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Histology of Lymphatic System
Histology of Lymphatic System
52
Histology
Professional
10/01/2013

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Term
two semi-independent parts of the lymphatic system
Definition
• Lymphatic vessels
• Lymphoid tissues and organ
Term
o Lymphatic system functions
Definition
• Transport fluids back to the blood
• Play essential roles in body defense and resistance to disease
Term
What types of pumps propel lymph through the vessels?
Definition
NO PUMPS!
Skeletal (milking action) and Smooth muscle (rhythmic contraction) propel the lymph through the vessels
Term
Name the various types of vessels in lymphatic tissue
Definition
Lymph Capillaries

Collecting Vessels
Term
Flap-ike minivalves are present in which type of lymph vessels
Definition
Lymph capillaries
Term
How does lymphatic fluid leak into lymph capillaries?
Definition
significant gaps and spaces between endothelial cells
Term
How are lymph capillaries anchored to connective tissue?
Definition
By filaments, which hold and maintain space and position of capillaries in surrounding tissue
Term
What causes minivalves in lymphatic cpaillaries to close?
Definition
High pressure on the inside closes mini valves.
Term
What types of harmful materials enter lymph vessels?
Definition
Bacteria, viruses, cancer cells, cell debris
Term
Which materials are returned to the blood through the endothelium via lymph?
Definition
water, blood cells, proteins
Term
Purpose of collecting vessels in lymphatic system?
Definition
• Collects lymph from lymph capillaries
carries lymph TO and AWAY from lymph nodes

Returns fluid to the circulatory veins near the heart

Right lymphatic duct & Thoracic duct
Term
o After exchange in the tissue, then the collecting vessels bring the lymph back to the heart via the.......
Definition
right lymphatic duct
Term
Two lymph ducts
Definition
Right lymphatic duct & Thoracic duct
Term
Purpose of lymph ducts
Definition
drain lymph fluid
Term
• Components of the Lymphatic System
Definition
o Circulating lymphocytes
Lymphatic nodules
Lymph nodes
Term
Is diffuse lymphatic encapsulated?
Definition
NO
Term
Where is diffuse lymphatic tissue found?
Definition
mucosa of the digestive tract, respiratory tree, and genitourinary tract
Term
Diffuse lymphatic tissue is located below the epithelium in the.....
Definition
lamina propria
Term
Lymphatic Nodules (lymphatic follicles)
Definition
high concentrations of lymphocytes but not surrounded by capsulated
Term
Examples of lymphatic nodules are found where?
Definition
tonsils, Peyer's patches, appendix
Term
what happens to lymphatic nodules when exposed to antigens?
Definition
enlargement/ swelling

upon infection, cells undergo rounds of cell division
Term
Are lymph nodes encapsulated?
Definition
Yes, they are defined by the capsule
Term
Purpose of lymph nodes
Definition
• important filter for lymph (which collects tissues from body fluids) as it makes it's way to blood vascular system

removes it or triggers and immune response

contains macrophages(non specific) in medulla and lymphocytes (specific) in cortex
Term
Mucosa-Associated Lymphatic Tissue (MALT)
Definition
acts as a sentinel (capture & kill) to protect respiratory & digestive tracts

• Contain T & B cells
Term
Which lymphatic components are included in MALT?
Definition
 Peyer’s patches
 Tonsils
 Other small accumulations of lymphoid tissue
Term
Where are Peyer's patches found?
Definition
wall of the small intestine
Term
Purpose of Peyer's patches
Definition
o Capture and destroy bacteria in the intestine
o Classified as a lymphatic nodule
o Concentrations of lymphocytes
Term
2 components of lymph nodes
Definition
cortex and medulla
Term
Medullary component of lymph node
Definition
• Inner part
• Contains phagocytic macrophages
• Stain lighter b/c they contain less lymphocytes
Term
Cortex component of lymph node
Definition
• Outer part
• Contains follicles – collections of lymphocytes
Term
Describe Flow of Lymph Through Nodes
Definition
Lymph first comes in contact with the capsule, which branches out and continues into the parenchyma via teh trabeculae
enters cortex through AFFERENT lymphatic vessel
Flows through sinuses inside the node
Exits through Efferent
Term
Why are there fewer efferent than afferent?
Definition
causes flow to be slowed
Term
Hilum
Definition
o On the concave surface (Hilum) vessels take the lymph fluid out of the node
Term
high endothelial venules (HEV)
Definition
• Enable lymphocytes circulating in the blood to directly enter the lymph nodes

have a columnar shape
Term
What types of fibers support macrophages and lymphocytes in the medulla?
Definition
Reticular fibers
Term
Other Lymphoid Organs that contribute to the lymphatic function
Definition
o Spleen
o Thymus
o Tonsils
o Peyer’s patches
Term
Purpose of the spleen
Definition
destroys worn out blood cells

forms blood cells in the fetus

acts as a blood reservoir
Term
White pulp of the spleen
Definition
high concentration of lymphocytes surrounding a branch of the splenic artery

stains very dark because of dense heterochromatin in nuclei
Term
Peri-Arietal Lymphatic Sheath (PALS)
Definition
the accumulation of lymphocytes investing the central arteries of the spleen and comprising the white pulp
Term
Red Pulp of the spleen
Definition
• filters and degrades erythrocytes

• consists of splenic sinuses and splenic cords
Term
Cords of Bilroth
Definition
• consists of splenic sinuses and splenic cords
Term
Describe the sinuses of the spleen
Definition
cells are NOT tightly attached to neighbor to facilitate old red blood cells to come in
Term
Describe the splenic cords
Definition
Contain loose connective tissue including macrophages for erythophagocytosis
Term
Purpose of Thymus
Definition
Production of mature and immature T-cells

encapsulated

become less effective with age

peak levels only during childhood

Produces hormones (like thymosin) to program lymphocyte production
Term
Thymic Lobules
Definition
established by the thymic lobules

where mature and immature T cells are produced
Term
thymocytes
Definition
T-cells of the thymic cortex
Term
Are macrophages present in the thymic medulla?
Definition
no macrophages present
Term
Hassall's Corpuscles
Definition
synthesis of thymic hormones

Tightly packed concentric arrangement of epithelial-like squamous cells

• Hallmark of thymic medulla

includes desmosomes, keratinohyalin granules, hyaline
Term
Purpose of tonsils
Definition
trap and remove bacteria and other foreign materials
Term
What causes tonsillitis?
Definition
congestion of bacteria
Term
Histological characteristics of tonsils
Definition
Crypts, stratified squamous epithelium, lymphatic nodules, and connective tissue.
Term
• Waldeyer’s Ring
Definition
o Collection of tonsils monitoring the oral cavity, nasal cavity, and pharynx
o Allows exposure of entering pathogens to lymphocytes in the tonsils
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