8: lymphatic vessels and lymphoid tissue - · pdf filelymphatic vascular system functions...
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8: Lymphatic vessels
and lymphoid tissue
nur
Lymphatic vascular system
Functions
return to the blood extracellular fluid (Lymph) from connective tissue spaces.
ensures the return of water, electrolytes and plasma proteins to the blood.
i.e plays a key role in homeostasis of the volume of extracellular fluid.
also returns lymphocytes from the lymph nodes to the blood
transports immunoglobulins (antibodies) from the lymphnodes to the blood.
Lymph capillaries
in most organs close to blood capillaries
(an exception is the CNS, cartilage, bone,
bone marrow, placenta, teeth and thymus)
begin as small blind-ending tubes.
Have numerous valves
Similar in structure to blood capillaries but
thinner
lack a basal lamina
lack erythrocytes
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Lymph vessels drain into lymph nodes (for
filtration)
ultimately drain into two large lymphatic
ducts in the area at the base of the neck
thoracic duct,
right lymphatic duct)
to return the lymph to the blood.
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Lymphatic tissues
characterized by an abundance of lymphocytes
no lymphatic tissue in myeloid tissue
involved with lymphocyte production and
immune responses.
constant recirculation of lymphocytes
(especially T-lymphocytes) between the
lymph and blood.
When they encounter foreign molecules or cells
they activate a series of immune responses to
neutralize and destroy the invader.
TYPES OF LYMPHATIC TISSUE
3 basic types:
Loose lymphatic tissue
dominated by reticular cells and fibers
forms a loose, spongy network through which lymph
flow is slow and cells are temporarily trapped
Dense lymphatic tissue
dominated by large populations of closely aggregated
lymphocytes
Nodular lymphatic tissue (lymphatic nodules)
found in all the lymphatic organs apart from the
thymus.
Thymus
site where T-lymphocytes develop
Located in the anterior neck
First lymphoid tissue in embryonic dev’t
from epithelial outgrowths of primitive
pharynx
Lobulated and encapsulated
2 zones: cortex and medulla – density of
lymphocytes
Low mag of the thymus
Cortex
(C)
Medull
a
(M) C
C
M
M
Dark nuclei
= T-cells
Larger
nuclei =
endothelial
reticular
cells
Arrow =
Hassell’s
Corpuscle
High mag of the medulla of the thymus
Lymph Nodes
kidney-shaped structures situated along
lymphatic vessels
2 key functions
serve as in-line mechanical filters of lymph by
macrophages
Storage of B and T-lymphocytes
Encapsulated
capsule forms radial extensions: trabeculae - to
form incomplete compartments
lymph node is divided into two regions:
An outer cortical region
An inner medullary region
2 key functions of lypmhnodes
Filtration of lymph by the macrophages
Storage of B and T-lymphocytes
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Diagram of a lymph node
Low mag of a lymph node
Cx = cortex w/ lymphatic nodules (F); M = medulla; C = CT capsule
A lymphatic nodule with germinal center (GC)
Non-encapsulated Lymphatic
Nodules
temporary structures, which may appear
and disappear in the same site
lack a connective tissue capsule
mainly composed of dense aggregates of
small B-lymphocytes
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Structure cells at the center of the nodule are much
larger, with more cytoplasm
less-stained central area is known as the
germinal center - develops according to
the functional state of the nodule
ring of small B-lymphocytes surrounding
the germinal center is referred to as the
corona or mantle zone
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Cell types of the germinal center include
activated B-lymphocytes (B-immunoblasts)
mitotic cells
plasma cells
dendritic reticular cells
macrophages
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Peyers Patches = lymphatic nodules in the ileum
Low mag of a palatine or lingual tonsil
Palatine Tonsil w/ SS
non-K (arrow)
Pharyngeal Tonsil w/ Resp
epith (arrow = nodule)
The Spleen
largest lymphatic organ of the circulatory system
acts as a blood filter to defend against
microorganisms that succeeded to penetrate the
blood system
aged erythrocytes are broken down and destroyed by
macrophages
site of formation of activated lymphocytes
responds promptly to antigens carried in the
blood. Infection can result in an enlarged spleen
(splenomegaly)
fetal spleen (months 4-6) is hematopoietic
(producing granulocytes and erythrocytes)
Structure
dense connective tissue capsule, with
connective tissue trabeculae
White pulp
lymphatic tissue surrounding arteries and
nodules
Red pulp
sponge composed of cords of cells (splenic
cords) and splenic sinusoids (venous
sinusoids)
Splenic cords (Billroth cords) are
composed of :
reticular cells and fibers
fixed and wandering macrophages
lymphocytes
plasma cells
blood cells (erythrocytes, granulocytes) and
platelets
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Diagram of the Spleen
White pulp
(lymphatic nodules)
Thick CT capsule
CT Trabeculae
Red Pulp
CT
Trabeculae
Low magnification of the Spleen
CT Trabeculae
Lymphatic
nodules
White pulp
Red
Pulp
Splenic circulation
Splenic artery
enters at the hilum and divides into trabecular
arteries
Trabecular arteries
completely surrounded by a sheath of T-
lymphocytes (periarterial lymphatic sheath or
PALS)
Central arteries (or central arterioles)
penetrate the lymphatic nodules, usually in
the periphery
Lead to sinusoids
Circulatory System in the Spleen
White Pulp
White Pulp
Red Pulp
Red Pulp
High mag of the splenic red pulp
Break
1. In the next session:
Gastro-intestinal system and
Respiratory system
2. Review : lymphatic system nur