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83 Cards in this Set

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What is the major cellular component of the immune system?
Lymphocytes
2 main types of immune system organs:
-Primary lymphatic organs
-Secondary lymphatic organs
What are lymphocytes a type of?
WBC
T lymphs mature in____
B lymphs mature in ____
T in Thymus
B in Bone marrow
Where are clusters of lymphocytes found?
In lymph nodes, tonsils, and spleen.
Where are smaller aggregates of lymphocytes found?
In MALT
Are lymphocytes part of innate or adaptive immunity?
Adaptive
What are Bcells responsible for?
Humoral immunity
What are Tcells responsible for?
Cell mediated immunity
What is the characteristic microstructure of a plasma cell?
-Clock faced heterochromatin
-Eccentric nucleus
-Extensive rER
-Perinuclear golgi apparatus
What does the structure of a plasma cell indicate about its function?
It is a very active cell that is intensely making and secreting protein for export (Antibody)!
What are the 5 Ig types made by Bcells?
GAMED
What is the thymus surrounded by?
Loose connective tissue CAPSULE
What does the capsule do?
Extends into the thymus as SEPTAE
What do the capsular septae divide the thymus into?
Lobules
What lies within the septae of the thymus?
-Blood vessels
-Nerves
-Efferent lymphatic vessels (?)
What differentiates the cortex and medulla of the thymus?
Cortex = basophilic
Medulla = paler
Why are the medullary portions of adjacent lobules continuous?
Because septae only penetrate the thymus to the cortico-medullary junction.
Where in the thymus are thymocytes more concentrated?
In the cortex
What happens to immature thymocytes if they survive positive selection in the cortex?
They migrate to the medulla to undergo negative selection
What happens to Tcells that survive negative selection in the medulla?
They enter efferent lymphatic vessels and go to 2ndary lymphatic organs or other tissues.
What cells are in the thymus other than lymphs?
Epithelial cells
What links epithelial cells to form a supportive scaffolding for thymocytes?
Dendritic processes, connected by Desmosomes
How is the supportive scaffold in the thymus unique from other lymphatic organs?
Most lymphatic organs have a scaffold of reticular fibers
What happens to thymocytes whose receptors bind weakly with peptide/mhc complexes presented by epithelial cells?
They die via PCD.
What percent of thymocytes survive positive selection?
2%
What are the onion shaped aggregates of eosinophilic epithelial cells in the medulla of the thymus?
Hassall's corpuscles
What do Hassall's corpuscles do?
Catabolize apoptotic thymocytes
What is the function of the Blood-thymus barrier?
To ensure that Tcells do not come in contact with foreign antigens during the process of negative selection.
What happens in secondary lymphatic organs?
Mounting of an immune response using the competent lymphocytes from the primary organs.
What are secondary lymphatic organs like?
Flimsy meshlike filter bags
What is the mesh? What is it made of it it's lymph nodes? What if it's spleen?
Stroma
-made of reticular fibers in lymph nodes
-made of combined smooth muscle and reticular fibers in spleen
What are the 'filter' components in lymph nodes?
-Tcells
-Bcells
-Macrophages
How are T/Bcells and Macrophages arranged in lymph nodes?
-Bcells are peripheral/cortical
-Tcells and macrophages in medulla
What is the filter component of the spleen?
White pulp
What does white pulp consist of?
-Follicles of Bcells
-PALS of Tcells
What is red pulp in the spleen?
Where RBCs are degraded
What are the small, blindended capillary-like structures that drain ECF from almost all tissue spaces?
Lymphatic capillaries
What happens to the lymph fluid in the lymphatic system before it is returned to the circulation via the thoracic duct?
It gets FILTERED by our meshlike filter bags - lymph nodes - to remove foreign antigens that may be floating in the ECF.
What makes up the stroma of the lymph node, and what is it for?
-Reticular fibers
-Fibroblasts
It slows the flow of lymph so it comes in good contact with lymphocytes and macrophages.
what surrounds lymph nodes?
