Histo Midterm 2 - Lymphoid Organs Flashcards
What are the characteristics of lymphoid organs?
Consists of: bone marrow, lymph nodes, spleen, thymus, and MALT (mucosa-associated lymphoid tissue)
What are the primary lymphoid organs?
Sites where lymphocytes differentiate and develop the ability to recognize self from non-self.
Bone marrow - B lymphocytes
Thymus - T lymphocytes
What are secondary lymphoid organs?
Places where B and T lymphocytes encounter the antigen and immune response occurs
What is the role of the immune system and its functions?
Destroy microorganisms, cancer cells, and transplants
What can the immune response be?
Cellular - utilize T lymphocytes
Hormonal - utilize B lymphocytes
What are the cells of the Immune system?
B lymphocytes - produce colonies of plasma cells, need helper T’s to activate
T lymphocytes
- Helper T’s - make cytokines, activate macrophages and killer T’s
- Killer T’s - attack foreign cell directly by punching holes in the membrane or inducing apoptosis
Natural killer cells - no markers, only 10-15% of B’s in blood, attack: virus infected cells, transplant cells, and cancer cells
What is the role of the thymus as a primary immune organ?
Establishes immune system and cell-mediated immunity
Produce T-lymphocytes from stem cells from embryonic yolk sac
Produces hormone thymosin - acts as growth factors to stimulate production and differentiation of T-lymphocytes
What are some physical features of the Thymus?
Capillaries are non-fenestrated and have thick basal lamina, which forms thymic-blood barrier (prevents antigens from reaching cortex)
Cortex contains macrophages and themocytes
Stroma made up of stellate shaped epithelioreticular cells to form a cytoreticulum
Medulla contains epithelioreticular cells, differentiated T’s and thymic/Hassle’s Corpuscles (possible graveyard for incomplete lymphocytes)
What are some features of the spleen?
Largest lymphatic organ, blood filter, graveyard for RBCs, found in the left hypochondriac region, well defined hilum
Surrounded by a capsule with trabeculae (may have smooth muscle in both capsule and trabeculae)
What does the spleen consist of?
Splenic pulp - red pulp and white pulp
Stroma - reticular tissue
What is the white pulp/splenic nodules of the spleen?
have a central artery
mostly B lymphocytes
What are PALS?
Periarteriolar Lympatic Sheath - sheath of T cells that cover trabecular arteries leaving the trabeculae. These arteries become central arteries.
What is Red Pulp?
Contains venous sinusoids separated by splenic cords/cords of billroth (cellular partitions), reticular tissue with T and B lymphocytes, macrophages, plasma cells, and other blood cells
What are lymph nodes?
Secondary lymphatic tissue
Afferent lymphatic vessels enter through capsule
Efferent lymphatic vessels leave through hilum
What are the features of Lymph Nodes?
Stroma - reticular tissue
Parenchyma - lymphocytes
Cortex - nodules, diffuse lymphatic tissue
Medulla - medullary cords, sinuses
