpuscles (arrow).
The cortexof each lobule contains densely packed lymphocytes that do not
form lymphatic nodules. in contrast the medulla contains fewer lymphocytes
but more epithelial reticular cells.Themedulla also contains numerous
thymic (Hassall) corpuscles which are oval structures consist of round or
flattened epithelial cells.
The spleenis a large lymphoid organ with a rich blood supply. Its
surrounded by a dense connective tissue capsule from which arise
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connective tissue trabeculae that extend deep into the spleen´s interior and
may contains blood vessels.
The spleen is consist of white pulp and red pulp:
The white pulp is the immune component of the spleen and consists mainly
from lymphatic nodules, germinal center, and central artery.
Red pulp containsvenous sinuses,and splenic cords.
The picture shows The capsule (C) of the spleen connects to trabeculae (T) which
partially subdivide the pulp—like interior of the organ. The red pulp (R) occupies
most of the parenchyma, with white pulp (W)
restricted to smaller areas, mainly around the
central arterioles.
Names of these splenic areas refer to their
color in the fresh state: red pulp is filled with blood cells of all types, located
both in cords and sinuses; white pulp is lymphoid tissue.
Differences between spleen and lymph node
The spleen does not exhibit a distinct cortex and medulla as seen in lymph
nodes. However lymphatic nodules are found throughout the spleen.
In addition, the spleen contains venous sinuses, in contrast to lymphatic
sinuses that are found in the lymph nodes.
The spleen also does not exhibit subcapsular or trabeculae sinuses
The capsule and trabeculae in the spleen are thicker than those around the
lymph nodes and contain some smooth muscle cells.
Langerhans cells
The lymphatic system
Langerhans cells are dendritic antigen—presenting cells of the epidermis
and other epithelia of body surfaces, where they comprise an important
defense against pathogens.
they develop in the bone marrow, move into the blood circulation, and
finally migrate into stratified squamous epithelia.
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