A connective tissue capsule
What is the little space underneath the capsule?
Subcapsular sinus
What are the circular clusters in the cortex that are uniform in intesnsity? What do they consist of?
Primary lymphoid follicles - naieve Bcells that are quiescent.
What are the 2 visible features of a secondary lymphoid follicle?
-Mantle zone
-Light germinal center
What could be visible within the germinal center?
Mitotic figures
What happens as activated Bcells from germinal centers migrate to the medulla?
They form cellular tissues called Medullary cords separated by lymph-filled sinuses.
What do Bcells do when they get to the medulla of the lymph node?
Release their antibodies to the antigen they had reacted to to go into the general circulation.
What area lies between the cortex and medulla of the lymph node?
Paracortex
What cell dominates the paracortex?
T cells
What other important structure is in the paracortex?
High endothelial venules
Why do lymph nodes ABSOLUTELY NEED high endothelial venules?
Because that's where lymphocytes from the blood enter the nodes via homing receptors.
What does a germinal center in a lymph follicle indicate?
That new B cells are being produced in response to an antigenic stimulus
What does a high endothelial venule do?
Serves as the conduit by which lymphocytes enter and are sequestered in lymph nodes.
When you palpate a patient's "swollen glands" what are you really palpating?
lymph nodes that are enlarged and have triggered a pain response.
What does the carbon stain show in a lymph node?
The reticular stroma
What cells sequester carbon?
Macrophages
Where the lymph nodes filter foreign antigens from lymph, what does the spleen do?
Filters them from blood
On an H/E slide of spleen, what color is red pulp? White pulp?
Red = red - RBCs
White = blue - WBCs
What does red pulp consist of?
Blood-filled sinusoids
What separates these sinusoids?
Cords of densely packed lymphocytes which are White pulp
What is the approx age of RBC?
120 days
When small branches of the splenic artery enter the substance of the spleen, what are they surrounded by?
Periarterial lymphatic sheath
What type of cell is in PALS?
Tcells
What is within PALS?
Lymphoid follicles of Bcells
What are the vessels that are surrounded by PALS?
Central arterioles
What do the arterioles and surround PALS together make up?
White pulp
What fibers are abundant in the splenic capsule, trabeculae, and blood vessel tunics?
Reticular fibers
What are 3 solid organs that have a stroma composed of reticular fibers?
-Spleen
-Lymph nodes
-Liver
What do we remember makes up the stroma of the thymus?
Epithelial cells
What type of epithelium covers the surface of the palatine tonsil?
Stratified squamous
What are the tonsils an example of?
Isolated lymphatic tissue
How are the palatine tonsils organized?
Into crypts, with follicles that are lined up along them.
What do we call the structure of the palatine tonsils?
Organized follicles
What is the function of the lymphatic tissue that encircles the entrance to the GI tract?
To protect the GI tract by reducing the number of foreign pathogens entering it.
In what other areas of the body would you find isolated lymphatic tissue organized as lymphatic follicles?
-Gastrointestinal tracts
-Urinary tracts
-Respiratory tracts
-Reproductive tracts
Where isolated lymphatic tissue forms organized follicles in the tonsils, what does it ALSO form in the ileum?
Diffuse lymph aggregates
Looking at the ileum, what are intensely basophilic structures just under the GI tract epithelium?
ORGANIZED lymph follicles
What is in the lamina propria of the epithelium?
DIFFUSE lymph aggregates
What cells make up diffuse lymph aggregates?
-Lymphocytes
-Plasma cells
-Eosinophils
What is the acronym for lymphatic tissue in the GI tract?
GALT
Plasma cells are the differentiated product of what cell type?
B cells
If plasma cells are intensely secreting antibody, why don't they have more heterochromatin?
Because it's all the same type of antibody - don't need all their genes active.
What are large collections of lymph follicles in the ileum called?
Peyer's patches