Lymphatic System Flashcards
What is the overall function of the lymphatic system?
secondary defense system
What methods of defense are present in the lymphatic system?
- humoral immune system
- cell mediated immune system
- filtration of lymph and blood
What is the primary method of defense?
What type of response is elicited?
Primary method of defense: epithelial cells
Type of response elicited: innate or nonspecific
What cells are involved in the innate immune system?
- neutrophils
- macrophages
- NK cells = natural killer cells
Secondary response is also known by this name?
acquired or specific immune system
Humoral cells
- B lymphocytes
- antibodies
- plasma cells
Cell mediated cells
- T lymphocytes = cell-to-cell contact
- cytokines = chemical signals
T/F: Humeral and Cell-mediated cells are not completely separate from each other.
True
Two types of lymphatic tissues
- diffuse
- dense
Diffuse lymphatic tissues
loosely scattered lymphocytes beneath epithelial layers
ex - lamina propria of G.I. tract
Dense Lymphatic Tissue
- more compact
- usually in form of spherical structures (nodules)
What is an aggregated lymph nodule?
accumulations of many nodules
ex - Peyer’s patches
Where are Peyer’s patches located?
small intestine, specifically ILEUM!!
What are “tonsils”?
-areas with lymphoid tissues very closely associated with epithelium
Key sign of tonsils?
Lymphocytes invading the epithelium
crypts
deep invaginations of epithelium
Does lymphatic TISSUE have a capsule?
No
Do lymphatic ORGANS have capsules?
Yes
Location of Lymph Nodes
Occur in constant locations
Lymphocenters = lymph nodes always occur in the same places and drain the same area
Shape and structure of the Lymph Node
Shape:
- usually bean shaped
- have a hilus in concave area
Structure:
- capsule
- stroma
What does the capsule of the lymph node do?
surrounds the node
What is the stroma of the lymph node?
-supporting part of organ
- made of trabeculae that arise from capsule
- trabeculae then divide the parenchyma into smaller compartments
What is the parenchyma of the lymph node?
functional part of the organ
What is in lymph vessels to encourage the flow of lymph in only one direction?
well developed valves
Cortex of Lymph Nodes
- outer region of parenchyma
- contains lymph nodules = primary and secondary
- also contains lymph sinuses = subcapsular and trabecular
In what species is the cortex of the lymph node NOT the outer region of parenchyma?
swine and elephants
Appearance of Primary Lymph Nodules
homogeneous appearance
Appearance of Secondary Lymph Nodules
-contain a germinal center = lighter center that indicates previous Ag exposure
What is found in secondary lymph nodules?
How does what’s found here affect the coloring of secondary lymph nodules?
activated lymphocytes
-have more vesicular nucleus and contain more cytoplasm
This gives the paler appearance to the germinal center
2 Possible Fates of Activated B Lymphocytes
- become plasma cells
- become memory cells
Medulla of Lymph Nodes
-inner region (except for swine and elephants)
Parts of lymph node medulla
- medullary cords
- medullary sinuses
- trabeculae extending down into medulla
Medullary cords
-lymphatic tissue is in this form vs. being in nodules
Cords contain:
- lymphocytes
- plasma cells
- macrophages
- reticular cells
Medullary sinuses
lymph sinuses along medullary cords
Direction of Lymph Flow
- Afferent vessels enter capsule on convex surface of node and drain into subcapsular and trabecular sinuses
- Lymph percolates through cortical sinuses into medullary sinuses
- Lymphocytes are added
- Efferent vessels leave the organ at hilus of node
In swine and elephants, is the flow of lymph from the outside inward or from the inside outward?
Inside outward
Still flows afferent into cortex and efferent out of medulla
Generic Immune Response Example
- Dendritic cell presents antigen to B cell with matching antibody
- B cell becomes “activated” and rapidly divides
- Some B cells become plasma cells
- Some B cells become memory cells as well
After plasma cells are formed, what do they do?
