cells and organs Flashcards
what are the primary lymphoid organs?
the Thymus and Bone Marrow - where immune cells develop
what are the secondary lymphoid organs?
Spleen, lymph nodes, MALT, GALT, SALT, etc - where the immune response is initiated
how are lymhoid organs interconnected to one another?
by blood vessels and the lymphatic system
what is the definition of hematopoiesis?
the formation of blood or blood cells
what are the hematopoeisis sites during fetal development?
red blood cell precursors are first found in the yolk sac around 3 weeks after fertilization. After 3-4 weeks of gestation, HSCs arise in distal aorta-gonad-mesonephros. They are they found in the fetal liver around 6 weeks after gestation, which becomes the primary site of hematopoeisis. eventually the blood marrow becomes the main site of hematopoeisis, about 5 months after gestation.
what is the job of stromal cells?
to regulate HSCs, i.e., quiescence, trafficking, and differentiation
what kind of cells include stromal cells?
macrophages, endothelial cells, perivascular cells, sympathetic nerves, and osteoblasts
what is hematopoeisis maintained by?
cytokines, produced by bone marrow stromal cells and non-hematopoietic cells such as T cells and macrophages. It is also maintained by regulation of receptors and removal of cells by programmed cell death.
what do self-renewing HSCs differentiate into?
all types of red-blood cells and white blood cells
what are white blood cells also called?
leukocytes
what two major types of progenitors do HSCs give rise to?
common myeloid progenitors and common lymphoid progenitors
what are cytokines and what is their role in the immune response?
they are a broad group of small proteins responsible for cell signalling (interferons, interleukins, colony growth factors)
what do cytokines must have to have in order to function as cell signallers?
a cognate receptor
what is apoptosis?
programmed cell death, that can be observed through morphological changes, i.e., cell blebbing, fragmentation, alteration of cell permeability, and the release of apoptotic bodies
what processes does apoptosis occur during?
- contraction phase of the immune response
- embryogenesis
- to suppress vestigial embryonic structure
- extended nutrient deprivation
- eliminating self-reacting lymphocytes
what is the main difference between apoptosis and necrosis?
necrosis causes inflammation and apoptosis does not. This is because during necrosis, disintegration of the cell occurs which releases intracellular contents. Whereas in apoptosis, cell blebbing occurs which keeps intracellar fragments in vesicles and is then ingested by phagocytes which degrade the material.
where do T cells mature?
in the thymus
what is the process of T cell maturation?
bone-marrow derived T cells enter the Thymus, where they travel up the cortex and undergo positive selection where they interact with nurse epithelial cells and mature. approximately 5% of T cells that enter the Thymus actually mature and differentiate. T cells then travel down the medulla where they undergo negative selection while interacting with nurse epithelial cells and DC’s, then exit the thymus. Through this process, they differentiate and gain specificity through acquiring different TCR’s
what happens with thymic volume?
as we age, thymic volume decreases soon after birth and the volume of true thymic tissue (thymocytes, epithelium, macrophages, etc) is replaced by adipose tissue
what is the spleen and why is it so important in the immune system?
the spleen is the major site of immune responses for “blood-borne” antigens/infection. Is it found behind the liver and over the kidney. The two main areas of the spleen are the red pulp and the white pulp. the red pulp is where hematopoeisis and delivery occurs, and the white pulp is where the lymphoid immune response occurs.
what are the two distinct areas of the white pulp in the spleen?
the T-cell area and the B-cell area
what is the role of lymphatic capillaries in the tissue?
they pick up interstitial fluid where it’s carried into larger lymphatic vessels into the regional lymph node
what are the three distinct environments of draining lymph nodes?
cortex & paracortex, follicles, and the medulla. The cortex and paracortex harbors macrophages, other Ag presenting cells and Th cells. B cells are found in the cortex which is located within follicles. The medulla carries the antibody producing plasma cells.
what are MALTs
Mucosal-associated Lymphoid Tissues. they represent about 50% of the lymphoid tissue and are often the first point of contact with an invading pathogen or other antigens. The role of MALT is to regulate mucosal immunity.