- move to medullary cords
- secrete antibodies
Hemal Nodes
- small, dark lymphatic organs that resemble lymph nodes
- filter BLOOD instead of lymph
- primarily in ruminants, seen in horses and humans, along vertebral canal and associated with some visceral organs
- sinuses contain blood
- are like “little spleens”
What is the largest mass of lymphatic tissue in the body?
Is it necessary for life?
Spleen; No
Function of the Spleen
- filters blood
- removes old (effete) RBC and abnormal RBC (sickle cell anemia, malaria)
- removes antigenic material; participates in immune response
- also good for handling bacteremia = bacteria in the blood
What is the lifespan of RBC?
How does the spleen know to remove them?
Lifespan: 120 days
RBCs become less flexible as they age, making it harder for them to pass through capillaries
Structure of the spleen
- capsule
- trabeculae
- NO distinct cortex and medulla
- reticular CT making up stroma
Capsule of the spleen
- made of dense CT and smooth muscle
- amount of smooth muscle varies with species
- more smooth muscle in spleen than in lymph nodes
Where are the major arteries and veins located in the spleen?
In the trabeculae
What is one easy way to tell difference between spleen and lymph nodes?
Spleen does not have a cortex and medulla
The parenchyma of the spleen is made up of….
white and red pulp
What is the white pulp in the spleen?
lymphatic tissue in the spleen
What is the red pulp in the spleen?
- venous sinuses = sinusoids
- splenic cords
What is PALS? Where is it found? What does it contain mostly?
PALS = periarteriolar lymphoid sheath
Found in white pulp of spleen, around central arteries
Mainly contains T lymphocytes
What would an expanded PALS form? What is found mostly in this area?
An expanded PALS would form peripheral white pulp, mainly in the form of nodules
Mostly B lymphocytes are found here
The splenic sinuses, found in the red pulp of the spleen, help remove old RBCs how?
Splenic sinuses have long slits between the endothelial cells where old RBCs tend to be trapped for removal
What is extramedullary hemopoiesis?
formation of blood cells outside the bone marrow
Where does extramedullary hemopoiesis occur in the fetus?
spleen and liver
Can extramedullary hemopoiesis occur in adults? If so, where and why?
Yes
spleen and liver
If necessary, such as when bone marrow is damaged
What can be a sign of extramedullary hemopoiesis?
- Presence of large megakaryocytes in the spleen
- enlargement of spleen and liver
What is the area between white and red pulp called? What happens here?
Marginal zone
Often where an immune response is initiated d/t great amount of blood flow through the area
Blood flow in and out of the lung?
Splenic artery -> trabecular artery -> central artery -> splenic sinuses -> trabecular vein -> splenic vein -> portal vein
Types of Spleens
- defensive
- reserve
Defensive Spleen
- comparatively more white pulp
- very little smooth muscle
ex - human
Reserve Spleen
- comparatively less white pulp
- lot of smooth muscle
- can store blood
ex- horse, dog, cat
What type of spleens do ruminants have?
An intermediate between defensive and reserve types
Splenomegaly
-enlarged spleen
Causes:
- chronic infection
- autoimmune disease
- neoplasia
Function of the Thymus
- production of T lymphocytes
- endocrine organ
T/F Only a few T lymphocytes are killed off d/t potential for autoimmune reaction.
False.
Roughly 95% of T lymphocytes are eliminated d/t reaction with self
Structure of the Thymus
- stroma formed by epithelial reticular cells
- cortex
- medulla
Thymus is divided into lobules
Thymus DOES NOT contain lymph nodes!!!
What forms the blood-thymus barrier?
sheets of epithelial reticular cells
When is the thymus the largest?
Maximum size at birth
Involutes (atrophies) rapidly after puberty, but does not entirely disappear
Are there afferent lymphatics going to the thymus?
No
Bursa of fabricius
Avain
- found in dorsal wall of proctodeum
- important in humoral immunity
- “Bursal Equivalent” = some animals, bone marrow; others, Peyer’s patches
- Birds do not have lymph nodes
